feat: WP-0003 complete — LEVEL3 advanced features + error framework

Implements full LEVEL3 feature set: cross-references (xref.py), numbered figures (figures.py), auto-diagrams (diagrams.py), bibliography/citations (bibliography.py), LEVEL3 capability detection (level3.py), and structured error/warning records (errors.py). Builder, importer, and differ updated for LEVEL3 round-trip support. REST and MCP interfaces updated with structured warning records. 259 tests passing. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-03-16 10:51:38 +00:00
parent 760047b82b
commit ac442ea41f
26 changed files with 3713 additions and 74 deletions
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -70,16 +70,22 @@ evidence artefacts
 |--------|--------|-------------|
 | `cli.py` | implemented — all commands wired (`build`, `import`, `compare`, `validate`, `serve`, `workflow`, `mcp`, `template`) | all |
 | `manifest.py` | implemented | FR-100 |
-| `builder.py` | implemented | FR-200 |
-| `importer.py` | implemented | FR-300/400 |
-| `differ.py` | implemented | FR-700 |
+| `builder.py` | implemented — LEVEL1 + LEVEL3 (xrefs, figures, diagrams, citations) | FR-200, FR-531–539 |
+| `importer.py` | implemented — LEVEL1 + LEVEL3 round-trip | FR-300/400, FR-531–536 |
+| `differ.py` | implemented — LEVEL1 + LEVEL3 drift detection | FR-700, FR-540–542 |
 | `templates.py` | implemented | FR-600 |
 | `evidence.py` | implemented | FR-1400 |
 | `workflows.py` | implemented (`single-file-roundtrip`, `multi-file-roundtrip`, `release-regression`, `family-switch-build`) | FR-1300 |
-| `rest.py` | implemented — FastAPI app, all endpoints | FR-900 |
-| `mcp_server.py` | implemented — FastMCP server, all tools and resources | FR-1000 |
+| `rest.py` | implemented — FastAPI app, all endpoints; structured warning records | FR-900, FR-1208 |
+| `mcp_server.py` | implemented — FastMCP server, all tools and resources; structured warnings | FR-1000, FR-1208 |
+| `errors.py` | implemented — `WarningRecord`, `FailureRecord`, `OutputState` | FR-1201–1210 |
+| `level3.py` | implemented — LEVEL3 support detection, capability disclosure | FR-537–539 |
+| `xref.py` | implemented — cross-reference round-trip helpers | FR-531, FR-540 |
+| `figures.py` | implemented — numbered figure round-trip helpers | FR-532, FR-541 |
+| `diagrams.py` | implemented — auto-diagram source-only + renderer path | FR-533, FR-534 |
+| `bibliography.py` | implemented — citation and references section round-trip | FR-535, FR-536, FR-542 |

-`tests/conftest.py` provides shared fixtures (`tmp_project`, `SIMPLE_MANIFEST_YAML`, `SIMPLE_MARKDOWN`). WP-0001 and WP-0002 complete — 135 tests passing. All interfaces (CLI, REST, MCP) implemented and parity-tested.
+`tests/conftest.py` provides shared fixtures. WP-0001, WP-0002, and WP-0003 complete — 259 tests passing. Full LEVEL1 + LEVEL3 feature coverage. All interfaces (CLI, REST, MCP) implemented and parity-tested.

 ---

--- a/src/markidocx/bibliography.py
+++ b/src/markidocx/bibliography.py
@@ -0,0 +1,208 @@
+"""Bibliography and citation support for LEVEL3 markidocx (FR-535, FR-536, FR-542).
+
+Handles the round-trip of inline citations and Bibliography/References sections
+between Markdown and DOCX.
+
+Markdown syntax:
+    Inline citation:   [@key]
+    References section:
+        ## References
+        - [@key]: Author. *Title*. Year.
+
+DOCX representation:
+    Inline: [key] (plain text marker)
+    References section: "References" heading + plain text entries
+    Source-intent markers embedded for importer restoration.
+"""
+
+from __future__ import annotations
+
+import re
+
+# Markdown citation patterns
+CITATION_RE = re.compile(r"\[@([\w:.-]+)\]")
+CITATION_ENTRY_RE = re.compile(r"^-\s+\[@([\w:.-]+)\]:\s+(.+)$")
+REFERENCES_HEADING_RE = re.compile(r"^#{1,3}\s+References\s*$", re.MULTILINE)
+
+# DOCX markers
+CITATION_MARKER_PREFIX = "citation:"
+REFERENCES_SECTION_MARKER = "references-section:"
+
+
+def has_citations(text: str) -> bool:
+    """Return True if *text* contains inline citations."""
+    return bool(CITATION_RE.search(text))
+
+
+def render_inline_citations(text: str) -> str:
+    """Replace [@key] markers with [key] for DOCX embedding.
+
+    Returns the transformed text suitable for DOCX paragraph text.
+    """
+    return CITATION_RE.sub(lambda m: f"[{m.group(1)}]", text)
+
+
+def extract_citation_keys(text: str) -> list[str]:
+    """Extract all citation keys from *text*."""
+    return CITATION_RE.findall(text)
+
+
+def is_references_heading(text: str) -> bool:
+    """Return True if *text* is a References section heading."""
+    return bool(REFERENCES_HEADING_RE.match(text.strip()))
+
+
+def parse_reference_entry(text: str) -> tuple[str, str] | None:
+    """Parse a reference list entry.
+
+    Returns (key, entry_text) or None.
+    """
+    m = CITATION_ENTRY_RE.match(text.strip())
+    if m:
+        return m.group(1), m.group(2)
+    return None
+
+
+def extract_references_section(md_text: str) -> tuple[list[tuple[str, str]], str]:
+    """Extract the references section from Markdown text.
+
+    Returns (entries, text_without_references_section).
+    entries: list of (key, entry_text)
+    """
+    # Find the References heading
+    m = REFERENCES_HEADING_RE.search(md_text)
+    if not m:
+        return [], md_text
+
+    refs_start = m.start()
+    entries: list[tuple[str, str]] = []
+
+    # Collect entries after the heading
+    rest = md_text[m.end():].strip()
+    for line in rest.split("\n"):
+        line = line.strip()
+        if not line:
+            continue
+        parsed = parse_reference_entry(line)
+        if parsed:
+            entries.append(parsed)
+        elif line.startswith("#"):
+            # New heading — stop collecting
+            break
+
+    text_without = md_text[:refs_start].rstrip()
+    return entries, text_without
+
+
+# ---------------------------------------------------------------------------
+# Builder helpers
+# ---------------------------------------------------------------------------
+
+BIBLIOGRAPHY_SECTION_HEADING = "References"
+BIBLIOGRAPHY_MARKER = "bibliography-section-start"
+
+
+def render_citation_text(text: str) -> str:
+    """Return citation text for DOCX embedding.
+
+    [@key] is kept as-is in the DOCX paragraph text so the importer
+    can restore it without ambiguity.
+    """
+    return text  # [@key] → [@key] (no transformation needed)
+
+
+def render_references_section(doc, entries: list[tuple[str, str]]) -> None:
+    """Add a References section to *doc* (FR-535).
+
+    Args:
+        doc: python-docx Document
+        entries: list of (key, entry_text)
+    """
+    # Section heading
+    try:
+        doc.add_heading(BIBLIOGRAPHY_SECTION_HEADING, level=2)
+    except Exception:
+        doc.add_paragraph(BIBLIOGRAPHY_SECTION_HEADING, style="Normal")
+
+    # Bibliography marker so importer can identify the section
+    marker_para = doc.add_paragraph(style="Normal")
+    from docx.shared import Pt
+
+    marker_run = marker_para.add_run(BIBLIOGRAPHY_MARKER)
+    marker_run.font.size = Pt(1)
+
+    # Entries — keep [@key] format directly in DOCX text for round-trip fidelity
+    for key, entry_text in entries:
+        para = doc.add_paragraph(style="Normal")
+        para.add_run(f"- [@{key}]: {entry_text}")
+
+
+# ---------------------------------------------------------------------------
+# Importer helpers
+# ---------------------------------------------------------------------------
+
+DOCX_CITATION_RE = re.compile(r"\[([^\]@]+)\](?!\[)")  # [key] without @, not followed by [
+BIBLIOGRAPHY_MARKER_PARA_RE = re.compile(r"^bibliography-section-start$")
+BIBLIOGRAPHY_ENTRY_RE = re.compile(r"^-\s+\[@([\w:.-]+)\]:\s+(.+)$")
+
+
+def restore_citations_in_text(text: str) -> str:
+    """Return imported text with citations already in [@key] form (no-op).
+
+    Since builder now embeds [@key] directly in DOCX, no restoration needed.
+    """
+    return text
+
+
+def is_bibliography_marker(text: str) -> bool:
+    return BIBLIOGRAPHY_MARKER_PARA_RE.match(text.strip()) is not None
+
+
+def is_bibliography_entry(text: str) -> bool:
+    return bool(BIBLIOGRAPHY_ENTRY_RE.match(text.strip()))
+
+
+# ---------------------------------------------------------------------------
+# Differ helpers
+# ---------------------------------------------------------------------------
+
+
+def compare_citations(
+    original: str,
+    reimported: str,
+    preserved: list[str],
+    degraded: list[str],
+    broken: list[str],
+    warning_records: list | None = None,
+) -> None:
+    """Compare citation markers and reference entries (FR-536, FR-542)."""
+    orig_keys = set(extract_citation_keys(original))
+    reim_keys = set(extract_citation_keys(reimported))
+
+    for key in orig_keys:
+        if key in reim_keys:
+            preserved.append(f"citation:[@{key}]")
+        else:
+            broken.append(f"citation:missing '[@{key}]'")
+            if warning_records is not None:
+                from markidocx.errors import Severity, WarningRecord
+
+                warning_records.append(
+                    WarningRecord(
+                        severity=Severity.WARNING,
+                        reason="citation-ambiguity",
+                        construct=f"@{key}",
+                    )
+                )
+
+    # References section
+    orig_entries, _ = extract_references_section(original)
+    reim_entries, _ = extract_references_section(reimported)
+    orig_ref_keys = {k for k, _ in orig_entries}
+    reim_ref_keys = {k for k, _ in reim_entries}
+
+    for key in orig_ref_keys:
+        if key in reim_ref_keys:
+            preserved.append(f"reference-entry:{key}")
+        else:
+            degraded.append(f"reference-entry:lost '{key}'")
--- a/src/markidocx/builder.py
+++ b/src/markidocx/builder.py
@@ -9,6 +9,7 @@ import mistune
 from docx.document import Document as DocxDocument
 from docx.shared import Pt, RGBColor

+from markidocx.errors import OutputState, Severity, WarningRecord
 from markidocx.manifest import FeatureLevel, Manifest
 from markidocx.templates import FamilyRegistry

@@ -19,8 +20,16 @@ class BuildResult:
    output_path: Path
    family: str
    feature_level: str
-    warnings: list[str] = field(default_factory=list)
+    warning_records: list[WarningRecord] = field(default_factory=list)
    errors: list[str] = field(default_factory=list)
+    output_state: OutputState = OutputState.FINAL
+    partial_level3: bool = False
+    missing_coverage: list[str] = field(default_factory=list)
+
+    @property
+    def warnings(self) -> list[str]:
+        """Backward-compatible string view of warning_records."""
+        return [str(w) for w in self.warning_records]


 def build_document(manifest: Manifest) -> BuildResult:
@@ -28,8 +37,27 @@ def build_document(manifest: Manifest) -> BuildResult:

    Returns a BuildResult regardless of success/failure.
    """
-    warnings: list[str] = []
+    warning_records: list[WarningRecord] = []
    errors: list[str] = []
+    partial_level3 = False
+    missing_coverage: list[str] = []
+
+    # For LEVEL3 projects, check external dependencies (FR-538, FR-539)
+    if manifest.project.feature_level == FeatureLevel.LEVEL3:
+        from markidocx.level3 import check_level3_support
+
+        support = check_level3_support()
+        if support.partial:
+            partial_level3 = True
+            missing_coverage = support.missing_coverage
+            for area in support.missing_coverage:
+                warning_records.append(
+                    WarningRecord(
+                        severity=Severity.WARNING,
+                        reason="processor-dependency-unavailable",
+                        construct=area,
+                    )
+                )

    # Compose all source files into one Markdown string
    parts: list[str] = []
@@ -48,11 +76,18 @@ def build_document(manifest: Manifest) -> BuildResult:
        core_props.author = str(manifest.metadata["author"])

    # Parse and render tokens into the document
-    unsupported: list[str] = []
-    _render_markdown(doc, markdown_text, manifest.project.feature_level, warnings, unsupported)
+    _render_markdown(
+        doc,
+        markdown_text,
+        manifest.project.feature_level,
+        warning_records,
+    )

-    for item in unsupported:
-        warnings.append(f"Unsupported construct skipped: {item}")
+    # Determine output state
+    has_warnings = bool(warning_records)
+    output_state = OutputState.PARTIAL if partial_level3 else (
+        OutputState.FINAL if not has_warnings else OutputState.FINAL
+    )

    # Ensure output dir exists
    manifest.output_dir.mkdir(parents=True, exist_ok=True)
@@ -64,8 +99,11 @@ def build_document(manifest: Manifest) -> BuildResult:
        output_path=output_path,
        family=manifest.project.family,
        feature_level=manifest.project.feature_level.value,
-        warnings=warnings,
+        warning_records=warning_records,
        errors=errors,
+        output_state=output_state,
+        partial_level3=partial_level3,
+        missing_coverage=missing_coverage,
    )


@@ -77,13 +115,45 @@ def _render_markdown(
    doc: DocxDocument,
    text: str,
    feature_level: FeatureLevel,
-    warnings: list[str],
-    unsupported: list[str],
+    warning_records: list[WarningRecord],
 ) -> None:
    """Parse *text* as Markdown and append elements to *doc*."""
-    tokens = _tokenise(text)
+    # For LEVEL3, extract references section before tokenising
+    ref_entries: list[tuple[str, str]] = []
+    body_text = text
+    if feature_level == FeatureLevel.LEVEL3:
+        from markidocx.bibliography import extract_references_section
+
+        ref_entries, body_text = extract_references_section(text)
+
+    tokens = _tokenise(body_text)
+
+    # Pre-compute known anchors for cross-ref validation (LEVEL3 only)
+    known_anchors: set[str] = set()
+    if feature_level == FeatureLevel.LEVEL3:
+        from markidocx.xref import extract_anchors
+
+        known_anchors = extract_anchors(body_text)
+
+    bookmark_counter = [0]  # mutable int for nested calls
+    figure_counter = [0]   # auto-incrementing figure number
+
    for token in tokens:
-        _render_token(doc, token, feature_level, warnings, unsupported)
+        _render_token(
+            doc,
+            token,
+            feature_level,
+            warning_records,
+            known_anchors,
+            bookmark_counter,
+            figure_counter,
+        )
+
+    # Render references section at the end (LEVEL3 only) (FR-535)
+    if feature_level == FeatureLevel.LEVEL3 and ref_entries:
+        from markidocx.bibliography import render_references_section
+
+        render_references_section(doc, ref_entries)


 def _tokenise(text: str) -> list[dict]:  # type: ignore[type-arg]
@@ -99,23 +169,74 @@ def _render_token(
    doc: DocxDocument,
    token: dict,
    feature_level: FeatureLevel,
-    warnings: list[str],
-    unsupported: list[str],
+    warning_records: list[WarningRecord],
+    known_anchors: set[str] | None = None,
+    bookmark_counter: list[int] | None = None,
+    figure_counter: list[int] | None = None,
 ) -> None:
    token_type = token.get("type", "")
+    if known_anchors is None:
+        known_anchors = set()
+    if bookmark_counter is None:
+        bookmark_counter = [0]
+    if figure_counter is None:
+        figure_counter = [0]

    if token_type == "heading":
        level = token.get("attrs", {}).get("level", 1)
-        text = _extract_text(token.get("children", []))
+        raw_text = _extract_text(token.get("children", []))
+
+        if feature_level == FeatureLevel.LEVEL3:
+            from markidocx.xref import (
+                add_bookmark_to_paragraph,
+                extract_anchor_from_heading,
+            )
+
+            clean_text, anchor = extract_anchor_from_heading(raw_text)
+        else:
+            clean_text, anchor = raw_text, None
+
        try:
-            doc.add_heading(text, level=level)
+            para = doc.add_heading(clean_text, level=level)
        except Exception:
-            doc.add_paragraph(text, style="Normal")
+            para = doc.add_paragraph(clean_text, style="Normal")
+
+        if anchor:
+            add_bookmark_to_paragraph(para, anchor, bookmark_counter[0])
+            bookmark_counter[0] += 1

    elif token_type == "paragraph":
-        text = _extract_text(token.get("children", []))
-        para = doc.add_paragraph(style="Normal")
-        _add_inline_runs(para, token.get("children", []))
+        raw_text = _extract_text_with_image_syntax(token.get("children", []))
+
+        if feature_level == FeatureLevel.LEVEL3:
+            from markidocx.figures import is_figure_paragraph, parse_figure
+            from markidocx.xref import has_xref_links, render_paragraph_with_xrefs
+
+            if is_figure_paragraph(raw_text):
+                parsed = parse_figure(raw_text)
+                if parsed:
+                    caption, path, label = parsed
+                    figure_counter[0] += 1
+                    from markidocx.figures import render_figure
+
+                    render_figure(doc, caption, path, label, figure_counter[0])
+                else:
+                    para = doc.add_paragraph(style="Normal")
+                    _add_inline_runs(para, token.get("children", []))
+            elif has_xref_links(raw_text):
+                para = doc.add_paragraph(style="Normal")
+                render_paragraph_with_xrefs(para, raw_text, known_anchors)
+            else:
+                para = doc.add_paragraph(style="Normal")
+                from markidocx.bibliography import has_citations, render_citation_text
+
+                if has_citations(raw_text):
+                    para.add_run(render_citation_text(raw_text))
+                else:
+                    _add_inline_runs(para, token.get("children", []))
+        else:
+            para = doc.add_paragraph(style="Normal")
+            _add_inline_runs(para, token.get("children", []))

    elif token_type == "list":
        ordered = token.get("attrs", {}).get("ordered", False)
@@ -135,10 +256,23 @@ def _render_token(

    elif token_type == "block_code":
        code = token.get("raw", "")
-        para = doc.add_paragraph(style="Normal")
-        run = para.add_run(code)
-        run.font.name = "Courier New"
-        run.font.size = Pt(9)
+        info = (token.get("attrs", {}) or {}).get("info", "") or ""
+
+        if feature_level == FeatureLevel.LEVEL3:
+            from markidocx.diagrams import is_diagram_info, render_diagram_block
+
+            if is_diagram_info(info):
+                render_diagram_block(doc, info.strip().lower(), code, warning_records)
+            else:
+                para = doc.add_paragraph(style="Normal")
+                run = para.add_run(code)
+                run.font.name = "Courier New"
+                run.font.size = Pt(9)
+        else:
+            para = doc.add_paragraph(style="Normal")
+            run = para.add_run(code)
+            run.font.name = "Courier New"
+            run.font.size = Pt(9)

    elif token_type == "block_quote":
        children = token.get("children", [])
@@ -151,14 +285,27 @@ def _render_token(
        doc.add_paragraph("—" * 20, style="Normal")

    elif token_type in ("html_block", "raw_html"):
-        unsupported.append(f"html ({token_type})")
+        warning_records.append(
+            WarningRecord(
+                severity=Severity.WARNING,
+                reason="unsupported-construct",
+                construct=f"html ({token_type})",
+            )
+        )

    elif token_type == "blank_line":
        pass  # ignore blank lines

    else:
-        # Unknown token — surface as unsupported (FR-508)
-        unsupported.append(token_type)
+        # Unknown token — surface as unsupported (FR-508, FR-1203)
+        if token_type:
+            warning_records.append(
+                WarningRecord(
+                    severity=Severity.WARNING,
+                    reason="unsupported-construct",
+                    construct=token_type,
+                )
+            )


 def _render_table(doc: DocxDocument, token: dict) -> None:
@@ -186,6 +333,26 @@ def _render_table(doc: DocxDocument, token: dict) -> None:
                    run.bold = True


+def _extract_text_with_image_syntax(children: list[dict]) -> str:
+    """Extract text from token children, reconstructing image MD syntax for figures."""
+    parts: list[str] = []
+    for child in children:
+        child_type = child.get("type", "")
+        if child_type == "image":
+            caption = _extract_text(child.get("children", []))
+            url = child.get("attrs", {}).get("url", "")
+            parts.append(f"![{caption}]({url})")
+        elif child_type == "text":
+            parts.append(child.get("raw", ""))
+        elif child_type in ("strong", "emphasis", "codespan", "link"):
+            parts.append(_extract_text(child.get("children", [])))
+        elif child.get("raw"):
+            parts.append(child["raw"])
+        elif child.get("children"):
+            parts.append(_extract_text_with_image_syntax(child["children"]))
+    return "".join(parts)
+
+
 def _extract_text(children: list[dict]) -> str:
    """Recursively extract plain text from a token children list."""
    parts: list[str] = []
--- a/src/markidocx/diagrams.py
+++ b/src/markidocx/diagrams.py
@@ -0,0 +1,190 @@
+"""Auto-diagram support for LEVEL3 markidocx (FR-533, FR-534).
+
+Handles fenced diagram source blocks (mermaid, graphviz, plantuml) in the
+Markdown ↔ DOCX round trip.
+
+Source-intent preservation:
+  When a renderer is unavailable, diagram source is embedded as a verbatim
+  code block and a source-intent marker paragraph is added so the importer
+  can restore the fenced block.  No source is silently discarded (FR-1205).
+"""
+
+from __future__ import annotations
+
+import re
+import shutil
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from docx.document import Document as DocxDocument
+
+# Diagram types recognised as LEVEL3 auto-diagram sources
+DIAGRAM_TYPES: frozenset[str] = frozenset({"mermaid", "graphviz", "plantuml"})
+
+# Renderer → CLI command mapping
+_RENDERER_COMMANDS: dict[str, str] = {
+    "mermaid": "mmdc",
+    "graphviz": "dot",
+    "plantuml": "plantuml",
+}
+
+# Marker prefix stored in DOCX paragraph to preserve source intent (FR-534)
+DIAGRAM_SOURCE_MARKER_PREFIX = "diagram-source:"
+DIAGRAM_SOURCE_MARKER_RE = re.compile(
+    r"^diagram-source:(\w+)\n(.*)", re.DOTALL
+)
+
+
+def is_diagram_info(info: str) -> bool:
+    """Return True if *info* is a recognised diagram type."""
+    return (info or "").strip().lower() in DIAGRAM_TYPES
+
+
+def check_renderer(diagram_type: str) -> bool:
+    """Return True if the required renderer for *diagram_type* is available."""
+    cmd = _RENDERER_COMMANDS.get(diagram_type.lower())
+    return bool(cmd and shutil.which(cmd))
+
+
+def render_diagram_block(
+    doc: DocxDocument,
+    diagram_type: str,
+    source: str,
+    warning_records: list,
+) -> None:
+    """Render a diagram fenced block into *doc* (FR-533, FR-534).
+
+    If a renderer is available → renders to PNG and embeds the image.
+    If unavailable → embeds source as verbatim code block + source-intent marker.
+    Never silently discards source (FR-1205).
+    """
+    from docx.shared import Pt
+
+    from markidocx.errors import Severity, WarningRecord
+
+    renderer_available = check_renderer(diagram_type)
+
+    if renderer_available:
+        _render_diagram_with_tool(doc, diagram_type, source, warning_records)
+        return
+
+    # Renderer not available — emit warning (FR-538) and use source-only path
+    warning_records.append(
+        WarningRecord(
+            severity=Severity.WARNING,
+            reason="processor-dependency-unavailable",
+            construct=f"{diagram_type} (no renderer: {_RENDERER_COMMANDS.get(diagram_type, diagram_type)} not found)",
+        )
+    )
+
+    # Verbatim code block (source preserved — FR-1205)
+    code_para = doc.add_paragraph(style="Normal")
+    run = code_para.add_run(f"```{diagram_type}\n{source}\n```")
+    run.font.name = "Courier New"
+    run.font.size = Pt(9)
+
+    # Source-intent marker paragraph so importer can restore (FR-534)
+    marker_para = doc.add_paragraph(style="Normal")
+    marker_run = marker_para.add_run(f"{DIAGRAM_SOURCE_MARKER_PREFIX}{diagram_type}\n{source}")
+    marker_run.font.size = Pt(1)  # make tiny — not for display
+
+
+def _render_diagram_with_tool(
+    doc: DocxDocument,
+    diagram_type: str,
+    source: str,
+    warning_records: list,
+) -> None:
+    """Attempt to render diagram source using an external tool and embed PNG."""
+    import subprocess
+    import tempfile
+    from pathlib import Path
+
+    from docx.shared import Inches, Pt
+
+    from markidocx.errors import Severity, WarningRecord
+
+    cmd = _RENDERER_COMMANDS[diagram_type]
+    try:
+        with tempfile.TemporaryDirectory() as tmp:
+            tmp_path = Path(tmp)
+            src_file = tmp_path / f"diagram.{diagram_type[:3]}"
+            png_file = tmp_path / "diagram.png"
+            src_file.write_text(source, encoding="utf-8")
+
+            if diagram_type == "mermaid":
+                args = [cmd, "-i", str(src_file), "-o", str(png_file)]
+            elif diagram_type == "graphviz":
+                args = [cmd, "-Tpng", str(src_file), "-o", str(png_file)]
+            else:  # plantuml
+                args = [cmd, "-tpng", str(src_file), "-o", str(tmp_path)]
+                png_file = tmp_path / f"diagram.{diagram_type[:3]}.png"
+
+            subprocess.run(args, capture_output=True, timeout=30)
+
+            if png_file.exists():
+                para = doc.add_paragraph(style="Normal")
+                run = para.add_run()
+                run.add_picture(str(png_file), width=Inches(5))
+                # Source-intent marker for round-trip (FR-534)
+                marker_para = doc.add_paragraph(style="Normal")
+                marker_run = marker_para.add_run(
+                    f"{DIAGRAM_SOURCE_MARKER_PREFIX}{diagram_type}\n{source}"
+                )
+                marker_run.font.size = Pt(1)
+                return
+    except Exception as exc:
+        warning_records.append(
+            WarningRecord(
+                severity=Severity.WARNING,
+                reason="diagram-render-failed",
+                construct=f"{diagram_type}: {exc}",
+            )
+        )
+
+    # Fallback: source-only path
+    from docx.shared import Pt
+
+    code_para = doc.add_paragraph(style="Normal")
+    run = code_para.add_run(f"```{diagram_type}\n{source}\n```")
+    run.font.name = "Courier New"
+    run.font.size = Pt(9)
+
+    marker_para = doc.add_paragraph(style="Normal")
+    marker_run = marker_para.add_run(
+        f"{DIAGRAM_SOURCE_MARKER_PREFIX}{diagram_type}\n{source}"
+    )
+    from docx.shared import Pt
+
+    marker_run.font.size = Pt(1)
+
+
+# ---------------------------------------------------------------------------
+# Importer helpers
+# ---------------------------------------------------------------------------
+
+
+def is_diagram_source_marker(text: str) -> bool:
+    """Return True if *text* is a diagram source-intent marker."""
+    return text.strip().startswith(DIAGRAM_SOURCE_MARKER_PREFIX)
+
+
+def parse_diagram_source_marker(text: str) -> tuple[str, str] | None:
+    """Parse a diagram source-intent marker into (diagram_type, source).
+
+    Returns None if the text is not a valid marker.
+    """
+    stripped = text.strip()
+    if not stripped.startswith(DIAGRAM_SOURCE_MARKER_PREFIX):
+        return None
+    rest = stripped[len(DIAGRAM_SOURCE_MARKER_PREFIX):]
+    # Format: "type\nsource..."
+    if "\n" in rest:
+        diagram_type, source = rest.split("\n", 1)
+        return diagram_type.strip(), source
+    return rest.strip(), ""
+
+
+def reconstruct_diagram_md(diagram_type: str, source: str) -> str:
+    """Reconstruct a fenced code block from diagram type and source."""
+    return f"```{diagram_type}\n{source}\n```"
--- a/src/markidocx/differ.py
+++ b/src/markidocx/differ.py
@@ -5,6 +5,8 @@ from __future__ import annotations
 import re
 from dataclasses import dataclass, field

+from markidocx.errors import OutputState
+
 HEADING_RE = re.compile(r"^(#{1,6})\s+(.+)$", re.MULTILINE)
 LIST_ITEM_RE = re.compile(r"^(\s*[-*+]|\s*\d+\.)\s+(.+)$", re.MULTILINE)
 TABLE_ROW_RE = re.compile(r"^\|.+\|$", re.MULTILINE)
@@ -19,6 +21,7 @@ class DriftReport:
    degraded: list[str] = field(default_factory=list)
    broken: list[str] = field(default_factory=list)
    unsupported: list[str] = field(default_factory=list)
+    output_state: OutputState = OutputState.FINAL


 def compare(original: str, reimported: str) -> DriftReport:
@@ -76,13 +79,29 @@ def compare(original: str, reimported: str) -> DriftReport:
        else:
            degraded.append(f"link:lost {link[:40]}")

+    # --- Cross-references (FR-531, FR-540) ---
+    _compare_xrefs(original, reimported, preserved, degraded, broken)
+
+    # --- Figures (FR-532, FR-541) ---
+    _compare_figures(original, reimported, preserved, degraded, broken)
+
+    # --- Citations & Bibliography (FR-535, FR-542) ---
+    from markidocx.bibliography import compare_citations
+
+    compare_citations(original, reimported, preserved, degraded, broken)
+
    has_drift = bool(degraded or broken)
+    output_state = (
+        OutputState.FINAL if not has_drift
+        else (OutputState.DEGRADED if not broken else OutputState.PARTIAL)
+    )
    return DriftReport(
        has_drift=has_drift,
        preserved=preserved,
        degraded=degraded,
        broken=broken,
        unsupported=unsupported,
+        output_state=output_state,
    )


@@ -104,6 +123,64 @@ def _count_tables(text: str) -> int:
    return count


+def _compare_figures(
+    original: str,
+    reimported: str,
+    preserved: list[str],
+    degraded: list[str],
+    broken: list[str],
+) -> None:
+    """Compare figure labels and captions (FR-532, FR-541)."""
+    from markidocx.figures import extract_figure_captions, extract_figure_labels
+
+    orig_labels = extract_figure_labels(original)
+    reim_labels = extract_figure_labels(reimported)
+    for label in orig_labels:
+        if label in reim_labels:
+            preserved.append(f"figure-label:{label}")
+        else:
+            broken.append(f"figure-label:missing '{label}'")
+
+    orig_captions = extract_figure_captions(original)
+    reim_captions = extract_figure_captions(reimported)
+    orig_set = set(orig_captions)
+    reim_set = set(reim_captions)
+    for caption in orig_set:
+        if caption in reim_set:
+            preserved.append(f"figure-caption:{caption[:40]}")
+        else:
+            degraded.append(f"figure-caption:lost '{caption[:40]}'")
+
+
+def _compare_xrefs(
+    original: str,
+    reimported: str,
+    preserved: list[str],
+    degraded: list[str],
+    broken: list[str],
+) -> None:
+    """Compare cross-reference anchors and links (FR-531, FR-540)."""
+    from markidocx.xref import extract_anchors, extract_xref_links
+
+    orig_anchors = extract_anchors(original)
+    reim_anchors = extract_anchors(reimported)
+    for anchor in orig_anchors:
+        if anchor in reim_anchors:
+            preserved.append(f"xref-anchor:{anchor}")
+        else:
+            broken.append(f"xref-anchor:missing '{anchor}'")
+
+    orig_xrefs = extract_xref_links(original)
+    reim_xrefs = extract_xref_links(reimported)
+    for link_text, anchor in orig_xrefs:
+        if (link_text, anchor) in reim_xrefs:
+            preserved.append(f"xref-link:[{link_text}][{anchor}]")
+        elif anchor not in reim_anchors:
+            broken.append(f"xref-link:broken-target [{link_text}][{anchor}]")
+        else:
+            degraded.append(f"xref-link:degraded [{link_text}][{anchor}]")
+
+
 def _compare_sets(
    kind: str,
    orig: list[str],
--- a/src/markidocx/errors.py
+++ b/src/markidocx/errors.py
@@ -0,0 +1,80 @@
+"""Structured error and warning types for markidocx (FR-1201–1210)."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from enum import StrEnum
+from typing import Any
+
+
+class Severity(StrEnum):
+    INFO = "info"
+    WARNING = "warning"
+    ERROR = "error"
+
+
+class OutputState(StrEnum):
+    """Lifecycle state of a build/import/workflow result (FR-1210)."""
+
+    FINAL = "final"
+    PARTIAL = "partial"
+    FALLBACK = "fallback"
+    DEGRADED = "degraded"
+    UNRESOLVED = "unresolved"
+
+
+@dataclass
+class WarningRecord:
+    """Structured warning record (FR-1208).
+
+    severity: info | warning | error
+    reason:   FR-code-aligned description
+    construct: the token/element that triggered the warning
+    """
+
+    severity: str
+    reason: str
+    construct: str = ""
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "severity": self.severity,
+            "reason": self.reason,
+            "construct": self.construct,
+        }
+
+    def __str__(self) -> str:
+        if self.construct:
+            return f"[{self.severity}] {self.reason}: {self.construct}"
+        return f"[{self.severity}] {self.reason}"
+
+
+@dataclass
+class FailureRecord:
+    """Structured failure record (FR-1209).
+
+    severity: info | warning | error
+    reason:   FR-code-aligned description
+    construct: the element that caused the failure
+    """
+
+    severity: str
+    reason: str
+    construct: str = ""
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "severity": self.severity,
+            "reason": self.reason,
+            "construct": self.construct,
+        }
+
+    def __str__(self) -> str:
+        if self.construct:
+            return f"[{self.severity}] {self.reason}: {self.construct}"
+        return f"[{self.severity}] {self.reason}"
+
+
+def warning_records_to_strings(records: list[WarningRecord]) -> list[str]:
+    """Convert a list of WarningRecords to plain strings (backward compat helper)."""
+    return [str(r) for r in records]
--- a/src/markidocx/figures.py
+++ b/src/markidocx/figures.py
@@ -0,0 +1,147 @@
+"""Numbered figure support for LEVEL3 markidocx (FR-532, FR-541).
+
+Handles round-trip of captioned numbered figures between Markdown and DOCX.
+
+Markdown syntax:
+    ![Caption text](path/to/image.png){#fig:label}
+
+DOCX representation:
+    [image paragraph or placeholder]
+    [caption paragraph: "Figure N — Caption text"]
+    (with alt-text marker: "figure-source:path/to/image.png#fig:label")
+"""
+
+from __future__ import annotations
+
+import re
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from docx.document import Document as DocxDocument
+
+# Markdown figure pattern: ![Caption](path){#fig:label}
+FIGURE_RE = re.compile(
+    r"^!\[([^\]]*)\]\(([^)]+)\)\{#(fig:[\w:-]+)\}$",
+    re.MULTILINE,
+)
+
+# Caption paragraph pattern in imported DOCX
+CAPTION_RE = re.compile(r"^Figure\s+(\d+)\s+[—\-–]\s+(.+)$")
+
+# Alt-text marker embedded in images to preserve source intent (FR-534)
+ALT_TEXT_MARKER_PREFIX = "figure-source:"
+
+
+def is_figure_paragraph(text: str) -> bool:
+    """Return True if *text* is a standalone figure declaration."""
+    return bool(FIGURE_RE.match(text.strip()))
+
+
+def parse_figure(text: str) -> tuple[str, str, str] | None:
+    """Parse a figure declaration.
+
+    Returns (caption, path, label) or None.
+    """
+    m = FIGURE_RE.match(text.strip())
+    if not m:
+        return None
+    return m.group(1), m.group(2), m.group(3)
+
+
+def render_figure(
+    doc: DocxDocument,
+    caption: str,
+    path: str,
+    label: str,
+    figure_number: int,
+) -> None:
+    """Render a figure declaration into *doc* (FR-532).
+
+    Adds:
+    1. A paragraph with alt-text marker (image placeholder — actual embedding
+       requires the file to exist and is omitted here for portability).
+    2. A caption paragraph: "Figure N — Caption"
+    """
+    # Alt-text marker so importer can reconstruct the figure (FR-534)
+    alt_marker = f"{ALT_TEXT_MARKER_PREFIX}{path}#{label}"
+
+    # Image placeholder paragraph with alt-text marker as text
+    placeholder = doc.add_paragraph(style="Normal")
+    run = placeholder.add_run(f"[Figure: {path}]")
+    # Store source-intent in the run's text (alt-text equivalent for round-trip)
+    run.italic = True
+
+    # Add DOCX comment/marker paragraph with the source-intent data
+    marker_para = doc.add_paragraph(style="Normal")
+    marker_run = marker_para.add_run(alt_marker)
+    marker_run.font.size = None  # inherit
+    # Hide the marker by making it very small (conceptual; keeps round-trip info)
+    from docx.shared import Pt
+
+    marker_run.font.size = Pt(1)
+    marker_run.font.color.rgb = None  # default color
+
+    # Caption paragraph
+    caption_para = doc.add_paragraph(style="Normal")
+    caption_para.add_run(f"Figure {figure_number} — {caption}")
+
+
+def extract_figures_from_md(text: str) -> list[tuple[str, str, str]]:
+    """Extract all figure declarations from Markdown text.
+
+    Returns list of (caption, path, label).
+    """
+    return [(m.group(1), m.group(2), m.group(3)) for m in FIGURE_RE.finditer(text)]
+
+
+# ---------------------------------------------------------------------------
+# Importer helpers
+# ---------------------------------------------------------------------------
+
+
+def is_caption_paragraph(text: str) -> bool:
+    """Return True if *text* looks like a figure caption."""
+    return bool(CAPTION_RE.match(text.strip()))
+
+
+def is_alt_text_marker(text: str) -> bool:
+    """Return True if *text* is a figure-source alt-text marker."""
+    return text.strip().startswith(ALT_TEXT_MARKER_PREFIX)
+
+
+def parse_alt_text_marker(text: str) -> tuple[str, str] | None:
+    """Parse a figure-source marker into (path, label).
+
+    Returns None if the text is not a valid marker.
+    """
+    stripped = text.strip()
+    if not stripped.startswith(ALT_TEXT_MARKER_PREFIX):
+        return None
+    rest = stripped[len(ALT_TEXT_MARKER_PREFIX):]
+    if "#" in rest:
+        path, label = rest.rsplit("#", 1)
+        return path, label
+    return rest, ""
+
+
+def reconstruct_figure_md(caption: str, path: str, label: str) -> str:
+    """Reconstruct a Markdown figure declaration from its parts."""
+    return f"![{caption}]({path}){{#{label}}}"
+
+
+# ---------------------------------------------------------------------------
+# Differ helpers
+# ---------------------------------------------------------------------------
+
+FIGURE_LABEL_RE = re.compile(r"\{#(fig:[\w:-]+)\}")
+FIGURE_CAPTION_MD_RE = re.compile(r"!\[([^\]]*)\]\([^)]+\)\{#fig:[\w:-]+\}")
+
+
+def extract_figure_labels(text: str) -> set[str]:
+    """Extract {#fig:label} declarations from Markdown text."""
+    return set(FIGURE_LABEL_RE.findall(text))
+
+
+def extract_figure_captions(text: str) -> list[str]:
+    """Extract captions from figure declarations in Markdown text."""
+    return [m.group(1) for m in FIGURE_CAPTION_MD_RE.finditer(text)]
--- a/src/markidocx/importer.py
+++ b/src/markidocx/importer.py
@@ -11,6 +11,7 @@ from docx.document import Document as DocxDocument
 from docx.table import Table
 from docx.text.paragraph import Paragraph

+from markidocx.errors import OutputState, Severity, WarningRecord
 from markidocx.manifest import Manifest

 HEADING_STYLE_RE = re.compile(r"^Heading (\d+)$", re.IGNORECASE)
@@ -23,7 +24,13 @@ class ImportResult:
    success: bool
    output_files: list[Path]
    mapping_status: str  # "redistributed" | "merged" | "failed"
-    warnings: list[str] = field(default_factory=list)
+    warning_records: list[WarningRecord] = field(default_factory=list)
+    output_state: OutputState = OutputState.FINAL
+
+    @property
+    def warnings(self) -> list[str]:
+        """Backward-compatible string view of warning_records."""
+        return [str(w) for w in self.warning_records]


 def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
@@ -33,14 +40,21 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
    content is redistributed to the original files.  Otherwise a single
    merged file is produced.
    """
-    warnings: list[str] = []
+    warning_records: list[WarningRecord] = []

    if not docx_path.exists():
        return ImportResult(
            success=False,
            output_files=[],
            mapping_status="failed",
-            warnings=[f"DOCX file not found: {docx_path}"],
+            warning_records=[
+                WarningRecord(
+                    severity=Severity.ERROR,
+                    reason="docx-not-found",
+                    construct=str(docx_path),
+                )
+            ],
+            output_state=OutputState.UNRESOLVED,
        )

    try:
@@ -50,10 +64,17 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
            success=False,
            output_files=[],
            mapping_status="failed",
-            warnings=[f"Could not open DOCX: {exc}"],
+            warning_records=[
+                WarningRecord(
+                    severity=Severity.ERROR,
+                    reason="docx-open-failed",
+                    construct=str(exc),
+                )
+            ],
+            output_state=OutputState.UNRESOLVED,
        )

-    md_text = _docx_to_markdown(doc, warnings)
+    md_text = _docx_to_markdown(doc, warning_records)

    manifest.output_dir.mkdir(parents=True, exist_ok=True)

@@ -65,7 +86,8 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
            success=True,
            output_files=[out_path],
            mapping_status="redistributed",
-            warnings=warnings,
+            warning_records=warning_records,
+            output_state=OutputState.FINAL,
        )

    # Multi-file: attempt redistribution by H1 boundary
@@ -79,13 +101,20 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
            success=True,
            output_files=output_files,
            mapping_status="redistributed",
-            warnings=warnings,
+            warning_records=warning_records,
+            output_state=OutputState.FINAL,
        )

-    # Fallback: merged single output (FR-406)
-    warnings.append(
-        f"Could not redistribute to {len(manifest.sources)} source files "
-        f"(found {len(sections)} H1 sections); writing merged output"
+    # Fallback: merged single output (FR-406, FR-1207)
+    warning_records.append(
+        WarningRecord(
+            severity=Severity.WARNING,
+            reason="fallback",
+            construct=(
+                f"could not redistribute to {len(manifest.sources)} source files "
+                f"(found {len(sections)} H1 sections); writing merged output"
+            ),
+        )
    )
    merged_path = manifest.output_dir / "imported_merged.md"
    merged_path.write_text(md_text, encoding="utf-8")
@@ -93,7 +122,8 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
        success=True,
        output_files=[merged_path],
        mapping_status="merged",
-        warnings=warnings,
+        warning_records=warning_records,
+        output_state=OutputState.FALLBACK,
    )


@@ -101,17 +131,95 @@ def import_document(manifest: Manifest, docx_path: Path) -> ImportResult:
 # DOCX → Markdown conversion
 # ---------------------------------------------------------------------------

-def _docx_to_markdown(doc: DocxDocument, warnings: list[str]) -> str:
+def _docx_to_markdown(doc: DocxDocument, warning_records: list[WarningRecord]) -> str:
    """Convert a python-docx Document to a Markdown string."""
+    from markidocx.bibliography import (
+        is_bibliography_entry,
+        is_bibliography_marker,
+        restore_citations_in_text,
+    )
+    from markidocx.diagrams import (
+        is_diagram_source_marker,
+        parse_diagram_source_marker,
+        reconstruct_diagram_md,
+    )
+    from markidocx.figures import (
+        CAPTION_RE,
+        is_alt_text_marker,
+        parse_alt_text_marker,
+        reconstruct_figure_md,
+    )
+
    lines: list[str] = []
+
    # Walk python-docx's block-level items
-    for block in _iter_blocks(doc):
+    blocks = list(_iter_blocks(doc))
+    idx = 0
+    while idx < len(blocks):
+        block = blocks[idx]
        if isinstance(block, Paragraph):
-            md = _paragraph_to_md(block, warnings)
+            text = block.text.strip()
+
+            # Detect diagram source-intent marker (tiny font) → restore fenced block (FR-534)
+            if is_diagram_source_marker(text):
+                parsed = parse_diagram_source_marker(text)
+                if parsed:
+                    diagram_type, source = parsed
+                    from markidocx.diagrams import reconstruct_diagram_md
+                    lines.append(reconstruct_diagram_md(diagram_type, source))
+                idx += 1
+                continue
+
+            # Detect alt-text marker (figure source intent) — skip it; consumed by caption
+            if is_alt_text_marker(text):
+                caption_text = ""
+                path = ""
+                label = ""
+                marker_parsed = parse_alt_text_marker(text)
+                if marker_parsed:
+                    path, label = marker_parsed
+
+                if idx + 1 < len(blocks) and isinstance(blocks[idx + 1], Paragraph):
+                    next_text = blocks[idx + 1].text.strip()
+                    cm = CAPTION_RE.match(next_text)
+                    if cm:
+                        caption_text = cm.group(2)
+                        idx += 1  # consume caption paragraph
+
+                if caption_text:
+                    lines.append(reconstruct_figure_md(caption_text, path, label))
+                    idx += 1
+                    continue
+
+            # Detect placeholder + alt-text marker pattern: "[Figure: path]"
+            if text.startswith("[Figure:") and text.endswith("]"):
+                idx += 1
+                continue  # skip placeholder; handled via alt-text marker
+
+            # Detect bibliography section marker (tiny invisible paragraph)
+            if is_bibliography_marker(text):
+                idx += 1
+                continue  # skip; section already started by heading
+
+            # Detect bibliography reference entry ([@key]: ...) — already in correct format
+            if is_bibliography_entry(text):
+                lines.append(text)
+                idx += 1
+                continue
+
+            md = _paragraph_to_md(block, warning_records)
            if md is not None:
                lines.append(md)
        elif isinstance(block, Table):
            lines.append(_table_to_md(block))
+        idx += 1
+
+    # Bibliography entries are already inline after heading; no extra work needed
+    result_text = "\n\n".join(line for line in lines if line is not None)
+
+    # Restore citations in the text ([@key] markers)
+    result_text = restore_citations_in_text(result_text)
+    return result_text

    return "\n\n".join(line for line in lines if line is not None)

@@ -128,7 +236,7 @@ def _iter_blocks(doc: DocxDocument):
            yield Table(child, doc)


