diff --git a/setup b/setup
index 49f05ffc2..a108c915e 100755
--- a/setup
+++ b/setup
@@ -721,7 +721,7 @@ link_codex_skill_dirs() {
 
   if [ ! -d "$agents_dir" ]; then
     echo "  Generating .agents/ skill docs..."
-    ( cd "$gstack_dir" && bun run gen:skill-docs --host codex )
+    ( cd "$gstack_dir" && bun_cmd run gen:skill-docs --host codex )
   fi
 
   if [ ! -d "$agents_dir" ]; then
@@ -958,7 +958,7 @@ link_factory_skill_dirs() {
 
   if [ ! -d "$factory_dir" ]; then
     echo "  Generating .factory/ skill docs..."
-    ( cd "$gstack_dir" && bun run gen:skill-docs --host factory )
+    ( cd "$gstack_dir" && bun_cmd run gen:skill-docs --host factory )
   fi
 
   if [ ! -d "$factory_dir" ]; then
@@ -990,7 +990,7 @@ link_opencode_skill_dirs() {
 
   if [ ! -d "$opencode_dir" ]; then
     echo "  Generating .opencode/ skill docs..."
-    ( cd "$gstack_dir" && bun run gen:skill-docs --host opencode )
+    ( cd "$gstack_dir" && bun_cmd run gen:skill-docs --host opencode )
   fi
 
