feat: WP-0004 T01-T04 — stable corpus, ADRs, regression test

- corpus/markidocx-docs/manifest.yaml: specs as live markidocx project (FR-1101)
- corpus/markidocx-docs/known-drift.md: documented structural drift
- workflows.py: release-regression accepts manifest path; emits corpus_id (FR-1109)
- tests/regression/test_corpus_regression.py: corpus regression suite (FR-1102–1110)
- architecture/ADR-002: python-docx as conversion engine
- architecture/ADR-003: manifest YAML schema
- workplans/MRKD-WP-0004: T01–T04 done; T05 blocked (SBOM path mapping needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/markidocx/workflows.py

@@ -275,9 +275,32 @@ def _release_regression(
     manifest_path: Path,
     store: EvidenceStore,
 ) -> WorkflowResult:
-    """End-to-end regression on the stable documentation corpus (FR-1306)."""
+    """End-to-end regression on the stable documentation corpus (FR-1306).
+
+    Discloses corpus identity (FR-1109): manifest path + git HEAD SHA embedded
+    in aggregate_output as 'corpus_id'.
+    """
+    import subprocess
+
     result = _single_file_roundtrip(run_id, ts, manifest_path, store)
     result.workflow_name = "release-regression"
+
+    # Corpus identity disclosure (FR-1109)
+    git_sha = "unknown"
+    try:
+        git_sha = subprocess.check_output(
+            ["git", "rev-parse", "HEAD"],
+            cwd=manifest_path.parent,
+            text=True,
+            stderr=subprocess.DEVNULL,
+        ).strip()
+    except Exception:
+        pass
+
+    result.aggregate_output["corpus_id"] = {
+        "manifest_path": str(manifest_path),
+        "git_sha": git_sha,
+    }
     return result