feat(#91): IMP-91 u2~u15 multi-mdx regression CI suite + status-board auto-update

- u2~u5: tests/integration/test_multi_mdx_regression.py — MDX_SET=(01..05)
  cached integration runs + status/structural/visual snapshots +
  full_mdx_coverage assertion (9 snapshots populated for 01-05).
- u6~u11: F0 normalize / F1 V4 ranking / F2 slot_payload /
  F3 classifier-only AI / F4 layout / F5 final.html axis per MDX_SET.
- u12: pyproject.toml — pytest-json-report>=1.5 in dev extras.
- u13: .github/workflows/multi-mdx-regression.yml — pytest+artifact CI.
- u14: scripts/update_status_board.py + tests/scripts/test_update_status_board.py
  — idempotent JSON marker updater (3 unit tests pass).
- u15: PHASE-Z-PIPELINE-STATUS-BOARD.md — 30 F0-F5 × mdx01-05 markers
  initialized `?` + workflow wiring.

Stage 4 verify: 59/59 PASS targeted (smoke 6 + updater 3 + integration 50),
386/386 PASS regression umbrella, 0 failures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/update_status_board.py

@@ -0,0 +1,75 @@
+"""IMP-#91 u14 — idempotent status-board marker updater.
+
+Reads a pytest-json-report artifact emitted by the IMP-91 CI workflow and
+rewrites paired ``<!-- IMP-91:<axis>:<mdx> -->...<!-- /IMP-91 -->`` markers
+inside the Phase Z status board with a single-character outcome symbol.
+
+Pure functions (``parse_outcomes`` / ``update_board_text``) are exposed so
+``tests/scripts/test_update_status_board.py`` can exercise the contract
+without invoking pytest. The CLI just wires file IO around them so the
+GitHub Actions step in u15 can call it deterministically. The updater is
+additive: untouched markers stay; missing outcomes render ``?`` so a
+collection failure is loud, not silent. [[feedback_auto_pipeline_first]]
+[[feedback_artifact_status_naming]]
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import re
+from pathlib import Path
+from typing import Dict, Mapping, Tuple
+
+AXIS_FROM_TEST = {
+    "test_normalize_snapshot_matches": "F0",
+    "test_v4_ranking_snapshot_matches": "F1",
+    "test_slot_payload_snapshot_matches": "F2",
+    "test_ai_classifier_snapshot_matches": "F3",
+    "test_layout_snapshot_matches": "F4",
+    "test_final_html_snapshot_matches": "F5",
+}
+SYMBOL = {"passed": "PASS", "failed": "FAIL", "error": "ERR", "skipped": "SKIP"}
+NODEID_RE = re.compile(r"::(test_[a-z0-9_]+)\[(\d{2})\]$")
+MARKER_RE = re.compile(
+    r"(<!-- IMP-91:(F[0-5]):(\d{2}) -->)(.*?)(<!-- /IMP-91 -->)", re.DOTALL
+)
+
+
+def parse_outcomes(report: Mapping[str, object]) -> Dict[Tuple[str, str], str]:
+    out: Dict[Tuple[str, str], str] = {}
+    for test in report.get("tests", []) or []:
+        m = NODEID_RE.search(str(test.get("nodeid", "")))
+        if not m:
+            continue
+        axis = AXIS_FROM_TEST.get(m.group(1))
+        if not axis:
+            continue
+        out[(axis, m.group(2))] = SYMBOL.get(str(test.get("outcome")), "?")
+    return out
+
+
+def update_board_text(board: str, outcomes: Mapping[Tuple[str, str], str]) -> str:
+    def repl(match: "re.Match[str]") -> str:
+        key = (match.group(2), match.group(3))
+        symbol = outcomes.get(key, "?")
+        return f"{match.group(1)}{symbol}{match.group(5)}"
+
+    return MARKER_RE.sub(repl, board)
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description="IMP-91 status-board updater")
+    parser.add_argument("--report", required=True, type=Path)
+    parser.add_argument("--board", required=True, type=Path)
+    args = parser.parse_args()
+    report = json.loads(args.report.read_text(encoding="utf-8"))
+    outcomes = parse_outcomes(report)
+    args.board.write_text(
+        update_board_text(args.board.read_text(encoding="utf-8"), outcomes),
+        encoding="utf-8",
+    )
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())