diff --git a/markitect/infospace/checks/__init__.py b/markitect/infospace/checks/__init__.py
new file mode 100644
index 00000000..3ec9625e
--- /dev/null
+++ b/markitect/infospace/checks/__init__.py
@@ -0,0 +1,23 @@
+"""
+Collection-level quality checks for infospaces.
+
+Five concerns: Redundancy (C1), Coverage (C2), Coherence (C3),
+Consistency (C4), Granularity (C5).
+"""
+
+from markitect.infospace.checks.redundancy import check_redundancy
+from markitect.infospace.checks.coverage import check_coverage
+from markitect.infospace.checks.coherence import check_coherence
+from markitect.infospace.checks.consistency import check_consistency
+from markitect.infospace.checks.granularity import check_granularity
+from markitect.infospace.checks.orchestrator import run_all_checks, CheckReport
+
+__all__ = [
+    "check_redundancy",
+    "check_coverage",
+    "check_coherence",
+    "check_consistency",
+    "check_granularity",
+    "run_all_checks",
+    "CheckReport",
+]
diff --git a/markitect/infospace/checks/coherence.py b/markitect/infospace/checks/coherence.py
new file mode 100644
index 00000000..ffce5691
--- /dev/null
+++ b/markitect/infospace/checks/coherence.py
@@ -0,0 +1,81 @@
+"""
+C3 — Structural coherence.
+
+Uses graph analysis to check that the entity relationship graph is
+well-connected and has meaningful community structure.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+
+from markitect.prompts.dependencies.models import DependencyGraph
+
+
+@dataclass
+class CoherenceReport:
+    """Results from coherence analysis."""
+
+    connected_components: int = 0
+    largest_component_size: int = 0
+    modularity: float = 0.0
+    community_count: int = 0
+    cohesion: float = 0.0
+    coupling: float = 0.0
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C3",
+            "connected_components": self.connected_components,
+            "largest_component_size": self.largest_component_size,
+            "modularity": round(self.modularity, 4),
+            "community_count": self.community_count,
+            "cohesion": round(self.cohesion, 4),
+            "coupling": round(self.coupling, 4),
+            "entity_count": self.entity_count,
+        }
+
+
+def check_coherence(
+    graph: Optional[DependencyGraph] = None,
+    entity_count: int = 0,
+) -> CoherenceReport:
+    """Check structural coherence of the entity relationship graph.
+
+    Args:
+        graph: The entity relationship graph.  If ``None``, returns
+            a report with zero values.
+        entity_count: Total number of entities (for context).
+
+    Returns:
+        :class:`CoherenceReport` with connectivity and community metrics.
+    """
+    if graph is None or len(graph.nodes) == 0:
+        return CoherenceReport(entity_count=entity_count)
+
+    try:
+        from markitect.analysis.graph import (
+            connected_components,
+            modularity_score,
+            detect_communities,
+            cohesion_coupling,
+        )
+    except ImportError:
+        return CoherenceReport(entity_count=entity_count)
+
+    components = connected_components(graph)
+    communities = detect_communities(graph, seed=42)
+    mod = modularity_score(graph, communities=communities)
+    cc = cohesion_coupling(graph, communities=communities)
+
+    return CoherenceReport(
+        connected_components=len(components),
+        largest_component_size=len(components[0]) if components else 0,
+        modularity=mod,
+        community_count=len(communities),
+        cohesion=cc["cohesion"],
+        coupling=cc["coupling"],
+        entity_count=entity_count or len(graph.nodes),
+    )
diff --git a/markitect/infospace/checks/consistency.py b/markitect/infospace/checks/consistency.py
new file mode 100644
index 00000000..50f91522
--- /dev/null
+++ b/markitect/infospace/checks/consistency.py
@@ -0,0 +1,58 @@
+"""
+C4 — Definitional consistency.
+
+Checks for cycles in the dependency graph and definitional conflicts
+between entities.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+
+from markitect.infospace.models import EntityMeta
+from markitect.prompts.dependencies.models import DependencyGraph
+
+
+@dataclass
+class ConsistencyReport:
+    """Results from consistency analysis."""
+
+    cycles: List[List[str]] = field(default_factory=list)
+    cycle_count: int = 0
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C4",
+            "cycle_count": self.cycle_count,
+            "cycles": self.cycles,
+            "entity_count": self.entity_count,
+        }
+
+
+def check_consistency(
+    entities: List[EntityMeta],
+    graph: Optional[DependencyGraph] = None,
+) -> ConsistencyReport:
+    """Check definitional consistency.
+
+    Args:
+        entities: Entity metadata list.
+        graph: Optional dependency graph for cycle detection.
