test(#3144): bound the git/worktree cluster onto the process seam (#3152)

* test(#3144): bound the git/worktree cluster onto the process seam

Migrates 180 unbounded sync spawn sites across 19 files. Every previously
unbounded call now carries an explicit timeout with a comment giving the
number and why.

The migration is not a callee swap. execSync and execFileSync throw on a
non-zero exit and the seam never does, so each site was classified first:
sites that rely on the throw route to gitOrThrow, and sites that already read
.status to detect an EXPECTED non-zero -- an intended cherry-pick conflict, a
rev-parse outside a repo driving a skip -- route to the never-throwing runGit
instead, which would otherwise throw on exactly the exit being probed for.

Two same-named git() helpers in worktree-cleanup.test.cjs have different
return contracts, one trimmed and one raw; both are preserved rather than
unified.

Collapses five hand-rolled throw wrappers onto one throwIfFailed in
git-fixture.cjs, which gitOrThrow now also uses so the shape cannot drift.

Allowlist drops 139 to 120; BASELINE lowered to match.

* test(#3144): fix pre-PR review findings

Documents throwIfFailed in the CONTEXT.md glossary and CONTRIBUTING.md --
it became the shared throw mechanism without either doc naming it.

Routes the sixth and seventh hand-rolled copies of the throw shape through
throwIfFailed (worktree-baseref-install, worktree-safety-reap); the first
consolidation missed both.

Converts ci-rebase-check's 8 fixture-setup calls from unchecked runGit to
gitOrThrow so a failed setup step aborts where it fails rather than
surfacing later as a confusing failure against the wrong subject.

Adds 12 direct unit tests for throwIfFailed, which until now was only
exercised transitively.

Splits verify.test.cjs's non-git grep/sed bound off GIT_TIMEOUT_MS.

---------

Co-authored-by: sim <sim@local>

tests/commit-files-deletion.test.cjs

@@ -13,9 +13,12 @@ const { describe, test, beforeEach, afterEach } = require('node:test');
 const assert = require('node:assert/strict');
 const fs = require('fs');
 const path = require('path');
-const { execSync } = require('child_process');
-
 const { createTempGitProject, cleanup, runGsdTools } = require('./helpers.cjs');
+const { gitOrThrow } = require('./helpers/git-fixture.cjs');
+
+// 15000ms: git plumbing (add/commit/diff) on a small mkdtemp fixture repo —
+// far over any observed duration for that class of call.
+const GIT_TIMEOUT_MS = 15000;
 
 describe('commit --files: missing files must not stage deletions (#2014)', () => {
   let tmpDir;
@@ -24,8 +27,8 @@ describe('commit --files: missing files must not stage deletions (#2014)', () =>
     tmpDir = createTempGitProject();
     // Commit STATE.md so it exists in git history
     fs.writeFileSync(path.join(tmpDir, '.planning', 'STATE.md'), '# State\n\nInitial state.\n');
-    execSync('git add .planning/STATE.md', { cwd: tmpDir, stdio: 'pipe' });
-    execSync('git commit -m "add STATE.md"', { cwd: tmpDir, stdio: 'pipe' });
+    gitOrThrow(['add', '.planning/STATE.md'], { cwd: tmpDir, timeoutMs: GIT_TIMEOUT_MS });
+    gitOrThrow(['commit', '-m', 'add STATE.md'], { cwd: tmpDir, timeoutMs: GIT_TIMEOUT_MS });
     // Delete STATE.md from disk -- now missing but tracked in git
     fs.unlinkSync(path.join(tmpDir, '.planning', 'STATE.md'));
   });
@@ -46,7 +49,7 @@ describe('commit --files: missing files must not stage deletions (#2014)', () =>
     // git diff HEAD~1 HEAD --name-status shows what changed between commits.
     let diffOutput = '';
     try {
-      diffOutput = execSync('git diff HEAD~1 HEAD --name-status', { cwd: tmpDir, encoding: 'utf-8' });
+      diffOutput = gitOrThrow(['diff', 'HEAD~1', 'HEAD', '--name-status'], { cwd: tmpDir, timeoutMs: GIT_TIMEOUT_MS });
     } catch (e) {
       // If nothing to commit, there is no HEAD~1 -- that's also acceptable
       return;
@@ -70,7 +73,7 @@ describe('commit --files: missing files must not stage deletions (#2014)', () =>
     assert.strictEqual(parsed.committed, true, 'should have committed when file exists');
 
     // Verify ROADMAP.md was added in the commit
-    const diffOutput = execSync('git diff HEAD~1 HEAD --name-status', { cwd: tmpDir, encoding: 'utf-8' });
+    const diffOutput = gitOrThrow(['diff', 'HEAD~1', 'HEAD', '--name-status'], { cwd: tmpDir, timeoutMs: GIT_TIMEOUT_MS });
     assert.ok(
       diffOutput.includes('A\t.planning/ROADMAP.md'),
       'ROADMAP.md should appear as added in the commit'
@@ -89,7 +92,7 @@ describe('commit --files: missing files must not stage deletions (#2014)', () =>
     // The commit must not include a deletion of STATE.md
     let diffOutput = '';
     try {
-      diffOutput = execSync('git diff HEAD~1 HEAD --name-status', { cwd: tmpDir, encoding: 'utf-8' });
+      diffOutput = gitOrThrow(['diff', 'HEAD~1', 'HEAD', '--name-status'], { cwd: tmpDir, timeoutMs: GIT_TIMEOUT_MS });
     } catch (e) {
       return; // nothing committed is fine
     }