-def _paragraph_to_md(para: Paragraph, warnings: list[str]) -> str | None:
+def _paragraph_to_md(para: Paragraph, warning_records: list[WarningRecord]) -> str | None:
    """Convert a paragraph to a Markdown line."""
    style_name = para.style.name if para.style else "Normal"
    text = para.text.strip()
@@ -137,7 +245,14 @@ def _paragraph_to_md(para: Paragraph, warnings: list[str]) -> str | None:
    m = HEADING_STYLE_RE.match(style_name)
    if m:
        level = int(m.group(1))
-        return f"{'#' * level} {text}"
+        # Check for bookmarks → restore {#anchor} labels (FR-531)
+        from markidocx.xref import extract_bookmarks_from_paragraph
+
+        bookmarks = extract_bookmarks_from_paragraph(para)
+        anchor_suffix = ""
+        if bookmarks:
+            anchor_suffix = " " + " ".join(f"{{#{b}}}" for b in bookmarks)
+        return f"{'#' * level} {text}{anchor_suffix}"

    # Lists
    if LIST_BULLET_RE.match(style_name):
@@ -145,13 +260,33 @@ def _paragraph_to_md(para: Paragraph, warnings: list[str]) -> str | None:
    if LIST_NUMBER_RE.match(style_name):
        return f"1. {text}"

-    # Normal text — preserve inline markup
+    # Normal text — check for internal hyperlinks (cross-refs) → [text][anchor]
+    from markidocx.xref import extract_internal_hyperlinks_from_paragraph
+
+    internal_links = extract_internal_hyperlinks_from_paragraph(para)
+    if internal_links:
+        return _runs_to_md_with_xrefs(para, internal_links)
+
    if not text:
        return None

    return _runs_to_md(para)


+def _runs_to_md_with_xrefs(
+    para: Paragraph, internal_links: list[tuple[str, str]]
+) -> str:
+    """Convert paragraph with internal hyperlinks to Markdown with [text][anchor].
+
+    para.text includes text from nested hyperlink elements, so we use it as
+    the base and replace each hyperlink text with [text][anchor] syntax.
+    """
+    result = para.text
+    for link_text, anchor in internal_links:
+        result = result.replace(link_text, f"[{link_text}][{anchor}]", 1)
+    return result
+
+
 def _runs_to_md(para: Paragraph) -> str:
    """Convert paragraph runs to Markdown with inline formatting."""
    parts: list[str] = []
--- a/src/markidocx/level3.py
+++ b/src/markidocx/level3.py
@@ -0,0 +1,83 @@
+"""LEVEL3 feature gating, processor-dependency disclosure, and support detection (FR-537–539)."""
+
+from __future__ import annotations
+
+import shutil
+from dataclasses import dataclass, field
+
+# Diagram renderers recognised by LEVEL3 auto-diagram support
+_DIAGRAM_TOOLS: dict[str, str] = {
+    "mmdc": "Mermaid CLI (mermaid diagrams)",
+    "dot": "Graphviz dot (graphviz diagrams)",
+    "plantuml": "PlantUML (plantuml diagrams)",
+}
+
+
+@dataclass
+class ProcessorDependency:
+    """An external tool required for a LEVEL3 construct (FR-538)."""
+
+    name: str
+    description: str
+    available: bool
+
+
+@dataclass
+class Level3Support:
+    """Summary of LEVEL3 processing capability on the current host (FR-537, FR-538).
+
+    available: True if *any* LEVEL3 processing is possible (always True —
+               core features like cross-refs / figures / bibliography work
+               without external tools).
+    dependencies: per-tool availability for diagram rendering.
+    partial: True when some LEVEL3 features are unavailable due to missing tools.
+    missing_coverage: human-readable list of unavailable feature areas.
+    """
+
+    available: bool = True
+    dependencies: list[ProcessorDependency] = field(default_factory=list)
+    partial: bool = False
+    missing_coverage: list[str] = field(default_factory=list)
+
+
+def check_level3_support() -> Level3Support:
+    """Detect external tool availability and compute Level3Support (FR-537, FR-538).
+
+    Core LEVEL3 features (cross-refs, figures, bibliography) are always available.
+    Diagram rendering requires external tools (mmdc / dot / plantuml).
+    """
+    deps: list[ProcessorDependency] = []
+    for cmd, description in _DIAGRAM_TOOLS.items():
+        available = shutil.which(cmd) is not None
+        deps.append(ProcessorDependency(name=cmd, description=description, available=available))
+
+    diagram_available = any(d.available for d in deps)
+    missing: list[str] = []
+    if not diagram_available:
+        missing.append("auto-diagrams (no renderer: mmdc/dot/plantuml not found)")
+
+    return Level3Support(
+        available=True,
+        dependencies=deps,
+        partial=bool(missing),
+        missing_coverage=missing,
+    )
+
+
+def capabilities_entry() -> dict:
+    """Return a capabilities dict fragment for LEVEL3 (FR-537)."""
+    support = check_level3_support()
+    return {
+        "level": "level3",
+        "available": support.available,
+        "partial": support.partial,
+        "missing_coverage": support.missing_coverage,
+        "dependencies": [
+            {
+                "name": d.name,
+                "description": d.description,
+                "available": d.available,
+            }
+            for d in support.dependencies
+        ],
+    }
--- a/src/markidocx/mcp_server.py
+++ b/src/markidocx/mcp_server.py
@@ -68,6 +68,8 @@ def validate_project(manifest_yaml: str) -> dict[str, Any]:
        except Exception:
            (tmp_path / "dist").mkdir(exist_ok=True)
        try:
+            from markidocx.level3 import capabilities_entry as level3_capabilities
+
            m = load_manifest(mp)
            return {
                "status": "ok",
@@ -79,6 +81,7 @@ def validate_project(manifest_yaml: str) -> dict[str, Any]:
                "context": {
                    "supported_families": sorted(SUPPORTED_FAMILIES),
                    "supported_feature_levels": [e.value for e in FeatureLevel],
+                    "level3": level3_capabilities(),
                },
            }
        except ManifestError as exc:
@@ -123,15 +126,24 @@ def build(manifest_yaml: str, sources: list[dict[str, str]]) -> dict[str, Any]:
        result = build_document(m)
        if result.success:
            docx_b64 = base64.b64encode(Path(result.output_path).read_bytes()).decode()
-            return {
+            out: dict[str, Any] = {
                "status": "ok",
                "docx_base64": docx_b64,
                "family": result.family,
                "feature_level": result.feature_level,
-                "warnings": result.warnings,
+                "output_state": result.output_state,
+                "warnings": [w.to_dict() for w in result.warning_records],
                "errors": [],
            }
-        return {"status": "error", "errors": result.errors, "warnings": result.warnings}
+            if result.partial_level3:
+                out["partial_level3"] = True
+                out["missing_coverage"] = result.missing_coverage
+            return out
+        return {
+            "status": "error",
+            "errors": result.errors,
+            "warnings": [w.to_dict() for w in result.warning_records],
+        }


@mcp.tool()
@@ -182,10 +194,15 @@ def import_docx(manifest_yaml: str, docx_base64: str) -> dict[str, Any]:
                "status": "ok",
                "files": files_md,
                "mapping_status": result.mapping_status,
-                "warnings": result.warnings,
+                "output_state": result.output_state,
+                "warnings": [w.to_dict() for w in result.warning_records],
                "errors": [],
            }
-        return {"status": "error", "errors": ["Import failed"], "warnings": result.warnings}
+        return {
+            "status": "error",
+            "errors": ["Import failed"],
+            "warnings": [w.to_dict() for w in result.warning_records],
+        }


@mcp.tool()
@@ -329,14 +346,17 @@ def get_evidence(run_id: str) -> dict[str, Any]:

@mcp.resource("markidocx://capabilities")
 def resource_capabilities() -> str:
-    """Capabilities: supported feature levels and families."""
+    """Capabilities: supported feature levels and families (FR-537)."""
    import json

+    from markidocx.level3 import capabilities_entry as level3_capabilities
+
    return json.dumps(
        {
            "version": __version__,
            "feature_levels": [e.value for e in FeatureLevel],
            "families": sorted(SUPPORTED_FAMILIES),
+            "level3": level3_capabilities(),
        }
    )

--- a/src/markidocx/rest.py
+++ b/src/markidocx/rest.py
@@ -23,14 +23,14 @@ from markidocx.templates import FamilyRegistry
 class ResponseEnvelope(BaseModel):
    status: str
    outputs: Any = None
-    warnings: list[str] = []
+    warnings: list[Any] = []  # list[WarningRecord.to_dict()] or list[str] (FR-1208)
    errors: list[str] = []
    context: dict[str, Any] = {}


 def _ok(
    outputs: Any = None,
-    warnings: list[str] | None = None,
+    warnings: list[Any] | None = None,
    context: dict[str, Any] | None = None,
 ) -> ResponseEnvelope:
    return ResponseEnvelope(
@@ -44,7 +44,7 @@ def _ok(

 def _error(
    errors: list[str],
-    warnings: list[str] | None = None,
+    warnings: list[Any] | None = None,
    context: dict[str, Any] | None = None,
 ) -> ResponseEnvelope:
    return ResponseEnvelope(
@@ -158,11 +158,14 @@ def create_app() -> FastAPI:

    @app.get("/capabilities", response_model=ResponseEnvelope)
    def capabilities() -> ResponseEnvelope:
-        """Capability inspection — feature levels and families (FR-909)."""
+        """Capability inspection — feature levels and families (FR-909, FR-537)."""
+        from markidocx.level3 import capabilities_entry as level3_capabilities
+
        return _ok(
            outputs={
                "feature_levels": [e.value for e in FeatureLevel],
                "families": sorted(SUPPORTED_FAMILIES),
+                "level3": level3_capabilities(),
            },
            context={"version": __version__},
        )
@@ -227,17 +230,29 @@ def create_app() -> FastAPI:
                **req.context,
                "family": result.family,
                "feature_level": result.feature_level,
+                "output_state": result.output_state,
            }
            if result.success:
                docx_b64 = base64.b64encode(Path(result.output_path).read_bytes()).decode()
+                outputs: dict[str, Any] = {
+                    "docx_base64": docx_b64,
+                    "output_path": str(result.output_path),
+                }
+                if result.partial_level3:
+                    outputs["partial_level3"] = True
+                    outputs["missing_coverage"] = result.missing_coverage
                return ResponseEnvelope(
                    status="ok",
-                    outputs={"docx_base64": docx_b64, "output_path": str(result.output_path)},
-                    warnings=result.warnings,
+                    outputs=outputs,
+                    warnings=[w.to_dict() for w in result.warning_records],
                    errors=[],
                    context=ctx,
                )
-            return _error(errors=result.errors, warnings=result.warnings, context=ctx)
+            return _error(
+                errors=result.errors,
+                warnings=[w.to_dict() for w in result.warning_records],
+                context=ctx,
+            )

    @app.post("/import", response_model=ResponseEnvelope)
    def import_docx(req: ImportRequest) -> ResponseEnvelope:
@@ -255,7 +270,7 @@ def create_app() -> FastAPI:
            except ManifestError as exc:
                return _error(errors=[str(exc)], context=req.context)
            result = import_document(m, docx_path)
-            ctx = {**req.context}
+            ctx = {**req.context, "output_state": result.output_state}
            if result.success:
                import contextlib

@@ -266,14 +281,14 @@ def create_app() -> FastAPI:
                return ResponseEnvelope(
                    status="ok",
                    outputs={"files": files_md, "mapping_status": result.mapping_status},
-                    warnings=result.warnings,
+                    warnings=[w.to_dict() for w in result.warning_records],
                    errors=[],
                    context=ctx,
                )
            return ResponseEnvelope(
                status="error",
                outputs=None,
-                warnings=result.warnings,
+                warnings=[w.to_dict() for w in result.warning_records],
                errors=["Import failed"],
                context=ctx,
            )
--- a/src/markidocx/xref.py
+++ b/src/markidocx/xref.py
@@ -0,0 +1,159 @@
+"""Cross-reference support for LEVEL3 markidocx (FR-531, FR-540).
+
+Handles the round-trip of heading anchors ({#anchor}) and cross-reference
+links ([text][anchor]) between Markdown and DOCX bookmarks/hyperlinks.
+"""
+
+from __future__ import annotations
+
+import re
+from typing import TYPE_CHECKING
+
+from lxml import etree
+
+if TYPE_CHECKING:
+    from docx.text.paragraph import Paragraph as DocxParagraph
+
+# Markdown patterns
+ANCHOR_LABEL_RE = re.compile(r"\s*\{#([\w-]+)\}\s*$")
+XREF_LINK_RE = re.compile(r"\[([^\]]+)\]\[([\w-]+)\]")
+
+# DOCX XML namespaces
+_W = "http://schemas.openxmlformats.org/wordprocessingml/2006/main"
+_R = "http://schemas.openxmlformats.org/officeDocument/2006/relationships"
+
+
+def extract_anchor_from_heading(text: str) -> tuple[str, str | None]:
+    """Strip `{#anchor}` suffix from heading text.
+
+    Returns (clean_text, anchor_name) — anchor_name is None if no anchor present.
+    """
+    m = ANCHOR_LABEL_RE.search(text)
+    if m:
+        anchor = m.group(1)
+        clean = text[: m.start()]
+        return clean, anchor
+    return text, None
+
+
+def add_bookmark_to_paragraph(para: DocxParagraph, bookmark_name: str, bookmark_id: int) -> None:
+    """Insert a bookmark start/end pair into a paragraph's XML (FR-531)."""
+    p_elem = para._p  # lxml element
+
+    # <w:bookmarkStart w:id="N" w:name="anchor"/>
+    bm_start = etree.SubElement(p_elem, f"{{{_W}}}bookmarkStart")
+    bm_start.set(f"{{{_W}}}id", str(bookmark_id))
+    bm_start.set(f"{{{_W}}}name", bookmark_name)
+
+    # <w:bookmarkEnd w:id="N"/>
+    bm_end = etree.SubElement(p_elem, f"{{{_W}}}bookmarkEnd")
+    bm_end.set(f"{{{_W}}}id", str(bookmark_id))
+
+
+def add_internal_hyperlink(para: DocxParagraph, text: str, anchor: str) -> None:
+    """Add an internal hyperlink run pointing to a bookmark anchor (FR-531).
+
+    Inserts a <w:hyperlink w:anchor="anchor"> element with a run.
+    """
+    p_elem = para._p
+
+    hyperlink = etree.SubElement(p_elem, f"{{{_W}}}hyperlink")
+    hyperlink.set(f"{{{_W}}}anchor", anchor)
+
+    run = etree.SubElement(hyperlink, f"{{{_W}}}r")
+    rpr = etree.SubElement(run, f"{{{_W}}}rPr")
+    style = etree.SubElement(rpr, f"{{{_W}}}rStyle")
+    style.set(f"{{{_W}}}val", "Hyperlink")
+    t = etree.SubElement(run, f"{{{_W}}}t")
+    t.text = text
+    if text and (text[0] == " " or text[-1] == " "):
+        t.set("{http://www.w3.org/XML/1998/namespace}space", "preserve")
+
+
+def render_paragraph_with_xrefs(
+    para: DocxParagraph,
+    text: str,
+    known_anchors: set[str],
+) -> None:
+    """Render paragraph text, converting [text][anchor] to internal hyperlinks (FR-531).
+
+    Falls back to plain text for references to unknown anchors.
+    """
+    last_end = 0
+    for m in XREF_LINK_RE.finditer(text):
+        link_text = m.group(1)
+        anchor = m.group(2)
+        # Add plain text before this match
+        if m.start() > last_end:
+            para.add_run(text[last_end : m.start()])
+        if anchor in known_anchors:
+            add_internal_hyperlink(para, link_text, anchor)
+        else:
+            # Unknown anchor — render as plain text with a note
+            para.add_run(f"{link_text} [→{anchor}]")
+        last_end = m.end()
+    # Remaining text
+    if last_end < len(text):
+        para.add_run(text[last_end:])
+
+
+def has_xref_links(text: str) -> bool:
+    """Return True if *text* contains any [text][anchor] patterns."""
+    return bool(XREF_LINK_RE.search(text))
+
+
+# ---------------------------------------------------------------------------
+# Importer helpers
+# ---------------------------------------------------------------------------
+
+
+def extract_bookmarks_from_paragraph(para: DocxParagraph) -> list[str]:
+    """Return bookmark names declared in the paragraph's XML."""
+    bookmarks: list[str] = []
+    for elem in para._p.iter(f"{{{_W}}}bookmarkStart"):
+        name = elem.get(f"{{{_W}}}name", "")
+        # Ignore Word-internal bookmarks (e.g. _GoBack)
+        if name and not name.startswith("_"):
+            bookmarks.append(name)
+    return bookmarks
+
+
+def extract_internal_hyperlinks_from_paragraph(
+    para: DocxParagraph,
+) -> list[tuple[str, str]]:
+    """Return (text, anchor) pairs for internal hyperlinks in *para*.
+
+    Internal = <w:hyperlink w:anchor="..."> (no relationship ID).
+    """
+    links: list[tuple[str, str]] = []
+    for hl in para._p.iter(f"{{{_W}}}hyperlink"):
+        anchor = hl.get(f"{{{_W}}}anchor")
+        # Only internal bookmark hyperlinks (no r:id)
+        if anchor and not hl.get(f"{{{_R}}}id"):
+            # Collect run text
+            parts: list[str] = []
+            for t_elem in hl.iter(f"{{{_W}}}t"):
+                if t_elem.text:
+                    parts.append(t_elem.text)
+            text = "".join(parts)
+            if text:
+                links.append((text, anchor))
+    return links
+
+
+# ---------------------------------------------------------------------------
+# Differ helpers
+# ---------------------------------------------------------------------------
+
+XREF_ANCHOR_RE = re.compile(r"\{#([\w-]+)\}")
+XREF_LINK_PATTERN = re.compile(r"\[([^\]]+)\]\[([\w-]+)\]")
+
+
+def extract_anchors(text: str) -> set[str]:
+    """Extract all {#anchor} declarations from Markdown text."""
+    return set(XREF_ANCHOR_RE.findall(text))
+
+
+def extract_xref_links(text: str) -> set[tuple[str, str]]:
+    """Extract all (text, anchor) cross-ref link pairs from Markdown text."""
+    return {(m.group(1), m.group(2)) for m in XREF_LINK_PATTERN.finditer(text)}
--- a/tests/regression/level3/init.py
+++ b/tests/regression/level3/init.py
--- a/tests/regression/level3/bibliography_document.md
+++ b/tests/regression/level3/bibliography_document.md
@@ -0,0 +1,35 @@
+# Research Document with Citations
+
+## Introduction
+
+Prior work by [@smith2020] established the foundation. The approach was later
+refined by [@jones2021], building on the original insights of [@smith2020].
+
+## Related Work
+
+Several key contributions inform this work. The landmark paper [@brown2019]
+introduced the core technique. Further development appeared in [@davis2022]
+and [@wilson2023].
+
+## Methodology
+
+Based on [@smith2020] and the refinements of [@jones2021], our methodology
+proceeds as follows.
+
+## Results
+
+Our results confirm the predictions of [@brown2019] and extend the findings
+of [@davis2022].
+
+## Conclusion
+
+This work synthesises [@smith2020], [@jones2021], [@brown2019], [@davis2022],
+and [@wilson2023].
+
+## References
+
+- [@smith2020]: Smith, J. *Foundational Work*. Journal of Research, 2020.
+- [@jones2021]: Jones, B. *Refinements and Extensions*. Proceedings, 2021.
+- [@brown2019]: Brown, C. *The Core Technique*. Nature, 2019.
+- [@davis2022]: Davis, A. *Further Development*. Science, 2022.
+- [@wilson2023]: Wilson, E. *Recent Advances*. Review, 2023.
--- a/tests/regression/level3/combined_document.md
+++ b/tests/regression/level3/combined_document.md
@@ -0,0 +1,63 @@
+# Combined LEVEL3 Feature Document {#combined}
+
+This document exercises all LEVEL3 constructs in a single file.
+
+## Introduction {#intro}
+
+This document demonstrates the full LEVEL3 feature set as described by [@smith2020].
+See [Background][bg] for context.
+
+## Background {#bg}
+
+Context and prerequisites are discussed here. Refer to [Introduction][intro]
+for the problem statement.
+
+## Architecture {#arch-section}
+
+The system architecture is shown below.
+
+![System Architecture](arch.png){#fig:arch}
+
+The architecture overview in [Architecture][arch-section] establishes the
+baseline from which the data flow is derived.
+
+## Data Flow
+
+The data flow diagram illustrates message routing.
+
+```mermaid
+graph LR
+    A[Input] --> B[Processor]
+    B --> C[Output]
+```
+
+## Algorithm {#algo}
+
+The algorithm formalises the approach described in [@jones2021].
+
+```graphviz
+digraph algorithm {
+    start -> step1 -> step2 -> end;
+}
+```
+
+## Results {#results}
+
+Experimental results confirm the algorithm in [Algorithm][algo].
+
+![Experimental Results](results.png){#fig:results}
+
+The results align with predictions from [@brown2019] and the architectural
+choices described in [Architecture][arch-section].
+
+## Conclusion {#conclusion}
+
+All LEVEL3 constructs — cross-references, figures, diagrams, and citations —
+have been demonstrated. See [Introduction][intro] through [Results][results]
+for the complete narrative.
+
+## References
+
+- [@smith2020]: Smith, J. *LEVEL3 Design Principles*. 2020.
+- [@jones2021]: Jones, B. *Algorithm Formalisation*. 2021.
+- [@brown2019]: Brown, C. *Experimental Validation*. 2019.
--- a/tests/regression/level3/diagrams_document.md
+++ b/tests/regression/level3/diagrams_document.md
@@ -0,0 +1,44 @@
+# Document with Diagram Sources
+
+## State Machine
+
+The following Mermaid diagram describes the state machine:
+
+```mermaid
+stateDiagram-v2
+    [*] --> Idle
+    Idle --> Processing: start
+    Processing --> Done: complete
+    Processing --> Error: fail
+    Done --> [*]
+    Error --> Idle: reset
+```
+
+## Dependency Graph
+
+The Graphviz diagram shows dependencies:
+
+```graphviz
+digraph G {
+    A -> B;
+    A -> C;
+    B -> D;
+    C -> D;
+}
+```
+
+## Sequence
+
+The PlantUML sequence diagram:
+
+```plantuml
+@startuml
+Alice -> Bob: Request
+Bob --> Alice: Response
+Alice -> Carol: Forward
+@enduml
+```
+
+## Summary
+
+All three diagram types are supported in LEVEL3 source-only mode.
--- a/tests/regression/level3/figures_document.md
+++ b/tests/regression/level3/figures_document.md
@@ -0,0 +1,29 @@
+# Technical Report with Figures
+
+## Overview
+
+This document contains multiple numbered figures for LEVEL3 round-trip testing.
+
+## System Architecture
+
+The overall architecture is illustrated below.
+
+![System Architecture Overview](figures/architecture.png){#fig:arch}
+
+The architecture shows the main components and their interactions.
+
+## Data Flow
+
+The data flow is shown in the following figure.
+
+![Data Flow Diagram](figures/dataflow.png){#fig:dataflow}
+
+Compare the architecture in [fig:arch] with the data flow above.
+
+## Results
+
+Final results are captured in this chart.
+
+![Results Summary Chart](figures/results.png){#fig:results}
+
+The chart confirms the findings from the data flow in Figure 2.
--- a/tests/regression/level3/xref_document.md
+++ b/tests/regression/level3/xref_document.md
@@ -0,0 +1,21 @@
+# Introduction {#intro}
+
+This document demonstrates cross-reference support for LEVEL3 processing.
+
+## Background {#bg}
+
+The background section provides context. See [Introduction][intro] for the overview.
+
+## Methodology {#method}
+
+This section describes the approach. Refer to [Background][bg] for prerequisites,
+and see [Introduction][intro] for the original problem statement.
+
+## Results {#results}
+
+Results are discussed here. The methodology in [Methodology][method] led to these findings.
+
+## Conclusion
+
+This concludes the document. All sections from [Introduction][intro] through
+[Results][results] have been covered.
--- a/tests/regression/test_level3_roundtrip.py
+++ b/tests/regression/test_level3_roundtrip.py
@@ -0,0 +1,261 @@
+"""LEVEL3 end-to-end round-trip regression tests (FR-1100, MRKD-WP-0003 T07).
+
+Tests the full build → import → compare cycle for each corpus file in
+tests/regression/level3/, using feature_level: level3.
+
+All LEVEL1 regression tests must remain green (non-regression gate).
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+import yaml
+
+from markidocx.builder import build_document
+from markidocx.differ import compare
+from markidocx.importer import import_document
+from markidocx.manifest import load_manifest
+
+# Corpus files in tests/regression/level3/
+CORPUS_DIR = Path(__file__).parent / "level3"
+CORPUS_FILES = [
+    "xref_document.md",
+    "figures_document.md",
+    "diagrams_document.md",
+    "bibliography_document.md",
+    "combined_document.md",
+]
+
+
+def _make_level3_project(tmp_path: Path, markdown: str, name: str = "test") -> Path:
+    (tmp_path / "doc.md").write_text(markdown, encoding="utf-8")
+    manifest_path = tmp_path / "manifest.yaml"
+    manifest_path.write_text(
+        yaml.dump(
+            {
+                "project": {"name": name, "feature_level": "level3", "family": "article"},
+                "sources": [{"path": "doc.md"}],
+                "output": {"dir": "./dist"},
+            }
+        )
+    )
+    (tmp_path / "dist").mkdir()
+    return manifest_path
+
+
+# ---------------------------------------------------------------------------
+# Corpus round-trip tests
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize("corpus_file", CORPUS_FILES)
+def test_level3_corpus_builds(tmp_path: Path, corpus_file: str) -> None:
+    """Each corpus file builds successfully under LEVEL3."""
+    md = (CORPUS_DIR / corpus_file).read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name=corpus_file.replace(".md", ""))
+    manifest = load_manifest(manifest_path)
+
+    result = build_document(manifest)
+    assert result.success, f"Build failed for {corpus_file}: {result.errors}"
+    assert result.output_path.exists()
+    assert result.feature_level == "level3"
+
+
+@pytest.mark.parametrize("corpus_file", CORPUS_FILES)
+def test_level3_corpus_imports(tmp_path: Path, corpus_file: str) -> None:
+    """Each corpus file imports successfully after build."""
+    md = (CORPUS_DIR / corpus_file).read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name=corpus_file.replace(".md", ""))
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success, f"Build failed for {corpus_file}"
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success, f"Import failed for {corpus_file}: {import_result.warnings}"
+
+
+@pytest.mark.parametrize("corpus_file", CORPUS_FILES)
+def test_level3_corpus_no_unexpected_breakage(tmp_path: Path, corpus_file: str) -> None:
+    """Round-trip diff for each corpus file has no broken headings."""
+    md = (CORPUS_DIR / corpus_file).read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name=corpus_file.replace(".md", ""))
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    report = compare(md, reimported)
+
+    # Headings must not be broken
+    broken_headings = [b for b in report.broken if b.startswith("heading:")]
+    assert not broken_headings, (
+        f"Broken headings in {corpus_file}: {broken_headings}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Specific corpus: xref_document — cross-ref anchors preserved
+# ---------------------------------------------------------------------------
+
+
+def test_xref_document_anchors_preserved(tmp_path: Path) -> None:
+    md = (CORPUS_DIR / "xref_document.md").read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name="xref")
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    # Core anchors must survive
+    assert "{#intro}" in reimported
+    assert "{#bg}" in reimported
+    assert "{#method}" in reimported
+    assert "{#results}" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Specific corpus: figures_document — figure labels preserved
+# ---------------------------------------------------------------------------
+
+
+def test_figures_document_labels_preserved(tmp_path: Path) -> None:
+    md = (CORPUS_DIR / "figures_document.md").read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name="figures")
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    assert "fig:arch" in reimported
+    assert "fig:dataflow" in reimported
+    assert "fig:results" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Specific corpus: diagrams_document — diagram sources preserved
+# ---------------------------------------------------------------------------
+
+
+def test_diagrams_document_sources_preserved(tmp_path: Path, monkeypatch) -> None:
+    """Diagram sources survive round-trip in source-only path."""
+    import shutil
+
+    monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+    md = (CORPUS_DIR / "diagrams_document.md").read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name="diagrams")
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    # At least one diagram type must appear in reimported
+    assert "mermaid" in reimported or "graphviz" in reimported or "plantuml" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Specific corpus: bibliography_document — citation keys preserved
+# ---------------------------------------------------------------------------
+
+
+def test_bibliography_document_citations_preserved(tmp_path: Path) -> None:
+    md = (CORPUS_DIR / "bibliography_document.md").read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name="bibliography")
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    assert "smith2020" in reimported
+    assert "jones2021" in reimported
+    assert "brown2019" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Specific corpus: combined_document — all LEVEL3 constructs
+# ---------------------------------------------------------------------------
+
+
+def test_combined_document_roundtrip(tmp_path: Path, monkeypatch) -> None:
+    """Combined document with all LEVEL3 constructs survives build+import."""
+    import shutil
+
+    monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+    md = (CORPUS_DIR / "combined_document.md").read_text(encoding="utf-8")
+    manifest_path = _make_level3_project(tmp_path, md, name="combined")
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+
+    # Anchors preserved
+    assert "{#intro}" in reimported
+
+    # Figures preserved (at least the label)
+    assert "fig:arch" in reimported
+
+    # Citations preserved
+    assert "smith2020" in reimported
+
+
+# ---------------------------------------------------------------------------
+# CLI: markidocx test executes LEVEL1 + LEVEL3 corpus (non-regression gate)
+# ---------------------------------------------------------------------------
+
+
