[Windows Desktop] git write-tree polling loop causes ~26% idle CPU (non-Git workspaces + bloated .git/objects)

Summary

Codex Desktop on Windows runs a high-frequency git write-tree polling loop for workspace change detection. When a workspace directory is either (a) not a Git repository, or (b) a Git repo with severely bloated .git/objects, this loop becomes a CPU spin that consumes ~26% idle CPU continuously.

Environment

• OS: Windows 10
• Codex: OpenAI.Codex 26.623.19656.0 (Microsoft Store / UWP)
• Git: 2.x (system git at D:\Program Files\Git\cmd\git.exe)

Root Cause

Codex appears to call git write-tree at high frequency (observed: 10 new git.exe processes in 10 seconds) to compute tree hashes for workspace change detection.

Two failure modes trigger the CPU spin:

1. Non-Git workspace directory → fatal retry loop

When the active workspace is not a Git repository, git write-tree returns fatal: not a git repository (exit 128). Codex appears to immediately retry, creating a tight failure-retry loop.

Reproduction:

# Set a non-Git directory as Codex workspace, then observe:
$seen=@{}; $t0=Get-Date
while((Get-Date) -lt $t0.AddSeconds(10)){
  Get-Process -Name "git" -ErrorAction SilentlyContinue | ForEach-Object {
    if(-not $seen.ContainsKey($_.Id)){ $seen[$_.Id]=1 }
  }
  Start-Sleep -Milliseconds 500
}
Write-Host "git processes spawned in 10s: $($seen.Count)"
# Result: 10+ processes, all running: git -c core.hooksPath=NUL -c core.fsmonitor= write-tree

2. Git repo with bloated .git/objects → slow operations × high frequency

A workspace repo with 6,086 unreachable loose objects (675 MB, from repeated git add of large files without committing) makes each git write-tree invocation extremely slow. Combined with the high polling frequency, CPU saturates.

Impact

• Idle CPU: ~26% sustained (8-core machine), no active task running
• Fan/heat: continuous fan activity with no workload
• System becomes sluggish even when Codex is idle

Evidence

# git process spawn monitoring (10s window)
git processes spawned in 10s: 10

# Command line of spawned git processes
"C:\...\git.exe" -c core.hooksPath=NUL -c core.fsmonitor= write-tree
Parent: Codex.exe (main process, PID 22024)

# CPU before fix
Average CPU usage: 18.42% (sustained, idle)

# .git/objects bloat in active workspace
loose objects: 6086, 675.47 MB
largest objects: 155MB, 155MB, 48MB, 27MB, 11MB

Workaround

1. For non-Git workspace dirs: run git init (even an empty repo makes write-tree return successfully instead of fatal)
2. For bloated repos: run git gc --prune=now --aggressive to remove unreachable objects
3. Secondary: clean logs_2.sqlite (232MB, related issue #31142) and old desktop logs

After workaround, idle CPU dropped from ~26% to 0.06%.

Suggested Fixes

1. Add a timeout or backoff for git write-tree failures (non-Git directories should not cause a tight retry loop)
2. Detect non-Git workspaces and skip git-based change detection (fall back to filesystem watcher or polling)
3. Limit git operation frequency when the previous invocation was slow (e.g., if write-tree takes >2s, increase the polling interval)
4. Auto-prune or warn when .git/objects exceeds a size threshold

Related Issues

• #31142 — logs_2.sqlite high-frequency WAL writes (secondary I/O contributor in this case)
• #31132 — Log level not configurable, sqlite grows to 1.4GB

Full Diagnostic Manual

A complete troubleshooting manual (detection methods, root cause analysis, fix scripts, prevention) is available at:
https://github.com/cngh0/codex-cpu-fix