feat!: remove gittensory-engine's settings.gateCheckMode yml back-compat parsing (#5373)

[JSONbored]

Summary

Final stage (2.10 of 10) of the gateCheckMode removal (#5373). The RepositorySettings.gateCheckMode field itself was removed entirely in #5459 (stage 2.9). This PR removes the last remaining vestige: @jsonbored/gittensory-engine's own .gittensory.yml parser (parseFocusManifest/parseFocusManifestContent) still recognized a bare settings.gateCheckMode key and derived reviewCheckMode from it for back-compat with older manifest files.

• packages/gittensory-engine/src/focus-manifest.ts: removed the gateCheckMode parse + derive-reviewCheckMode-when-unset logic from parseSettingsOverride; removed "gateCheckMode" from the FocusManifestSettings Pick<RepositorySettings, ...> list; rewrote the FocusManifestGateConfig doc comment (fixed a stale "master switch" claim while in the area).
• packages/gittensory-engine/src/types/manifest-deps-types.ts: removed the deprecated gateCheckMode?: "off" | "enabled" field from the engine's own RepositorySettings mirror type.
• scripts/check-docs-drift.mjs: dropped a now-dead SETTINGS_ALIAS_MANIFEST row for gateCheckMode — it's no longer iterated as a RepositorySettings field, so the alias entry was orphaned since feat!: remove the gateCheckMode field from RepositorySettings entirely #5459.
• Test fixes in test/unit/focus-manifest.test.ts (rewrote the settings.gateCheckMode back-compat describe block into a "fully removed, inert key" regression suite; removed the dead SETTINGS_GATE_ALIASED_FIELDS entry) and test/unit/gate-check-policy.test.ts (updated one assertion that expected the now-removed derivation).

settings.gateCheckMode is now a fully unrecognized key: it parses into nothing and derives nothing. settings.reviewCheckMode is the sole publish-authority key.

Blast radius / why this is safe to merge now

• parseFocusManifest/parseFocusManifestContent are the only public exports touched.
• @jsonbored/gittensory-mcp (published, v0.7.0 live) doesn't reference this code path at all.
• @jsonbored/gittensory-miner calls parseFocusManifestContent but never reads gateCheckMode/reviewCheckMode from the result, and isn't itself published to npm (git-clone-only).
• .github/workflows/publish-engine.yml is workflow_dispatch-only — merging this does not itself publish anything to the registry.
• packages/gittensory-engine/package.json is already at "1.0.0" (chore(release): cut engine v1.0.0 #4686, merged 2026-07-10, not yet published — npm registry still serves 0.2.0). Bundling this breaking removal into that not-yet-shipped 1.0.0 is the right timing: it sheds this back-compat parsing before the package commits to a stable public surface, rather than requiring a separate major bump later for the same change. No publish is triggered by this PR.

Test plan

• npm run build --workspace @jsonbored/gittensory-engine — clean
• npm run typecheck — clean (full monorepo)
• npx vitest run — full suite, 778 files / 15218 tests passed, 12 skipped, exit 0
• npm test --workspace @jsonbored/gittensory-engine (node:test) — 526/526 passing
• npm run manifest:drift-check / engine-parity:drift-check / docs:drift-check — all clean
• npm run ui:lint / npm run ui:typecheck — clean (pre-existing unrelated warnings only)
• npm audit --audit-level=moderate — 0 vulnerabilities
• Repo-wide grep confirms zero remaining gateCheckMode references outside historical comments and regression tests asserting the key is now inert

Closes #5373

[superagent-security]

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

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	gittensory-ui	0397826	Commit Preview URL Branch Preview URL	Jul 12 2026, 09:06 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.52%. Comparing base (30a6ffb) to head (0397826).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5463      +/-   ##
==========================================
- Coverage   94.52%   94.52%   -0.01%     
==========================================
  Files         554      554              
  Lines       44469    44466       -3     
  Branches    14666    14664       -2     
==========================================
- Hits        42034    42031       -3     
  Misses       1754     1754              
  Partials      681      681              

Flag	Coverage Δ
shard-1	44.07% <ø> (+<0.01%)	⬆️
shard-2	35.00% <ø> (+<0.01%)	⬆️
shard-3	31.99% <ø> (-0.01%)	⬇️
shard-4	31.68% <ø> (-0.01%)	⬇️
shard-5	32.71% <ø> (+<0.01%)	⬆️
shard-6	43.53% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/gittensory-engine/src/focus-manifest.ts	99.19% <ø> (-0.01%)	⬇️

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