fix(db): stop documenting 0090 as a grandfathered migration duplicate

[shin-core]

What & why

KNOWN_MIGRATION_DUPLICATES (src/db/migration-collisions.ts) is already correct — 0090 is not a key, because #8897 renumbered 0090_pull_request_detail_sync_head_sha to 0092, leaving a single 0090_contributor_cap_label file at 0090. But scripts/check-migrations.ts's header still documented 0090 as a grandfathered duplicate and cross-referenced "same reasoning as 0074/0090", so a future reader could re-add the dead entry straight from git history.

The fix

• Replace the 0090 header bullet with a one-line note that 0090 was renumbered to 0092 by fix(db): stale KNOWN_MIGRATION_DUPLICATES entry for migration 90 references a file that no longer exists #8897 (not grandfathered), so it must not be re-added.
• Correct the 0156 cross-reference to name only real grandfathers (0074).
• No behavioural change to the script or to KNOWN_MIGRATION_DUPLICATES (which is not edited). npm run db:migrations:check still reports the same "4 grandfathered duplicates: 0015, 0017, 0074, 0156".

Tests (test/unit/migration-collisions.test.ts)

Two guards so the header comment and the data can't silently diverge again:

• Every filename in KNOWN_MIGRATION_DUPLICATES exists in the real migrations/ directory — a re-added 0090 entry (naming the renumbered-away file) fails this (verified by injecting one).
• Every on-disk migration number with more than one file is a key of KNOWN_MIGRATION_DUPLICATES — the reverse direction, so a new un-grandfathered collision surfaces here, not only at premerge.

Validation

• npm run db:migrations:check green; npm run typecheck green; the migration-collisions and check-migrations-script suites green.
• scripts/** is outside Codecov's include, so the comment change carries no coverage obligation; the new tests import src/db/migration-collisions.ts, so coverage collection sees real src/** files.
• git diff --check <base> HEAD clean; diff is two files, no src/** source or migration change.

Closes #9653

[loopover-orb]

Warning

⏸️ LoopOver review result - manual review recommended

_{Review updated: 2026-07-29 12:45:22 UTC}

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

⏸️ Suggested Action - Manual Review

Review summary
This is a narrow documentation-and-test PR: it corrects a stale comment block in scripts/check-migrations.ts that mislabeled migration 0090 as a grandfathered duplicate (it's actually a single file today, per #8897's renumbering), and adds two bidirectional guard tests to migration-collisions.test.ts so the comment and KNOWN_MIGRATION_DUPLICATES can't silently diverge again. No src/** production logic is touched, and the diff matches its stated intent and closes #9653. One thing I can't fully reconcile: the reference snapshot of src/db/migration-collisions.ts shown to me still lists `90` as a key with both filenames, which would fail the new `has(90)).toBe(false)` assertion — but CI passed on this commit, so I'm treating that reference snapshot as stale rather than a real contradiction in the PR itself.

Nits — 3 non-blocking

• The bidirectional coverage test in test/unit/migration-collisions.test.ts (readdirSync("migrations")) assumes the test runner's cwd is the repo root — confirm that's guaranteed elsewhere in the suite rather than incidental.
• The reverse-direction test duplicates the same group-by-number logic already in scripts/check-migrations.ts; consider extracting a shared helper if this pattern grows, though for two call sites it's fine as-is.
• Consider a one-line comment cross-referencing fix(db): stale KNOWN_MIGRATION_DUPLICATES entry for migration 90 references a file that no longer exists #8897 directly next to the `has(90)` assertion in the test (as the header comment does) so a future reader hitting a failure has the same renumbering context without opening check-migrations.ts.

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	#9653
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: minor

Linked issue satisfaction

Addressed
The PR removes the stale 0090 grandfather bullet with an explanatory note about #8897's renumbering, corrects the 0156 cross-reference to name only 0074, and adds both required bidirectional guard tests (dead-entry check and reverse on-disk-collision check) mirroring the requested pattern without touching KNOWN_MIGRATION_DUPLICATES.

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 (4637c0c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9832   +/-   ##
=======================================
  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.