Desktop app: PreToolUse hook emitting an unrecognized `permissionDecision` fails the whole tool call with an opaque internal error (CLI ignores it)

Environment

• Claude Desktop app 1.37937.3 (macOS, Darwin 25.6.0)
• Claude Code CLI 2.1.243 (for comparison; not affected)

Summary

If a PreToolUse hook writes a hookSpecificOutput JSON whose permissionDecision is not one of the documented values (allow / deny / ask), the Desktop app fails the entire tool call with an opaque error, while the CLI silently ignores the unrecognized value. With a hook matched on Bash, this makes the Bash tool 100% unusable in Desktop sessions, and nothing in the error output points at hooks as the cause.

Minimal reproduction

Add to ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "printf '%s' '{\"hookSpecificOutput\":{\"hookEventName\":\"PreToolUse\",\"permissionDecision\":\"defer\",\"permissionDecisionReason\":\"repro\"}}'",
            "timeout": 10
          }
        ]
      }
    ]
  }
}

Then open a session in the Desktop app and ask for any Bash command (e.g. echo test).

Actual behavior

Every Bash tool call fails: the transcript shows Tool execution was interrupted. and the tool result is [Tool result missing due to internal error]. The underlying command never runs. There is no indication that a hook (or which hook) caused the failure.

Expected behavior

Either of:

• Lenient parsing: treat an unrecognized permissionDecision as "no opinion" (equivalent to emitting no decision), ideally with a warning naming the hook and the invalid value, or
• A clear validation error that names the offending hook command and the invalid value, instead of a generic internal error on the tool call.

The hooks documentation defines allow / deny / ask but does not specify behavior for unrecognized values, and the CLI and Desktop currently disagree.

Isolation evidence

• Hook command /usr/bin/true (no output): Bash works in Desktop.
• Hook printing the "defer" JSON above: every Bash call fails in Desktop.
• Same hook emitting valid values (allow / ask), or exiting 0 with no output: works in Desktop.
• The same "defer"-emitting hook had been running for months under the CLI without issues (value silently ignored).

Impact

A single hook emitting a nonstandard decision value (easy to ship in a hand-written or community hook script) bricks the Bash tool for all Desktop sessions, and the opaque error makes it very hard to trace back to hook configuration.