fix(hooks): skip read-guard advisory on Claude Code runtime (#2001)

* fix(hooks): skip read-guard advisory on Claude Code runtime (#1984)

Claude Code natively enforces read-before-edit at the runtime level,
so the gsd-read-guard.js advisory is redundant — it wastes ~80 tokens
per Write/Edit call and clutters tool flow with system-reminder noise.

Add early exit when CLAUDE_SESSION_ID is set (standard Claude Code
session env var). Non-Claude runtimes (OpenCode, Gemini, etc.) that
lack native read-before-edit enforcement continue to receive the
advisory as before.

Closes #1984

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(hooks): sanitize runHook env to prevent test failures in Claude Code

The runHook() test helper now blanks CLAUDE_SESSION_ID so positive-path
tests pass even when the test suite runs inside a Claude Code session.
The new skip test passes the env var explicitly via envOverrides.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

hooks/gsd-read-guard.js

@@ -36,6 +36,11 @@ process.stdin.on('end', () => {
       process.exit(0);
     }
 
+    // Claude Code natively enforces read-before-edit — skip the advisory (#1984)
+    if (process.env.CLAUDE_SESSION_ID) {
+      process.exit(0);
+    }
+
     const filePath = data.tool_input?.file_path || '';
     if (!filePath) {
       process.exit(0);