85 lines
5 KiB
Markdown
85 lines
5 KiB
Markdown
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# Fix: High CPU Usage on Long Auto-Mode Sessions
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## Problem Statement
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Long-running `/gsd auto` sessions exhibit high CPU usage due to multiple compounding issues:
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process leaks, unguarded async intervals, synchronous git process spawning on hot paths,
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and unbounded file I/O. These issues compound over time, making multi-hour sessions
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progressively slower.
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## Root Cause Analysis
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Five parallel investigations identified 8 distinct issues across 3 categories:
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### Category A: Process Lifecycle Leaks
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- **A1**: Native git module never loads — `execFileSync("git", ...)` spawns a new process every 15s
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- **A2**: Subagent isolation cleanup has no timeout — can hang indefinitely
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- **A3**: Dead bg-shell processes retained in memory for 10-60 minutes during auto-mode
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### Category B: Timer/Interval Leaks
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- **B1**: Idle watchdog `setInterval` async callback has no error handling — unhandled rejections leave interval running forever
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- **B2**: Recovery paths call `dispatchNextUnit()` without clearing old timers first — timer stacking
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- **B3**: Progress widget polls every 5s with synchronous file reads
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### Category C: I/O Accumulation
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- **C1**: STATE.md rebuilt after every single unit completion (100-400ms per rebuild)
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- **C2**: Dead process memory not pruned during auto-mode sessions
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## Implementation Plan
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### Fix 1: Wrap idle watchdog in try-catch (B1)
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**File**: `src/resources/extensions/gsd/auto.ts`
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**Change**: Wrap the entire `setInterval(async () => { ... }, 15000)` callback body in try-catch. On error, log warning and continue (don't let unhandled rejection orphan the interval). Add explicit `clearInterval` on caught errors that indicate unrecoverable state.
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### Fix 2: Cache `nativeHasChanges` with TTL (A1)
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**File**: `src/resources/extensions/gsd/native-git-bridge.ts`
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**Change**: Add a simple timestamp+result cache to `nativeHasChanges()`. Return cached result if called within 10 seconds of last check. This eliminates the synchronous `git status --short` process spawn on every 15-second watchdog tick — at most 1 spawn per 10 seconds instead of potentially multiple per tick.
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### Fix 3: Clear timers before recovery dispatch (B2)
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**File**: `src/resources/extensions/gsd/auto.ts`
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**Change**: In `recoverTimedOutUnit()`, call `clearUnitTimeout()` before each `dispatchNextUnit()` call. This prevents the old idle watchdog interval from running alongside new timers set by the recovery dispatch.
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### Fix 4: Add timeout to subagent isolation cleanup (A2)
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**File**: `src/resources/extensions/subagent/isolation.ts`
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**Change**: Wrap the `git worktree remove --force` call in a `Promise.race` with a 10-second timeout. If timeout fires, fall through to `fs.rmSync` fallback (which already exists in the catch block).
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### Fix 5: Prune dead bg-shell processes from auto-mode (A3/C2)
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**File**: `src/resources/extensions/gsd/auto.ts`
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**Change**: After each unit completion in `handleAgentEnd`, call the bg-shell `pruneDeadProcesses()` function (import it). This prevents dead process objects (each holding ~500KB-1MB of output buffers) from accumulating during long sessions.
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### Fix 6: Throttle STATE.md rebuilds (C1)
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**File**: `src/resources/extensions/gsd/auto.ts`
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**Change**: Add a minimum interval (30 seconds) between STATE.md rebuilds. Track `lastStateRebuildAt` timestamp; if a rebuild was done within 30s, skip it. Always rebuild on stop/pause for consistency. This reduces the 100-400ms per-unit I/O spike.
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### Fix 7: Increase progress widget update interval (B3)
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**File**: `src/resources/extensions/gsd/auto-dashboard.ts`
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**Change**: Increase the progress widget refresh timer from 5 seconds to 15 seconds. The widget shows slice/task progress which doesn't change faster than every ~30 seconds anyway.
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## Testing Strategy
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Each fix has a corresponding test:
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1. **Fix 1**: Unit test — verify idle watchdog doesn't throw unhandled rejections
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2. **Fix 2**: Unit test — verify `nativeHasChanges` returns cached result within TTL window
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3. **Fix 3**: Unit test — verify `clearUnitTimeout()` is called before recovery dispatch
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4. **Fix 4**: Unit test — verify isolation cleanup respects timeout
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5. **Fix 5**: Integration — verify dead processes are pruned after unit completion
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6. **Fix 6**: Unit test — verify STATE.md rebuild is throttled
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7. **Fix 7**: Visual inspection — progress widget still updates
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## Files Modified
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- `src/resources/extensions/gsd/auto.ts` (Fixes 1, 3, 5, 6)
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- `src/resources/extensions/gsd/native-git-bridge.ts` (Fix 2)
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- `src/resources/extensions/subagent/isolation.ts` (Fix 4)
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- `src/resources/extensions/gsd/auto-dashboard.ts` (Fix 7)
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- `src/resources/extensions/gsd/tests/` (new test files)
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## Risk Assessment
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All fixes are **defensive and backward-compatible**:
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- No behavior changes for the happy path
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- Caching only affects the frequency of side-effect-free reads
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- Timer cleanup is additive (clearing timers that should have been cleared)
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- Timeout on isolation cleanup already has a fallback path
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- Throttling STATE.md is cosmetic (STATE.md is only used for human debugging)
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