+
+    Returns:
+        :class:`ConsistencyReport` with cycles found.
+    """
+    n = len(entities)
+    cycles: List[List[str]] = []
+
+    if graph is not None and len(graph.nodes) > 0:
+        raw_cycles = graph.detect_cycles()
+        cycles = raw_cycles
+
+    return ConsistencyReport(
+        cycles=cycles,
+        cycle_count=len(cycles),
+        entity_count=n,
+    )
diff --git a/markitect/infospace/checks/coverage.py b/markitect/infospace/checks/coverage.py
new file mode 100644
index 00000000..887ffcbb
--- /dev/null
+++ b/markitect/infospace/checks/coverage.py
@@ -0,0 +1,111 @@
+"""
+C2 — Coverage completeness.
+
+Uses FCA and cross-tabulation to detect structural coverage gaps:
+attribute combinations (domain × VSM system) with no entities.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Dict, List, Optional
+
+from markitect.infospace.models import EntityMeta
+from markitect.analysis.fca import FormalContext, find_empty_cells, find_gap_concepts
+
+
+@dataclass
+class CoverageReport:
+    """Results from coverage analysis."""
+
+    coverage_ratio: float = 0.0
+    empty_cells: List[dict] = field(default_factory=list)
+    gap_concepts: List[dict] = field(default_factory=list)
+    domain_counts: Dict[str, int] = field(default_factory=dict)
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C2",
+            "coverage_ratio": round(self.coverage_ratio, 4),
+            "empty_cells": self.empty_cells,
+            "gap_concepts_count": len(self.gap_concepts),
+            "domain_counts": self.domain_counts,
+            "entity_count": self.entity_count,
+        }
+
+
+def _extract_attributes(entity: EntityMeta) -> set[str]:
+    """Extract FCA attributes from an entity."""
+    attrs: set[str] = set()
+    if entity.domain:
+        attrs.add(f"domain:{entity.domain}")
+    if entity.source_chapter:
+        attrs.add(f"chapter:{entity.source_chapter}")
+    return attrs
+
+
+def check_coverage(
+    entities: List[EntityMeta],
+    extra_attributes: Optional[Dict[str, set[str]]] = None,
+) -> CoverageReport:
+    """Check coverage completeness using FCA gap analysis.
+
+    Args:
+        entities: Entity metadata list.
+        extra_attributes: Optional ``{slug: {attr, ...}}`` to merge
+            with auto-extracted attributes (e.g. VSM mappings).
+
+    Returns:
+        :class:`CoverageReport` with gaps and coverage ratio.
+    """
+    n = len(entities)
+    if n == 0:
+        return CoverageReport()
+
+    # Build entity → attributes mapping
+    entity_attrs: Dict[str, set[str]] = {}
+    for e in entities:
+        attrs = _extract_attributes(e)
+        if extra_attributes and e.slug in extra_attributes:
+            attrs.update(extra_attributes[e.slug])
+        entity_attrs[e.slug] = attrs
+
+    # Domain counts
+    domain_counts: Dict[str, int] = {}
+    for e in entities:
+        d = e.domain or "(unspecified)"
+        domain_counts[d] = domain_counts.get(d, 0) + 1
+
+    # Build FCA context
+    context = FormalContext.from_dict(entity_attrs)
+
+    # Cross-tabulation: domain × chapter
+    domains = sorted({a for attrs in entity_attrs.values() for a in attrs if a.startswith("domain:")})
+    chapters = sorted({a for attrs in entity_attrs.values() for a in attrs if a.startswith("chapter:")})
+
+    empty = []
+    if domains and chapters:
+        raw_empty = find_empty_cells(context, domains, chapters)
+        empty = [{"dimension_a": a, "dimension_b": b} for a, b in raw_empty]
+
+    # FCA gap concepts
+    gaps = find_gap_concepts(context)
+    gap_dicts = [
+        {"intent": sorted(g.intent), "extent_size": g.extent_size}
+        for g in gaps
+        if g.intent_size <= 4  # Only report manageable gaps
+    ]
+
+    # Coverage ratio: populated cells / total possible cells
+    total_cells = len(domains) * len(chapters) if domains and chapters else 1
+    populated = total_cells - len(empty)
+    ratio = populated / total_cells if total_cells > 0 else 0.0
+
+    return CoverageReport(
+        coverage_ratio=ratio,
+        empty_cells=empty,
+        gap_concepts=gap_dicts,
+        domain_counts=domain_counts,
+        entity_count=n,
+    )
diff --git a/markitect/infospace/checks/granularity.py b/markitect/infospace/checks/granularity.py
new file mode 100644
index 00000000..9fc6092e
--- /dev/null
+++ b/markitect/infospace/checks/granularity.py
@@ -0,0 +1,98 @@
+"""
+C5 — Granularity balance.