+def test_level1_regression_still_passes(tmp_path: Path) -> None:
+    """LEVEL1 round-trip must remain green after LEVEL3 changes (non-regression)."""
+    from tests.regression.test_roundtrip import LEVEL1_MARKDOWN
+
+    (tmp_path / "doc.md").write_text(LEVEL1_MARKDOWN, encoding="utf-8")
+    manifest_path = tmp_path / "manifest.yaml"
+    manifest_path.write_text(
+        yaml.dump(
+            {
+                "project": {"name": "l1-nonreg", "feature_level": "level1", "family": "article"},
+                "sources": [{"path": "doc.md"}],
+                "output": {"dir": "./dist"},
+            }
+        )
+    )
+    (tmp_path / "dist").mkdir()
+    manifest = load_manifest(manifest_path)
+
+    build_result = build_document(manifest)
+    assert build_result.success
+    assert not build_result.errors
+
+    import_result = import_document(manifest, build_result.output_path)
+    assert import_result.success
+
+    reimported = import_result.output_files[0].read_text(encoding="utf-8")
+    report = compare(LEVEL1_MARKDOWN, reimported)
+    broken_headings = [b for b in report.broken if b.startswith("heading:")]
+    assert not broken_headings
--- a/tests/test_error_framework.py
+++ b/tests/test_error_framework.py
@@ -0,0 +1,380 @@
+"""Tests for structured error & warning framework (FR-1201–1210)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+# ---------------------------------------------------------------------------
+# WarningRecord / FailureRecord / OutputState types (FR-1208–1210)
+# ---------------------------------------------------------------------------
+
+
+class TestWarningRecord:
+    def test_to_dict(self) -> None:
+        from markidocx.errors import Severity, WarningRecord
+
+        w = WarningRecord(severity=Severity.WARNING, reason="unsupported-construct", construct="html_block")
+        d = w.to_dict()
+        assert d["severity"] == "warning"
+        assert d["reason"] == "unsupported-construct"
+        assert d["construct"] == "html_block"
+
+    def test_str_with_construct(self) -> None:
+        from markidocx.errors import WarningRecord
+
+        w = WarningRecord(severity="warning", reason="test-reason", construct="my-token")
+        assert "warning" in str(w)
+        assert "test-reason" in str(w)
+        assert "my-token" in str(w)
+
+    def test_str_without_construct(self) -> None:
+        from markidocx.errors import WarningRecord
+
+        w = WarningRecord(severity="info", reason="test-reason")
+        s = str(w)
+        assert "info" in s
+        assert "test-reason" in s
+
+
+class TestFailureRecord:
+    def test_to_dict(self) -> None:
+        from markidocx.errors import FailureRecord, Severity
+
+        f = FailureRecord(severity=Severity.ERROR, reason="docx-not-found", construct="some.docx")
+        d = f.to_dict()
+        assert d["severity"] == "error"
+        assert d["reason"] == "docx-not-found"
+
+
+class TestOutputState:
+    def test_all_states_defined(self) -> None:
+        from markidocx.errors import OutputState
+
+        assert OutputState.FINAL == "final"
+        assert OutputState.PARTIAL == "partial"
+        assert OutputState.FALLBACK == "fallback"
+        assert OutputState.DEGRADED == "degraded"
+        assert OutputState.UNRESOLVED == "unresolved"
+
+
+# ---------------------------------------------------------------------------
+# Builder emits WarningRecord for unsupported constructs (FR-1203, FR-1205)
+# ---------------------------------------------------------------------------
+
+
+class TestBuilderWarningRecords:
+    def test_unsupported_html_emits_warning_record(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.errors import Severity
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text(
+            "# Hello\n\n<div>raw html</div>\n\nNormal paragraph.",
+            encoding="utf-8",
+        )
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert len(result.warning_records) > 0
+        html_warnings = [w for w in result.warning_records if "html" in w.construct]
+        assert html_warnings, "Expected warning for html construct"
+        assert all(w.severity == Severity.WARNING for w in html_warnings)
+
+    def test_warning_records_have_reason(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text(
+            "# Hello\n\n<div>raw html</div>",
+            encoding="utf-8",
+        )
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        for w in result.warning_records:
+            assert w.reason, "WarningRecord must have a non-empty reason"
+
+    def test_warnings_property_returns_strings(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text("# Hello\n\n<div>html</div>", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert all(isinstance(w, str) for w in result.warnings)
+
+    def test_output_state_on_clean_build(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.errors import OutputState
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text("# Hello\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: clean
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.output_state == OutputState.FINAL
+
+
+# ---------------------------------------------------------------------------
+# Importer emits WarningRecord for errors and fallback paths (FR-1206, FR-1207)
+# ---------------------------------------------------------------------------
+
+
+class TestImporterWarningRecords:
+    def test_not_found_emits_error_warning_record(self, tmp_path: Path) -> None:
+        from markidocx.errors import OutputState, Severity
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text("# Hello", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = import_document(m, tmp_path / "missing.docx")
+        assert not result.success
+        assert result.output_state == OutputState.UNRESOLVED
+        assert len(result.warning_records) > 0
+        assert result.warning_records[0].severity == Severity.ERROR
+        assert result.warning_records[0].reason == "docx-not-found"
+
+    def test_warnings_property_returns_strings(self, tmp_path: Path) -> None:
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        (tmp_path / "doc.md").write_text("# Hello", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = import_document(m, tmp_path / "missing.docx")
+        assert all(isinstance(w, str) for w in result.warnings)
+
+    def test_fallback_emits_fallback_warning(self, tmp_path: Path) -> None:
+        """Multi-source import that can't redistribute produces fallback WarningRecord."""
+        from markidocx.builder import build_document
+        from markidocx.errors import OutputState
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        # Create two source files — the DOCX will have a single H1 so redistribution fails
+        (tmp_path / "a.md").write_text("# Alpha\n\nContent.", encoding="utf-8")
+        (tmp_path / "b.md").write_text("# Beta\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: multi
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: a.md
+                  - path: b.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        # Build first to get a DOCX
+        build_result = build_document(m)
+        assert build_result.success
+
+        # Now import with a manifest that has 3 sources (mismatch)
+        (tmp_path / "c.md").write_text("# Gamma\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest3.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: multi
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: a.md
+                  - path: b.md
+                  - path: c.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m3 = load_manifest(tmp_path / "manifest3.yaml")
+        result = import_document(m3, build_result.output_path)
+        assert result.success
+        assert result.mapping_status == "merged"
+        assert result.output_state == OutputState.FALLBACK
+        fallback_warnings = [w for w in result.warning_records if w.reason == "fallback"]
+        assert fallback_warnings, "Expected fallback WarningRecord"
+
+
+# ---------------------------------------------------------------------------
+# Differ output_state (FR-1204)
+# ---------------------------------------------------------------------------
+
+
+class TestDifferOutputState:
+    def test_final_state_on_clean_diff(self) -> None:
+        from markidocx.differ import compare
+        from markidocx.errors import OutputState
+
+        text = "# Hello\n\nSome paragraph.\n\n- item one\n- item two"
+        report = compare(text, text)
+        assert not report.has_drift
+        assert report.output_state == OutputState.FINAL
+
+    def test_degraded_state_on_degraded_diff(self) -> None:
+        from markidocx.differ import compare
+        from markidocx.errors import OutputState
+
+        original = "# Hello\n\n- item one\n- item two\n- item three"
+        reimported = "# Hello\n\n- item one"
+        report = compare(original, reimported)
+        assert report.has_drift
+        assert report.output_state in (OutputState.DEGRADED, OutputState.PARTIAL)
+
+    def test_partial_state_on_broken_diff(self) -> None:
+        from markidocx.differ import compare
+        from markidocx.errors import OutputState
+
+        original = "# Section A\n\n## Sub\n\nParagraph."
+        reimported = ""
+        report = compare(original, reimported)
+        assert report.has_drift
+        assert report.output_state == OutputState.PARTIAL
+
+
+# ---------------------------------------------------------------------------
+# REST response envelope warnings are WarningRecord dicts (FR-1208)
+# ---------------------------------------------------------------------------
+
+
+class TestRestWarningRecords:
+    def test_build_warnings_are_dicts(self, tmp_path: Path) -> None:
+        """When build produces warnings, REST response warnings are dicts, not bare strings."""
+
+        from fastapi.testclient import TestClient
+
+        from markidocx.rest import create_app
+
+        manifest_yaml = textwrap.dedent("""\
+            project:
+              name: test
+              feature_level: level1
+              family: article
+            sources:
+              - path: doc.md
+            output:
+              dir: ./dist
+        """)
+        # HTML in source will produce warnings
+        sources = [{"name": "doc.md", "content": "# Hello\n\n<div>html</div>"}]
+        client = TestClient(create_app())
+        resp = client.post("/build", json={"manifest_yaml": manifest_yaml, "sources": sources})
+        assert resp.status_code == 200
+        body = resp.json()
+        warnings = body.get("warnings", [])
+        # Each warning should be a dict with severity/reason/construct keys
+        for w in warnings:
+            assert isinstance(w, dict), f"Expected dict warning, got {type(w)}: {w}"
+            assert "severity" in w
+            assert "reason" in w
+
+    def test_import_warnings_are_dicts_on_failure(self) -> None:
+        """Import failure warns with WarningRecord dict, not bare string."""
+        import base64
+
+        from fastapi.testclient import TestClient
+
+        from markidocx.rest import create_app
+
+        manifest_yaml = textwrap.dedent("""\
+            project:
+              name: test
+              feature_level: level1
+              family: article
+            sources:
+              - path: doc.md
+            output:
+              dir: ./dist
+        """)
+        # Send an invalid (empty) DOCX
+        empty_docx = base64.b64encode(b"not-a-docx").decode()
+        client = TestClient(create_app())
+        resp = client.post(
+            "/import",
+            json={"manifest_yaml": manifest_yaml, "docx_base64": empty_docx},
+        )
+        body = resp.json()
+        warnings = body.get("warnings", [])
+        for w in warnings:
+            assert isinstance(w, dict), f"Expected dict warning, got {type(w)}: {w}"
--- a/tests/test_level3_bibliography.py
+++ b/tests/test_level3_bibliography.py
@@ -0,0 +1,349 @@
+"""Tests for LEVEL3 bibliography & citation support (FR-535, FR-536, FR-542)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+LEVEL3_MANIFEST = textwrap.dedent("""\
+    project:
+      name: bib-test
+      feature_level: level3
+      family: article
+    sources:
+      - path: doc.md
+    output:
+      dir: ./dist
+""")
+
+
+def _make_project(tmp_path: Path, markdown: str) -> Path:
+    (tmp_path / "doc.md").write_text(markdown, encoding="utf-8")
+    (tmp_path / "manifest.yaml").write_text(LEVEL3_MANIFEST, encoding="utf-8")
+    return tmp_path
+
+
+# ---------------------------------------------------------------------------
+# bibliography module helpers
+# ---------------------------------------------------------------------------
+
+
+class TestBibliographyHelpers:
+    def test_has_citations_true(self) -> None:
+        from markidocx.bibliography import has_citations
+
+        assert has_citations("See [@smith2020] for details.")
+
+    def test_has_citations_false(self) -> None:
+        from markidocx.bibliography import has_citations
+
+        assert not has_citations("Normal paragraph without citations.")
+
+    def test_extract_citation_keys(self) -> None:
+        from markidocx.bibliography import extract_citation_keys
+
+        text = "See [@smith2020] and [@jones2021:chap] for more."
+        keys = extract_citation_keys(text)
+        assert "smith2020" in keys
+        assert "jones2021:chap" in keys
+
+    def test_is_references_heading(self) -> None:
+        from markidocx.bibliography import is_references_heading
+
+        assert is_references_heading("## References")
+        assert is_references_heading("# References")
+        assert is_references_heading("### References")
+        assert not is_references_heading("## Introduction")
+
+    def test_parse_reference_entry(self) -> None:
+        from markidocx.bibliography import parse_reference_entry
+
+        result = parse_reference_entry("- [@smith2020]: Smith, J. *Title*. 2020.")
+        assert result is not None
+        key, entry = result
+        assert key == "smith2020"
+        assert "Smith, J." in entry
+
+    def test_extract_references_section(self) -> None:
+        from markidocx.bibliography import extract_references_section
+
+        md = textwrap.dedent("""\
+            # Document
+
+            See [@smith2020].
+
+            ## References
+
+            - [@smith2020]: Smith, J. *A Book*. 2020.
+            - [@jones2021]: Jones, B. *Another*. 2021.
+        """)
+        entries, text_without = extract_references_section(md)
+        assert len(entries) == 2
+        assert entries[0][0] == "smith2020"
+        assert entries[1][0] == "jones2021"
+        assert "## References" not in text_without
+
+    def test_render_citation_text_unchanged(self) -> None:
+        from markidocx.bibliography import render_citation_text
+
+        text = "See [@smith2020] for details."
+        assert render_citation_text(text) == text
+
+
+# ---------------------------------------------------------------------------
+# Builder: citations and references section (FR-535)
+# ---------------------------------------------------------------------------
+
+
+class TestBuilderBibliography:
+    def test_build_with_citation_succeeds(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Document
+
+            As shown by [@smith2020], the approach works.
+
+            ## References
+
+            - [@smith2020]: Smith, J. *A Work*. 2020.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.output_path.exists()
+
+    def test_build_docx_contains_citation_marker(self, tmp_path: Path) -> None:
+        """The built DOCX should contain the citation text."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Doc\n\nSee [@smith2020].\n\n## References\n\n- [@smith2020]: Smith. *T*. 2020."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        citation_paras = [t for t in texts if "smith2020" in t]
+        assert citation_paras, f"No citation found in DOCX. Paragraphs: {texts}"
+
+    def test_build_docx_contains_references_heading(self, tmp_path: Path) -> None:
+        """The built DOCX should have a References heading."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Doc\n\nText.\n\n## References\n\n- [@k1]: Author. *T*. 2020."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        assert "References" in texts, f"No References heading. Paragraphs: {texts}"
+
+    def test_build_multi_citation_document(self, tmp_path: Path) -> None:
+        """Multiple citations and references entries all appear in DOCX."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Introduction
+
+            According to [@smith2020] and [@jones2021], this is true.
+
+            ## References
+
+            - [@smith2020]: Smith, J. *Work A*. 2020.
+            - [@jones2021]: Jones, B. *Work B*. 2021.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        all_text = " ".join(p.text for p in doc.paragraphs)
+        assert "smith2020" in all_text
+        assert "jones2021" in all_text
+
+
+# ---------------------------------------------------------------------------
+# Importer: citations and references restoration (FR-536)
+# ---------------------------------------------------------------------------
+
+
+class TestImporterBibliography:
+    def test_roundtrip_preserves_citation(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Doc\n\nSee [@smith2020].\n\n## References\n\n- [@smith2020]: Smith. *T*. 2020."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "smith2020" in reimported
+
+    def test_roundtrip_preserves_reference_entry(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Doc
+
+            See [@k1].
+
+            ## References
+
+            - [@k1]: Author. *Title*. 2020.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "k1" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Differ: citation and bibliography comparison (FR-542)
+# ---------------------------------------------------------------------------
+
+
+class TestDifferBibliography:
+    def test_preserved_citation(self) -> None:
+        from markidocx.differ import compare
+
+        text = "# Doc\n\nSee [@smith2020].\n\n## References\n\n- [@smith2020]: Smith. *T*. 2020."
+        report = compare(text, text)
+        assert any("citation:[@smith2020]" in p for p in report.preserved)
+
+    def test_missing_citation_broken(self) -> None:
+        from markidocx.differ import compare
+
+        original = "See [@smith2020]."
+        reimported = "See something."
+        report = compare(original, reimported)
+        assert any("citation:missing '[@smith2020]'" in b for b in report.broken)
+        assert report.has_drift
+
+    def test_missing_reference_entry_degraded(self) -> None:
+        from markidocx.differ import compare
+
+        original = textwrap.dedent("""\
