diff --git a/scripts/ensure_gitignore_claude_rules.py b/scripts/ensure_gitignore_claude_rules.py
new file mode 100644
index 0000000..27e27db
--- /dev/null
+++ b/scripts/ensure_gitignore_claude_rules.py
@@ -0,0 +1,63 @@
+"""Ensure repos track .claude/rules/ while ignoring other Claude Code local state."""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+SNIPPET_PATH = ROOT / "scripts" / "project_rules" / "gitignore-claude.template"
+MARKER = "# state-hub: track .claude/rules"
+TRACK_RULE = "!.claude/rules/"
+BLANKET_IGNORE_RE = re.compile(r"^\.claude/?\s*$", re.MULTILINE)
+
+
+def load_snippet() -> str:
+    text = SNIPPET_PATH.read_text(encoding="utf-8").strip()
+    return f"{MARKER}\n{text}\n"
+
+
+def snippet_present(text: str) -> bool:
+    return TRACK_RULE in text
+
+
+def ensure_claude_gitignore(gitignore_path: Path) -> bool:
+    """Return True when the file was created or modified."""
+    snippet = load_snippet()
+    if gitignore_path.exists():
+        text = gitignore_path.read_text(encoding="utf-8")
+        if snippet_present(text):
+            return False
+        if BLANKET_IGNORE_RE.search(text):
+            updated = BLANKET_IGNORE_RE.sub(snippet.rstrip(), text, count=1)
+            if updated != text:
+                gitignore_path.write_text(_ensure_trailing_newline(updated), encoding="utf-8")
+                return True
+        separator = "" if text.endswith("\n") or not text else "\n"
+        gitignore_path.write_text(f"{text}{separator}\n{snippet}", encoding="utf-8")
+        return True
+
+    gitignore_path.write_text(snippet, encoding="utf-8")
+    return True
+
+
+def _ensure_trailing_newline(text: str) -> str:
+    return text if text.endswith("\n") else f"{text}\n"
+
+
+def main() -> int:
+    import argparse
+
+    parser = argparse.ArgumentParser(description="Ensure .gitignore tracks .claude/rules/.")
+    parser.add_argument("path", type=Path, help="Repo root or .gitignore file path")
+    args = parser.parse_args()
+
+    target = args.path
+    gitignore = target if target.name == ".gitignore" else target / ".gitignore"
+    changed = ensure_claude_gitignore(gitignore)
+    print(f"{'updated' if changed else 'ok'}: {gitignore}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
\ No newline at end of file
diff --git a/scripts/project_rules/gitignore-claude.template b/scripts/project_rules/gitignore-claude.template
new file mode 100644
index 0000000..6022b83
--- /dev/null
+++ b/scripts/project_rules/gitignore-claude.template
@@ -0,0 +1,4 @@
+# Claude Code local state (track shared rules; ignore machine-specific files)
+.claude/*
+!.claude/rules/
+!.claude/rules/*.md
\ No newline at end of file
diff --git a/scripts/register_project.sh b/scripts/register_project.sh
index e6f1dee..a9652d0 100755
--- a/scripts/register_project.sh
+++ b/scripts/register_project.sh
@@ -147,6 +147,9 @@ if [[ "$ADDITIONAL" != "true" ]]; then
         echo "==> SCOPE.md already exists — skipping."
     fi
 
+    echo "==> Ensuring .gitignore tracks .claude/rules/ ..."
+    python3 "$SCRIPT_DIR/ensure_gitignore_claude_rules.py" "$PROJECT_PATH"
+
     if [[ "$CODEX_MODE" == "true" ]]; then
         # ── 5b: Codex — write AGENTS.md from HTTP-API template ────────────────
         AGENTS_MD="$PROJECT_PATH/AGENTS.md"
diff --git a/scripts/update_agent_instruction_files.py b/scripts/update_agent_instruction_files.py
index cf1ec57..8f84a71 100644
--- a/scripts/update_agent_instruction_files.py
+++ b/scripts/update_agent_instruction_files.py
@@ -12,6 +12,13 @@ from pathlib import Path
 
