fix(blast): preserve precise ranges with custom Git diff prefixes

[cookerpapa]

Git prefix settings can prevent patch paths from matching changed files, causing blast to lose line ranges and fall back to whole-file seeds.

Pin a/ and b/ prefixes for the internal patch command. User configuration is preserved. Tests cover working-tree, explicit-base, and last-commit comparisons, plus precise CLI symbol seeds.

Fixes #369.

Validation:

• 14 new tests; 9 fail before the fix.
• 55 blast tests pass.
• Full suite: 1231 passed, 4 skipped.
• Build and git diff --check pass.

[trailhq-graft]

🌱 graft blast radius

1 area changed → 2 areas can be affected. 2 dependent symbols, depth 2.
Tests: no test reaches File Diffing.
Tag: @anirudhkumar-nanonets — 3 of 3 areas

flowchart TB
  A0(("Pull Request Review<br/>1 symbol"))
  A1(("Blast CLI<br/>1 symbol"))
  classDef reached fill:#D9EDF3,stroke:#3AA7C9,stroke-width:1.5px,color:#0E313C;
  class A0,A1 reached;

Loading

Can be affected	Symbols	Nearest hop	Reached from
Pull Request Review	1	src/app/review.ts:L45-L99 reviewPullRequest — calls, depth 2	File Diffing
Blast CLI	1	src/blast/blast-cli.ts:L63-L124 runBlastCommand — calls, depth 2	File Diffing

Who knows this code — 1 person across 3 areas

Area	Who knows it
File Diffing · changed	@anirudhkumar-nanonets — 2 commits, last 25d ago
Pull Request Review · affected	@anirudhkumar-nanonets — 3 commits, last 13d ago
Blast CLI · affected	@anirudhkumar-nanonets — 7 commits, last 18d ago

Ownership is git history over each area's own files, weighted towards recent work (120-day half-life). Merge commits and bots are dropped, and you are dropped from your own PR. A name with no @ has no GitHub handle in its commit email — tag them by hand, or add a .mailmap entry. A suggestion from history, not a CODEOWNERS rule.

All 2 dependent symbols, grouped by area

Pull Request Review — 1 symbol in 1 file

• src/app/review.ts:L45-L99 — reviewPullRequest (calls, depth 2)
  93: // The token is in git's error text on a permissions failure, and this string

Blast CLI — 1 symbol in 1 file

• src/blast/blast-cli.ts:L63-L124 — runBlastCommand (calls, depth 2)
  77: // git's own message ("unknown revision or path not in the working tree") sends

Test signal per changed area — 1 ✗

Reached = a node under a test path has a resolved edge into the changed symbol. It undercounts anything called indirectly — through a CLI, a spawned process or a dynamic import — so read a low ratio as “look here”, never as a coverage gate.

• ✗ File Diffing — 0 of 1 reached · no test file reaches it
  • not reached: diffFiles

_{graft blast · origin/main...HEAD · depth 2 · 3 changed files}

Open the interactive graph → — click an area to see its dependent symbols at file:line.