fix(§22/G-15): make the branch/edit/body subsystem three-tier aware (v0.53.0)

§22 migrated the READ/catalog path to the three-tier (project/collection)
model but the WRITE/branch/body subsystem still hardcoded the default
project's default collection — resolving every meta-resident entry to the
default content repo at rfcs/<slug>.md, ignoring the entry's project (its own
content repo) and collection (a <subfolder>/rfcs/ prefix). An entry outside
the default collection rendered a blank canonical body and every edit/PR/
body-write path hit the wrong file.

- New single resolver: projects.content_repo_for_collection() +
  projects.entry_location(config, cid, slug) -> (org, repo, md_path)
  (collection -> project -> content_repo + subfolder; falls back to the
  default repo for a legacy/unknown collection).
- Every entry write/read path resolves via it: api_branches (body GET + all
  branch write paths), api_prs (pr-draft/open/merge/withdraw/review/
  resolution-branch), api_graduation (graduate/claim/retire/unretire +
  orchestrator + state-flip), api.py mark-reviewed + idea-PR merge/decline/
  withdraw + proposal preview, api_metadata. bot.open_metadata_pr and
  bot.mark_entry_reviewed gained a file_path param. refresh_meta_branches,
  the webhook corpus-refresh dispatch, and the hygiene branch-delete now
  span every project's content repo, not just the default.
- New additive collection-scoped body-read routes:
  GET /api/projects/{pid}/collections/{cid}/rfcs/{slug}/main and
  .../branches/{branch} disambiguate a slug across collections (G-5) and read
  the entry's own repo. Slug-only routes kept (now collection-aware via the
  cached row). Frontend getRFCMain/getBranch take optional pid+cid; RFCView
  threads them (mirrors the v0.52.1 entry-detail fix).

No migration, no config change. Existing default-collection entries
unaffected. Tests: backend resolver + collection-scoped branch/body + graduate-
in-subfolder write path; frontend api unit. backend 677 / frontend 60 green.

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

backend/app/webhooks.py

@@ -80,10 +80,17 @@ def make_router(config: Config, gitea: Gitea) -> APIRouter:
             payload = {}
         repo_full = (payload.get("repository") or {}).get("full_name") or ""
         registry_full = f"{config.gitea_org}/{config.registry_repo}"
-        content_repo = projects_mod.default_content_repo(config)
-        if not content_repo:
-            log.warning("webhook: default project content_repo is unknown; corpus refresh skipped")
-        content_full = f"{config.gitea_org}/{content_repo}" if content_repo else None
+        # §22/G-15: a corpus push can land on ANY project's content_repo, not
+        # just the default — recognise the full set so a non-default project's
+        # push triggers the (multi-project) corpus/branch/PR refresh.
+        content_fulls = {
+            f"{config.gitea_org}/{r['content_repo']}"
+            for r in db.conn().execute(
+                "SELECT content_repo FROM projects "
+                "WHERE content_repo IS NOT NULL AND content_repo != ''")
+        }
+        if not content_fulls:
+            log.warning("webhook: no project content_repo is known; corpus refresh skipped")
         try:
             if repo_full == registry_full:
                 # §22.2: a registry-repo push re-mirrors the projects table.
@@ -94,7 +101,7 @@ def make_router(config: Config, gitea: Gitea) -> APIRouter:
                     await registry_mod.refresh_registry(config, gitea)
                 except registry_mod.RegistryError:
                     log.exception("registry webhook: invalid projects.yaml; keeping last-good")
-            elif content_full and (repo_full == content_full or not repo_full):
+            elif content_fulls and (repo_full in content_fulls or not repo_full):
                 await cache.refresh_meta_repo(config, gitea)
                 await cache.refresh_meta_branches(config, gitea)
                 await cache.refresh_meta_pulls(config, gitea)