 ROOT = Path(__file__).resolve().parent.parent
 TEMPLATE_DIR = ROOT / "scripts" / "project_rules"
+
+import sys
+
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+from scripts.ensure_gitignore_claude_rules import ensure_claude_gitignore  # noqa: E402
 API_BASE = "http://127.0.0.1:8000"
 HOME_ROOT = Path("/home/worsch")
 WP_FILE_RE = re.compile(r"^([A-Za-z][A-Za-z0-9-]*-WP)-\d+", re.IGNORECASE)
@@ -189,6 +196,8 @@ def update_repo(
     if not scope_path.exists():
         scope_path.write_text(render(scope_template, values), encoding="utf-8")
 
+    ensure_claude_gitignore(path / ".gitignore")
+
     rules_dir = path / ".claude" / "rules"
     rules_dir.mkdir(parents=True, exist_ok=True)
     for name, template in rule_templates.items():
diff --git a/statehub_register.py b/statehub_register.py
index 323853a..76778f4 100644
--- a/statehub_register.py
+++ b/statehub_register.py
@@ -20,6 +20,8 @@ STATE_HUB_DIR = Path(__file__).resolve().parent
 API_BASE = os.environ.get("API_BASE", "http://127.0.0.1:8000")
 RULES_TEMPLATES_DIR = STATE_HUB_DIR / "scripts" / "project_rules"
 
+from scripts.ensure_gitignore_claude_rules import ensure_claude_gitignore  # noqa: E402
+
 KEY_CONTEXT_FILES = [
     "INTENT.md",
     "README.md",
@@ -291,6 +293,10 @@ def write_registration_files(
         )
         written.append(brief_path)
 
+    gitignore_path = project_path / ".gitignore"
+    if ensure_claude_gitignore(gitignore_path):
+        written.append(gitignore_path)
+
     return written
 
 
diff --git a/tests/test_ensure_gitignore_claude_rules.py b/tests/test_ensure_gitignore_claude_rules.py
new file mode 100644
index 0000000..b99f105
--- /dev/null
+++ b/tests/test_ensure_gitignore_claude_rules.py
@@ -0,0 +1,41 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from scripts.ensure_gitignore_claude_rules import ensure_claude_gitignore, snippet_present
+
+
+def test_ensure_claude_gitignore_creates_file(tmp_path: Path):
+    gitignore = tmp_path / ".gitignore"
+
+    assert ensure_claude_gitignore(gitignore) is True
+    text = gitignore.read_text(encoding="utf-8")
+    assert snippet_present(text)
+    assert "!.claude/rules/" in text
+
+
+def test_ensure_claude_gitignore_replaces_blanket_ignore(tmp_path: Path):
+    gitignore = tmp_path / ".gitignore"
+    gitignore.write_text("# Claude Code local state\n.claude/\n", encoding="utf-8")
+
+    assert ensure_claude_gitignore(gitignore) is True
+    text = gitignore.read_text(encoding="utf-8")
+    assert ".claude/" not in text or "!.claude/rules/" in text
+    assert "!.claude/rules/*.md" in text
+
+
+def test_ensure_claude_gitignore_is_idempotent(tmp_path: Path):
+    gitignore = tmp_path / ".gitignore"
+
+    assert ensure_claude_gitignore(gitignore) is True
+    assert ensure_claude_gitignore(gitignore) is False
+
+
+def test_ensure_claude_gitignore_appends_when_other_rules_present(tmp_path: Path):
+    gitignore = tmp_path / ".gitignore"
+    gitignore.write_text(".venv/\n", encoding="utf-8")
+
+    assert ensure_claude_gitignore(gitignore) is True
+    text = gitignore.read_text(encoding="utf-8")
+    assert text.startswith(".venv/\n")
+    assert "!.claude/rules/" in text
\ No newline at end of file
diff --git a/tests/test_statehub_register_cli.py b/tests/test_statehub_register_cli.py
index 20f9862..a5f7b05 100644
--- a/tests/test_statehub_register_cli.py
+++ b/tests/test_statehub_register_cli.py
@@ -89,7 +89,9 @@ def test_write_registration_files_primes_codex_repo(tmp_path: Path):
         "AGENTS.md",
         ".custodian-brief.md",
         "DEMO-WP-0001-statehub-bootstrap.md",
+        ".gitignore",
     }
+    assert "!.claude/rules/" in (tmp_path / ".gitignore").read_text()
     assert (tmp_path / "INTENT.md").read_text() == "# INTENT\n\nDemo service intent.\n"
     assert "**Repo slug:** demo-service" in (tmp_path / "AGENTS.md").read_text()
     assert "Run the demo service." in (tmp_path / "SCOPE.md").read_text()