On Windows, decision bins silently file everything under slug unknown (resolveSlug spawn fails) #2396

Environment

• Windows 10 (10.0.19045), Git for Windows bash on PATH
• bun 1.3.14
• gstack HEAD a325940 (team-mode install)

Bug

lib/bin-context.ts resolveSlug() spawns the gstack-slug helper directly:

const r = spawnSync(slugBinPath, { encoding: "utf-8" });

bin/gstack-slug is a #!/usr/bin/env bash script. Windows cannot exec a shebang script, so the spawn fails and resolveSlug returns its "unknown" fallback:

$ bun -e 'const {spawnSync}=require("child_process"); const r=spawnSync("C:/Users/<user>/.claude/skills/gstack/bin/gstack-slug",{encoding:"utf-8"}); console.log(String(r.error), r.stdout)'
Error: ENOENT: no such file or directory, uv_spawn 'C:/Users/<user>/.claude/skills/gstack/bin/gstack-slug' null

Because only the bun-based bins use resolveSlug (gstack-decision-search, gstack-decision-log), the effect on Windows is:

• every decision, from every repo on the machine, is written to and read from ~/.gstack/projects/unknown/ — no error, no warning;
• repo-scoped decisions bleed across unrelated projects (they all share the unknown store, and filterByScope passes scope: "repo" rows unconditionally);
• the bash-based bins (gstack-learnings-search etc.), which eval "$(gstack-slug)" in bash, resolve the slug correctly — so on Windows the learnings store and the decision store for the same repo live under different slugs, and the decision store is invisible to anything that looks under the real slug.

Observed in the wild before diagnosing: a project whose learnings landed under its real slug while its one logged decision sat in projects/unknown/.

Fix (tested on Windows + does not change POSIX behavior)

Fall back to running the helper through bash when the direct spawn fails. Two Windows-specific gotchas, both measured:

1. bun's import.meta.dir returns backslash paths, and bash consumes backslashes in arguments — spawnSync("bash", ["C:\\...\\bin/gstack-slug"]) launches bash fine but exits 127. The path must be handed over with forward slashes.
2. With forward slashes it works: exit 0, SLUG=<owner-repo> parsed as on POSIX.

/** Resolve the project slug via the `gstack-slug` helper (parses `SLUG=...`). */
export function resolveSlug(slugBinPath: string): string {
  let r = spawnSync(slugBinPath, { encoding: "utf-8" });
  if (r.error || !r.stdout) {
    // Windows cannot exec a shebang script directly (uv_spawn ENOENT); re-run it
    // through bash (Git for Windows ships one). Bash eats backslashes in its
    // arguments, so the path must cross over with forward slashes.
    r = spawnSync("bash", [slugBinPath.replace(/\\/g, "/")], { encoding: "utf-8" });
  }
  const m = (r.stdout || "").match(/^SLUG=(.+)$/m);
  return m ? m[1].trim() : "unknown";
}

Verified after patching: gstack-decision-search resolves the real slug and reads ~/.gstack/projects/<owner-repo>/ (proved by moving the unknown/ store aside and observing the decision still returned from the correct dir).

Migration note for affected users

Existing Windows users will have decisions stranded in ~/.gstack/projects/unknown/. After the fix, those files need a one-time move/merge into the real slug dir (append-only JSONL; decisions.active.json can be rebuilt from the log). It may be worth a line in the changelog or a check in gstack-upgrade.