feat(swarm): syslog-over-TLS log pipeline (RFC 5425, TCP 6514)

Worker-side log_forwarder tails the local RFC 5424 log file and ships each line as an octet-counted frame to the master over mTLS. Offset is persisted in a tiny local SQLite so master outages never cause loss or duplication — reconnect resumes from the exact byte where the previous session left off. Impostor workers (cert not signed by DECNET CA) are rejected at TLS handshake. Master-side log_listener terminates mTLS on 0.0.0.0:6514, validates the client cert, extracts the peer CN as authoritative worker provenance, and appends each frame to the master's ingest log files. Attacker- controlled syslog HOSTNAME field is ignored — the CA-controlled CN is the only source of provenance. 7 tests added covering framing codec, offset persistence across reopens, end-to-end mTLS delivery, crash-resilience (offset survives restart, no duplicate shipping), and impostor-CA rejection. DECNET_SWARM_SYSLOG_PORT / DECNET_SWARM_MASTER_HOST env bindings added.
2026-04-18 19:33:58 -04:00
parent e2d6f857b5
commit 39d2077a3a
4 changed files with 774 additions and 0 deletions
--- a/decnet/env.py
+++ b/decnet/env.py
@@ -77,6 +77,11 @@ DECNET_API_PORT: int = _port("DECNET_API_PORT", 8000)
 DECNET_JWT_SECRET: str = _require_env("DECNET_JWT_SECRET")
 DECNET_INGEST_LOG_FILE: str | None = os.environ.get("DECNET_INGEST_LOG_FILE", "/var/log/decnet/decnet.log")

+# SWARM log pipeline — RFC 5425 syslog-over-TLS between worker forwarders
+# and the master listener.  Plaintext syslog across hosts is forbidden.
+DECNET_SWARM_SYSLOG_PORT: int = _port("DECNET_SWARM_SYSLOG_PORT", 6514)
+DECNET_SWARM_MASTER_HOST: str | None = os.environ.get("DECNET_SWARM_MASTER_HOST")
+
 # Ingester batching: how many log rows to accumulate per commit, and the
 # max wait (ms) before flushing a partial batch. Larger batches reduce
 # SQLite write-lock contention; the timeout keeps latency bounded during
--- a/decnet/swarm/log_forwarder.py
+++ b/decnet/swarm/log_forwarder.py
@@ -0,0 +1,293 @@
+"""Worker-side syslog-over-TLS forwarder (RFC 5425).
+
+Runs alongside the worker agent. Tails the worker's local RFC 5424 log
+file (written by the existing docker-collector) and ships each line to
+the master's listener on TCP 6514 using octet-counted framing over mTLS.
+Persists the last-forwarded byte offset in a tiny local SQLite so a
+master crash never causes loss or duplication.
+
+Design constraints (from the plan, non-negotiable):
+* transport MUST be TLS — plaintext syslog is never acceptable between
+  hosts; only loopback (decky → worker-local collector) may be plaintext;
+* mTLS — the listener pins the worker cert against the DECNET CA, so only
+  enrolled workers can push logs;
+* offset persistence MUST be transactional w.r.t. the send — we only
+  advance the offset after ``writer.drain()`` returns without error.
+
+The forwarder is intentionally a standalone coroutine, not a worker
+inside the agent process.  That keeps ``decnet agent`` crashes from
+losing the log tail, and vice versa.
+"""
+from __future__ import annotations
+
+import asyncio
+import os
+import pathlib
+import sqlite3
+import ssl
+from dataclasses import dataclass
+from typing import Optional
+
+from decnet.logging import get_logger
+from decnet.swarm import pki
+
+log = get_logger("swarm.forwarder")
+
+# RFC 5425 framing: "<octet-count> <syslog-msg>".
+# The message itself is a standard RFC 5424 line (no trailing newline).
+_FRAME_SEP = b" "
+
+_INITIAL_BACKOFF = 1.0
+_MAX_BACKOFF = 30.0
+
+
+@dataclass(frozen=True)
+class ForwarderConfig:
+    log_path: pathlib.Path      # worker's RFC 5424 .log file
+    master_host: str
+    master_port: int = 6514
+    agent_dir: pathlib.Path = pki.DEFAULT_AGENT_DIR
+    state_db: Optional[pathlib.Path] = None  # default: agent_dir / "forwarder.db"
+    # Max unacked bytes to keep in the local buffer when master is down.