+
+Checks that entities are at a consistent level of abstraction,
+measured by word count distribution and Shannon entropy of domain
+assignments.
+"""
+
+from __future__ import annotations
+
+import math
+from dataclasses import dataclass, field
+from typing import Dict, List
+
+from markitect.infospace.models import EntityMeta
+
+
+@dataclass
+class GranularityReport:
+    """Results from granularity analysis."""
+
+    domain_entropy: float = 0.0
+    word_count_stats: Dict[str, float] = field(default_factory=dict)
+    domain_distribution: Dict[str, int] = field(default_factory=dict)
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C5",
+            "domain_entropy": round(self.domain_entropy, 4),
+            "word_count_stats": {
+                k: round(v, 2) for k, v in self.word_count_stats.items()
+            },
+            "domain_distribution": self.domain_distribution,
+            "entity_count": self.entity_count,
+        }
+
+
+def _shannon_entropy(counts: Dict[str, int]) -> float:
+    """Compute Shannon entropy of a distribution."""
+    total = sum(counts.values())
+    if total == 0:
+        return 0.0
+    entropy = 0.0
+    for count in counts.values():
+        if count > 0:
+            p = count / total
+            entropy -= p * math.log2(p)
+    return entropy
+
+
+def check_granularity(entities: List[EntityMeta]) -> GranularityReport:
+    """Check granularity balance across entities.
+
+    Metrics:
+    - Domain entropy: higher = more balanced distribution.
+    - Word count statistics: mean, min, max, std dev.
+
+    Args:
+        entities: Entity metadata list.
+
+    Returns:
+        :class:`GranularityReport` with balance metrics.
+    """
+    n = len(entities)
+    if n == 0:
+        return GranularityReport()
+
+    # Domain distribution
+    domain_counts: Dict[str, int] = {}
+    for e in entities:
+        d = e.domain or "(unspecified)"
+        domain_counts[d] = domain_counts.get(d, 0) + 1
+
+    entropy = _shannon_entropy(domain_counts)
+
+    # Word count statistics
+    word_counts = [e.definition_word_count for e in entities]
+    if not word_counts:
+        word_counts = [0]
+
+    mean_wc = sum(word_counts) / len(word_counts)
+    min_wc = min(word_counts)
+    max_wc = max(word_counts)
+    variance = sum((wc - mean_wc) ** 2 for wc in word_counts) / len(word_counts)
+    std_wc = math.sqrt(variance)
+
+    return GranularityReport(
+        domain_entropy=entropy,
+        word_count_stats={
+            "mean": mean_wc,
+            "min": float(min_wc),
+            "max": float(max_wc),
+            "std": std_wc,
+        },
+        domain_distribution=domain_counts,
+        entity_count=n,
+    )
diff --git a/markitect/infospace/checks/orchestrator.py b/markitect/infospace/checks/orchestrator.py
new file mode 100644
index 00000000..789dc76b
--- /dev/null
+++ b/markitect/infospace/checks/orchestrator.py
@@ -0,0 +1,102 @@
+"""
+Unified orchestrator for all five collection-level checks.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Dict, List, Optional
+
+from markitect.infospace.models import EntityMeta
+from markitect.prompts.dependencies.models import DependencyGraph
+
+from .redundancy import RedundancyReport, check_redundancy
+from .coverage import CoverageReport, check_coverage
+from .coherence import CoherenceReport, check_coherence
+from .consistency import ConsistencyReport, check_consistency
+from .granularity import GranularityReport, check_granularity
+
+
+@dataclass
+class CheckReport:
+    """Unified report from all five collection-level checks."""
+
+    redundancy: Optional[RedundancyReport] = None
+    coverage: Optional[CoverageReport] = None
+    coherence: Optional[CoherenceReport] = None
+    consistency: Optional[ConsistencyReport] = None
+    granularity: Optional[GranularityReport] = None
+
+    def to_dict(self) -> Dict[str, Any]:
+        d: Dict[str, Any] = {}
+        if self.redundancy:
+            d["redundancy"] = self.redundancy.to_dict()
+        if self.coverage:
+            d["coverage"] = self.coverage.to_dict()
+        if self.coherence:
+            d["coherence"] = self.coherence.to_dict()
+        if self.consistency:
+            d["consistency"] = self.consistency.to_dict()
+        if self.granularity:
+            d["granularity"] = self.granularity.to_dict()
+        return d
+
+    def metrics(self) -> Dict[str, float]:
+        """Extract key metrics for viability checking."""
