feat(antigravity): add support for Antigravity IDE storage on Windows

[Battiatus]

Summary

• Adds support for detecting Antigravity IDE usage on Windows from VSCode-style storage
• Extends provider to scan %APPDATA%\Antigravity IDE\User\globalStorage\state.vscdb
• Improves path classification to distinguish IDE vs CLI sessions
• Handles missing per-call timestamps by using file mtime as fallback source

Resolves: CodeBurn reporting zero usage when Antigravity IDE is actively used

Issue id: #411 (comment)

Changes

• antigravity.ts: Add APPDATA IDE storage root; refine antigravityAppDataDirFromSourcePath() to classify IDE dirs; add stampFallbackTimestamp() helper for missing timestamps across all emission paths; bump CACHE_VERSION to 4
• session-cache.ts: Update parser fingerprint to worktree-project-grouping-v5
• main.ts: Clarify CLI install message that IDE sessions are auto-detected
• docs: Clarify that state.vscdb stores trajectory metadata only
• tests: Add helper withTempAntigravityHome(); add coverage for IDE path detection and timestamp fallback

Test Plan

• All 27 antigravity provider tests pass
• TypeScript compilation clean (tsc)
• Manual: Run `npx tsx src/cli.ts` today with Antigravity IDE usage and verify sessions are detected without --provider flag
• Manual: Run `npx tsx src/cli.ts` a second time and verify cache hit (no reparse)

[ozymandiashh]

Thanks for this — the underlying problem it targets (SQLite gen_metadata calls with no per-call timestamp being silently dropped by the date-range filters) is real and worth fixing. A few things to resolve before it can merge:

1. Scope/title is stale vs main. Antigravity IDE discovery already landed in #418 (35a8518): ~/.gemini/antigravity-ide/conversations (+ implicit) are in CONVERSATION_ROOTS on main today. This PR does not add a new storage root, so "add support for Antigravity IDE storage" / "previously only detected Antigravity CLI" no longer describe the change. Please retitle to what it actually does (timestamp fallback + path classification).

2. The new APPDATA classifier branch is unreachable. antigravityAppDataDirFromSourcePath's if (lower.includes('/antigravity ide/')) (src/providers/antigravity.ts:471) can't fire in normal operation: discoverAntigravitySessionSources only walks the ~/.gemini/... roots, so no discovered source.path is ever an APPDATA path — and your own doc note says the %APPDATA%\...\state.vscdb DB holds trajectory metadata, "not token usage". As written it is dead code. Either wire APPDATA discovery for real, or drop the branch.

3. If kept, that classifier misroutes a real case. It is a broad substring match checked after the .gemini/antigravity-{ide,cli}/ cases, so a base-app path under a folder literally named "Antigravity IDE" — e.g. C:\Users\Antigravity IDE\.gemini\antigravity\conversations\x.db — classifies as antigravity-ide, and detectServer then targets the wrong server. Guard the base path first: if (lower.includes('/.gemini/antigravity/')) return 'antigravity' before the APPDATA line. No test covers this; the added test only checks the .gemini/antigravity-cli/ precedence case.

4. mtime-as-timestamp misattributes cost across date ranges. stampFallbackTimestamp assigns the same new Date(s.mtimeMs) to every timeless call and persists it into the cache. Consequences: (a) an entire multi-turn session's cost buckets onto the day the .db was last written, so today/week/month views are wrong for older sessions; (b) any later file rewrite shifts all historical calls forward to the new mtime. Antigravity already exposes real per-entry times (RPC chatStartMetadata.createdAt, and the state.vscdb trajectory metadata you documented), so prefer those over a shared file mtime. At minimum, don't persist a synthesized mtime into the cache, so a re-write can't retro-date history.

CI is green and types are clean, so none of this is blocking on CI — but 2-4 are correctness issues. Happy to re-review once addressed.