AskUserQuestion silently broken: PreToolUse hook emits permissionDecision:'defer' → 'Tool result missing due to internal error'

Summary

The PreToolUse hook for AskUserQuestion (question-preference-hook) emits permissionDecision: "defer" on its no-op path. Current Claude Code builds choke on that value and abort the tool call, so every AskUserQuestion call fails with:

[Tool result missing due to internal error]

This hits the common case: any AUQ call where no never-ask preference matches falls through to defer(), which is essentially all of them. The result is that the questions UI is silently broken for the user — the call is made, no answer ever comes back.

Environment

gstack: v1.55.1.0
Claude Code: recent build (Opus 4.8 era, June 2026), VSCode extension
OS: macOS (darwin 25.5.0)
bun present and on PATH. The hook itself runs cleanly — exit 0, no entries in ~/.gstack/hook-errors.log. The problem is the output it emits, not a crash.

Root cause

hosts/claude/hooks/question-preference-hook.ts → defer():

function defer(additionalContext?: string): void {
  const out: Record<string, unknown> = {
    hookEventName: 'PreToolUse',
    permissionDecision: 'defer',
  };
  if (additionalContext) out.additionalContext = additionalContext;
  process.stdout.write(JSON.stringify({ hookSpecificOutput: out }));
  process.exit(0);
}

defer() is the default/fall-through path for any AUQ call without a matching never-ask preference. On a normal question it emits:

{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"defer"}}

Empirically, current Claude Code builds reject this permissionDecision: "defer" and abort the tool call with an internal error. (The hooks docs are ambiguous on whether "defer" is an accepted permissionDecision value alongside allow/deny/ask; regardless, emitting it currently breaks the call, whereas the documented "no decision" form — exit 0 with no stdout — works.)

Reproduction

gstack 1.55.1.0 with the PreToolUse hook registered in ~/.claude/settings.json (matcher: "(AskUserQuestion|mcp__.*__AskUserQuestion)").
Trigger any AskUserQuestion that has no matching never-ask preference.
The tool result is [Tool result missing due to internal error]. 100% reproducible.

Isolation evidence

Neutralizing the shims to exit 0 no-ops pinpoints the PreToolUse hook:

PreToolUse	PostToolUse	Result
real	real	❌ internal error
no-op	no-op	✅ works
no-op	real	✅ works → culprit is PreToolUse
fixed (below)	real	✅ works

Suggested fix

The documented "no decision / proceed via the normal permission flow" output is exit 0 with no stdout. Only emit JSON when there is actually additionalContext to inject, and without a permissionDecision:

function defer(additionalContext?: string): void {
  // "Proceed via the normal permission flow" is exit 0 with no output.
  // Emitting permissionDecision:'defer' makes recent Claude Code builds reject
  // the tool call with an internal error, silently breaking every AUQ call.
  if (additionalContext) {
    process.stdout.write(
      JSON.stringify({
        hookSpecificOutput: {
          hookEventName: 'PreToolUse',
          additionalContext,
        },
      }),
    );
  }
  process.exit(0);
}

Verified locally: with this change, AskUserQuestion works with both gstack hooks active (PreToolUse + PostToolUse).

The deny() path is unaffected — permissionDecision: "deny" is a standard value and works fine; only the defer() no-op path needs changing.

Reproduced on plain Claude for Desktop 1.14271.0 (bundled Claude Code 2.1.181), no Conductor involved — CLAUDE_CODE_ENABLE_ASK_USER_QUESTION_TOOL=true. Every AskUserQuestion call returns [Tool result missing due to internal error] and the picker never renders.

Isolated to a single variable: with the PreToolUse question-preference-hook emitting permissionDecision:"defer" → broken; with it emitting nothing (exit 0) → works. So this isn't Conductor-specific — the mainstream Desktop host is also strict about the unknown defer value. Fixed by #1924 / #1816; flagging the broader blast radius as a reason to prioritize the merge.

This looks like a tool permission decision contract issue.

AskUserQuestion is not an ordinary tool call. It is a control-flow tool that asks the user for required input.

If a PreToolUse hook emits permissionDecision: "defer" but the runtime interprets that as an internal missing tool result, the user-facing question path breaks.

