fix(upgrade): detectBunLink fails because bun resolves symlinks in argv[1]

[MrAladdin]

Problem

gbrain upgrade returns unknown for bun-link installs — the README's recommended standalone install path (git clone && bun install && bun link).

$ gbrain upgrade
Detected install method: unknown
Could not detect installation method.

Root cause: detectBunLink() (added in v0.28.5, closes #656) gates on lstatSync(process.argv[1]).isSymbolicLink(). But bun resolves the entire symlink chain before setting process.argv[1], so argv[1] is already the real path (e.g. /path/to/gbrain/src/cli.ts), never a symlink. The check always returns false, short-circuiting the git-config walk that would have correctly identified the repo.

Verified with a minimal reproduction:

// Create a symlink and run via shebang
ln -sf /tmp/test.ts /tmp/test-link
/tmp/test-link
// process.argv[1] = "/private/tmp/test.ts" (resolved), NOT "/tmp/test-link"
// lstatSync(argv1).isSymbolicLink() === false

Related: #368 (open — the broader bun-link upgrade story), #656 (closed by v0.28.5 but fix incomplete), #538 (open PR with alternative approach, stale against master).

Fix

Minimal change to the existing detectBunLink():

1. Remove the broken symlink gate — lstatSync / isSymbolicLink check deleted. argv[1] is already the real path inside the checkout, which is exactly what the git-config walk needs.

2. Return { repoRoot } instead of 'bun-link' — the upgrade path now knows the checkout location and can auto-execute the upgrade.

3. Auto-upgrade instead of printing manual instructions — the bun-link case in runUpgrade() now runs:

   execFileSync('git', ['-C', repoRoot, 'pull', '--ff-only'], ...);
   execFileSync('bun', ['install'], { cwd: repoRoot, ... });

   Uses execFileSync with array args (no shell) per the codebase pattern in dry-fix.ts:172, addressing the shell-injection concern raised in fix(upgrade): detect README "Standalone CLI" installs as 'source' #538's review. Falls back to a clear manual command on failure.

4. --ff-only prevents surprise merge commits — if the user has local commits, git gives a clear error rather than silently creating a merge.

Before

$ gbrain upgrade
Detected install method: unknown
Could not detect installation method.

After

$ gbrain upgrade
Detected install method: bun-link
Upgrading bun-link source clone at /path/to/gbrain...
Already up to date.

Tests

test/upgrade.test.ts — 3 new tests (12 → 15 total, all pass):

• detectBunLink does not gate on isSymbolicLink — regression guard; extracts the function body and asserts no isSymbolicLink / lstatSync
• detectBunLink returns repoRoot, not a string literal — pins the return shape contract
• bun-link upgrade uses execFileSync for shell-injection safety — pins execFileSync with array args (not execSync with template strings)

$ bun test test/upgrade.test.ts
 15 pass, 0 fail, 32 expect() calls

Typecheck passes (bun run typecheck).

Out of scope

• No new install method type (unlike fix(upgrade): detect README "Standalone CLI" installs as 'source' #538's 'source' approach — this fix keeps the existing 'bun-link' type)
• No changes to check-update.ts (already returns 'gbrain upgrade' for bun-link)
• No changes to other detection branches

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[garrytan]

Closing — your fix landed in master via the v0.30.3 fix-wave PR #776 (merged at ff53a4c9): "detectBunLink symlink-in-argv[1] fix".

Thank you for the contribution — credit is preserved in the v0.30.3 CHANGELOG entry. 🙏