chore: .claude hooks (pretooluse_bash, posttooluse_writeedit, sessionstart) + settings.local.json.example (#15) (#37)

Port the three .claude/hooks/*.py scripts and settings.local.json.example
verbatim from Teller. Drop .svelte from PRETTIER_EXTENSIONS and add .jsx
(template uses React, not Svelte). Strip Teller-specific PR references in
comments. Run ruff format on the result.

.claude/bash-log.txt and .claude/settings.local.json are already in .gitignore
from #5.

Closes #15

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

Author: constk

.claude/hooks/posttooluse_writeedit.py

@@ -0,0 +1,102 @@
+#!/usr/bin/env python3
+"""PostToolUse hook for Write | Edit — formatter dispatch.
+
+After a successful Write or Edit, format the touched file in place:
+
+  - `.py`                         -> `uv run ruff check --fix` + `uv run ruff format`
+  - `.ts .tsx .js .jsx .json`     -> `npx --no-install prettier -w` (from frontend/)
+  - `.css .html .md`              -> `npx --no-install prettier -w` (from frontend/)
+
+Silent on failure — the write already landed; formatting is best-effort. Exit code
+is always 0 so Claude Code never rolls back the edit over a missing formatter.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import json
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+PY_EXTENSIONS = {".py"}
+PRETTIER_EXTENSIONS = {
+    ".ts",
+    ".tsx",
+    ".js",
+    ".jsx",
+    ".json",
+    ".css",
+    ".html",
+    ".md",
+}
+
+
+def project_dir() -> Path:
+    env = os.environ.get("CLAUDE_PROJECT_DIR")
+    if env:
+        return Path(env)
+    return Path(__file__).resolve().parent.parent.parent
+
+
+def run_quiet(cmd: list[str], cwd: Path) -> None:
+    with contextlib.suppress(FileNotFoundError, subprocess.TimeoutExpired):
+        subprocess.run(
+            cmd,
+            cwd=cwd,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+            check=False,
+            timeout=60,
+        )
+
+
+def format_python(path: Path, base: Path) -> None:
+    run_quiet(["uv", "run", "ruff", "check", "--fix", str(path)], cwd=base)
+    run_quiet(["uv", "run", "ruff", "format", str(path)], cwd=base)
+
+
+def format_prettier(path: Path, base: Path) -> None:
+    frontend = base / "frontend"
+    if not frontend.is_dir():
+        return
+    # --no-install so a checkout without prettier installed silently no-ops
+    # instead of triggering an npx download.
+    run_quiet(
+        ["npx", "--no-install", "prettier", "-w", str(path)],
+        cwd=frontend,
+    )
+
+
+def main() -> None:
+    try:
+        payload = json.load(sys.stdin)
+    except json.JSONDecodeError:
+        return
+    if not isinstance(payload, dict):
+        return
+    tool_input = payload.get("tool_input")
+    if not isinstance(tool_input, dict):
+        return
+    file_path = tool_input.get("file_path", "")
+    if not isinstance(file_path, str) or not file_path:
+        return
+
+    path = Path(file_path)
+    if not path.is_absolute():
+        path = project_dir() / path
+    if not path.exists():
+        return
+
+    suffix = path.suffix.lower()
+    base = project_dir()
+
+    if suffix in PY_EXTENSIONS:
+        format_python(path, base)
+    elif suffix in PRETTIER_EXTENSIONS:
+        format_prettier(path, base)
+
+
+if __name__ == "__main__":
+    main()