+        m: Dict[str, float] = {}
+        if self.redundancy:
+            m["redundancy_ratio"] = self.redundancy.redundancy_ratio
+        if self.coverage:
+            m["coverage_ratio"] = self.coverage.coverage_ratio
+        if self.coherence:
+            m["coherence_components"] = float(self.coherence.connected_components)
+            m["modularity"] = self.coherence.modularity
+        if self.consistency:
+            m["consistency_cycles"] = float(self.consistency.cycle_count)
+        if self.granularity:
+            m["granularity_entropy"] = self.granularity.domain_entropy
+        return m
+
+
+def run_all_checks(
+    entities: List[EntityMeta],
+    embeddings: Optional[Dict[str, list[float]]] = None,
+    graph: Optional[DependencyGraph] = None,
+    extra_attributes: Optional[Dict[str, set[str]]] = None,
+    checks: Optional[List[str]] = None,
+) -> CheckReport:
+    """Run all (or selected) collection-level checks.
+
+    Args:
+        entities: Entity metadata list.
+        embeddings: Pre-computed embedding vectors for C1.
+        graph: Entity relationship graph for C3 and C4.
+        extra_attributes: Extra FCA attributes for C2.
+        checks: List of check names to run.  If ``None``, runs all five.
+            Valid names: ``redundancy``, ``coverage``, ``coherence``,
+            ``consistency``, ``granularity``.
+
+    Returns:
+        :class:`CheckReport` with results from each check.
+    """
+    run_all = checks is None
+    check_set = set(checks) if checks else set()
+
+    report = CheckReport()
+
+    if run_all or "redundancy" in check_set:
+        report.redundancy = check_redundancy(entities, embeddings=embeddings)
+
+    if run_all or "coverage" in check_set:
+        report.coverage = check_coverage(entities, extra_attributes=extra_attributes)
+
+    if run_all or "coherence" in check_set:
+        report.coherence = check_coherence(graph=graph, entity_count=len(entities))
+
+    if run_all or "consistency" in check_set:
+        report.consistency = check_consistency(entities, graph=graph)
+
+    if run_all or "granularity" in check_set:
+        report.granularity = check_granularity(entities)
+
+    return report
diff --git a/markitect/infospace/checks/redundancy.py b/markitect/infospace/checks/redundancy.py
new file mode 100644
index 00000000..42abf304
--- /dev/null
+++ b/markitect/infospace/checks/redundancy.py
@@ -0,0 +1,98 @@
+"""
+C1 — Redundancy detection.
+
+Uses embedding similarity to find entity pairs with overlapping
+meanings that may be candidates for merging.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+
+from markitect.infospace.models import EntityMeta
+from markitect.llm.similarity import find_similar_pairs
+
+
+@dataclass
+class RedundancyReport:
+    """Results from redundancy analysis."""
+
+    similar_pairs: List[dict] = field(default_factory=list)
+    redundancy_ratio: float = 0.0
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C1",
+            "redundancy_ratio": round(self.redundancy_ratio, 4),
+            "similar_pairs": self.similar_pairs,
+            "entity_count": self.entity_count,
+        }
+
+
+def check_redundancy(
+    entities: List[EntityMeta],
+    embeddings: Optional[Dict[str, list[float]]] = None,
+    threshold: float = 0.85,
+) -> RedundancyReport:
+    """Check for redundant entities using embedding similarity.
+
+    Args:
+        entities: Entity metadata list.
+        embeddings: Pre-computed ``{slug: vector}`` mapping.
+            If ``None``, redundancy is checked structurally (title overlap).
+        threshold: Similarity threshold for flagging pairs.
+
+    Returns:
+        :class:`RedundancyReport` with similar pairs and ratio.