   if [ ! -d "$opencode_dir" ]; then
@@ -1372,7 +1372,13 @@ if [ -x "$DETECT_BIN" ]; then
         log "gbrain detected — regenerating Claude SKILL.md with brain-aware blocks (~250 token overhead per planning skill)..."
         (
           cd "$SOURCE_GSTACK_DIR"
-          bun_cmd run gen:skill-docs:user --host claude 2>&1 | tail -3
+          # No pipe before the || guard: `cmd | tail -3` reports TAIL's exit
+          # status, so a generator crash read as success (same masking the
+          # main gen:skill-docs site had). Capture, show the tail, propagate.
+          _GEN_USER_OUT=$(bun_cmd run gen:skill-docs:user --host claude 2>&1)
+          _GEN_USER_RC=$?
+          printf '%s\n' "$_GEN_USER_OUT" | tail -3
+          exit "$_GEN_USER_RC"
         ) || log "  warning: gen:skill-docs:user failed — run 'bun run gen:skill-docs:user' manually if you want brain-aware blocks"
       fi
     else
diff --git a/test/setup-bun-cmd-and-pipe-bugs.test.ts b/test/setup-bun-cmd-and-pipe-bugs.test.ts
new file mode 100644
index 000000000..695a1d447
--- /dev/null
+++ b/test/setup-bun-cmd-and-pipe-bugs.test.ts
@@ -0,0 +1,122 @@
+import { describe, test, expect } from 'bun:test';
+import { spawnSync } from 'child_process';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const SETUP_SRC = fs.readFileSync(path.join(ROOT, 'setup'), 'utf-8');
+
+// Run a bash snippet, return {stdout, stderr, status}.
+function runBash(script: string): { stdout: string; stderr: string; status: number } {
+  const r = spawnSync('bash', ['-c', script], { encoding: 'utf-8' });
+  return { stdout: r.stdout || '', stderr: r.stderr || '', status: r.status ?? -1 };
+}
+
+describe('setup: gen:skill-docs:user exit-code propagation (pipe-masking fix)', () => {
+  // The bug: `cmd 2>&1 | tail -3` makes the subshell exit status `tail`'s,
+  // so `(...) || log "warning"` never fires when `cmd` fails. The fix removes
+  // the pipe. These tests RUN the pattern (not grep source) to prove the
+  // exit-code semantics actually change.
+
+  test('without pipe: failing bun_cmd triggers the || warning clause', () => {
+    const r = runBash(`
+      set +e
+      bun_cmd() { return 1; }      # stub: gen:skill-docs:user failed
+      log() { echo "LOG:$*"; }
+      (
+        cd /tmp
+        bun_cmd run gen:skill-docs:user --host claude
+      ) || log "  warning: gen:skill-docs:user failed"
+    `);
+    expect(r.stdout).toContain('LOG:  warning: gen:skill-docs:user failed');
+  });
+
+  test('with pipe (the bug shape): failing bun_cmd does NOT trigger the warning', () => {
+    const r = runBash(`
+      set +e
+      bun_cmd() { return 1; }      # stub: gen:skill-docs:user failed
+      log() { echo "LOG:$*"; }
+      (
+        cd /tmp
+        bun_cmd run gen:skill-docs:user --host claude 2>&1 | tail -3
+      ) || log "  warning: gen:skill-docs:user failed"
+    `);
+    expect(r.stdout).not.toContain('LOG:  warning');
+  });
+
+  test('setup: the live gbrain regen block has no pipe before the || guard', () => {
+    // Slice the exact block from setup and confirm the fix is in place
+    // without resorting to a fragile line-number check.
+    const start = SETUP_SRC.indexOf('gbrain detected — regenerating');
+    expect(start).toBeGreaterThan(-1);
+    const end = SETUP_SRC.indexOf('|| log', start);
+    expect(end).toBeGreaterThan(start);
+    const block = SETUP_SRC.slice(start, end);
+    expect(block).toContain('bun_cmd run gen:skill-docs:user --host claude');
+    // The bug shape: `... | tail -N` between the call and the `|| log` guard.
+    expect(block).not.toMatch(/gen:skill-docs:user[^\n]*\|\s*tail/);
+  });
+});
+
+describe('setup: bun_cmd routing in link_*_skill_dirs (Windows non-ASCII path fix)', () => {
+  // The bug: `bun run ...` bypasses the BUN_CMD wrapper installed by
+  // prepare_bun_for_windows_compile. On a non-ASCII Windows username,
+  // BUN_CMD points to an ASCII-path copy of bun and the literal `bun`
+  // on PATH may not work. Test by stubbing BUN_CMD to a sentinel that
+  // writes a marker file, and proving the wrapper path actually invokes it.
+
+  test('bun_cmd wrapper invokes $BUN_CMD (not literal bun on PATH)', () => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-buncmd-'));
+    const marker = path.join(tmp, 'invoked');
+    const sentinel = path.join(tmp, 'fake-bun');
+    fs.writeFileSync(sentinel, `#!/usr/bin/env bash\necho "ARGS:$*" > "${marker}"\n`);
+    fs.chmodSync(sentinel, 0o755);
+
+    const r = runBash(`
+      set -e
+      BUN_CMD="${sentinel}"
+      bun_cmd() { "$BUN_CMD" "$@"; }
+      ( cd /tmp && bun_cmd run gen:skill-docs --host codex )
+    `);
+
+    expect(r.status).toBe(0);
+    expect(fs.existsSync(marker)).toBe(true);
+    expect(fs.readFileSync(marker, 'utf-8').trim()).toBe('ARGS:run gen:skill-docs --host codex');
+
+    fs.rmSync(tmp, { recursive: true, force: true });
+  });
+
+  test('setup: the three link_*_skill_dirs helpers all use bun_cmd, not literal bun', () => {
+    // Extract each helper body and check the gen:skill-docs invocation
+    // inside it. Source-anchored (not line-number) and not a global grep,
+    // so we only assert about the actual code path the bug fix touches.
+    for (const fn of [
+      'link_codex_skill_dirs',
+      'link_factory_skill_dirs',
+      'link_opencode_skill_dirs',
+    ]) {
+      const start = SETUP_SRC.indexOf(`${fn}() {`);
+      expect(start).toBeGreaterThan(-1);
+      const end = SETUP_SRC.indexOf('\n}\n', start);
+      expect(end).toBeGreaterThan(start);
+      const body = SETUP_SRC.slice(start, end);
+      // Must call through the wrapper.
+      expect(body).toMatch(/bun_cmd run gen:skill-docs/);
+      // Bug shape: a literal `bun run gen:skill-docs` in executable position
+      // (skipping any comment / warning-string mentions that aren't being run).
+      const lines = body.split('\n').filter((l) => {
+        const t = l.trim();
+        if (!t || t.startsWith('#')) return false;
+        // Strings inside echo/warning messages don't execute bun.
+        if (/echo\s+['"]/.test(t)) return false;
+        return true;
+      });
+      for (const l of lines) {
+        // `bun_cmd run ...` is fine; a bare `bun run ...` is the bug.
+        const stripped = l.replace(/bun_cmd run/g, '');
+        expect(stripped).not.toMatch(/\bbun run gen:skill-docs/);
+      }
+    }
+  });
+});