/goal stop hook: 'JSON validation failed' when condition contains @file reference

Summary

Using /goal with an @filename reference in the condition string causes the session-scoped stop hook to fail with Stop hook error: JSON validation failed on every session stop attempt.

Environment

• Claude Code version: 2.1.140
• Platform: macOS (darwin arm64)
• Shell: zsh

Steps to Reproduce

1. Run /goal <some condition text that includes @FILENAME>
2. Attempt to stop the session
3. Observe the error in the stop hook output

Example goal condition used:

using /ck: prefix commands as appropriate, ensure the @FEATURES.md tier 1 and tier 2 are fully built. A bunch of work has been done, and we must not redo work, but it must be tested.

Observed Behavior

Four stop hooks fire. Three complete successfully. The /goal condition hook fails:

Stop hook error: JSON validation failed

The session cannot stop cleanly. The goal never clears even after the condition is met.

Expected Behavior

The /goal stop hook should either:

• Resolve @FEATURES.md to its file contents when evaluating the condition, or
• Treat unresolvable @file references as plain text and evaluate the condition on available context

Either way, it should return valid JSON {"decision": "allow"|"block", "reason": "..."} rather than producing output that fails JSON schema validation.

Additional Context

• The error appears to be in the goal hook's own LLM evaluation output, not caused by other stop hooks interfering
• Other stop hooks (cavemem, cavekit loop driver, Warp notification) all exit cleanly with no stdout pollution
• The issue is specific to @file syntax in the goal condition — plain text conditions may work correctly (not verified)
• The session-scoped stop hook appears to be a native Claude Code built-in, not a plugin