+    """
+    n = len(entities)
+    if n < 2:
+        return RedundancyReport(entity_count=n)
+
+    pairs: list[dict] = []
+
+    if embeddings:
+        # Embedding-based similarity
+        raw_pairs = find_similar_pairs(embeddings, threshold=threshold)
+        for slug_a, slug_b, sim in raw_pairs:
+            pairs.append({
+                "entity_a": slug_a,
+                "entity_b": slug_b,
+                "similarity": round(sim, 4),
+                "method": "embedding",
+            })
+    else:
+        # Fallback: structural overlap (shared definition words)
+        slug_to_words = {}
+        for e in entities:
+            words = set(e.definition.lower().split()) if e.definition else set()
+            slug_to_words[e.slug] = words
+
+        slugs = sorted(slug_to_words)
+        for i, a in enumerate(slugs):
+            for b in slugs[i + 1:]:
+                wa, wb = slug_to_words[a], slug_to_words[b]
+                if wa and wb:
+                    overlap = len(wa & wb) / min(len(wa), len(wb))
+                    if overlap >= threshold:
+                        pairs.append({
+                            "entity_a": a,
+                            "entity_b": b,
+                            "similarity": round(overlap, 4),
+                            "method": "word_overlap",
+                        })
+
+    # redundancy_ratio: fraction of entities involved in similar pairs
+    involved = set()
+    for p in pairs:
+        involved.add(p["entity_a"])
+        involved.add(p["entity_b"])
+    ratio = len(involved) / n if n > 0 else 0.0
+
+    return RedundancyReport(
+        similar_pairs=pairs,
+        redundancy_ratio=ratio,
+        entity_count=n,
+    )
diff --git a/markitect/infospace/cli.py b/markitect/infospace/cli.py
index c158187b..2af1d2dd 100644
--- a/markitect/infospace/cli.py
+++ b/markitect/infospace/cli.py
@@ -273,3 +273,61 @@ def viability(config_path: Optional[str]):
         click.echo(f"Viable: YES ({state.viability_pass_count}/{state.viability_total_count} thresholds met)")
     else:
         click.echo(f"Viable: NO ({state.viability_pass_count}/{state.viability_total_count} thresholds met)")
+
+
+# ── check ───────────────────────────────────────────────────────────
+
+
+@infospace_commands.command()
+@click.option("--config", "config_path", default=None, help="Path to infospace.yaml.")
+@click.option(
+    "--concern", "concerns", multiple=True,
+    type=click.Choice(["redundancy", "coverage", "coherence", "consistency", "granularity"]),
+    help="Run specific concern(s). Omit to run all five.",
+)
+@click.option("--json", "as_json", is_flag=True, help="Output results as JSON.")
+def check(config_path: Optional[str], concerns: tuple, as_json: bool):
+    """Run collection-level quality checks (C1–C5)."""
+    cfg, cfg_path = _load_config_or_exit(config_path)
+    root = cfg_path.parent
+
+    entities_dir = root / cfg.entities_dir
+    if not entities_dir.is_dir():
+        click.echo("Error: No entities directory found.", err=True)
+        raise SystemExit(1)
+
+    entity_list = parse_entity_directory(entities_dir)
+    if not entity_list:
+        click.echo("No entities to check.")
+        return
+
+    from markitect.infospace.checks import run_all_checks
+
+    checks_list = list(concerns) if concerns else None
+
+    report = run_all_checks(
+        entities=entity_list,
+        checks=checks_list,
+    )
+
+    if as_json:
+        import json
+        click.echo(json.dumps(report.to_dict(), indent=2))
+    else:
+        click.echo(f"Collection checks — {len(entity_list)} entities\n")
+        d = report.to_dict()
+        for concern_name, concern_data in d.items():
+            label = concern_data.get("concern", concern_name.upper())
+            click.echo(f"  {label} — {concern_name}")
+            for k, v in concern_data.items():
+                if k == "concern":
+                    continue
+                click.echo(f"    {k}: {v}")
+            click.echo()
+
+    # Show summary metrics
+    m = report.metrics()
+    if m and not as_json:
+        click.echo("Metrics summary:")
+        for k, v in sorted(m.items()):
+            click.echo(f"  {k}: {v:.4f}")
diff --git a/tests/unit/infospace/test_checks.py b/tests/unit/infospace/test_checks.py
new file mode 100644
index 00000000..b43e8d66
--- /dev/null
+++ b/tests/unit/infospace/test_checks.py
@@ -0,0 +1,413 @@
+"""
+Tests for collection-level quality checks (S2.4).
+
+Covers all five concerns: Redundancy (C1), Coverage (C2), Coherence (C3),
+Consistency (C4), Granularity (C5), and the orchestrator.
+"""
+
+from __future__ import annotations
+
+import math
+
+import pytest
+
+from markitect.infospace.models import EntityMeta
+from markitect.prompts.dependencies.models import DependencyGraph
+
+
+# ── helpers ──────────────────────────────────────────────────────────
+
+
+def _entity(slug: str, domain: str = "", definition: str = "",
+            source_chapter: str = "", word_count: int = 0) -> EntityMeta:
+    wc = word_count if word_count else (len(definition.split()) if definition else 0)
+    return EntityMeta(
+        slug=slug,
+        title=slug.replace("-", " ").title(),
+        h1_raw=slug.replace("-", " ").title(),
+        definition=definition,
+        domain=domain,
+        source_chapter=source_chapter,
+        definition_word_count=wc,
+        total_word_count=wc,
+    )
+
+
+def _sample_entities() -> list[EntityMeta]:
+    return [
+        _entity("alpha", domain="economics", definition="the first concept in our model", source_chapter="ch01"),
+        _entity("beta", domain="economics", definition="the second concept about markets", source_chapter="ch01"),
+        _entity("gamma", domain="sociology", definition="a social structure framework", source_chapter="ch02"),
+        _entity("delta", domain="sociology", definition="a social dynamic pattern", source_chapter="ch02"),
+        _entity("epsilon", domain="philosophy", definition="an epistemic principle", source_chapter="ch03"),
+    ]
+
+
+def _linear_graph() -> DependencyGraph:
+    """A -> B -> C -> D."""
