chore(mcp): convert lib/local-branch.js to TypeScript (Phase 2 of #7291)

[jaytbarimbao-collab]

Summary

Phase 2 of the packages/loopover-mcp TypeScript migration (#7291): convert lib/local-branch.js to real TypeScript, using the tsc build pipeline landed in Phase 1 (#7409).

• lib/local-branch.js → lib/local-branch.ts (592 lines). Types only — runtime behavior is byte-identical. The compiled lib/local-branch.js differs from the original only in tsc formatting, normalized trailing commas, and the elision of an already-dead node:path join import (imported but never called in the original).
• Strict-mode compliant against the root config's noUncheckedIndexedAccess and exactOptionalPropertyTypes: provably-in-bounds index accesses use non-null assertions (erase at compile time — no new runtime branches), and optional fields that may receive undefined are declared ?: T | undefined.
• Imports keep their .js extension (NodeNext), matching the Phase 1 files.

Test coverage

lib/local-branch.js shipped a substantial, previously-untested local scorer-preview surface (runExternalScorePreview, classifyScorerExecFailure, setupGuidanceForLocalScorer, probeLocalScorer, normalizeScorerOutput, and helpers). Now that the file is real TypeScript under the 99% patch gate, this PR adds the missing unit coverage:

• +26 test cases across test/unit/local-scorer-adapter.test.ts (scorer exec-failure classification, JSON-shape parsing, guidance, redaction, timeouts — driven by fixture subprocesses and a selective child_process mock) and test/unit/local-branch.test.ts (git-metadata branch partials via real temp repos: base-ref resolution priorities, remote-tracking SHA, CI hints, typechange status codes, workspace-root normalization).
• A handful of structurally-unreachable defensive fallbacks (e.g. titleFromBranch is never nullish, git diff -M never emits copy codes) are marked with /* v8 ignore -- <reason> */, matching the pattern already used across the converted packages/loopover-miner/lib TypeScript files.
• Result: lib/local-branch.ts is at 100% line and branch coverage.

Test adjustment

Removes the now-unused // @ts-expect-error package helper is plain JS ... directives above the dynamic import("../../packages/loopover-mcp/lib/local-branch.js") calls in test/unit/local-branch.test.ts and test/unit/local-scorer-adapter.test.ts — those imports resolved to the untyped plain .js before this conversion and now resolve to the typed .ts source.

Verification

• npm run build (mcp package): tsc compile + node --check verify both pass.
• npx vitest run test/unit/local-branch.test.ts test/unit/local-scorer-adapter.test.ts: 99/99 pass; local-branch.ts coverage 100% lines / 100% branch.
• Root tsc -p tsconfig.json --noEmit: clean.

Closes #7329

[JSONbored]

Issue already completed, closing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.34%. Comparing base (fe3a344) to head (bbab76c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7423      +/-   ##
==========================================
+ Coverage   91.27%   91.34%   +0.07%     
==========================================
  Files         716      716              
  Lines       72972    72983      +11     
  Branches    21528    21628     +100     
==========================================
+ Hits        66605    66667      +62     
+ Misses       5327     5272      -55     
- Partials     1040     1044       +4     

Flag	Coverage Δ
shard-1	32.63% <53.53%> (-0.02%)	⬇️
shard-2	36.12% <68.77%> (+0.04%)	⬆️
shard-3	34.53% <0.00%> (-0.01%)	⬇️
shard-4	42.89% <0.00%> (-0.01%)	⬇️
shard-5	36.97% <0.00%> (-0.01%)	⬇️
shard-6	33.55% <0.00%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
packages/loopover-mcp/lib/local-branch.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes