fix: gbrain-sync orchestrator resolves brain-sync sibling via import.meta.dir

Codex M9: runBrainSyncPush hardcoded ~/.claude/skills/gstack/bin/gstack-brain-sync,
so any host that wasn't Claude Code (Codex CLI, dev workspace) hit the existsSync
guard and silently skipped curated-artifact push. Replace with the sibling-resolution
pattern already in runMemoryIngest at line 193.

Regression test asserts the orchestrator no longer takes the lying-skip path when
HOME has no ~/.claude/skills/gstack tree.

bin/gstack-gbrain-sync.ts

@@ -219,7 +219,7 @@ function runBrainSyncPush(args: CliArgs): StageResult {
     return { name: "brain-sync", ran: false, ok: true, duration_ms: 0, summary: "would: gstack-brain-sync --discover-new --once" };
   }
 
-  const brainSyncPath = join(HOME, ".claude", "skills", "gstack", "bin", "gstack-brain-sync");
+  const brainSyncPath = join(import.meta.dir, "gstack-brain-sync");
   if (!existsSync(brainSyncPath)) {
     return { name: "brain-sync", ran: false, ok: true, duration_ms: 0, summary: "skipped (gstack-brain-sync not installed)" };
   }

test/gstack-gbrain-sync.test.ts

@@ -137,4 +137,26 @@ describe("gstack-gbrain-sync CLI", () => {
     expect(state.last_stages.length).toBe(0);
     rmSync(home, { recursive: true, force: true });
   });
+
+  it("brain-sync stage resolves the sibling binary, not a HOME-rooted path", () => {
+    // Regression for Codex M9: pre-fix the orchestrator looked up
+    // ~/.claude/skills/gstack/bin/gstack-brain-sync, which silently no-op'd
+    // on Codex installs and dev workspaces with the misleading summary
+    // "skipped (gstack-brain-sync not installed)". Post-fix it resolves
+    // a sibling via import.meta.dir and actually invokes the script.
+    const home = makeTestHome();
+    const gstackHome = join(home, ".gstack");
+    mkdirSync(gstackHome, { recursive: true });
+
+    const r = runScript(
+      ["--incremental", "--no-code", "--no-memory", "--quiet"],
+      { HOME: home, GSTACK_HOME: gstackHome },
+    );
+
+    // Don't assert exit code (sibling spawn may legitimately error in a
+    // sandboxed test). Assert only that we did NOT take the lying-skip path.
+    const combined = r.stdout + r.stderr;
+    expect(combined).not.toContain("skipped (gstack-brain-sync not installed)");
+    rmSync(home, { recursive: true, force: true });
+  });
 });