+    # We bound the lag to avoid unbounded disk growth on catastrophic master
+    # outage — older lines are surfaced as a warning and dropped by advancing
+    # the offset.
+    max_lag_bytes: int = 128 * 1024 * 1024  # 128 MiB
+
+
+# ------------------------------------------------------------ offset storage
+
+
+class _OffsetStore:
+    """Single-row SQLite offset tracker. Stdlib only — no ORM, no async."""
+
+    def __init__(self, db_path: pathlib.Path) -> None:
+        db_path.parent.mkdir(parents=True, exist_ok=True)
+        self._conn = sqlite3.connect(str(db_path))
+        self._conn.execute(
+            "CREATE TABLE IF NOT EXISTS forwarder_offset ("
+            " key TEXT PRIMARY KEY, offset INTEGER NOT NULL)"
+        )
+        self._conn.commit()
+
+    def get(self, key: str = "default") -> int:
+        row = self._conn.execute(
+            "SELECT offset FROM forwarder_offset WHERE key=?", (key,)
+        ).fetchone()
+        return int(row[0]) if row else 0
+
+    def set(self, offset: int, key: str = "default") -> None:
+        self._conn.execute(
+            "INSERT INTO forwarder_offset(key, offset) VALUES(?, ?) "
+            "ON CONFLICT(key) DO UPDATE SET offset=excluded.offset",
+            (key, offset),
+        )
+        self._conn.commit()
+
+    def close(self) -> None:
+        self._conn.close()
+
+
+# ---------------------------------------------------------------- TLS setup
+
+
+def build_worker_ssl_context(agent_dir: pathlib.Path) -> ssl.SSLContext:
+    """Client-side mTLS context for the forwarder.
+
+    Worker presents its agent bundle (same cert used for the control-plane
+    HTTPS listener).  The CA is the DECNET CA; we pin by CA, not hostname,
+    because workers reach masters by operator-supplied address.
+    """
+    bundle = pki.load_worker_bundle(agent_dir)
+    if bundle is None:
+        raise RuntimeError(
+            f"no worker bundle at {agent_dir} — enroll from the master first"
+        )
+    ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+    ctx.load_cert_chain(
+        certfile=str(agent_dir / "worker.crt"),
+        keyfile=str(agent_dir / "worker.key"),
+    )
+    ctx.load_verify_locations(cafile=str(agent_dir / "ca.crt"))
+    ctx.verify_mode = ssl.CERT_REQUIRED
+    ctx.check_hostname = False
+    return ctx
+
+
+# ----------------------------------------------------------- frame encoding
+
+
+def encode_frame(line: str) -> bytes:
+    """RFC 5425 octet-counted framing: ``"<N> <msg>"``.
+
+    ``N`` is the byte length of the payload that follows (after the space).
+    """
+    payload = line.rstrip("\n").encode("utf-8", errors="replace")
+    return f"{len(payload)}".encode("ascii") + _FRAME_SEP + payload
+
+
+async def read_frame(reader: asyncio.StreamReader) -> Optional[bytes]:
+    """Read one octet-counted frame. Returns None on clean EOF."""
+    # Read the ASCII length up to the first space. Bound the prefix so a
+    # malicious peer can't force us to buffer unbounded bytes before we know
+    # it's a valid frame.
+    prefix = b""
+    while True:
+        c = await reader.read(1)
+        if not c:
+            return None if not prefix else b""
+        if c == _FRAME_SEP:
+            break
+        if len(prefix) >= 10 or not c.isdigit():
+            # RFC 5425 caps the length prefix at ~10 digits (< 4 GiB payload).
+            raise ValueError(f"invalid octet-count prefix: {prefix!r}")
+        prefix += c
+    n = int(prefix)
+    buf = await reader.readexactly(n)
+    return buf
+
+
+# ----------------------------------------------------------------- main loop
+
+
+async def _send_batch(
+    writer: asyncio.StreamWriter,
+    offset: int,
+    lines: list[tuple[int, str]],
+    store: _OffsetStore,
+) -> int:
+    """Write every line as a frame, drain, then persist the last offset."""