+    g = DependencyGraph()
+    g.add_edge("A", "B")
+    g.add_edge("B", "C")
+    g.add_edge("C", "D")
+    return g
+
+
+def _cyclic_graph() -> DependencyGraph:
+    """A -> B -> C -> A (one cycle)."""
+    g = DependencyGraph()
+    g.add_edge("A", "B")
+    g.add_edge("B", "C")
+    g.add_edge("C", "A")
+    return g
+
+
+def _can_import_graph_analysis():
+    try:
+        from markitect.analysis.graph import connected_components  # noqa: F401
+        return True
+    except ImportError:
+        return False
+
+
+# ── C1: Redundancy ──────────────────────────────────────────────────
+
+
+class TestRedundancy:
+    def test_empty_entities(self):
+        from markitect.infospace.checks.redundancy import check_redundancy
+        report = check_redundancy([])
+        assert report.entity_count == 0
+        assert report.redundancy_ratio == 0.0
+        assert report.similar_pairs == []
+
+    def test_single_entity(self):
+        from markitect.infospace.checks.redundancy import check_redundancy
+        report = check_redundancy([_entity("a", definition="hello world")])
+        assert report.entity_count == 1
+        assert report.redundancy_ratio == 0.0
+
+    def test_no_overlap_word_fallback(self):
+        from markitect.infospace.checks.redundancy import check_redundancy
+        entities = [
+            _entity("a", definition="apple banana cherry"),
+            _entity("b", definition="delta epsilon zeta"),
+        ]
+        report = check_redundancy(entities, threshold=0.5)
+        assert report.similar_pairs == []
+        assert report.redundancy_ratio == 0.0
+
+    def test_high_overlap_word_fallback(self):
+        from markitect.infospace.checks.redundancy import check_redundancy
+        entities = [
+            _entity("a", definition="the quick brown fox"),
+            _entity("b", definition="the quick brown dog"),
+        ]
+        report = check_redundancy(entities, threshold=0.5)
+        assert len(report.similar_pairs) == 1
+        assert report.similar_pairs[0]["method"] == "word_overlap"
+        assert report.similar_pairs[0]["entity_a"] == "a"
+        assert report.similar_pairs[0]["entity_b"] == "b"
+        assert report.redundancy_ratio == 1.0  # both entities involved
+
+    def test_embedding_based(self):
+        from markitect.infospace.checks.redundancy import check_redundancy
+        entities = [
+            _entity("a", definition="x"),
+            _entity("b", definition="y"),
+            _entity("c", definition="z"),
+        ]
+        # a and b are very similar; c is different
+        embeddings = {
+            "a": [1.0, 0.0, 0.0],
+            "b": [0.99, 0.1, 0.0],
+            "c": [0.0, 0.0, 1.0],
+        }
+        report = check_redundancy(entities, embeddings=embeddings, threshold=0.9)
+        assert len(report.similar_pairs) >= 1
+        assert report.similar_pairs[0]["method"] == "embedding"
+        assert report.redundancy_ratio > 0.0
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.redundancy import RedundancyReport
+        r = RedundancyReport(similar_pairs=[], redundancy_ratio=0.25, entity_count=10)
+        d = r.to_dict()
+        assert d["concern"] == "C1"
+        assert d["redundancy_ratio"] == 0.25
+        assert d["entity_count"] == 10
+
+
+# ── C2: Coverage ────────────────────────────────────────────────────
+
+
+class TestCoverage:
+    def test_empty_entities(self):
+        from markitect.infospace.checks.coverage import check_coverage
+        report = check_coverage([])
+        assert report.entity_count == 0
+        assert report.coverage_ratio == 0.0
+
+    def test_full_coverage(self):
+        """All domain×chapter cells are populated."""
