Add GET /repos/todo-md-staleness for daily TODO.md review

Scan registered repos for TODO.md files unchanged longer than a
configurable threshold (default 6 days). Feeds activity-core stale-review.

api/routers/repos.py

@@ -253,6 +253,71 @@ async def onboard_repo(body: RepoOnboardRequest) -> RepoOnboardResult:
     )
 
 
+def _todo_md_entry(repo_slug: str, todo_path: Path, mtime: datetime) -> dict:
+    if mtime.tzinfo is None:
+        mtime = mtime.replace(tzinfo=timezone.utc)
+    age_days = max(0, (datetime.now(timezone.utc) - mtime).days)
+    return {
+        "repo_slug": repo_slug,
+        "has_todo": True,
+        "todo_path": str(todo_path),
+        "mtime": mtime.isoformat(),
+        "age_days": age_days,
+    }
+
+
+@router.get("/todo-md-staleness")
+async def list_todo_md_staleness(
+    stale_days: int = 6,
+    session: AsyncSession = Depends(get_session),
+) -> dict:
+    """Scan registered repos for TODO.md files unchanged longer than stale_days.
+
+    Used by activity-core daily stale-review automation. Only repos with an
+    accessible checkout and an existing TODO.md are included.
+    """
+    if stale_days < 1:
+        raise HTTPException(status_code=400, detail="stale_days must be >= 1")
+
+    result = await session.execute(
+        select(ManagedRepo, Domain.slug)
+        .join(Domain, Domain.id == ManagedRepo.domain_id)
+        .where(ManagedRepo.status == "active")
+        .order_by(ManagedRepo.slug)
+    )
+
+    all_with_todo: list[dict] = []
+    scanned = 0
+    for repo, _domain_slug in result.all():
+        scanned += 1
+        repo_dict = _repo_doi_dict(repo, _domain_slug)
+        resolved_path = resolve_repo_path(repo_dict)
+        if not resolved_path:
+            continue
+        todo_path = Path(resolved_path) / "TODO.md"
+        if not todo_path.is_file():
+            continue
+        mtime = datetime.fromtimestamp(todo_path.stat().st_mtime, tz=timezone.utc)
+        all_with_todo.append(_todo_md_entry(repo.slug, todo_path, mtime))
+
+    stale_entries = [e for e in all_with_todo if e["age_days"] >= stale_days]
+    stale_count = len(stale_entries)
+    worst = max(stale_entries, key=lambda e: e["age_days"], default=None)
+    payload: dict = {
+        "stale_days": stale_days,
+        "repos": stale_entries,
+        "stale_count": stale_count,
+        "total_with_todo": len(all_with_todo),
+        "total_scanned": scanned,
+        "worst_repo_slug": worst["repo_slug"] if worst else None,
+        "worst_age_days": worst["age_days"] if worst else None,
+        "worst_mtime": worst["mtime"] if worst else None,
+    }
+    if worst:
+        payload.update(worst)
+    return payload
+
+
 @router.get("/doi/summary", response_model=list[DoISummaryEntry])
 async def doi_summary(session: AsyncSession = Depends(get_session)) -> list[DoISummaryEntry]:
     """Return DoI tier for all active repos, worst tier first.