What does this PR do?

Fixes full-text search indexing raw Portable Text JSON instead of prose. On the audited production deployment (Macabro festival site, emdash 0.31.1), structural tokens were 27–29% of the FTS index: searching normal (a PT style value) matched 870/906 posts, _type matched 2,096 documents, and snippets showed JSON fragments.

Why the fix isn't "just call extractPlainText": the FTS sync is done by SQL triggers, which can't call into JS — and the tables were external-content FTS5 (content='ec_<slug>'), which requires the index to exactly mirror the raw column values (snippet() reads them, and the 'delete' command must be fed the inserted values or the index corrupts — the exact corruption class migration 039 exists to fix). So indexing extracted text under external content is structurally impossible without materializing it into real columns on every ec_* table, which would touch every content write path in the codebase.

Instead, this PR rebuilds the FTS tables as self-contained FTS5 whose Portable Text columns hold extracted prose, with the extraction done in SQL so triggers and population share one source of truth:

• json_tree() collects every JSON string under a text, alt, caption, or code key — span text, image alt/caption, and code blocks, the same semantics as extractPlainText in text-extraction.ts. json_valid() guards legacy rows holding a bare string (indexed as-is).
• Self-contained tables retire the external-content 'delete' choreography entirely: removal is a plain DELETE, a harmless no-op for never-indexed (soft-deleted) rows, so the SQLITE_CORRUPT_VTAB corruption class from SQLite Database Corrupt Error on new site #649/migration 039 can no longer occur. INSERT OR REPLACE makes concurrent D1 populates converge (verified: a plain duplicate-rowid insert throws on self-contained FTS5).
• Snippets now come from the stored prose — searching content returns readable text, not {"_type":"block"....

Existing deployments rebuild automatically: migration 055_fts_plain_text drops and recreates every search-enabled collection's FTS table and triggers and repopulates from content, following 039's structure (self-contained lock-step SQL copy, IF NOT EXISTS forms for D1's lockless concurrent migrators, defensive identifier validation). No manual reindex step.

The search query layer is unchanged: it joins ec_* by id for metadata, bm25 weight positions and the snippet column index are preserved (same column order), and Postgres is unaffected (FTS5 is SQLite-gated throughout). Trade-off worth noting for review: a self-contained FTS table stores its own copy of the indexed text (external content stored none), while the inverted index itself shrinks by the removed structural tokens; net size impact on the audited data set is roughly neutral, and the correctness/corruption-immunity gains are structural.

The 039 migration test's fixture was updated to explicitly construct the historical external-content table shape it needs (the current FTSManager now builds self-contained tables, on which the historical "broken" triggers are actually correct) — 039's own frozen migration SQL is untouched.

Coordinates with the upcoming write-amplification fix (WHEN guards on these same triggers): whichever lands second rebases and ships its own lock-step migration, per 039's rule.

Found during a measured database audit of a production deployment.

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main. — n/a: no admin UI strings changed
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion — n/a: bug fix

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: Claude Fable 5 (Claude Code)

Screenshots / test output

Failing first (on main, before the fix):

× does not match Portable Text structural tokens
  → "normal" must not match: expected [ …(1) ] to deeply equal []
× returns prose snippets, not JSON fragments

After the fix — new search-quality suite, migration 055 upgrade-path suite (pre-migration assertion proves the polluted baseline, post-migration assertions prove the cleanup and working triggers), plus all existing search/FTS/registry/migration suites:

Tests  36 passed   (tests/integration/search/, 039 migration suite)
Tests  17 passed   (055 migration suite, migrations integration)
Full packages/core suite: 5074 passed — the single virtual-modules.test.ts failure is
pre-existing on a clean main checkout in this environment (macOS temp-dir realpath).

🤖 Generated with Claude Code