fix(hooks): passThrough() two-branch contract — never emit permissionDecision:'defer' (#2035, #2006)

Every AskUserQuestion died with "Tool result missing due to internal error"
on current Claude Code builds (Desktop 1.14271.0, CC 2.1.177). Root cause:
the question-preference-hook emitted permissionDecision:'defer' on every
pass-through path. 'defer' is a real PreToolUse value, but since CC v2.1.89
its semantics are "pause this tool call for external resumption" (headless
resume) — never "abstain". Interactive sessions have nothing to resume the
paused call, so the tool orphaned. Pre-2.1.89 builds ignored the unknown
value, which is why the hook worked when it shipped and broke later.

The fix is the two-branch pass-through contract:
- no context -> exit 0 with EXACTLY empty stdout
- memory nuggets present -> hookSpecificOutput with hookEventName +
  additionalContext ONLY (the documented shape; plan-tune Layer 8 memory
  injection ships through this branch and keeps working)

defer() is renamed passThrough() so the function says what it does, and
docs/spikes/claude-code-hook-mutation.md's protocol contract (cited by the
hook header) is corrected in the same commit — it taught '"defer" — let
permission flow continue' and was the reintroduction vector.

Test contract rewritten in the same commit (13 assertions across 3 files,
verified fail-first against the unfixed hook): pass-through paths assert
exact-empty stdout (a garbage/partial write cannot slip past an
optional-chained parse), the nugget path asserts permissionDecision is
ABSENT while additionalContext survives, and a new tripwire asserts no
non-deny path ever puts the string "permissionDecision" on stdout. The
deny (auto-decide) and Conductor prose-redirect paths are unchanged.

Deployment: no migration needed — settings.json points at the absolute
bash shim which execs the .ts live; /gstack-upgrade delivers the fix.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/memory-cache-injection.test.ts

@@ -2,7 +2,7 @@
  * Layer 8 memory cache + injection (plan-tune cathedral T12).
  *
  * Verifies the PreToolUse hook reads ~/.gstack/free-text-memory.json and
- * surfaces matching nuggets via additionalContext on the hook response.
+ * surfaces matching nuggets via additionalContext-only output (#2035: never a permissionDecision).
  * Cache: per-session memory-cache.json populated on first read, sub-1ms
  * thereafter (D13 perf).
  */
@@ -43,9 +43,9 @@ function runHook(stdin: object): { stdout: string; stderr: string; status: numbe
   env.GSTACK_STATE_ROOT = stateRoot;
   env.GSTACK_QUESTION_LOG_NO_DERIVE = '1';
   delete env.GSTACK_HOME;
-  // These cases assert the defer-path memoryContext injection. Strip ambient
+  // These cases assert the pass-through memoryContext injection. Strip ambient
   // Conductor markers so running inside Conductor (CONDUCTOR_WORKSPACE_PATH/PORT
-  // set) doesn't flip the hook into the [conductor] prose deny instead of defer.
+  // set) doesn't flip the hook into the [conductor] prose deny instead of pass-through.
   delete env.CONDUCTOR_WORKSPACE_PATH;
   delete env.CONDUCTOR_PORT;
   const res = spawnSync(HOOK, [], {
@@ -69,7 +69,7 @@ function runHook(stdin: object): { stdout: string; stderr: string; status: numbe
 // ----------------------------------------------------------------------
 
 describe('memory injection', () => {
-  test('injects matching nugget into additionalContext on defer', () => {
+  test('injects matching nugget into additionalContext on pass-through', () => {
     writeMemory([
       {
         nugget: 'User prefers verbose explanations with tradeoffs',
@@ -91,7 +91,10 @@ describe('memory injection', () => {
         ],
       },
     });
-    expect(r.parsed?.hookSpecificOutput?.permissionDecision).toBe('defer');
+    // #2035: nugget delivery is additionalContext-ONLY — a permissionDecision
+    // here (any value) would orphan the tool call on CC >= 2.1.89.
+    expect('permissionDecision' in (r.parsed?.hookSpecificOutput ?? {})).toBe(false);
+    expect(r.parsed?.hookSpecificOutput?.hookEventName).toBe('PreToolUse');
     expect(r.parsed?.hookSpecificOutput?.additionalContext).toContain('verbose explanations');
   });
 
@@ -115,8 +118,9 @@ describe('memory injection', () => {
         ],
       },
     });
-    expect(r.parsed?.hookSpecificOutput?.permissionDecision).toBe('defer');
-    expect(r.parsed?.hookSpecificOutput?.additionalContext).toBeUndefined();
+    // No nugget → pure pass-through: exit 0 with EXACTLY empty stdout.
+    expect(r.status).toBe(0);
+    expect(r.stdout).toBe('');
   });
 
   test('caps to 3 most-recent nuggets when many match', () => {
@@ -219,7 +223,8 @@ describe('per-session memory cache', () => {
         ],
       },
     });
-    expect(r.parsed?.hookSpecificOutput?.permissionDecision).toBe('defer');
-    expect(r.parsed?.hookSpecificOutput?.additionalContext).toBeUndefined();
+    // No nugget → pure pass-through: exit 0 with EXACTLY empty stdout.
+    expect(r.status).toBe(0);
+    expect(r.stdout).toBe('');
   });
 });