+            See [@k1].
+
+            ## References
+
+            - [@k1]: Author. *T*. 2020.
+        """)
+        reimported = "See [@k1]."
+        report = compare(original, reimported)
+        assert any("reference-entry" in d for d in report.degraded)
+
+    def test_unresolvable_citation_emits_warning(self) -> None:
+        """Missing citation in reimported emits citation-ambiguity warning."""
+        from markidocx.bibliography import compare_citations
+        from markidocx.errors import WarningRecord
+
+        original = "See [@missing]."
+        reimported = "See something."
+        preserved: list[str] = []
+        degraded: list[str] = []
+        broken: list[str] = []
+        warning_records: list[WarningRecord] = []
+
+        compare_citations(original, reimported, preserved, degraded, broken, warning_records)
+
+        ambiguity = [w for w in warning_records if w.reason == "citation-ambiguity"]
+        assert ambiguity, "Expected citation-ambiguity warning"
+        assert ambiguity[0].construct == "@missing"
+
+
+# ---------------------------------------------------------------------------
+# Single citation round-trip
+# ---------------------------------------------------------------------------
+
+
+class TestCitationRoundTrip:
+    def test_single_citation_roundtrip(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.differ import compare
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Introduction
+
+            According to [@smith2020], things are good.
+
+            ## References
+
+            - [@smith2020]: Smith, J. *Good Stuff*. 2020.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        report = compare(md, reimported)
+
+        broken_citations = [b for b in report.broken if "citation" in b]
+        assert not broken_citations, f"Broken citations: {broken_citations}"
+
+    def test_multi_citation_document(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Paper
+
+            First point from [@a2020]. Second from [@b2021].
+
+            ## References
+
+            - [@a2020]: A. *Work A*. 2020.
+            - [@b2021]: B. *Work B*. 2021.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "a2020" in reimported
+        assert "b2021" in reimported
--- a/tests/test_level3_diagrams.py
+++ b/tests/test_level3_diagrams.py
@@ -0,0 +1,231 @@
+"""Tests for LEVEL3 auto-diagram support (FR-533, FR-534)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+LEVEL3_MANIFEST = textwrap.dedent("""\
+    project:
+      name: diag-test
+      feature_level: level3
+      family: article
+    sources:
+      - path: doc.md
+    output:
+      dir: ./dist
+""")
+
+
+def _make_project(tmp_path: Path, markdown: str) -> Path:
+    (tmp_path / "doc.md").write_text(markdown, encoding="utf-8")
+    (tmp_path / "manifest.yaml").write_text(LEVEL3_MANIFEST, encoding="utf-8")
+    return tmp_path
+
+
+# ---------------------------------------------------------------------------
+# diagrams module helpers
+# ---------------------------------------------------------------------------
+
+
+class TestDiagramHelpers:
+    def test_is_diagram_info_mermaid(self) -> None:
+        from markidocx.diagrams import is_diagram_info
+
+        assert is_diagram_info("mermaid")
+
+    def test_is_diagram_info_graphviz(self) -> None:
+        from markidocx.diagrams import is_diagram_info
+
+        assert is_diagram_info("graphviz")
+
+    def test_is_diagram_info_plantuml(self) -> None:
+        from markidocx.diagrams import is_diagram_info
+
+        assert is_diagram_info("plantuml")
+
+    def test_is_diagram_info_python_false(self) -> None:
+        from markidocx.diagrams import is_diagram_info
+
+        assert not is_diagram_info("python")
+        assert not is_diagram_info("")
+        assert not is_diagram_info(None)
+
+    def test_is_diagram_source_marker(self) -> None:
+        from markidocx.diagrams import is_diagram_source_marker
+
+        assert is_diagram_source_marker("diagram-source:mermaid\ngraph TD\nA-->B")
+        assert not is_diagram_source_marker("normal text")
+
+    def test_parse_diagram_source_marker(self) -> None:
+        from markidocx.diagrams import parse_diagram_source_marker
+
+        source = "graph TD\nA-->B"
+        result = parse_diagram_source_marker(f"diagram-source:mermaid\n{source}")
+        assert result is not None
+        diagram_type, parsed_source = result
+        assert diagram_type == "mermaid"
+        assert parsed_source == source
+
+    def test_reconstruct_diagram_md(self) -> None:
+        from markidocx.diagrams import reconstruct_diagram_md
+
+        result = reconstruct_diagram_md("mermaid", "graph TD\nA-->B")
+        assert result.startswith("```mermaid")
+        assert "graph TD" in result
+        assert result.endswith("```")
+
+
+# ---------------------------------------------------------------------------
+# Builder: diagram blocks → source-only path (no renderer in test env) (FR-533)
+# ---------------------------------------------------------------------------
+
+
+class TestBuilderDiagrams:
+    def test_build_with_mermaid_block_succeeds(self, tmp_path: Path) -> None:
+        """Mermaid block builds without error (source-only path)."""
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Document
+
+            ```mermaid
+            graph TD
+            A --> B --> C
+            ```
+
+            Some text.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+    def test_build_emits_warning_for_unavailable_renderer(
+        self, tmp_path: Path, monkeypatch
+    ) -> None:
+        """Warns about missing diagram renderer (FR-538)."""
+        import shutil
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        md = "```mermaid\ngraph TD\nA-->B\n```"
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        dep_warnings = [
+            w for w in result.warning_records
+            if w.reason == "processor-dependency-unavailable"
+        ]
+        assert dep_warnings
+
+    def test_build_docx_contains_source_marker(
+        self, tmp_path: Path, monkeypatch
+    ) -> None:
+        """DOCX contains diagram-source marker for round-trip."""
+        import shutil
+
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        md = "```mermaid\ngraph TD\nA-->B\n```"
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        marker_texts = [t for t in texts if t.startswith("diagram-source:")]
+        assert marker_texts, f"No diagram-source marker found. Paragraphs: {texts}"
+
+    def test_build_graphviz_block_succeeds(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "```graphviz\ndigraph G { A -> B }\n```"
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+    def test_non_diagram_code_block_not_warned(
+        self, tmp_path: Path
+    ) -> None:
+        """Python code blocks don't trigger diagram warnings."""
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "```python\nprint('hello')\n```"
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        dep_warnings = [
+            w for w in result.warning_records
+            if w.reason == "processor-dependency-unavailable"
+        ]
+        # Only level3 diagram types trigger this warning, not python
+        # (may still warn for mmdc/dot if level3 partial check fires, but not for python block)
+        python_warnings = [w for w in dep_warnings if "python" in w.construct]
+        assert not python_warnings
+
+
+# ---------------------------------------------------------------------------
+# Importer: diagram source-intent marker → fenced block (FR-534)
+# ---------------------------------------------------------------------------
+
+
+class TestImporterDiagrams:
+    def test_roundtrip_source_only_path(self, tmp_path: Path, monkeypatch) -> None:
+        """Source-only round-trip: diagram source is preserved in reimported MD."""
+        import shutil
+
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        diagram_source = "graph TD\nA --> B --> C"
+        md = f"# Document\n\n```mermaid\n{diagram_source}\n```\n\nText."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "mermaid" in reimported
+        assert "graph TD" in reimported
+
+    def test_no_source_discarded(self, tmp_path: Path, monkeypatch) -> None:
+        """Diagram source is never silently dropped (FR-1205)."""
+        import shutil
+
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        md = "```plantuml\n@startuml\nAlice -> Bob: Hi\n@enduml\n```"
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        # Source content must be present somewhere in the reimported text
+        assert "plantuml" in reimported or "@startuml" in reimported
--- a/tests/test_level3_figures.py
+++ b/tests/test_level3_figures.py
@@ -0,0 +1,342 @@
+"""Tests for LEVEL3 numbered figure support (FR-532, FR-541)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+LEVEL3_MANIFEST = textwrap.dedent("""\
+    project:
+      name: fig-test
+      feature_level: level3
+      family: article
+    sources:
+      - path: doc.md
+    output:
+      dir: ./dist
+""")
+
+
+def _make_project(tmp_path: Path, markdown: str) -> Path:
+    (tmp_path / "doc.md").write_text(markdown, encoding="utf-8")
+    (tmp_path / "manifest.yaml").write_text(LEVEL3_MANIFEST, encoding="utf-8")
+    return tmp_path
+
+
+# ---------------------------------------------------------------------------
+# figures module helpers
+# ---------------------------------------------------------------------------
+
+
+class TestFigureHelpers:
+    def test_is_figure_paragraph_true(self) -> None:
+        from markidocx.figures import is_figure_paragraph
+
+        assert is_figure_paragraph("![My Caption](img/photo.png){#fig:photo}")
+
+    def test_is_figure_paragraph_false(self) -> None:
+        from markidocx.figures import is_figure_paragraph
+
+        assert not is_figure_paragraph("Normal paragraph text.")
+        assert not is_figure_paragraph("![alt](img.png)")  # no {#fig:} label
+
+    def test_parse_figure(self) -> None:
+        from markidocx.figures import parse_figure
+
+        result = parse_figure("![Architecture Diagram](arch.png){#fig:arch}")
+        assert result is not None
+        caption, path, label = result
+        assert caption == "Architecture Diagram"
+        assert path == "arch.png"
+        assert label == "fig:arch"
+
+    def test_extract_figures_from_md(self) -> None:
+        from markidocx.figures import extract_figures_from_md
+
+        md = textwrap.dedent("""\
+            # Title
+
+            Some text.
+
+            ![Figure One](fig1.png){#fig:f1}
+
+            More text.
+
+            ![Figure Two](fig2.png){#fig:f2}
+        """)
+        figs = extract_figures_from_md(md)
+        assert len(figs) == 2
+        assert figs[0] == ("Figure One", "fig1.png", "fig:f1")
+        assert figs[1] == ("Figure Two", "fig2.png", "fig:f2")
+
+    def test_extract_figure_labels(self) -> None:
+        from markidocx.figures import extract_figure_labels
+
+        md = "![Cap1](a.png){#fig:f1}\n\n![Cap2](b.png){#fig:f2}"
+        labels = extract_figure_labels(md)
+        assert labels == {"fig:f1", "fig:f2"}
+
+    def test_is_caption_paragraph(self) -> None:
+        from markidocx.figures import is_caption_paragraph
+
+        assert is_caption_paragraph("Figure 1 — My Caption")
+        assert is_caption_paragraph("Figure 3 - Another Caption")
+        assert not is_caption_paragraph("Some normal text")
+
+    def test_reconstruct_figure_md(self) -> None:
+        from markidocx.figures import reconstruct_figure_md
+
+        result = reconstruct_figure_md("My Caption", "img/photo.png", "fig:photo")
+        assert result == "![My Caption](img/photo.png){#fig:photo}"
+
+
+# ---------------------------------------------------------------------------
+# Builder: figure declaration → DOCX caption paragraph (FR-532)
+# ---------------------------------------------------------------------------
+
+
+class TestBuilderFigures:
+    def test_build_with_figure_succeeds(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Document {#doc}
+
+            Introduction.
+
+            ![Architecture Diagram](arch.png){#fig:arch}
+
+            More text.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.output_path.exists()
+
+    def test_build_docx_contains_figure_caption(self, tmp_path: Path) -> None:
+        """The built DOCX should contain a caption paragraph with 'Figure 1'."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "![My Diagram](diag.png){#fig:diag}\n\nSome text."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        caption_paras = [t for t in texts if t.startswith("Figure 1")]
+        assert caption_paras, f"No 'Figure 1' caption found. Paragraphs: {texts}"
+
+    def test_multiple_figures_numbered_sequentially(self, tmp_path: Path) -> None:
+        """Multiple figures get Figure 1, Figure 2, Figure 3."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Doc
+
+            ![First](a.png){#fig:a}
+
+            Some text.
+
+            ![Second](b.png){#fig:b}
+
+            More text.
+
+            ![Third](c.png){#fig:c}
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        assert any("Figure 1" in t for t in texts)
+        assert any("Figure 2" in t for t in texts)
+        assert any("Figure 3" in t for t in texts)
+
+    def test_figure_not_activated_for_level1(self, tmp_path: Path) -> None:
+        """LEVEL1: figure syntax is not stripped (no caption paragraphs added)."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        manifest_yaml = textwrap.dedent("""\
+            project:
+              name: l1-fig
+              feature_level: level1
+              family: article
+            sources:
+              - path: doc.md
+            output:
+              dir: ./dist
+        """)
+        (tmp_path / "doc.md").write_text(
+            "# Title\n\n![My Diagram](diag.png){#fig:diag}", encoding="utf-8"
+        )
+        (tmp_path / "manifest.yaml").write_text(manifest_yaml, encoding="utf-8")
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        doc = DocxReader(str(result.output_path))
+        texts = [p.text for p in doc.paragraphs]
+        # No "Figure N" captions in LEVEL1 output
+        assert not any(t.startswith("Figure ") for t in texts)
+
+
+# ---------------------------------------------------------------------------
+# Importer: DOCX caption paragraphs → figure markdown (FR-532)
+# ---------------------------------------------------------------------------
+
+
+class TestImporterFigures:
+    def test_roundtrip_preserves_figure_caption(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Title\n\n![Architecture](arch.png){#fig:arch}\n\nText."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "Architecture" in reimported
+        assert "fig:arch" in reimported
+
+    def test_roundtrip_preserves_figure_label(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = "![Cap](img.png){#fig:myimg}\n\nText."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "{#fig:myimg}" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Differ: figure identity coherence (FR-541)
+# ---------------------------------------------------------------------------
+
+
+class TestDifferFigures:
+    def test_preserved_figure_label(self) -> None:
+        from markidocx.differ import compare
+
+        text = "# Title\n\n![Cap](img.png){#fig:img}\n\nText."
+        report = compare(text, text)
+        assert any("figure-label:fig:img" in p for p in report.preserved)
+
+    def test_missing_figure_label_broken(self) -> None:
+        from markidocx.differ import compare
+
+        original = "![Cap](img.png){#fig:img}\n\nText."
+        reimported = "Text."
+        report = compare(original, reimported)
+        assert any("figure-label:missing 'fig:img'" in b for b in report.broken)
+        assert report.has_drift
+
+    def test_missing_caption_degraded(self) -> None:
+        from markidocx.differ import compare
+
+        original = "![My Caption](img.png){#fig:img}"
+        reimported = "![Different Caption](img.png){#fig:img}"
+        report = compare(original, reimported)
+        assert any("figure-caption" in d for d in report.degraded)
+
+    def test_preserved_caption(self) -> None:
+        from markidocx.differ import compare
+
+        text = "![Same Caption](img.png){#fig:img}"
+        report = compare(text, text)
+        assert any("figure-caption" in p for p in report.preserved)
+
+
+# ---------------------------------------------------------------------------
+# Full figure round-trip
+# ---------------------------------------------------------------------------
+
+
+class TestFigureRoundTrip:
+    def test_single_figure_roundtrip(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.differ import compare
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Document
+
+            Introduction.
+
+            ![System Architecture](arch.png){#fig:arch}
+
+            Conclusion.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        report = compare(md, reimported)
+
+        # No broken figures
+        broken_figs = [b for b in report.broken if "figure" in b]
+        assert not broken_figs, f"Broken figures found: {broken_figs}"
+
+    def test_multiple_figures_identity_coherent(self, tmp_path: Path) -> None:
+        """Multiple figures survive round-trip with correct labels."""
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Doc
+
+            ![Figure One Caption](fig1.png){#fig:f1}
+
+            Text between figures.
+
+            ![Figure Two Caption](fig2.png){#fig:f2}
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "{#fig:f1}" in reimported
+        assert "{#fig:f2}" in reimported
--- a/tests/test_level3_plumbing.py
+++ b/tests/test_level3_plumbing.py
@@ -0,0 +1,271 @@
+"""Tests for LEVEL3 plumbing — feature-level gating & disclosure (FR-537–539)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+from markidocx.level3 import (
+    Level3Support,
+    ProcessorDependency,
+    capabilities_entry,
+    check_level3_support,
+)
+from markidocx.manifest import FeatureLevel, load_manifest
+
+# ---------------------------------------------------------------------------
+# Level3 support detection (FR-537, FR-538)
+# ---------------------------------------------------------------------------
+
+
+class TestCheckLevel3Support:
+    def test_returns_level3_support(self) -> None:
+        support = check_level3_support()
+        assert isinstance(support, Level3Support)
+
+    def test_always_available(self) -> None:
+        support = check_level3_support()
+        assert support.available is True
+
+    def test_dependencies_are_processor_dependency_instances(self) -> None:
+        support = check_level3_support()
+        for dep in support.dependencies:
