1 files changed, 94 insertions, 0 deletions
diff --git a/hooks/rulesets-write-boundary.py b/hooks/rulesets-write-boundary.py
new file mode 100755
index 0000000..35088ea
--- /dev/null
+++ b/hooks/rulesets-write-boundary.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+"""Block cross-project Edit/Write calls that resolve into rulesets.
+
+Global Claude rules, hooks, skills, commands, and bin tools are symlinks into
+~/code/rulesets. Editing one from another project's session silently dirties
+rulesets and can block every later startup. The sanctioned path is inbox-send;
+the rulesets session owns the canonical edit and its wrap.
+"""
+
+from __future__ import annotations
+
+import os
+import re
+from pathlib import Path
+from typing import Any, Iterable
+
+from _common import read_payload, respond_deny
+
+
+PATCH_PATH = re.compile(
+    r"^\*\*\* (?:Add|Update|Delete) File: (.+)$|^\*\*\* Move to: (.+)$",
+    re.MULTILINE,
+)
+
+
+def inside(path: Path, parent: Path) -> bool:
+    try:
+        path.relative_to(parent)
+        return True
+    except ValueError:
+        return False
+
+
+def candidate_paths(tool_input: Any) -> Iterable[str]:
+    if isinstance(tool_input, dict):
+        for key, value in tool_input.items():
+            if key in {"file_path", "path"} and isinstance(value, str):
+                yield value
+            elif key in {"patch", "input"} and isinstance(value, str):
+                for match in PATCH_PATH.finditer(value):
+                    yield match.group(1) or match.group(2)
+    elif isinstance(tool_input, str):
+        for match in PATCH_PATH.finditer(tool_input):
+            yield match.group(1) or match.group(2)
+
+
+def resolve(raw: str, cwd: Path) -> Path:
+    expanded = Path(os.path.expandvars(os.path.expanduser(raw)))
+    if not expanded.is_absolute():
+        expanded = cwd / expanded
+    return expanded.resolve(strict=False)
+
+
+def main() -> int:
+    payload = read_payload()
+    tool_name = payload.get("tool_name", "")
+    if tool_name not in {"Edit", "Write", "apply_patch"}:
+        return 0
+
+    rulesets = Path(
+        os.environ.get("RULESETS_ROOT", "~/code/rulesets")
+    ).expanduser().resolve(strict=False)
+    cwd = Path(payload.get("cwd") or os.getcwd()).resolve(strict=False)
+
+    # A rulesets session owns its own canonical files.
+    if inside(cwd, rulesets):
+        return 0
+
+    blocked: list[str] = []
+    for raw in candidate_paths(payload.get("tool_input", {})):
+        try:
+            target = resolve(raw, cwd)
+        except (OSError, RuntimeError):
+            blocked.append(f"{raw} (real path could not be verified)")
+            continue
+        if inside(target, rulesets):
+            blocked.append(str(target))
+
+    if not blocked:
+        return 0
+
+    shown = ", ".join(blocked)
+    reason = (
+        "Blocked cross-project write into rulesets: "
+        f"{shown}. This path may have been reached through an installed "
+        "symlink. Send the proposed change with inbox-send rulesets instead, "
+        "then let a rulesets session apply and wrap it."
+    )
+    respond_deny(reason, system_message=reason)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())