A standard AISP-style contract could make the expected states explicit:

[
  {
    "role": "system",
    "content": {
      "protocol": "AISP V1.0.0",
      "axiom_0": "Human_Sovereignty_and_Wellbeing",
      "id": "gstack_ask_user_question_permission_contract_aisp",
      "name": "gstack AskUserQuestion Permission Contract",
      "version": "1.0.0",
      "license": "MIT",
      "summary": "Machine-checkable contract for AskUserQuestion pre-tool permission decisions.",
      "flow_format": "mermaid",
      "loading_mode": "node",
      "tools": ["user_interaction"],
      "params": {
        "tool_name": "AskUserQuestion",
        "hook_decision": "string"
      },
      "system_prompt": ""
    }
  },
  {
    "role": "user",
    "content": {
      "instruction": "STRICTLY OBEY aisp_contract; its non_negotiable rules are inviolable; then RUN aisop.main",
      "user_input": "{user_input}",
      "aisp_contract": {
        "profile": "aisp.skill.v1",
        "invocation": {
          "mode": "tool_permission_policy",
          "when_to_use": [
            "before AskUserQuestion tool execution",
            "when PreToolUse hook returns allow, deny, or defer",
            "when user clarification is required"
          ],
          "when_not_to_use": [
            "non-interactive execution",
            "tools that do not involve user question cards"
          ]
        },
        "non_negotiable": [
          {
            "rule": "AskUserQuestion defer must route to the user-question card flow, not internal missing result.",
            "enforced_by": "route.step2:sys.assert"
          },
          {
            "rule": "Every permission decision must map to a valid runtime state.",
            "enforced_by": "validate.step2:sys.assert"
          }
        ],
        "discovery": {
          "category": "tool_permission",
          "tags": ["gstack", "AskUserQuestion", "PreToolUse", "defer", "aisp"]
        },
        "risk_level": "medium",
        "resources": []
      },
      "aisop": {
        "main": "graph TD\n    read[Read hook decision] --> validate[Validate decision state]\n    validate --> route[Route AskUserQuestion behavior]\n    route --> report[Emit tool-state trace]\n    report --> end_node((End))"
      },
      "functions": {
        "read": {
          "step1": "Read tool_name and hook_decision.",
          "output_mapping": "permission_input"
        },
        "validate": {
          "step1": "Validate hook_decision is allow, deny, defer, or ask_user.",
          "step2": "sys.assert('hook decision maps to valid runtime state', 'Invalid or unhandled permission decision')",
          "output_mapping": "permission_validation"
        },
        "route": {
          "step1": "If tool_name is AskUserQuestion and hook_decision is defer, route to user-question card flow.",
          "step2": "sys.assert('AskUserQuestion defer maps to user interaction flow', 'AskUserQuestion defer must not become missing tool result')",
          "output_mapping": "tool_route"
        },
        "report": {
          "step1": "Record tool name, hook decision, routed state, and result.",
          "output_mapping": "tool_permission_trace"
        },
        "end_node": {
          "step1": "Return tool_permission_trace."
        }
      }
    }
  }
]

The implementation fix is likely small:

1. Treat AskUserQuestion as a control-flow tool.
2. Do not let defer become an internal missing-result state.
3. Add an explicit mapping table for permissionDecision values.
4. Add regression test for AskUserQuestion + defer.

The invariant:

a user-question tool must never fail as an internal missing tool result when the intended state is "ask the user".

@16francej

@16francej — recommend closing this issue only after a current-source fix derived from #1924 passes multi-host pass-through, deny, and logging checks. The report independently shows that defer is not neutral and that silent pass-through restores normal behavior. Preserve the Desktop reproduction and no-op isolation coverage alongside #2006.

fix(hooks): stop emitting permissionDecision defer from question-pref…

fix(hooks): tighten AUQ pass-through coverage and restore spike docs

fix(gstack2): packaged QUESTION-FORMAT contract + documented-only hoo…

v1.61.0.0 fix wave: guards failing open / silent failures (9 fixes, 4…

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AskUserQuestion silently broken: PreToolUse hook emits permissionDecision:'defer' → 'Tool result missing due to internal error' #2035

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AskUserQuestion silently broken: PreToolUse hook emits permissionDecision:'defer' → 'Tool result missing due to internal error' #2035

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hotsauce0817 commented on Jun 23, 2026

optimization2026 commented on Jun 30, 2026

time-attack commented on Jul 15, 2026

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