+            assert isinstance(dep, ProcessorDependency)
+            assert dep.name in ("mmdc", "dot", "plantuml")
+            assert isinstance(dep.available, bool)
+            assert dep.description
+
+    def test_partial_when_no_diagram_tools(self, monkeypatch) -> None:
+        """When no diagram tool is found, partial=True and missing_coverage is populated."""
+        import shutil
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        support = check_level3_support()
+        assert support.partial is True
+        assert len(support.missing_coverage) > 0
+        assert any("diagram" in m for m in support.missing_coverage)
+
+    def test_not_partial_when_diagram_tool_present(self, monkeypatch) -> None:
+        """When at least one diagram tool is found, partial=False."""
+        import shutil
+
+        def fake_which(cmd: str) -> str | None:
+            return "/usr/bin/mmdc" if cmd == "mmdc" else None
+
+        monkeypatch.setattr(shutil, "which", fake_which)
+        support = check_level3_support()
+        assert support.partial is False
+        assert support.missing_coverage == []
+
+
+# ---------------------------------------------------------------------------
+# capabilities_entry (FR-537)
+# ---------------------------------------------------------------------------
+
+
+class TestCapabilitiesEntry:
+    def test_returns_dict_with_level(self) -> None:
+        entry = capabilities_entry()
+        assert entry["level"] == "level3"
+
+    def test_available_is_true(self) -> None:
+        entry = capabilities_entry()
+        assert entry["available"] is True
+
+    def test_has_dependencies_list(self) -> None:
+        entry = capabilities_entry()
+        assert isinstance(entry["dependencies"], list)
+        for dep in entry["dependencies"]:
+            assert "name" in dep
+            assert "available" in dep
+            assert "description" in dep
+
+    def test_has_partial_and_missing_coverage(self) -> None:
+        entry = capabilities_entry()
+        assert "partial" in entry
+        assert "missing_coverage" in entry
+
+
+# ---------------------------------------------------------------------------
+# Manifest accepts feature_level: level3 (FR-537)
+# ---------------------------------------------------------------------------
+
+
+class TestManifestLevel3:
+    def test_level3_accepted(self, tmp_path: Path) -> None:
+        (tmp_path / "doc.md").write_text("# Hello", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test
+                  feature_level: level3
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        assert m.project.feature_level == FeatureLevel.LEVEL3
+
+    def test_level3_routes_to_level3_processing(self, tmp_path: Path) -> None:
+        """Building with feature_level: level3 succeeds (processing path reached)."""
+        from markidocx.builder import build_document
+
+        (tmp_path / "doc.md").write_text("# Hello\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test-l3
+                  feature_level: level3
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.feature_level == "level3"
+
+
+# ---------------------------------------------------------------------------
+# partial_level3 flag and processor-dependency disclosure (FR-538, FR-539)
+# ---------------------------------------------------------------------------
+
+
+class TestPartialLevel3Flag:
+    def test_partial_level3_set_when_no_diagram_tools(
+        self, tmp_path: Path, monkeypatch
+    ) -> None:
+        import shutil
+
+        from markidocx.builder import build_document
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        (tmp_path / "doc.md").write_text("# Hello\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test-partial
+                  feature_level: level3
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.partial_level3 is True
+        assert len(result.missing_coverage) > 0
+
+    def test_partial_level3_false_for_level1(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+
+        (tmp_path / "doc.md").write_text("# Hello\n\nContent.", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: test-l1
+                  feature_level: level1
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.partial_level3 is False
+        assert result.missing_coverage == []
+
+    def test_dependency_warning_emitted_for_unavailable_tool(
+        self, tmp_path: Path, monkeypatch
+    ) -> None:
+        import shutil
+
+        from markidocx.builder import build_document
+        from markidocx.errors import Severity
+
+        monkeypatch.setattr(shutil, "which", lambda _cmd: None)
+        (tmp_path / "doc.md").write_text("# Hello", encoding="utf-8")
+        (tmp_path / "manifest.yaml").write_text(
+            textwrap.dedent("""\
+                project:
+                  name: t
+                  feature_level: level3
+                  family: article
+                sources:
+                  - path: doc.md
+                output:
+                  dir: ./dist
+            """),
+            encoding="utf-8",
+        )
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        dep_warnings = [
+            w for w in result.warning_records
+            if w.reason == "processor-dependency-unavailable"
+        ]
+        assert dep_warnings, "Expected processor-dependency-unavailable warning"
+        assert all(w.severity == Severity.WARNING for w in dep_warnings)
+
+
+# ---------------------------------------------------------------------------
+# REST capabilities includes level3 (FR-537)
+# ---------------------------------------------------------------------------
+
+
+class TestRestCapabilitiesLevel3:
+    def test_capabilities_includes_level3(self) -> None:
+        from fastapi.testclient import TestClient
+
+        from markidocx.rest import create_app
+
+        client = TestClient(create_app())
+        resp = client.get("/capabilities")
+        assert resp.status_code == 200
+        body = resp.json()
+        outputs = body["outputs"]
+        assert "level3" in outputs
+        assert outputs["level3"]["level"] == "level3"
+        assert outputs["level3"]["available"] is True
+        assert "dependencies" in outputs["level3"]
+
+
+# ---------------------------------------------------------------------------
+# MCP validate_project includes level3 in context (FR-537)
+# ---------------------------------------------------------------------------
+
+
+class TestMcpLevel3:
+    def test_validate_project_includes_level3(self) -> None:
+        from markidocx.mcp_server import validate_project
+
+        manifest_yaml = textwrap.dedent("""\
+            project:
+              name: test
+              feature_level: level3
+              family: article
+            sources:
+              - path: doc.md
+            output:
+              dir: ./dist
+        """)
+        result = validate_project(manifest_yaml)
+        assert result["status"] == "ok"
+        assert result["feature_level"] == "level3"
+        assert "level3" in result["context"]
+        assert result["context"]["level3"]["available"] is True
--- a/tests/test_level3_xref.py
+++ b/tests/test_level3_xref.py
@@ -0,0 +1,326 @@
+"""Tests for LEVEL3 cross-reference support (FR-531, FR-540)."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+LEVEL3_MANIFEST = textwrap.dedent("""\
+    project:
+      name: xref-test
+      feature_level: level3
+      family: article
+    sources:
+      - path: doc.md
+    output:
+      dir: ./dist
+""")
+
+
+def _make_project(tmp_path: Path, markdown: str, manifest_yaml: str = LEVEL3_MANIFEST) -> Path:
+    (tmp_path / "doc.md").write_text(markdown, encoding="utf-8")
+    (tmp_path / "manifest.yaml").write_text(manifest_yaml, encoding="utf-8")
+    return tmp_path
+
+
+# ---------------------------------------------------------------------------
+# xref module helpers
+# ---------------------------------------------------------------------------
+
+
+class TestXrefHelpers:
+    def test_extract_anchor_from_heading_plain(self) -> None:
+        from markidocx.xref import extract_anchor_from_heading
+
+        clean, anchor = extract_anchor_from_heading("Introduction {#intro}")
+        assert clean == "Introduction"
+        assert anchor == "intro"
+
+    def test_extract_anchor_from_heading_no_anchor(self) -> None:
+        from markidocx.xref import extract_anchor_from_heading
+
+        clean, anchor = extract_anchor_from_heading("Introduction")
+        assert clean == "Introduction"
+        assert anchor is None
+
+    def test_extract_anchors_from_text(self) -> None:
+        from markidocx.xref import extract_anchors
+
+        text = "# Section {#sec1}\n\n## Subsection {#sec2}\n\nNormal."
+        anchors = extract_anchors(text)
+        assert anchors == {"sec1", "sec2"}
+
+    def test_extract_xref_links(self) -> None:
+        from markidocx.xref import extract_xref_links
+
+        text = "See [Section One][sec1] and [Section Two][sec2]."
+        links = extract_xref_links(text)
+        assert ("Section One", "sec1") in links
+        assert ("Section Two", "sec2") in links
+
+    def test_has_xref_links_true(self) -> None:
+        from markidocx.xref import has_xref_links
+
+        assert has_xref_links("See [Intro][intro] for details.")
+
+    def test_has_xref_links_false(self) -> None:
+        from markidocx.xref import has_xref_links
+
+        assert not has_xref_links("Normal paragraph without refs.")
+
+
+# ---------------------------------------------------------------------------
+# Builder: headings with anchors → DOCX bookmarks (FR-531)
+# ---------------------------------------------------------------------------
+
+
+class TestBuilderXref:
+    def test_build_with_anchor_succeeds(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Introduction {#intro}\n\nSome text.\n\n## Section One {#sec1}\n\nContent."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.output_path.exists()
+
+    def test_build_docx_contains_bookmark(self, tmp_path: Path) -> None:
+        """The built DOCX XML should contain a bookmarkStart for {#intro}."""
+        from docx import Document as DocxReader
+
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Introduction {#intro}\n\nContent."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+
+        doc = DocxReader(str(result.output_path))
+        _W = "http://schemas.openxmlformats.org/wordprocessingml/2006/main"
+        bookmarks = [
+            elem.get(f"{{{_W}}}name")
+            for elem in doc.element.body.iter(f"{{{_W}}}bookmarkStart")
+            if elem.get(f"{{{_W}}}name") and not elem.get(f"{{{_W}}}name", "").startswith("_")
+        ]
+        assert "intro" in bookmarks
+
+    def test_build_with_cross_ref_link(self, tmp_path: Path) -> None:
+        """Cross-ref links [text][anchor] render without errors."""
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Introduction {#intro}
+
+            Some text.
+
+            # Methodology {#method}
+
+            See [Introduction][intro] for background.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        assert result.output_path.exists()
+
+    def test_build_xref_not_activated_for_level1(self, tmp_path: Path) -> None:
+        """Level1 build: {#anchor} syntax is treated as literal heading text."""
+        from markidocx.builder import build_document
+        from markidocx.manifest import load_manifest
+
+        manifest_yaml = textwrap.dedent("""\
+            project:
+              name: l1-test
+              feature_level: level1
+              family: article
+            sources:
+              - path: doc.md
+            output:
+              dir: ./dist
+        """)
+        # In LEVEL1, {#anchor} is not stripped and no bookmark is added
+        md = "# Introduction {#intro}\n\nContent."
+        _make_project(tmp_path, md, manifest_yaml)
+        m = load_manifest(tmp_path / "manifest.yaml")
+        result = build_document(m)
+        assert result.success
+        # No cross-ref warnings
+        xref_warnings = [w for w in result.warning_records if "xref" in w.reason.lower()]
+        assert not xref_warnings
+
+
+# ---------------------------------------------------------------------------
+# Importer: DOCX bookmarks → {#anchor} labels (FR-531)
+# ---------------------------------------------------------------------------
+
+
+class TestImporterXref:
+    def test_roundtrip_preserves_anchor(self, tmp_path: Path) -> None:
+        """Build LEVEL3 doc with {#anchor}, import back → heading has {#anchor}."""
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = "# Introduction {#intro}\n\nSome text."
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "{#intro}" in reimported
+
+    def test_roundtrip_preserves_cross_ref_link(self, tmp_path: Path) -> None:
+        """Cross-ref link [text][anchor] survives a round trip."""
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Introduction {#intro}
+
+            Some intro text.
+
+            # Methodology {#method}
+
+            See [Introduction][intro] for background.
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        assert "{#intro}" in reimported
+        assert "[Introduction][intro]" in reimported
+
+
+# ---------------------------------------------------------------------------
+# Differ: cross-ref detection (FR-540)
+# ---------------------------------------------------------------------------
+
+
+class TestDifferXref:
+    def test_preserved_anchor_reported(self) -> None:
+        from markidocx.differ import compare
+
+        original = "# Introduction {#intro}\n\nText."
+        reimported = "# Introduction {#intro}\n\nText."
+        report = compare(original, reimported)
+        assert any("xref-anchor:intro" in p for p in report.preserved)
+        assert not any("xref-anchor" in b for b in report.broken)
+
+    def test_missing_anchor_reported_as_broken(self) -> None:
+        from markidocx.differ import compare
+
+        original = "# Introduction {#intro}\n\nText."
+        reimported = "# Introduction\n\nText."
+        report = compare(original, reimported)
+        assert any("xref-anchor:missing 'intro'" in b for b in report.broken)
+        assert report.has_drift
+
+    def test_preserved_xref_link(self) -> None:
+        from markidocx.differ import compare
+
+        text = "# Intro {#intro}\n\nSee [Intro][intro]."
+        report = compare(text, text)
+        assert any("xref-link" in p for p in report.preserved)
+
+    def test_broken_xref_link_target_missing(self) -> None:
+        from markidocx.differ import compare
+
+        original = "# Intro {#intro}\n\nSee [Intro][intro]."
+        reimported = "# Intro\n\nSee something."
+        report = compare(original, reimported)
+        # anchor missing → broken xref link
+        broken_xref = [b for b in report.broken if "xref" in b]
+        assert broken_xref
+
+
+# ---------------------------------------------------------------------------
+# Full single-file xref round-trip
+# ---------------------------------------------------------------------------
+
+
+class TestXrefRoundTrip:
+    def test_single_file_xref_roundtrip(self, tmp_path: Path) -> None:
+        from markidocx.builder import build_document
+        from markidocx.differ import compare
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Introduction {#intro}
+
+            Welcome.
+
+            # Background {#bg}
+
+            See [Introduction][intro] and [Background][bg].
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        report = compare(md, reimported)
+
+        # No broken cross-refs
+        broken_xrefs = [b for b in report.broken if "xref" in b]
+        assert not broken_xrefs, f"Broken xrefs found: {broken_xrefs}"
+
+    def test_multi_ref_document(self, tmp_path: Path) -> None:
+        """Document with multiple anchors and refs doesn't produce broken xrefs."""
+        from markidocx.builder import build_document
+        from markidocx.importer import import_document
+        from markidocx.manifest import load_manifest
+
+        md = textwrap.dedent("""\
+            # Chapter One {#ch1}
+
+            Opening.
+
+            # Chapter Two {#ch2}
+
+            See [Chapter One][ch1].
+
+            # Chapter Three {#ch3}
+
+            Refers to [Chapter One][ch1] and [Chapter Two][ch2].
+        """)
+        _make_project(tmp_path, md)
+        m = load_manifest(tmp_path / "manifest.yaml")
+
+        build_result = build_document(m)
+        assert build_result.success
+
+        import_result = import_document(m, build_result.output_path)
+        assert import_result.success
+
+        reimported = import_result.output_files[0].read_text(encoding="utf-8")
+        # All three anchors should be in reimported
+        assert "{#ch1}" in reimported
+        assert "{#ch2}" in reimported
+        assert "{#ch3}" in reimported
--- a/workplans/MRKD-WP-0003-level3-advanced-features.md
+++ b/workplans/MRKD-WP-0003-level3-advanced-features.md
@@ -3,7 +3,7 @@ id: MRKD-WP-0003
 type: workplan
 domain: markitect
 repo: marki-docx
-status: active
+status: done
 state_hub_workstream_id: b04fe706-6e4e-48a8-b6c1-194d9e308215
 created: 2026-03-17
 updated: 2026-03-17
@@ -28,7 +28,7 @@ through the existing interface layer once the core modules support them.

 ```task
 id: MRKD-WP-0003-T01
-status: todo
+status: done
 priority: high
 state_hub_task_id: 51e1b53e-a62f-496b-892d-615513c35d67
 ```
@@ -53,7 +53,7 @@ Deliverable: `pytest tests/test_level3_plumbing.py` passes; level3 appears in ca

 ```task
 id: MRKD-WP-0003-T02
-status: todo
+status: done
 priority: high
 state_hub_task_id: f4010618-9d35-4c04-bc1c-c599f254edff
 ```
@@ -81,7 +81,7 @@ Deliverable: `pytest tests/test_error_framework.py` passes; all modules emit str

 ```task
 id: MRKD-WP-0003-T03
-status: todo
+status: done
 priority: high
 state_hub_task_id: 0bb9c7ce-5eb8-4997-833f-c801e37f282c
 ```
@@ -104,7 +104,7 @@ Deliverable: `pytest tests/test_level3_xref.py` passes.

 ```task
 id: MRKD-WP-0003-T04
-status: todo
+status: done
 priority: high
 state_hub_task_id: af6b82b7-da44-4ef8-8976-6e40fee5f73c
 ```
@@ -128,7 +128,7 @@ Deliverable: `pytest tests/test_level3_figures.py` passes.

 ```task
 id: MRKD-WP-0003-T05
-status: todo
+status: done
 priority: medium
 state_hub_task_id: 3700e0e4-cc3b-4ef3-8b85-6cef24c35fc0
 ```
@@ -151,7 +151,7 @@ Deliverable: `pytest tests/test_level3_diagrams.py` passes.

 ```task
 id: MRKD-WP-0003-T06
-status: todo
+status: done
 priority: medium
 state_hub_task_id: 7c0acbd3-65f0-440b-9ad4-a5f09fabef3c
 ```
@@ -175,7 +175,7 @@ Deliverable: `pytest tests/test_level3_bibliography.py` passes.

 ```task
 id: MRKD-WP-0003-T07
-status: todo
+status: done
 priority: medium
 state_hub_task_id: b26241b9-0fff-45a2-a95c-dd886a449038
 ```