Replace git check-ignore with pure-Go gitignore matcher

[loganj]

Problem

Penpal spawns git check-ignore subprocesses on hot paths:

1. Full scan (scanProjectSources): a persistent git check-ignore --stdin subprocess per project scan
2. Single-file resolution (ResolveFileInfo): N one-shot git check-ignore -q spawns per ancestor directory — called from UpsertFile on every .md file-watcher event

For a file 5 levels deep, that's 5 process spawns per file change.

Solution

New internal/gitignore package — a pure-Go gitignore matcher that parses .gitignore files, .git/info/exclude, and the global gitignore once, then answers IsIgnoredDir() queries in-process with caching.

Subprocess cost: from 1 persistent + N per-file → 0 (except a single sync.Once-cached git config core.excludesFile for global gitignore path).

Changes

Area	What changed
internal/gitignore/	New package. Pattern parser (*, **, ?, [abc], negation, anchored, directory-only, escaped trailing spaces), hierarchical .gitignore loading with precedence, directory result caching.
internal/cache/cache.go	Replaced gitIgnoreChecker and isAncestorDirGitIgnored with gitignore.Matcher. Added matcherCache on Cache so ResolveFileInfo reuses matchers across file events.
cmd/penpal-server/main.go	Removed saveMu lock from debounce AfterFunc callback — Record() no longer blocks on activity disk I/O.
frontend/src-tauri/src/lib.rs	Bug fix: Destroyed handler saves session before removing window (was only saving on last window, losing multi-window sessions). Extracted ensure_geo_entry() helper.
frontend/src/hooks/useTabs.ts	Fixed double-parse of localStorage during init — loadPersistedTabs called once, shared by both useState initializers.
frontend/src/hooks/useTabs.test.ts	Added happy-path test for restoring valid persisted tab state.
internal/gitignore/gitignore_test.go	15 tests: basic patterns, wildcards, negation, **, nested .gitignore, anchored, .git/info/exclude, caching, no-trailing-slash, escaped spaces.
internal/cache/cache_test.go	Added TestResolveFileInfo_SkipsGitignored. Updated existing tests for new signature.
ERD.md, TESTING.md	Updated to reflect pure-Go matcher and new test coverage.

Testing

• go test ./... — all 14 Go packages pass
• npx vitest run — all frontend tests pass
• anchors check . — 0 warnings, 0 errors

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Serialize debounced activity saves

The debounce AfterFunc now calls act.Save without taking saveMu, while shutdown still performs a locked save, so two saves can run concurrently against the same activityPath. Because Tracker.Save writes to a fixed temp file (activity.json.tmp) before rename, concurrent writers can race and produce rename errors (no such file or directory), which can drop the final persisted activity state during shutdown or heavy event bursts. Please reintroduce save serialization for the timer callback (or otherwise make saves mutually exclusive).

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[chatgpt-codex-connector]

Invalidate cached matcher when ignore rules change

This cache path reuses a single parsed gitignore.Matcher for all subsequent UpsertFile events, but the matcher is only rebuilt on RescanWith; edits to .gitignore/.git/info/exclude during normal runtime are not observed. As a result, incremental updates can keep including files that were newly ignored (or excluding files that were unignored) until a full rescan/restart, which is a behavioral regression from the previous per-call git check-ignore checks.

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