✨ feat(playbook): auto-inject AGENTS.md into CLAUDE.md

When any sync action runs and the target project already has a CLAUDE.md,
automatically insert @AGENTS.md / @AGENT_RULES.md import block so
Claude Code picks up the same rules as Codex without manual setup.

- Add sync_claude_md() called at end of sync_agents_template()
- Uses <!-- playbook:claude:start/end --> block markers for idempotent updates
- Skips if no CLAUDE.md exists (Codex users unaffected)
- Skips if @AGENTS.md already present (manual setups respected)
- Add 4 tests covering: no file, append, update block, already-referenced

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/playbook.py

@@ -721,9 +721,56 @@ def sync_agents_template(context: dict) -> int:
         date_value,
         playbook_scripts,
     )
+    sync_claude_md(project_root)
     return 0
 
 
+_CLAUDE_BLOCK_START = "<!-- playbook:claude:start -->"
+_CLAUDE_BLOCK_END = "<!-- playbook:claude:end -->"
+
+
+def sync_claude_md(project_root: Path) -> None:
+    claude_md = project_root / "CLAUDE.md"
+    if not claude_md.exists():
+        return
+
+    block_lines = [
+        _CLAUDE_BLOCK_START,
+        "",
+        "@AGENTS.md",
+        "@AGENT_RULES.md",
+        "",
+        _CLAUDE_BLOCK_END,
+    ]
+
+    text = claude_md.read_text(encoding="utf-8")
+
+    if _CLAUDE_BLOCK_START in text:
+        lines = text.splitlines()
+        updated: list[str] = []
+        in_block = False
+        replaced = False
+        for line in lines:
+            if not replaced and line.strip() == _CLAUDE_BLOCK_START:
+                updated.extend(block_lines)
+                in_block = True
+                replaced = True
+                continue
+            if in_block:
+                if line.strip() == _CLAUDE_BLOCK_END:
+                    in_block = False
+                continue
+            updated.append(line)
+        claude_md.write_text("\n".join(updated) + "\n", encoding="utf-8")
+        log("Updated CLAUDE.md (playbook block).")
+    elif "@AGENTS.md" in text:
+        log("Skip: CLAUDE.md already references AGENTS.md")
+    else:
+        appended = text.rstrip("\n") + "\n\n" + "\n".join(block_lines) + "\n"
+        claude_md.write_text(appended, encoding="utf-8")
+        log("Appended playbook block to CLAUDE.md")
+
+
 def should_sync_agents(config: dict) -> bool:
     for key in ("sync_rules", "sync_memory_bank", "sync_prompts", "sync_standards"):
         if key in config: