§22 M3-backend Plan B (2/2, read path): per-project RFC serving (v0.37.0)

A second project's corpus now renders under /p/<id>/, isolated by its own
slug namespace. Completes step (1) "RFC app supports multiple projects" for
the read path.

- api.py: GET /api/projects/{pid}/rfcs (scoped catalog) + /{slug} (entry by
  (project_id,slug)), behind the §22.5 read gate. Unscoped /api/rfcs stay as
  default-project compat.
- cache.py: refresh_meta_repo iterates every projects row, mirroring each
  content_repo into cached_rfcs stamped with its project_id (_upsert_cached_rfc
  gains a project_id arg).
- frontend: api.listRFCs(projectId)/getRFC(projectId,slug); Catalog + RFCView
  pass useProjectId(); ProjectLayout's NotServedPlaceholder guard removed (every
  project serves), 404/not-readable branch kept; NotServedPlaceholder deleted.
- tests: test_project_scoped_serving.py (catalog scoping, entry isolation,
  gated 404); ProjectLayout.test updated (non-default renders). 445 backend +
  11 Vitest green; clean build.

Known limitation (next slice): write path + default-id re-stamp not yet scoped
(non-default project read-only); no live impact (no 2nd project in prod yet).
Per docs/superpowers/specs/2026-06-04-m3-backend-planb-design.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api.py

@@ -708,6 +708,88 @@ def make_router(
         payload["proposed_use_case"] = uc["use_case"] if uc else None
         return payload
 
+    # ---------------------------------------------------------------
+    # §22.4 (Plan B): per-project RFC serving — the catalog + entry view
+    # scoped to one project, identified by its own slug namespace
+    # (project_id, slug). The unscoped /api/rfcs[/{slug}] above stay as the
+    # default-project compat path; the frontend reads these scoped routes so a
+    # second project's corpus renders under /p/<id>/.
+    # ---------------------------------------------------------------
+
+    @router.get("/api/projects/{project_id}/rfcs")
+    async def list_project_rfcs(
+        project_id: str, request: Request, unreviewed: str | None = None
+    ) -> dict[str, Any]:
+        viewer = auth.current_user(request)
+        # §22.5 read gate: a gated project's catalog 404s to a non-member.
+        auth.require_project_readable(viewer, project_id)
+        viewer_id = viewer.user_id if viewer else None
+        unreviewed_clause = ""
+        if unreviewed is not None and unreviewed.lower() in ("1", "true", "yes"):
+            unreviewed_clause = " AND unreviewed = 1 AND state = 'active'"
+        rows = db.conn().execute(
+            f"""
+            SELECT slug, title, state, rfc_id, repo,
+                   owners_json, arbiters_json, tags_json,
+                   last_main_commit_at, last_entry_commit_at, updated_at
+              FROM cached_rfcs
+             WHERE state IN ('super-draft', 'active')
+               AND project_id = ?{unreviewed_clause}
+             ORDER BY COALESCE(last_main_commit_at, last_entry_commit_at) DESC
+            """,
+            (project_id,),
+        ).fetchall()
+        starred = set()
+        if viewer_id is not None:
+            starred = {
+                r["rfc_slug"]
+                for r in db.conn().execute(
+                    "SELECT rfc_slug FROM stars WHERE user_id = ? AND project_id = ?",
+                    (viewer_id, project_id),
+                )
+            }
+        items = [
+            {
+                "slug": r["slug"],
+                "title": r["title"],
+                "state": r["state"],
+                "id": r["rfc_id"],
+                "repo": r["repo"],
+                "owners": json.loads(r["owners_json"] or "[]"),
+                "arbiters": json.loads(r["arbiters_json"] or "[]"),
+                "tags": json.loads(r["tags_json"] or "[]"),
+                "last_active_at": r["last_main_commit_at"] or r["last_entry_commit_at"] or r["updated_at"],
+                "starred_by_me": r["slug"] in starred,
+                "has_open_prs": False,
+            }
+            for r in rows
+        ]
+        return {"items": items}
+
+    @router.get("/api/projects/{project_id}/rfcs/{slug}")
+    async def get_project_rfc(project_id: str, slug: str, request: Request) -> dict[str, Any]:
+        viewer = auth.current_user(request)
+        auth.require_project_readable(viewer, project_id)
+        row = db.conn().execute(
+            "SELECT * FROM cached_rfcs WHERE project_id = ? AND slug = ?",
+            (project_id, slug),
+        ).fetchone()
+        if row is None:
+            raise HTTPException(404, "Not found")
+        if row["state"] == "retired" and (viewer is None or viewer.role != "owner"):
+            raise HTTPException(404, "Not found")
+        payload = _serialize_rfc(row)
+        uc = db.conn().execute(
+            """
+            SELECT use_case FROM proposed_use_cases
+             WHERE scope = 'rfc' AND rfc_slug = ? AND project_id = ?
+             ORDER BY id DESC LIMIT 1
+            """,
+            (slug, project_id),
+        ).fetchone()
+        payload["proposed_use_case"] = uc["use_case"] if uc else None
+        return payload
+
     # ---------------------------------------------------------------
     # §22.4c: mark-reviewed — clear an active entry's `unreviewed` flag
     # ---------------------------------------------------------------