perf(snapshot): cache/reduce fs.stat calls during tracking

[kilo-code-bot]

Summary

Snapshot.add() called fs.stat on every candidate path — tracked and untracked — on every Snapshot.track() (2–3× per turn), but the stat result was only ever used for a 2 MB size cap applied to the untracked subset (see the block set below the stat loop). On very large repos like jetbrains/intellij-community (~75k+ tracked files) that was tens of thousands of syscalls per turn, which hung the CLI on startup.

This PR keeps the cap's behavior and only stats untracked candidates. Tracked files are always staged regardless of size, so statting them was dead work. The remaining stat calls also run at higher concurrency (64 vs 8) since the working set is now much smaller and typically contains only new files.

Why this is correct

Before and after this change, the only use of the stat result is:

const block = new Set(untracked.filter((item) => large.has(item)))

block is constructed from untracked only. A tracked file could never end up in block, so whether we stat it or not, it gets staged. Skipping stat on tracked files preserves snapshot correctness 1:1.

Tests

New regression tests in packages/opencode/test/kilocode/snapshot-stat-perf.test.ts:

• Large (>2 MB) tracked file modification is still captured in the snapshot.
• Large (>2 MB) untracked file is still blocked (not staged).
• track() over a 1000-tracked-file repo completes well under the timing bound.

Existing snapshot tests (snapshot-cache, snapshot-freeze-repro, test/snapshot/snapshot.test.ts) still pass. The one failing test in this area (test/session/snapshot-tool-race.test.ts) fails on main too — it's unrelated to this change.

Scope

• Leaves JS enumeration and check-ignore logic alone (those are separate PRs).
• Based on main.

Built for Imanol Maiztegui by Kilo for Slack

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• .changeset/snapshot-skip-tracked-stat.md
• packages/opencode/src/snapshot/index.ts
• packages/opencode/test/kilocode/snapshot-stat-perf.test.ts

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_{Reviewed by gpt-5.5-2026-04-23 · 188,750 tokens}