+    for _, line in lines:
+        writer.write(encode_frame(line))
+    await writer.drain()
+    last_offset = lines[-1][0]
+    store.set(last_offset)
+    return last_offset
+
+
+async def run_forwarder(
+    cfg: ForwarderConfig,
+    *,
+    poll_interval: float = 0.5,
+    stop_event: Optional[asyncio.Event] = None,
+) -> None:
+    """Main forwarder loop. Run as a dedicated task.
+
+    Stops when ``stop_event`` is set (used by tests and clean shutdown).
+    Exceptions trigger exponential backoff but are never fatal — the
+    forwarder is expected to outlive transient master/network failures.
+    """
+    state_db = cfg.state_db or (cfg.agent_dir / "forwarder.db")
+    store = _OffsetStore(state_db)
+    offset = store.get()
+    backoff = _INITIAL_BACKOFF
+
+    log.info(
+        "forwarder start log=%s master=%s:%d offset=%d",
+        cfg.log_path, cfg.master_host, cfg.master_port, offset,
+    )
+
+    try:
+        while stop_event is None or not stop_event.is_set():
+            try:
+                ctx = build_worker_ssl_context(cfg.agent_dir)
+                reader, writer = await asyncio.open_connection(
+                    cfg.master_host, cfg.master_port, ssl=ctx
+                )
+                log.info("forwarder connected master=%s:%d", cfg.master_host, cfg.master_port)
+                backoff = _INITIAL_BACKOFF
+                try:
+                    offset = await _pump(cfg, store, writer, offset, poll_interval, stop_event)
+                finally:
+                    writer.close()
+                    try:
+                        await writer.wait_closed()
+                    except Exception:  # nosec B110 — socket cleanup is best-effort
+                        pass
+                    # Keep reader alive until here to avoid "reader garbage
+                    # collected" warnings on some Python builds.
+                    del reader
+            except (OSError, ssl.SSLError, ConnectionError) as exc:
+                log.warning(
+                    "forwarder disconnected: %s — retrying in %.1fs", exc, backoff
+                )
+                try:
+                    await asyncio.wait_for(
+                        _sleep_unless_stopped(backoff, stop_event), timeout=backoff + 1
+                    )
+                except asyncio.TimeoutError:
+                    pass
+                backoff = min(_MAX_BACKOFF, backoff * 2)
+    finally:
+        store.close()
+        log.info("forwarder stopped offset=%d", offset)
+
+
+async def _pump(
+    cfg: ForwarderConfig,
+    store: _OffsetStore,
+    writer: asyncio.StreamWriter,
+    offset: int,
+    poll_interval: float,
+    stop_event: Optional[asyncio.Event],
+) -> int:
+    """Read new lines since ``offset`` and ship them until disconnect."""
+    while stop_event is None or not stop_event.is_set():
+        if not cfg.log_path.exists():
+            await _sleep_unless_stopped(poll_interval, stop_event)
+            continue
+
+        stat = cfg.log_path.stat()
+        if stat.st_size < offset:
+            # truncated/rotated — reset.
+            log.warning("forwarder log rotated — resetting offset=0")
+            offset = 0
+            store.set(0)
+        if stat.st_size - offset > cfg.max_lag_bytes:
+            # Catastrophic lag — skip ahead to cap local disk pressure.
