Summary

On Windows (Git Bash + Bun runtime), stage 3 of the unified gstack-gbrain-sync.ts (the brain-sync stage for curated artifacts → git pipeline) fails with gstack-brain-sync exited undefined. Functional impact is limited (running gstack-brain-sync directly works fine), but the noise pollutes the sync summary on every gstack skill start and makes real errors harder to spot.

Environment

• OS: Windows 11
• Shell: Git Bash (MSYS2)
• gstack version: 1.45.0.0
• Bun version: (Bun-bundled with gstack install)
• gbrain version: 0.18.2

Root cause

bin/gstack-gbrain-sync.ts:964-971 — the runBrainSyncPush function uses:

spawnSync(brainSyncPath, ["--once"], { stdio: [...], timeout: 60000 })

— without shell: true.

gstack-brain-sync is a bash-shebang script:

#!/usr/bin/env bash

Windows can't exec a shebang file directly without going through a shell. So spawnSync fails to spawn (returns result.status === undefined), and the wrapper interprets that as a stage failure.

Reproduction

On any Windows machine with gstack installed + gbrain configured:

# In Git Bash
gstack-gbrain-sync --incremental

Expected: stage 3 completes cleanly.
Actual: stage 3 reports gstack-brain-sync exited undefined, even though running gstack-brain-sync --once directly works (exits 0, empty queue).

Proposed fix

Add shell: true to both spawnSync calls in runBrainSyncPush, OR wrap with explicit bash invocation on Windows:

// Option A — simple:
spawnSync(brainSyncPath, ["--once"], { stdio: [...], timeout: 60000, shell: true })

// Option B — explicit cross-platform:
const isWindows = process.platform === "win32";
const cmd = isWindows ? "bash" : brainSyncPath;
const args = isWindows ? [brainSyncPath, "--once"] : ["--once"];
spawnSync(cmd, args, { stdio: [...], timeout: 60000 });

Workaround currently in use

gstack-gbrain-sync --no-brain-sync to skip stage 3 explicitly. Functional but noisy in the sync summary.

Discovered by

Surfaced by Harry Malinski (@hmalinski) during a Liquid Acre dev-machine cleanup session on 2026-05-26 after upgrading gstack 1.35.0.0 → 1.45.0.0. Logged in the LA project's observations log (docs/orchestration/_observations-log.md, session 2026-05-26 afternoon, obs #4).

Related context: a separate gstack-memory-ingest Windows incompat from gstack 1.35.x was already fixed in 1.45.0.0 — same session confirmed that stage works cleanly now. This runBrainSyncPush gap appears to be the last remaining Windows-spawn issue in the unified sync.