New opt-in PreToolUse hook that warns when Claude edits files outside
a GSD workflow context (no active /gsd: command or subagent).
Soft guard — advises, does not block. The edit proceeds but Claude
sees a reminder to use /gsd:fast or /gsd:quick for state tracking.
Enable: set hooks.workflow_guard: true in .planning/config.json
Default: disabled (false)
Allows without warning:
- .planning/ files (GSD state management)
- Config files (.gitignore, .env, CLAUDE.md, settings.json)
- Subagent contexts (executor, planner, etc.)
Includes 3s stdin timeout guard and silent fail-safe.
Closes#678
a6ba3e268e