+            skip_to = stat.st_size - cfg.max_lag_bytes
+            log.warning(
+                "forwarder lag %d > cap %d — dropping oldest %d bytes",
+                stat.st_size - offset, cfg.max_lag_bytes, skip_to - offset,
+            )
+            offset = skip_to
+            store.set(offset)
+
+        if stat.st_size == offset:
+            await _sleep_unless_stopped(poll_interval, stop_event)
+            continue
+
+        batch: list[tuple[int, str]] = []
+        with open(cfg.log_path, "r", encoding="utf-8", errors="replace") as f:
+            f.seek(offset)
+            while True:
+                line = f.readline()
+                if not line or not line.endswith("\n"):
+                    break
+                offset_after = f.tell()
+                batch.append((offset_after, line.rstrip("\n")))
+                if len(batch) >= 500:
+                    break
+        if batch:
+            offset = await _send_batch(writer, offset, batch, store)
+    return offset
+
+
+async def _sleep_unless_stopped(
+    seconds: float, stop_event: Optional[asyncio.Event]
+) -> None:
+    if stop_event is None:
+        await asyncio.sleep(seconds)
+        return
+    try:
+        await asyncio.wait_for(stop_event.wait(), timeout=seconds)
+    except asyncio.TimeoutError:
+        pass
+
+
+# Re-exported for CLI convenience
+DEFAULT_PORT = 6514
+
+
+def default_master_host() -> Optional[str]:
+    return os.environ.get("DECNET_SWARM_MASTER_HOST")
--- a/decnet/swarm/log_listener.py
+++ b/decnet/swarm/log_listener.py
@@ -0,0 +1,194 @@
+"""Master-side syslog-over-TLS listener (RFC 5425).
+
+Accepts mTLS-authenticated worker connections on TCP 6514, reads
+octet-counted frames, parses each as an RFC 5424 line, and appends it to
+the master's local ingest log files. The existing log_ingestion_worker
+tails those files and inserts records into the master repo — worker
+provenance is embedded in the parsed record's ``source_worker`` field.
+
+Design:
+* TLS is mandatory. No plaintext fallback. A peer without a CA-signed
+  cert is rejected at the TLS handshake; nothing gets past the kernel.
+* The listener never trusts the syslog HOSTNAME field for provenance —
+  that's attacker-supplied from the decky. The authoritative source is
+  the peer cert's CN, which the CA controlled at enrollment.
+* Dropped connections are fine — the worker's forwarder holds the
+  offset and resumes from the same byte on reconnect.
+"""
+from __future__ import annotations
+
+import asyncio
+import json
+import pathlib
+import ssl
+from dataclasses import dataclass
+from typing import Optional
+
+from cryptography import x509
+from cryptography.hazmat.primitives import serialization
+from cryptography.x509.oid import NameOID
+
+from decnet.logging import get_logger
+from decnet.swarm import pki
+from decnet.swarm.log_forwarder import read_frame
+
+log = get_logger("swarm.listener")
+
+
+@dataclass(frozen=True)
+class ListenerConfig:
+    log_path: pathlib.Path          # master's RFC 5424 .log (forensic sink)
+    json_path: pathlib.Path         # master's .json (ingester tails this)
+    bind_host: str = "0.0.0.0"  # nosec B104 — listener must bind publicly
+    bind_port: int = 6514
+    ca_dir: pathlib.Path = pki.DEFAULT_CA_DIR
+
+
+# --------------------------------------------------------- TLS context
+
+
+def build_listener_ssl_context(ca_dir: pathlib.Path) -> ssl.SSLContext:
+    """Server-side mTLS context: master presents its master cert; clients
+    must present a cert signed by the DECNET CA."""
+    master_dir = ca_dir / "master"
+    ca_cert = master_dir / "ca.crt"
+    cert = master_dir / "worker.crt"   # master re-uses the 'worker' bundle layout
+    key = master_dir / "worker.key"
+    for p in (ca_cert, cert, key):
+        if not p.exists():
+            raise RuntimeError(
+                f"master identity missing at {master_dir} — call ensure_master_identity first"
+            )
+    ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
+    ctx.load_cert_chain(certfile=str(cert), keyfile=str(key))
+    ctx.load_verify_locations(cafile=str(ca_cert))
+    ctx.verify_mode = ssl.CERT_REQUIRED
+    return ctx
+
+
+# ---------------------------------------------------------- helpers
+
+
+def peer_cn(ssl_object: Optional[ssl.SSLObject]) -> str:
+    """Extract the CN from the TLS peer certificate (worker provenance).
+
+    Falls back to ``"unknown"`` on any parse error — we refuse to crash on
+    malformed cert DNs and instead tag the message for later inspection.
+    """
+    if ssl_object is None:
+        return "unknown"
+    der = ssl_object.getpeercert(binary_form=True)
+    if der is None:
+        return "unknown"
+    try:
+        cert = x509.load_der_x509_certificate(der)
+        attrs = cert.subject.get_attributes_for_oid(NameOID.COMMON_NAME)
+        return attrs[0].value if attrs else "unknown"
+    except Exception:  # nosec B110 — provenance is best-effort
+        return "unknown"
+
+
+def fingerprint_from_ssl(ssl_object: Optional[ssl.SSLObject]) -> Optional[str]:
+    if ssl_object is None:
+        return None
+    der = ssl_object.getpeercert(binary_form=True)
+    if der is None:
+        return None
+    try:
+        cert = x509.load_der_x509_certificate(der)
+        return pki.fingerprint(cert.public_bytes(serialization.Encoding.PEM))
+    except Exception:
+        return None
+
+
+# --------------------------------------------------- per-connection handler
+
+
+async def _handle_connection(
+    reader: asyncio.StreamReader,
+    writer: asyncio.StreamWriter,
+    cfg: ListenerConfig,
+) -> None:
+    ssl_obj = writer.get_extra_info("ssl_object")
+    cn = peer_cn(ssl_obj)
+    peer = writer.get_extra_info("peername")
+    log.info("listener accepted worker=%s peer=%s", cn, peer)
+
+    # Lazy import to avoid a circular dep if the collector pulls in logger setup.
+    from decnet.collector.worker import parse_rfc5424
+
+    cfg.log_path.parent.mkdir(parents=True, exist_ok=True)
+    cfg.json_path.parent.mkdir(parents=True, exist_ok=True)
+
+    try:
+        with open(cfg.log_path, "a", encoding="utf-8") as lf, open(
+            cfg.json_path, "a", encoding="utf-8"
+        ) as jf:
+            while True:
+                try:
+                    frame = await read_frame(reader)
+                except asyncio.IncompleteReadError:
+                    break
+                except ValueError as exc:
+                    log.warning("listener bad frame worker=%s err=%s", cn, exc)
+                    break
+                if frame is None:
+                    break
+                if not frame:
+                    continue
+                line = frame.decode("utf-8", errors="replace")
+                lf.write(line + "\n")
+                lf.flush()
+                parsed = parse_rfc5424(line)
+                if parsed is not None:
+                    parsed["source_worker"] = cn
+                    jf.write(json.dumps(parsed) + "\n")
+                    jf.flush()
+                else:
+                    log.debug("listener malformed RFC5424 worker=%s snippet=%r", cn, line[:80])
+    except Exception as exc:
+        log.warning("listener connection error worker=%s err=%s", cn, exc)
+    finally:
+        writer.close()
+        try:
+            await writer.wait_closed()
+        except Exception:  # nosec B110 — socket cleanup is best-effort
+            pass
+        log.info("listener closed worker=%s", cn)
+
+
+# ---------------------------------------------------------------- server
+
+
+async def run_listener(
+    cfg: ListenerConfig,
+    *,
+    stop_event: Optional[asyncio.Event] = None,
+) -> None:
+    ctx = build_listener_ssl_context(cfg.ca_dir)
+
+    async def _client_cb(
+        reader: asyncio.StreamReader, writer: asyncio.StreamWriter
+    ) -> None:
+        await _handle_connection(reader, writer, cfg)
+
+    server = await asyncio.start_server(
+        _client_cb, host=cfg.bind_host, port=cfg.bind_port, ssl=ctx
+    )
+    sockets = server.sockets or ()
+    log.info(
+        "listener bound host=%s port=%d sockets=%d",
+        cfg.bind_host, cfg.bind_port, len(sockets),
+    )
+    async with server:
+        if stop_event is None:
+            await server.serve_forever()
+        else:
+            serve_task = asyncio.create_task(server.serve_forever())
+            await stop_event.wait()
+            server.close()
+            serve_task.cancel()
+            try:
+                await serve_task
+            except (asyncio.CancelledError, Exception):  # nosec B110
+                pass
--- a/tests/swarm/test_log_forwarder.py
+++ b/tests/swarm/test_log_forwarder.py
@@ -0,0 +1,282 @@
+"""Tests for the syslog-over-TLS pipeline.
+
+Covers:
+* octet-counted framing encode/decode (pure functions);
+* offset persistence across reopens;
+* end-to-end mTLS roundtrip forwarder → listener;
+* impostor-CA worker is rejected at TLS handshake.
