fix(baseline): synthesize PHASE1_AUDIT_BASELINE.json from inventory docs

Phase 1 deviation from spec: the original PHASE1_AUDIT_BASELINE.json
was gitignored (tests/artifacts/ is in .gitignore) and lost when the
working tree rebuilt. Per spec FR1-1 we needed to re-run the audit
and save the JSON; but a live re-run produces the CURRENT (post-
migration) state, not the BASELINE state. That broke 5 of 7 tests
that asserted pre-migration counts (88 sites across 3 files).

The actual fix is to reconstruct the baseline JSON from the per-file
inventory docs (PHASE1_INVENTORY_*.md), which ARE committed (under
tests/artifacts/, but the directory's gitignore exempts them by being
present-and-needed).

The new scripts/tier2/artifacts/result_migration_cruft_removal_20260620/
synth_baseline_json.py parses the 3 per-file inventory docs and emits
tests/artifacts/PHASE1_AUDIT_BASELINE.json with the exact shape the
tests expect (forward-slash-free Windows paths to match the EXPECTED
dict in test_baseline_result.py).

Result: 31/31 baseline tests pass (was 26/31); 16/16 heuristic tests
still pass; no source code changed.

Test plan note: any future regeneration must use the inventory docs as
source of truth, NOT a live audit. The audit is a moving target once
migration begins.

scripts/tier2/artifacts/result_migration_cruft_removal_20260620/synth_baseline_json.py

@@ -0,0 +1,67 @@
+"""Synthesize tests/artifacts/PHASE1_AUDIT_BASELINE.json from the per-file inventory docs.
+
+The original PHASE1_AUDIT_BASELINE.json was gitignored and lost when the
+working tree was rebuilt. The per-file inventory docs (PHASE1_INVENTORY_*.md)
+are the source of truth for the BASELINE state (88 sites across 3 files).
+This script parses them and produces a JSON in the same shape the tests expect.
+
+Output schema (per the test's _load_audit):
+  {"files": [{"filename": "src/mcp_client.py", "findings": [{...}, ...]}, ...]}
+"""
+import json
+import re
+from pathlib import Path
+
+INV_DIR = Path("tests/artifacts")
+OUT = Path("tests/artifacts/PHASE1_AUDIT_BASELINE.json")
+FILES = {
+    "src\\mcp_client.py": INV_DIR / "PHASE1_INVENTORY_mcp_client.md",
+    "src\\ai_client.py":  INV_DIR / "PHASE1_INVENTORY_ai_client.md",
+    "src\\rag_engine.py": INV_DIR / "PHASE1_INVENTORY_rag_engine.md",
+}
+
+ROW_RE = re.compile(r"^\|\s*\d+\s*\|\s*L(\d+)\s*\|\s*([A-Z_]+)\s*\|")
+
+CATEGORY_MAP = {
+    "INTERNAL_BROAD_CATCH": "INTERNAL_BROAD_CATCH",
+    "INTERNAL_SILENT_SWALLOW": "INTERNAL_SILENT_SWALLOW",
+    "INTERNAL_OPTIONAL_RETURN": "INTERNAL_OPTIONAL_RETURN",
+    "INTERNAL_RETHROW": "INTERNAL_RETHROW",
+    "UNCLEAR": "UNCLEAR",
+    "INTERNAL_COMPLIANT": "INTERNAL_COMPLIANT",
+}
+
+
+def parse_inventory(path: Path, filename: str) -> dict:
+    findings = []
+    for line in path.read_text(encoding="utf-8").splitlines():
+        m = ROW_RE.match(line)
+        if not m:
+            continue
+        lineno, cat = m.group(1), m.group(2)
+        if cat not in CATEGORY_MAP:
+            continue
+        findings.append({
+            "line": int(lineno),
+            "category": CATEGORY_MAP[cat],
+        })
+    return {"filename": filename, "findings": findings}
+
+
+def main():
+    files = [parse_inventory(p, fname) for fname, p in FILES.items()]
+    data = {"files": files}
+    OUT.write_text(json.dumps(data, indent=2), encoding="utf-8")
+    total = sum(len(f["findings"]) for f in files)
+    mig = sum(
+        1 for f in files for s in f["findings"]
+        if s["category"] in {
+            "INTERNAL_BROAD_CATCH", "INTERNAL_SILENT_SWALLOW",
+            "INTERNAL_OPTIONAL_RETURN", "INTERNAL_RETHROW", "UNCLEAR",
+        }
+    )
+    print(f"Wrote {OUT}: {total} sites total, {mig} migration-target")
+
+
+if __name__ == "__main__":
+    main()