.claude/hooks/pretooluse_bash.py

@@ -0,0 +1,126 @@
+#!/usr/bin/env python3
+"""PreToolUse hook for Bash — forbidden-flag blocker, secret scanner, audit log.
+
+Invoked by Claude Code on every Bash tool call. Reads the hook payload as JSON
+on stdin and performs three checks in order:
+
+1. Forbidden-flag blocker  — deny `git --no-verify`, `--no-hooks`, `--no-gpg-sign`.
+2. Secret scanner          — on `git commit`, scan the staged diff for known
+                              secret shapes (AWS keys, sk-*, ghp_/ghs_*, PEMs,
+                              Slack tokens).
+3. Audit log               — append a timestamped record of every command the
+                              agent runs to .claude/bash-log.txt (gitignored).
+
+Exit codes
+----------
+0  — command allowed
+2  — command blocked (Claude Code surfaces stderr back to the agent)
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import re
+import subprocess
+import sys
+from datetime import UTC, datetime
+from pathlib import Path
+
+FORBIDDEN_FLAG = re.compile(r"\bgit\b[^\n]*--(?:no-verify|no-hooks|no-gpg-sign)\b")
+
+SECRET_PATTERNS: list[tuple[str, re.Pattern[str]]] = [
+    ("AWS access key id", re.compile(r"AKIA[0-9A-Z]{16}")),
+    (
+        "AWS secret access key assignment",
+        re.compile(r"aws_secret_access_key\s*=", re.IGNORECASE),
+    ),
+    ("OpenAI-style API key", re.compile(r"sk-[A-Za-z0-9]{20,}")),
+    ("GitHub personal access token", re.compile(r"ghp_[A-Za-z0-9]{36}")),
+    ("GitHub server-to-server token", re.compile(r"ghs_[A-Za-z0-9]{36}")),
+    ("Slack bot token", re.compile(r"xoxb-[A-Za-z0-9-]+")),
+    ("PEM private key block", re.compile(r"-----BEGIN [A-Z ]*PRIVATE KEY-----")),
+]
+
+
+def project_dir() -> Path:
+    env = os.environ.get("CLAUDE_PROJECT_DIR")
+    if env:
+        return Path(env)
+    return Path(__file__).resolve().parent.parent.parent
+
+
+def load_payload() -> dict[str, object]:
+    try:
+        data = json.load(sys.stdin)
+    except json.JSONDecodeError:
+        return {}
+    return data if isinstance(data, dict) else {}
+
+
+def block(reason: str) -> None:
+    print(reason, file=sys.stderr)
+    sys.exit(2)
+
+
+def scan_staged_diff(cwd: Path) -> str | None:
+    """Return matched pattern name when a secret shape appears in staged diff."""
+    try:
+        diff = subprocess.check_output(
+            ["git", "diff", "--cached", "--no-color"],
+            cwd=cwd,
+            stderr=subprocess.DEVNULL,
+            text=True,
+            errors="replace",
+        )
+    except subprocess.CalledProcessError, FileNotFoundError:
+        return None
+    for name, pattern in SECRET_PATTERNS:
+        if pattern.search(diff):
+            return name
+    return None
+
+
+def audit(command: str, base: Path) -> None:
+    log = base / ".claude" / "bash-log.txt"
+    try:
+        log.parent.mkdir(parents=True, exist_ok=True)
+        ts = datetime.now(UTC).strftime("%Y-%m-%dT%H:%M:%SZ")
+        with log.open("a", encoding="utf-8") as fh:
+            fh.write(f"{ts}\t{command}\n")
+    except OSError:
+        pass
+
+
+def main() -> None:
+    payload = load_payload()
+    tool_input = payload.get("tool_input")
+    if not isinstance(tool_input, dict):
+        return
+    command = tool_input.get("command", "")
+    if not isinstance(command, str) or not command.strip():
+        return
+
+    if FORBIDDEN_FLAG.search(command):
+        block(
+            "Blocked by PreToolUse hook: forbidden git flag "
+            "(--no-verify | --no-hooks | --no-gpg-sign). "
+            "Fix the underlying issue instead of bypassing the check."
+        )
+
+    base = project_dir()
+    stripped = command.lstrip()
+    if stripped.startswith(("git commit", '"git commit', "'git commit")):
+        match = scan_staged_diff(base)
+        if match:
+            block(
+                "Blocked by PreToolUse hook: "
+                f"staged diff matches secret pattern ({match}). "
+                "Remove the secret, rotate if already committed, and re-stage."
+            )
+
+    audit(command, base)
+
+
+if __name__ == "__main__":
+    main()

.claude/hooks/sessionstart.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+"""SessionStart hook — inject current branch + working-tree state as session context.
+
+Claude Code treats stdout as `additionalContext` on SessionStart, so this script
+prints the current git branch and `git status --short` — giving the agent the
+same orientation a human gets from opening the terminal. Runs once per session.
+
+Silent and zero-exit on any failure: a missing git directory or a transient
+command error must never block session startup.
+"""
+
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+
+def project_dir() -> Path:
+    env = os.environ.get("CLAUDE_PROJECT_DIR")
+    if env:
+        return Path(env)
+    return Path(__file__).resolve().parent.parent.parent
+
+
+def git_output(args: list[str], cwd: Path) -> str:
+    try:
+        return subprocess.check_output(
+            ["git", *args],
+            cwd=cwd,
+            stderr=subprocess.DEVNULL,
+            text=True,
+            errors="replace",
+            timeout=5,
+        ).strip()
+    except (
+        subprocess.CalledProcessError,
+        subprocess.TimeoutExpired,
+        FileNotFoundError,
+    ):
+        return ""
+
+
+def main() -> None:
+    base = project_dir()
+    branch = git_output(["branch", "--show-current"], base)
+    status = git_output(["status", "--short"], base)
+
+    if not branch and not status:
+        return
+
+    lines = ["# Repository context (injected by SessionStart hook)"]
+    if branch:
+        lines.append(f"- Current branch: `{branch}`")
+    if status:
+        lines.append("")
+        lines.append("Working tree (`git status --short`):")
+        lines.append("```")
+        lines.append(status)
+        lines.append("```")
+    else:
+        lines.append("- Working tree: clean")
+
+    sys.stdout.write("\n".join(lines) + "\n")
+
+
+if __name__ == "__main__":
+    main()

.claude/settings.local.json.example

@@ -0,0 +1,39 @@
+{
+  "$schema": "https://json.schemastore.org/claude-code-settings.json",
+  "_comment": "Copy this file to .claude/settings.local.json (gitignored) to enable the agent hook stack. See docs/DEVELOPMENT.md#local-agent-hook-setup.",
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python \"$CLAUDE_PROJECT_DIR/.claude/hooks/pretooluse_bash.py\""
+          }
+        ]
+      }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Write|Edit",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python \"$CLAUDE_PROJECT_DIR/.claude/hooks/posttooluse_writeedit.py\""
+          }
+        ]
+      }
+    ],
+    "SessionStart": [
+      {
+        "matcher": "startup|resume",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python \"$CLAUDE_PROJECT_DIR/.claude/hooks/sessionstart.py\""
+          }
+        ]
+      }
+    ]
+  }
+}