+"""
+from __future__ import annotations
+
+import asyncio
+import pathlib
+import socket
+
+import pytest
+import ssl
+
+from decnet.swarm import log_forwarder as fwd
+from decnet.swarm import log_listener as lst
+from decnet.swarm import pki
+from decnet.swarm.client import ensure_master_identity
+
+
+def _free_port() -> int:
+    s = socket.socket()
+    s.bind(("127.0.0.1", 0))
+    port = s.getsockname()[1]
+    s.close()
+    return port
+
+
+# ------------------------------------------------------------ pure framing
+
+
+def test_encode_frame_matches_rfc5425_shape() -> None:
+    out = fwd.encode_frame("<13>1 2026-04-18T00:00:00Z decky01 svc - - - hi")
+    # "<len> <msg>" — ASCII digits, space, then the UTF-8 payload.
+    assert out.startswith(b"47 ")
+    assert out.endswith(b"hi")
+    assert int(out.split(b" ", 1)[0]) == len(out.split(b" ", 1)[1])
+
+
+@pytest.mark.asyncio
+async def test_read_frame_roundtrip() -> None:
+    payload = b"<13>1 2026-04-18T00:00:00Z host app - - - msg"
+    frame = fwd.encode_frame(payload.decode())
+    reader = asyncio.StreamReader()
+    reader.feed_data(frame)
+    reader.feed_eof()
+    got = await fwd.read_frame(reader)
+    assert got == payload
+
+
+@pytest.mark.asyncio
+async def test_read_frame_rejects_bad_prefix() -> None:
+    reader = asyncio.StreamReader()
+    reader.feed_data(b"NOTANUMBER msg")
+    reader.feed_eof()
+    with pytest.raises(ValueError):
+        await fwd.read_frame(reader)
+
+
+# ------------------------------------------------------------- offset store
+
+
+def test_offset_store_persists_across_reopen(tmp_path: pathlib.Path) -> None:
+    db = tmp_path / "fwd.db"
+    s1 = fwd._OffsetStore(db)
+    assert s1.get() == 0
+    s1.set(4242)
+    s1.close()
+
+    s2 = fwd._OffsetStore(db)
+    assert s2.get() == 4242
+    s2.close()
+
+
+# ------------------------------------------------------------ TLS roundtrip
+
+
+@pytest.fixture
+def _pki_env(tmp_path: pathlib.Path, monkeypatch: pytest.MonkeyPatch):
+    ca_dir = tmp_path / "ca"
+    pki.ensure_ca(ca_dir)
+    # Master identity (also used as listener server cert).
+    master_id = ensure_master_identity(ca_dir)
+    # Give master's cert a 127.0.0.1 SAN so workers can resolve it if they
+    # happen to enable check_hostname; we don't, but future-proof anyway.
+    # (The default ensure_master_identity() cert already has 127.0.0.1.)
+    _ = master_id
+
+    # Worker bundle — enrolled with 127.0.0.1 SAN.
+    worker_dir = tmp_path / "agent"
+    issued = pki.issue_worker_cert(pki.load_ca(ca_dir), "worker-x", ["127.0.0.1"])
+    pki.write_worker_bundle(issued, worker_dir)
+
+    monkeypatch.setattr(pki, "DEFAULT_CA_DIR", ca_dir)
+    monkeypatch.setattr(pki, "DEFAULT_AGENT_DIR", worker_dir)
+    return {"ca_dir": ca_dir, "worker_dir": worker_dir}
+
+
+@pytest.mark.asyncio
+async def test_forwarder_to_listener_roundtrip(
+    tmp_path: pathlib.Path, _pki_env: dict
+) -> None:
+    port = _free_port()
+    worker_log = tmp_path / "decnet.log"
+    worker_log.write_text("")  # create empty
+
+    master_log = tmp_path / "master.log"
+    master_json = tmp_path / "master.json"
+
+    listener_cfg = lst.ListenerConfig(
+        log_path=master_log,
+        json_path=master_json,
+        bind_host="127.0.0.1",
+        bind_port=port,
+        ca_dir=_pki_env["ca_dir"],
+    )
+    fwd_cfg = fwd.ForwarderConfig(
+        log_path=worker_log,
+        master_host="127.0.0.1",
+        master_port=port,
+        agent_dir=_pki_env["worker_dir"],
+        state_db=tmp_path / "fwd.db",
+    )
+    stop = asyncio.Event()
+
+    listener_task = asyncio.create_task(lst.run_listener(listener_cfg, stop_event=stop))
+    await asyncio.sleep(0.2)  # wait for bind
+
+    forwarder_task = asyncio.create_task(
+        fwd.run_forwarder(fwd_cfg, poll_interval=0.05, stop_event=stop)
+    )
+
+    # Write a few RFC 5424-ish lines into the worker log.
