diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3bf50e06..51d7745c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,6 +30,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
 
+      - name: Keep local AI tooling out of Git
+        run: python3 tools/check_local_tooling.py
+
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@4360b52568e2003a75bf9bc1d59f33a8e3fc893c # stable
         with:
diff --git a/.gitignore b/.gitignore
index 9932abf4..7d04a0d8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -162,5 +162,24 @@ rustchan-e2e-*/
 /.cargo/credentials
 /.cargo/credentials.toml
 
-# Personal working instructions.
+# Local AI tooling: keep instructions, configuration, and sessions on this machine.
+# CI checks this block even if an ignored file is accidentally force-added.
+AGENTS.md
+CLAUDE.md
+GEMINI.md
+.agents/
+.codex/
+.claude/
+.cursor/
+.continue/
+.windsurf/
+.aider*
+/.mcp.json
+/mcp.json
+/.cursorrules
+/.windsurfrules
+/.github/copilot-instructions.md
+/.github/instructions/
+/.github/prompts/
 /rules.md
+# End local AI tooling.
diff --git a/AGENTS.md b/AGENTS.md
deleted file mode 100644
index 60fd1a81..00000000
--- a/AGENTS.md
+++ /dev/null
@@ -1,4 +0,0 @@
-# Repository instructions
-
-- Never create or push a branch whose name contains `codex`, regardless of case.
-- Use plain, descriptive branch names.
diff --git a/tools/check_local_tooling.py b/tools/check_local_tooling.py
new file mode 100644
index 00000000..c4c5c233
--- /dev/null
+++ b/tools/check_local_tooling.py
@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Reject tracked files covered by the local-tooling block in .gitignore."""
+
+from pathlib import Path
+import subprocess
+import sys
+import tempfile
+
+
+def main():
+    lines = Path(".gitignore").read_text().splitlines()
+    start = lines.index(
+        "# Local AI tooling: keep instructions, configuration, and sessions on this machine."
+    )
+    end = lines.index("# End local AI tooling.", start)
+    patterns = "\n".join(lines[start + 1 : end]) + "\n"
+    with tempfile.NamedTemporaryFile(mode="w+", encoding="utf-8") as excludes:
+        excludes.write(patterns)
+        excludes.flush()
+        result = subprocess.run(
+            [
+                "git", "ls-files", "--cached", "--ignored", "-z",
+                f"--exclude-from={excludes.name}",
+            ],
+            check=True,
+            capture_output=True,
+        )
+    paths = result.stdout.decode("utf-8", errors="replace").split("\0")
+    tracked = [path for path in paths if path]
+    if tracked:
+        print("Local AI tooling must remain untracked:", file=sys.stderr)
+        for path in tracked:
+            print(f"  {path!r}", file=sys.stderr)
+        return 1
+    print("No local AI tooling is tracked.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())