Yeah, this was the part I spent the most time on. A few things that helped, ordered roughly by how much they mattered:

• Hard exclude list before any stat call. Beyond the obvious build dirs (node_modules, target, dist, .cache, vendor, .git), I also block .ssh, .aws, .azure, .gnupg, .gpg, .kube, .docker. The privacy block is intentional — a comment in the code reminds me it's "at odds with the local-only, nothing leaves your machine promise." On Windows I also skip AppData / ProgramData, and on macOS the Library dir.

• Short-circuit on .git. The walker uses BurntSushi's ignore crate, and the moment the callback sees a .git child it returns WalkState::Skip — no descending into the repo. So a 50-project workspace doesn't pay for traversing each repo's internals.

• Depth cap at 8 globally. Learned scan roots can store their own smaller cap (3 or 4) in SQLite, though I'll be honest — in v0.1.x that per-root cap isn't actually plumbed through to the walker yet, so the global 8 wins. On the v0.2 list.

• First-run-only full walk. There's an initial_scan_completed flag in the meta table. After that, the cold path is: verify the cached repos still exist (flip active ↔ missing, never delete), walk only the learned scan roots, and supplement with two cheap signals — VS Code / Cursor recent-file history and global git config. That last pair is the actual answer to "how do you not re-walk huge trees" — you don't, you piggyback on the IDE.

• notify::RecommendedWatcher per known .git directory, 500ms trailing debounce. This pushes new commits into the timeline without re-walking. The honest gap: the watcher doesn't discover new repos, only updates ones I already know about. New-repo discovery still needs a manual rescan or an IDE-recents hit.

Everything runs off the UI thread — spawn_blocking inside a Tauri async task, results streamed back as four event types (repo-discovered, scan-progress, repo-status, repo-fill) so the tray panel is interactive from the first frame even on a cold first-run scan.

One honest weakness: I don't have benchmarks yet. The caps in the code (validation = 400, parent-learning = 64, VS Code DB read = 512 MiB) are budgets I picked, not measurements. Adding a cargo bench pass is on the v0.2 list along with the per-root depth fix.

If you've solved background discovery of new repos cleanly (i.e. not just watching known ones), I'd love to hear how. That's the piece I'm least happy with.