Adds a new `notepad-write-guard` hook that intercepts Write tool calls
whose target path matches `**/.sisyphus/notepads/**` and throws an
actionable error instead of allowing the write to proceed.
Without this guard, an agent that hits an Edit hash-mismatch failure
could silently fall back to Write, destroying the entire history of an
append-only notepad file (decisions.md, issues.md, etc.). The file
carries an explicit "NEVER overwrite" warning that the agent ignores
under context pressure.
The guard is path-based so it works regardless of plan name or nesting
depth. Non-notepad `.sisyphus/**` paths (e.g. plan files) are
unaffected. The hook is wired into `create-tool-guard-hooks` under the
hook name `notepad-write-guard` and follows the same safeCreateHook +
HookName schema pattern as every other tool-guard hook.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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