+        from markitect.infospace.checks.coverage import check_coverage
+        entities = [
+            _entity("a", domain="d1", source_chapter="ch1"),
+            _entity("b", domain="d2", source_chapter="ch1"),
+            _entity("c", domain="d1", source_chapter="ch2"),
+            _entity("d", domain="d2", source_chapter="ch2"),
+        ]
+        report = check_coverage(entities)
+        assert report.coverage_ratio == 1.0
+        assert report.empty_cells == []
+
+    def test_partial_coverage(self):
+        """One cell is missing → coverage < 1.0."""
+        from markitect.infospace.checks.coverage import check_coverage
+        entities = [
+            _entity("a", domain="d1", source_chapter="ch1"),
+            _entity("b", domain="d2", source_chapter="ch1"),
+            _entity("c", domain="d1", source_chapter="ch2"),
+            # Missing: d2×ch2
+        ]
+        report = check_coverage(entities)
+        assert report.coverage_ratio < 1.0
+        assert len(report.empty_cells) == 1
+        assert report.empty_cells[0]["dimension_a"] == "domain:d2"
+        assert report.empty_cells[0]["dimension_b"] == "chapter:ch2"
+
+    def test_domain_counts(self):
+        from markitect.infospace.checks.coverage import check_coverage
+        entities = _sample_entities()
+        report = check_coverage(entities)
+        assert report.domain_counts["economics"] == 2
+        assert report.domain_counts["sociology"] == 2
+        assert report.domain_counts["philosophy"] == 1
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.coverage import CoverageReport
+        r = CoverageReport(coverage_ratio=0.75, entity_count=8)
+        d = r.to_dict()
+        assert d["concern"] == "C2"
+        assert d["coverage_ratio"] == 0.75
+
+    def test_extra_attributes(self):
+        from markitect.infospace.checks.coverage import check_coverage
+        entities = [
+            _entity("a", domain="d1", source_chapter="ch1"),
+        ]
+        extra = {"a": {"vsm:production"}}
+        report = check_coverage(entities, extra_attributes=extra)
+        assert report.entity_count == 1
+
+
+# ── C3: Coherence ───────────────────────────────────────────────────
+
+
+class TestCoherence:
+    def test_no_graph(self):
+        from markitect.infospace.checks.coherence import check_coherence
+        report = check_coherence(graph=None, entity_count=5)
+        assert report.connected_components == 0
+        assert report.entity_count == 5
+
+    def test_empty_graph(self):
+        from markitect.infospace.checks.coherence import check_coherence
+        g = DependencyGraph()
+        report = check_coherence(graph=g, entity_count=0)
+        assert report.connected_components == 0
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.coherence import CoherenceReport
+        r = CoherenceReport(connected_components=2, modularity=0.3456, entity_count=10)
+        d = r.to_dict()
+        assert d["concern"] == "C3"
+        assert d["modularity"] == 0.3456
+        assert d["connected_components"] == 2
+
+    @pytest.mark.skipif(
+        not _can_import_graph_analysis(),
+        reason="networkx not available",
+    )
+    def test_with_graph(self):
+        from markitect.infospace.checks.coherence import check_coherence
+        g = _linear_graph()
+        report = check_coherence(graph=g, entity_count=4)
+        assert report.connected_components >= 1
+        assert report.entity_count == 4
+
+
+# ── C4: Consistency ─────────────────────────────────────────────────
+
+
+class TestConsistency:
+    def test_no_graph(self):
+        from markitect.infospace.checks.consistency import check_consistency
+        entities = _sample_entities()
+        report = check_consistency(entities)
+        assert report.cycle_count == 0
+        assert report.entity_count == 5
+
+    def test_acyclic_graph(self):
+        from markitect.infospace.checks.consistency import check_consistency
+        entities = _sample_entities()
+        g = _linear_graph()
+        report = check_consistency(entities, graph=g)
+        assert report.cycle_count == 0
+
+    def test_cyclic_graph(self):
+        from markitect.infospace.checks.consistency import check_consistency
+        entities = _sample_entities()
+        g = _cyclic_graph()
+        report = check_consistency(entities, graph=g)
+        assert report.cycle_count >= 1
+        assert len(report.cycles) >= 1
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.consistency import ConsistencyReport
+        r = ConsistencyReport(cycles=[["A", "B", "A"]], cycle_count=1, entity_count=5)
+        d = r.to_dict()
+        assert d["concern"] == "C4"
+        assert d["cycle_count"] == 1
+
+
+# ── C5: Granularity ─────────────────────────────────────────────────
+
+
+class TestGranularity:
+    def test_empty_entities(self):
+        from markitect.infospace.checks.granularity import check_granularity
+        report = check_granularity([])
+        assert report.entity_count == 0
+        assert report.domain_entropy == 0.0
+
+    def test_single_domain(self):
