v0.46.1 — fix migration 029 for the §22.13 re-stamp aftermath (OHM deploy fault)

Deploying the three-tier series onto OHM crash-looped on migration 029:
`NOT NULL constraint failed: cached_branches__new.collection_id`, then a UNIQUE
collision. Root cause: the v0.39.0 default→ohm re-stamp updated
cached_rfcs.project_id but NOT the entry-satellite tables, so ~1.3k
cached_branches rows were stranded at project_id='default' — which 029's
per-project collection backfill can't map (NULL), some of which also duplicate
freshly-re-mirrored 'ohm' rows (UNIQUE), and some of which reference entries
that no longer exist.

Fix — a repair prologue at the top of 029 (no schema change):
- drop stale rows that duplicate an already-correctly-stamped row (keep the
  fresh copy) for the branch-keyed tables;
- re-derive each satellite's project_id from its entry (cached_rfcs, by slug);
- drop rows whose entry no longer exists (stale cache, rebuildable from gitea).
A no-op on clean/fresh deployments (empty or consistent satellites).

Validated against a snapshot of the live OHM DB: 029→032 apply cleanly, zero
NULL collection_id, FK check clean, watches/RFCs/branch_visibility preserved,
cached_branches 1397 → 1291 (−67 no-RFC, −39 dups). Fresh-install path
unchanged: existing 029 suite green + a new regression test for the
stale/dup/orphan shape. Full backend suite 547 passed.

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

backend/migrations/029_collections.sql

@@ -26,6 +26,53 @@
 -- they carry a project-grain tag, untouched in S1. See
 -- docs/design/2026-06-05-three-tier-projects-collections.md §A.6 / Part E.
 
+-- ── §22.13 repair: re-stamp stale satellite project_id before rekeying ──────
+-- The §22.13 default→ohm re-stamp (v0.39.0, `projects.restamp_default_project`)
+-- updated `cached_rfcs.project_id` but NOT the entry-satellite tables, leaving
+-- rows with a stale `project_id` (e.g. 'default') that the per-project collection
+-- backfill below cannot map — the subquery returns NULL and the NOT NULL rebuild
+-- fails (`cached_branches__new.collection_id`). Before rebuilding, re-derive each
+-- satellite's `project_id` from its entry (`cached_rfcs`, joined by slug — slugs
+-- are unique per collection and, pre-rebuild, globally), and drop rows whose
+-- entry no longer exists (stale cache; the `cached_*` tables are rebuildable from
+-- gitea). On a clean/fresh deployment every satellite is empty or already
+-- consistent, so this whole block is a no-op. (Discovered on the OHM data:
+-- ~1.3k `cached_branches` rows stranded at project_id='default'.)
+-- First drop stale rows that DUPLICATE an already-correctly-stamped row (the same
+-- branch cached under both the stale and the real project_id) — re-stamping them
+-- would collide on the (project_id, rfc_slug, branch_name) key. The correctly-
+-- stamped copy is kept (it carries the current head_sha / visibility). Only the
+-- branch-keyed tables can hold such a pair; the others key on (rfc_slug,user_id)
+-- /(scope,pr_number) and have no stale data here, so they need no dedup.
+DELETE FROM cached_branches WHERE project_id NOT IN (SELECT id FROM projects)
+  AND EXISTS (SELECT 1 FROM cached_branches o WHERE o.rfc_slug = cached_branches.rfc_slug AND o.branch_name = cached_branches.branch_name AND o.project_id IN (SELECT id FROM projects));
+DELETE FROM branch_visibility WHERE project_id NOT IN (SELECT id FROM projects)
+  AND EXISTS (SELECT 1 FROM branch_visibility o WHERE o.rfc_slug = branch_visibility.rfc_slug AND o.branch_name = branch_visibility.branch_name AND o.project_id IN (SELECT id FROM projects));
+UPDATE rfc_invitations         SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = rfc_invitations.rfc_slug)         WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM rfc_invitations          WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE cached_branches         SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = cached_branches.rfc_slug)         WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM cached_branches          WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE branch_visibility       SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = branch_visibility.rfc_slug)       WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM branch_visibility        WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE branch_contribute_grants SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = branch_contribute_grants.rfc_slug) WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM branch_contribute_grants WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE stars                   SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = stars.rfc_slug)                   WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM stars                    WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE watches                 SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = watches.rfc_slug)                 WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM watches                  WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE pr_seen                 SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = pr_seen.rfc_slug)                 WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM pr_seen                  WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE branch_chat_seen        SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = branch_chat_seen.rfc_slug)        WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM branch_chat_seen         WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE funder_consents         SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = funder_consents.rfc_slug)         WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM funder_consents          WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE rfc_collaborators       SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = rfc_collaborators.rfc_slug)       WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM rfc_collaborators        WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE contribution_requests   SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = contribution_requests.rfc_slug)   WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM contribution_requests    WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+UPDATE proposed_use_cases      SET project_id = (SELECT r.project_id FROM cached_rfcs r WHERE r.slug = proposed_use_cases.rfc_slug)      WHERE rfc_slug IN (SELECT slug FROM cached_rfcs);
+DELETE FROM proposed_use_cases       WHERE rfc_slug NOT IN (SELECT slug FROM cached_rfcs);
+
 -- ── collections: the new typed-corpus grain beneath projects ───────────────
 CREATE TABLE collections (
     id            TEXT NOT NULL,