Switch PG to wxyc-postgres image; add F0000 precheck to migration 0003

[jakebromberg]

Problem

The CREATE TEXT SEARCH DICTIONARY wxyc_unaccent step in migrations/0003_wxyc_identity_match_functions.sql requires wxyc_unaccent.rules to be present at $SHAREDIR/tsearch_data/ on the destination PG. Today, CI provisions this via docker cp into the postgres:16-alpine service container; production Railway PG has no provisioning step in rebuild-cache.yml. The next workflow_dispatch run against a fresh Railway PG will fail at sqlx migrate run with ConfigFileError.

Sibling defect to WXYC/discogs-etl#223. Closed deploy ticket #37 was a paper tiger — the migration applied via CI but the production Railway destination has never been exercised against a fresh DB. Verified 2026-05-20 (against postgres:16-alpine): /usr/local/share/postgresql/tsearch_data/ is root:root 0755, so no in-migration write strategy can self-provision the file. SQLSTATE for the missing-rules-file error is F0000 (config_file_error).

Desired end state

Switch local + production PG to the new ghcr.io/wxyc/wxyc-postgres:pg16 image (built + published by WXYC/wxyc-etl — see the blocking issue, filed alongside this one). Migration 0003 gets a fail-fast precheck for SQLSTATE F0000 that re-raises with an actionable error pointing operators at the wxyc-postgres runbook when the rules file is missing.

Where

• docker-compose.yml — image: postgres:16-alpine → image: ghcr.io/wxyc/wxyc-postgres:pg16
• .github/workflows/ci.yml — drop the Install wxyc_unaccent rules into the PG service container step; update PG service image: to ghcr.io/wxyc/wxyc-postgres:pg16
• migrations/0003_wxyc_identity_match_functions.sql — wrap CREATE TEXT SEARCH DICTIONARY in a plpgsql DO block that catches SQLSTATE 'F0000' and re-raises with an actionable error including the runbook URL
• tests/wxyc_identity_match_parity_test.rs — add a negative-path test that runs the migration against a stock postgres:16-alpine (no rules file), asserts the exception message contains wxyc_unaccent.rules and the runbook URL
• CLAUDE.md — note the wxyc-postgres image dependency in the migration/CI section

Plpgsql precheck shape

DO $$
BEGIN
    CREATE TEXT SEARCH DICTIONARY wxyc_unaccent (
        TEMPLATE = unaccent,
        RULES = 'wxyc_unaccent'
    );
EXCEPTION
    WHEN SQLSTATE 'F0000' THEN
        RAISE EXCEPTION USING
            MESSAGE = 'wxyc_unaccent.rules is missing from $SHAREDIR/tsearch_data/. '
                      'The destination PG must run the wxyc-postgres image '
                      '(ghcr.io/wxyc/wxyc-postgres:pg16). Runbook: '
                      'https://github.com/WXYC/wxyc-etl/blob/main/docs/wxyc-postgres-image.md',
            ERRCODE = 'F0000';
END;
$$;

Other SQLSTATEs propagate unchanged.

Constraints

• Don't regress the existing parity test against the dictionary-functional path (file present → dictionary works → byte-equality holds).
• Operator action (Railway PG service swap) is one-time, documented in the wxyc-postgres runbook. This issue covers the per-repo code changes only.
• Don't bump migration numbers; edit 0003_wxyc_identity_match_functions.sql in place. The migration is idempotent and re-applying after the precheck is added against an already-stamped DB is a no-op.

Acceptance criteria

• Local docker-compose.yml uses ghcr.io/wxyc/wxyc-postgres:pg16
• CI workflow drops the docker-cp step; uses the wxyc-postgres image as the PG service
• Migration 0003 plpgsql precheck catches F0000 → actionable error with runbook URL
• Negative test: stock postgres:16-alpine + sqlx migrate run → expected message
• Positive test: existing parity test still passes against the wxyc-postgres image
• Operator: Railway PG service swapped to ghcr.io/wxyc/wxyc-postgres:pg16 (manual, tracked in the wxyc-etl runbook checklist)
• workflow_dispatch of rebuild-cache.yml against post-swap Railway PG succeeds end-to-end

Related

• Blocking issue (parent of the wxyc-postgres image): WXYC/wxyc-etl#127
• E3 deployment leg: WXYC/wxyc-etl#73
• Sibling cache work: WXYC/discogs-etl#223, WXYC/musicbrainz-cache (filed alongside this)
• Out of scope: WXYC/Backend-Service#805 — RDS constraint, Python-side path
• Predecessor: WXYC/wikidata-cache#37 — original Postgres-analog deploy ticket (closed; this is the production-deploy follow-up)