Add Gitea-push webhook for auto-deploy

webhook.py: HMAC-signed receiver (X-Gitea-Signature), validates ref==main,
  one-concurrent-deploy lock, no request data reaches shell.
deploy-webhook.sh: installs llm-bench-webhook systemd service (runs as
  aygea, in docker group), generates + stores secret in .webhook.secret.
deploy.sh: port read from compose (now 31415).

Installed on mewtwo: listening 0.0.0.0:41798, enabled for boot.
Gitea webhook target: http://10.0.0.22:41798/hook

Co-Authored-By: Claude <noreply@anthropic.com>

webhook.py

@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+"""
+Gitea push webhook receiver for the benchmark dashboard.
+
+- Listens on 0.0.0.0:PORT (obscure port; Gitea calls http://10.0.0.22:PORT/hook)
+- Validates the shared secret via the X-Gitea-Signature header (HMAC-SHA256 of the body)
+- On a valid push to `main`, runs: git fetch + reset to origin/main + ./deploy.sh up
+- One concurrent deploy at a time (a lock prevents overlapping rebuilds)
+
+Security notes:
+- No request data reaches the shell. The only string passed to the shell is a
+  hardcoded script (cd to this file's own dir, git fetch/reset, deploy.sh up).
+- The pushed ref is validated against a fixed constant (refs/heads/main) before deploy.
+Run via the systemd unit llm-bench-webhook.service (see deploy-webhook.sh).
+"""
+import asyncio, hmac, hashlib, os, json, logging
+from http import HTTPStatus
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+PORT = int(os.environ.get("WEBHOOK_PORT", "41798"))
+SECRET = os.environ.get("WEBHOOK_SECRET", "").encode()
+REF_FILTER = os.environ.get("WEBHOOK_REF", "refs/heads/main")
+MAX_BODY = 2 * 1024 * 1024  # 2 MB cap
+
+logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s")
+log = logging.getLogger("webhook")
+_deploy_lock = asyncio.Lock()
+
+# Hardcoded deploy script — NO request data interpolated into it.
+_DEPLOY_CMD = "cd " + HERE + " && git fetch origin && git reset --hard origin/main && ./deploy.sh up"
+
+
+def verify(signature_hex, body: bytes) -> bool:
+    if not SECRET:
+        log.warning("WEBHOOK_SECRET not set — accepting WITHOUT signature check (dev only)")
+        return True
+    if not signature_hex:
+        return False
+    mac = hmac.new(SECRET, body, hashlib.sha256).hexdigest()
+    return hmac.compare_digest(mac, signature_hex)
+
+
+async def redeploy():
+    if _deploy_lock.locked():
+        log.info("deploy already running, skipping")
+        return
+    async with _deploy_lock:
+        log.info("starting redeploy")
+        proc = await asyncio.create_subprocess_exec(
+            "bash", "-lc", _DEPLOY_CMD,
+            stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.STDOUT,
+        )
+        out, _ = await proc.communicate()
+        log.info("redeploy exit=%s\n%s", proc.returncode, (out or b"").decode(errors="replace"))
+
+
+async def handle(reader, writer):
+    try:
+        req = await reader.readuntil(b"\r\n\r\n")
+    except Exception:
+        writer.close(); return
+    try:
+        head, _, body_start = req.partition(b"\r\n\r\n")
+        lines = head.decode("latin1").split("\r\n")
+        method, path, _ = lines[0].split(" ", 2)
+        headers = {}
+        for ln in lines[1:]:
+            if ":" in ln:
+                k, v = ln.split(":", 1)
+                headers[k.strip().lower()] = v.strip()
+        cl = int(headers.get("content-length", "0") or 0)
+        body = body_start
+        while len(body) < cl and len(body) < MAX_BODY:
+            chunk = await reader.read(min(65536, cl - len(body)))
+            if not chunk:
+                break
+            body += chunk
+
+        if path.split("?")[0] not in ("/hook", "/webhook"):
+            writer.write(b"HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\n\r\n"); await writer.drain(); return
+        if method != "POST":
+            writer.write(b"HTTP/1.1 405 Method Not Allowed\r\nContent-Length: 0\r\n\r\n"); await writer.drain(); return
+
+        if not verify(headers.get("x-gitea-signature", ""), body):
+            log.warning("bad signature from %s", writer.get_extra_info("peername"))
+            writer.write(b"HTTP/1.1 403 Forbidden\r\nContent-Length: 0\r\n\r\n"); await writer.drain(); return
+
+        try:
+            ref = json.loads(body).get("ref", "") if body else ""
+        except Exception:
+            ref = ""
+        if ref and ref != REF_FILTER:
+            writer.write(b'HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: 17\r\n\r\nignored: wrong ref')
+            await writer.drain(); return
+
+        asyncio.create_task(redeploy())
+        writer.write(b'HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: 12\r\n\r\ndeploying...\n')
+        await writer.drain()
+    finally:
+        writer.close()
+
+
+async def main():
+    server = await asyncio.start_server(handle, "0.0.0.0", PORT)
+    log.info("webhook receiver listening on 0.0.0.0:%d (filter=%s)", PORT, REF_FILTER)
+    async with server:
+        await server.serve_forever()
+
+if __name__ == "__main__":
+    asyncio.run(main())