fix(db): index decision_ledger_anchors on (row_hash, status)

[shin-core]

What & why

anchorBackendsMissingForRowHash (#9489, src/review/ledger-anchor-persistence.ts) runs

SELECT DISTINCT backend FROM decision_ledger_anchors WHERE row_hash = ? AND status = 'ok' AND backend IN (...)

once per row being re-anchored, but decision_ledger_anchors had no index on row_hash. So each call was a full table scan whose cost grows with the anchor ledger.

The fix

Add migration 0203 creating:

CREATE INDEX IF NOT EXISTS decision_ledger_anchors_row_hash_status ON decision_ledger_anchors (row_hash, status);

row_hash leads (the equality predicate); status is included so the status = 'ok' filter is served from the index rather than a row fetch. This mirrors the decision_ledger_record_id index added in migrations/0198. The migration contains nothing else — no schema or data change.

Note: the issue names migration 0202, but that number is now taken (0202_orb_signal_rollups.sql), so this uses the next contiguous free number, 0203.

Tests (test/unit/ledger-anchor-persistence.test.ts)

• After replaying migrations/** (via createTestEnv), the index decision_ledger_anchors_row_hash_status exists, and EXPLAIN QUERY PLAN for the exact anchorBackendsMissingForRowHash predicate SEARCHes via it, not SCANs (fails without the migration).
• The existing anchorBackendsMissingForRowHash behaviour cases (all-missing / some-present / all-present / different-rowHash) confirm results are unchanged after the migration.

Validation

• npm run db:migrations:check green (contiguous 0001..0203); npm run db:schema-drift:check green (index on a raw-SQL table, no Drizzle change); npm run typecheck green.
• migrations/** is outside Codecov's include, so the migration carries no coverage obligation; the test imports createTestEnv, so shards see real src/**.
• git diff --check <base> HEAD clean; diff is the one migration + its test, no src/** source change.

Closes #9652

[loopover-orb]

Warning

⏸️ LoopOver review result - manual review recommended

_{Review updated: 2026-07-29 12:45:12 UTC}

2 files · 1 AI reviewer · no blockers · CI green · clean

⏸️ Suggested Action - Manual Review

Review summary
This PR adds a single migration (0203) creating an index on `decision_ledger_anchors(row_hash, status)` to fix the full-table-scan behind `anchorBackendsMissingForRowHash`, plus a regression test that asserts via `EXPLAIN QUERY PLAN` that the query now SEARCHes via the index rather than SCANs the table. The migration is a plain `CREATE INDEX IF NOT EXISTS`, which is D1-remote-safe (no TEMP, ATTACH, PRAGMA, or explicit transaction control), and the composite column order (row_hash leading, status included) correctly matches the equality/filter shape of the query it targets. The change is narrow, closes linked issue #9652, and the test is a real regression test (fails without the migration per the PR's own claim, and is anchored to the exact predicate the production code runs) rather than a fabricated scenario.

Nits — 3 non-blocking

• test/unit/ledger-anchor-persistence.test.ts:258 — the `not.toContain("SCAN decision_ledger_anchors ")` string match is brittle to any change in SQLite's EXPLAIN QUERY PLAN wording/formatting across versions; consider asserting on the `detail` containing `SEARCH` instead for a more robust positive assertion.
• migrations/0203_decision_ledger_anchors_row_hash_index.sql — worth double-checking locally that 0202 is indeed already taken and 0203 is the correct next contiguous number, since `db:migrations:check` passing in CI is the real source of truth here.
• Nothing structural to change — this is a well-targeted, single-purpose index migration with a real regression test; merge as-is once migration numbering is reconfirmed against the latest default branch.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#9652
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	❌ 5/25	Preflight is holding this PR: the review lane is unavailable, so it is not ready for automated review.
Contributor workload	✅ 10/10	Author activity: 63 registered-repo PR(s), 46 merged, 0 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	shin-core; Gittensor profile; 63 PR(s), 0 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Addressed
The PR adds a single-purpose migration creating the exact CREATE INDEX IF NOT EXISTS decision_ledger_anchors_row_hash_status ON decision_ledger_anchors (row_hash, status) statement with a header comment naming anchorBackendsMissingForRowHash, #9489, and the migrations/0198 sibling precedent, and adds tests confirming both index existence via sqlite_master and unchanged/behavior-preserving results

Review context

• Author: shin-core
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is registered but has no active allocation in the current snapshot.
• Public profile languages: not available
• Official Gittensor activity: 63 PR(s), 0 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Start here: Await review-lane availability.
• Then work through the remaining 2 steps in the Signals table above.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.59%. Comparing base (9d7f567) to head (874ea68).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9830   +/-   ##
=======================================
  Coverage   91.59%   91.59%           
=======================================
  Files         915      915           
  Lines      112700   112700           
  Branches    27077    27077           
=======================================
  Hits       103229   103229           
  Misses       8144     8144           
  Partials     1327     1327           

Flag	Coverage Δ
backend	95.58% <ø> (ø)

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[loopover-orb]

LoopOver approves — the gate is satisfied and CI is green.