diff --git a/backend/.env.example b/backend/.env.example
index 245371b..9fa08d9 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -9,19 +9,18 @@ GITEA_URL=http://localhost:3000
 GITEA_BOT_USER=rfc-bot
 GITEA_BOT_TOKEN=
 
-# The Gitea org or user that owns the meta repo and every RFC repo
-# the bot will create on graduation.
+# The Gitea org or user that owns every RFC repo the bot will create on
+# graduation.
 GITEA_ORG=wiggleverse
-META_REPO=meta
 
-# --- Multi-project registry (§22) ---
-# The registry repo (under GITEA_ORG) the framework reads to learn which
-# projects this deployment hosts. Optional through Slice M1: the registry
-# mirror lands in M3, and until then the single default project's content
-# repo is taken from META_REPO above. The repo's name is the deployment's
-# choice. When the mirror lands, REGISTRY_REPO becomes required and
-# supersedes META_REPO.
-# REGISTRY_REPO=wiggleverse-registry
+# §22.2 — the project registry repo (REQUIRED). The framework reads
+# `projects.yaml` at its root to learn which projects exist. The repo name is
+# the deployment's choice; the app fails to start if this is unset.
+REGISTRY_REPO=registry
+# §22.13 — optional id for the bootstrap/default project. Reserved for the
+# Plan B re-stamp; leave unset in Plan A (the default project id stays
+# `default`). When set, it must match an `id` in projects.yaml.
+# DEFAULT_PROJECT_ID=ohm
 
 # --- OAuth (Gitea) ---
 # In Gitea: Site Administration → Applications → Add OAuth2 Application.
diff --git a/backend/app/hygiene.py b/backend/app/hygiene.py
index 4a18004..7431966 100644
--- a/backend/app/hygiene.py
+++ b/backend/app/hygiene.py
@@ -299,7 +299,14 @@ async def _delete_branch_via_bot(
         log.warning("hygiene: cannot delete %s/%s — slug missing from cache", slug, branch)
         return False
     if not rfc["repo"]:
-        owner, repo = config.gitea_org, (projects_mod.default_content_repo(config) or "")
+        repo = projects_mod.default_content_repo(config)
+        if not repo:
+            log.warning(
+                "hygiene: default project has no content_repo; skipping branch delete for %s/%s",
+                slug, branch,
+            )
+            return False
+        owner = config.gitea_org
     elif "/" in rfc["repo"]:
         owner, repo = rfc["repo"].split("/", 1)
     else:
diff --git a/backend/app/webhooks.py b/backend/app/webhooks.py
index 272a310..56d0412 100644
--- a/backend/app/webhooks.py
+++ b/backend/app/webhooks.py
@@ -80,16 +80,21 @@ 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}"
-        meta_repo = projects_mod.default_content_repo(config)
-        meta_full = f"{config.gitea_org}/{meta_repo}" if meta_repo else None
+        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
         try:
             if repo_full == registry_full:
                 # §22.2: a registry-repo push re-mirrors the projects table.
+                # Tolerate a malformed projects.yaml (keep last-good rows); let a
+                # transport error bubble to the outer 500 so an unreachable Gitea
+                # on a registry push is loud rather than silently dropped.
                 try:
                     await registry_mod.refresh_registry(config, gitea)
                 except registry_mod.RegistryError:
                     log.exception("registry webhook: invalid projects.yaml; keeping last-good")
-            elif meta_full and (repo_full == meta_full or not repo_full):
+            elif content_full and (repo_full == content_full 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)
diff --git a/backend/tests/test_multi_project_spine_vertical.py b/backend/tests/test_multi_project_spine_vertical.py
index aa7a3ad..35ce1dd 100644
--- a/backend/tests/test_multi_project_spine_vertical.py
+++ b/backend/tests/test_multi_project_spine_vertical.py
@@ -110,15 +110,21 @@ def test_registry_mirror_is_idempotent(app_with_fake_gitea):
     """Re-running the registry mirror is safe — it upserts (overwrites) the
     projects row from projects.yaml each time without raising. M3 retirement
     of seed_default_project: the registry mirror is now the sole authority."""
-    from app import db
+    import asyncio
+    from app import db, registry as registry_mod
 
     app, _ = app_with_fake_gitea
     with TestClient(app):
-        # After startup the row should have content_repo from projects.yaml.
-        got = db.conn().execute(
-            "SELECT content_repo FROM projects WHERE id = 'default'"
-        ).fetchone()["content_repo"]
-        assert got == "meta"
+        before = db.conn().execute("SELECT COUNT(*) AS n FROM projects").fetchone()["n"]
+        cfg = app.state.config
+        gitea = app.state.gitea
+        asyncio.run(registry_mod.refresh_registry(cfg, gitea))
+        after = db.conn().execute("SELECT COUNT(*) AS n FROM projects").fetchone()["n"]
+        assert after == before
+        row = db.conn().execute(
+            "SELECT content_repo FROM projects WHERE id='default'"
+        ).fetchone()
+        assert row["content_repo"] == "meta"
 
 
 def test_registry_repo_config_wired(app_with_fake_gitea, monkeypatch):