PG 15→17 upgrade fails at completion ("pg_cron has no update path from 1.6 to 1.6.4"), leaves project with no valid restart target and rest/auth down

# Bug report - [x] I confirm this is a bug with Supabase, not with my own application. - [x] I confirm I have searched the [Docs](https://docs.supabase.com), GitHub [Discussions](https://github.com/supabase/supabase/discussions), and [Discord](https://discord.supabase.com). ## Describe the bug An in-place Postgres 15 → 17 upgrade failed at the finalization step and left the project in a broken, unrecoverable-by-user state, taking our production application fully down. - Project ref: `mxxqgiqimawzeoajiklw` (ca-central-1, GA release channel) - Upgrade initiated: 2026-06-05 05:55:58 UTC - `GET /v1/projects/{ref}/upgrade/status` returns: `{"error":"5_data_upgrade_completion_failed","status":2,"target_version":"17","latest_status_at":"2026-06-05T06:01:33"}` The root cause visible in the Postgres logs is the extension update that runs during upgrade completion: ERROR: extension "pg_cron" has no update path from version "1.6" to "1.6.4" Resulting state: 1. The database itself **did** come up on the new version (17.6.1.127) and accepts connections — `realtime`, `storage`, and `pooler` are all ACTIVE_HEALTHY and connected to it. 2. `rest` (PostgREST), `auth` (GoTrue), and the `db` health check are UNHEALTHY. All API requests fail with: `upstream connect error or disconnect/reset before headers ... delayed connect error: 111` (HTTP 503). 3. **Dashboard "Restart project" fails** with: `Unable to locate a single valid target for the restart; found 0 for mxxqgiqimawzeoajiklw` — the control plane appears to have lost the project's compute target. 4. Management API `POST /v1/projects/{ref}/database/query/read-only` times out (HTTP 544). 5. Because the completion step aborted at the pg_cron error, the rest of finalization never ran: logs are flooded with collation version mismatch warnings (`created using collation version 2.39, but the operating system provides 2.40`), i.e. `REFRESH COLLATION VERSION` / reindexing was never performed. 6. `GET /v1/proje…