+        from markitect.infospace.checks.granularity import check_granularity
+        entities = [
+            _entity("a", domain="d1", word_count=10),
+            _entity("b", domain="d1", word_count=20),
+        ]
+        report = check_granularity(entities)
+        assert report.domain_entropy == 0.0  # single domain = zero entropy
+        assert report.entity_count == 2
+        assert report.word_count_stats["mean"] == 15.0
+
+    def test_balanced_domains(self):
+        from markitect.infospace.checks.granularity import check_granularity
+        entities = [
+            _entity("a", domain="d1", word_count=10),
+            _entity("b", domain="d2", word_count=10),
+        ]
+        report = check_granularity(entities)
+        assert report.domain_entropy == pytest.approx(1.0)  # log2(2) = 1.0
+        assert report.domain_distribution == {"d1": 1, "d2": 1}
+
+    def test_word_count_stats(self):
+        from markitect.infospace.checks.granularity import check_granularity
+        entities = [
+            _entity("a", domain="d1", word_count=10),
+            _entity("b", domain="d1", word_count=30),
+        ]
+        report = check_granularity(entities)
+        assert report.word_count_stats["mean"] == 20.0
+        assert report.word_count_stats["min"] == 10.0
+        assert report.word_count_stats["max"] == 30.0
+        assert report.word_count_stats["std"] == 10.0
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.granularity import GranularityReport
+        r = GranularityReport(domain_entropy=1.5, entity_count=4)
+        d = r.to_dict()
+        assert d["concern"] == "C5"
+        assert d["domain_entropy"] == 1.5
+
+    def test_unspecified_domain(self):
+        from markitect.infospace.checks.granularity import check_granularity
+        entities = [_entity("a", domain="", word_count=10)]
+        report = check_granularity(entities)
+        assert "(unspecified)" in report.domain_distribution
+
+
+# ── Orchestrator ────────────────────────────────────────────────────
+
+
+class TestOrchestrator:
+    def test_run_all_default(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        report = run_all_checks(entities)
+        assert report.redundancy is not None
+        assert report.coverage is not None
+        assert report.coherence is not None
+        assert report.consistency is not None
+        assert report.granularity is not None
+
+    def test_run_selected_checks(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        report = run_all_checks(entities, checks=["redundancy", "granularity"])
+        assert report.redundancy is not None
+        assert report.granularity is not None
+        assert report.coverage is None
+        assert report.coherence is None
+        assert report.consistency is None
+
+    def test_to_dict(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        report = run_all_checks(entities, checks=["granularity"])
+        d = report.to_dict()
+        assert "granularity" in d
+        assert "redundancy" not in d
+
+    def test_metrics(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        report = run_all_checks(entities, checks=["redundancy", "granularity"])
+        m = report.metrics()
+        assert "redundancy_ratio" in m
+        assert "granularity_entropy" in m
+        assert isinstance(m["redundancy_ratio"], float)
+        assert isinstance(m["granularity_entropy"], float)
+
+    def test_metrics_empty_report(self):
+        from markitect.infospace.checks.orchestrator import CheckReport
+        report = CheckReport()
+        assert report.metrics() == {}
+
+    def test_run_all_with_graph(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        g = _linear_graph()
+        report = run_all_checks(entities, graph=g, checks=["consistency"])
+        assert report.consistency is not None
+        assert report.consistency.cycle_count == 0
+
+    def test_run_all_with_cyclic_graph(self):
+        from markitect.infospace.checks.orchestrator import run_all_checks
+        entities = _sample_entities()
+        g = _cyclic_graph()
+        report = run_all_checks(entities, graph=g, checks=["consistency"])
+        assert report.consistency.cycle_count >= 1
+
+
+# ── Shannon entropy helper ──────────────────────────────────────────
+
+
+class TestShannonEntropy:
+    def test_uniform_distribution(self):
+        from markitect.infospace.checks.granularity import _shannon_entropy
+        counts = {"a": 1, "b": 1, "c": 1, "d": 1}
+        assert _shannon_entropy(counts) == pytest.approx(2.0)  # log2(4)
+
+    def test_single_element(self):
+        from markitect.infospace.checks.granularity import _shannon_entropy
+        assert _shannon_entropy({"a": 10}) == 0.0
+
+    def test_empty(self):
+        from markitect.infospace.checks.granularity import _shannon_entropy
+        assert _shannon_entropy({}) == 0.0
+
+    def test_skewed(self):
+        from markitect.infospace.checks.granularity import _shannon_entropy
+        counts = {"a": 99, "b": 1}
+        entropy = _shannon_entropy(counts)
+        assert 0.0 < entropy < 1.0