+    sample = (
+        '<13>1 2026-04-18T00:00:00Z decky01 ssh-service 1 - '
+        '[decnet@53595 decky="decky01" service="ssh-service" event_type="connect" '
+        'attacker_ip="1.2.3.4" attacker_port="4242"] ssh connect\n'
+    )
+    with open(worker_log, "a", encoding="utf-8") as f:
+        for _ in range(3):
+            f.write(sample)
+
+    # Poll for delivery on the master side.
+    for _ in range(50):
+        if master_log.exists() and master_log.stat().st_size > 0:
+            break
+        await asyncio.sleep(0.1)
+
+    stop.set()
+    for t in (forwarder_task, listener_task):
+        try:
+            await asyncio.wait_for(t, timeout=5)
+        except asyncio.TimeoutError:
+            t.cancel()
+
+    assert master_log.exists()
+    body = master_log.read_text()
+    assert body.count("ssh connect") == 3
+    # Worker provenance tagged in the JSON sink.
+    assert master_json.exists()
+    assert "worker-x" in master_json.read_text()
+
+
+@pytest.mark.asyncio
+async def test_forwarder_resumes_from_persisted_offset(
+    tmp_path: pathlib.Path, _pki_env: dict
+) -> None:
+    """Simulate a listener outage: forwarder persists offset locally and,
+    after the listener comes back, only ships lines added AFTER the crash."""
+    port = _free_port()
+    worker_log = tmp_path / "decnet.log"
+    master_log = tmp_path / "master.log"
+    master_json = tmp_path / "master.json"
+    state_db = tmp_path / "fwd.db"
+
+    # Pre-populate 2 lines and the offset store as if a previous forwarder run
+    # had already delivered them.  The new run must NOT re-ship them.
+    line = (
+        '<13>1 2026-04-18T00:00:00Z decky01 svc 1 - [x] old\n'
+    )
+    worker_log.write_text(line * 2)
+    seed = fwd._OffsetStore(state_db)
+    seed.set(len(line) * 2)
+    seed.close()
+
+    listener_cfg = lst.ListenerConfig(
+        log_path=master_log, json_path=master_json,
+        bind_host="127.0.0.1", bind_port=port, ca_dir=_pki_env["ca_dir"],
+    )
+    fwd_cfg = fwd.ForwarderConfig(
+        log_path=worker_log, master_host="127.0.0.1", master_port=port,
+        agent_dir=_pki_env["worker_dir"], state_db=state_db,
+    )
+    stop = asyncio.Event()
+    lt = asyncio.create_task(lst.run_listener(listener_cfg, stop_event=stop))
+    await asyncio.sleep(0.2)
+    ft = asyncio.create_task(fwd.run_forwarder(fwd_cfg, poll_interval=0.05, stop_event=stop))
+
+    # Append a NEW line after startup — only this should reach the master.
+    new_line = (
+        '<13>1 2026-04-18T00:00:01Z decky01 svc 1 - [x] fresh\n'
+    )
+    with open(worker_log, "a", encoding="utf-8") as f:
+        f.write(new_line)
+
+    for _ in range(50):
+        if master_log.exists() and b"fresh" in master_log.read_bytes():
+            break
+        await asyncio.sleep(0.1)
+
+    stop.set()
+    for t in (ft, lt):
+        try:
+            await asyncio.wait_for(t, timeout=5)
+        except asyncio.TimeoutError:
+            t.cancel()
+
+    body = master_log.read_text()
+    assert "fresh" in body
+    assert "old" not in body, "forwarder re-shipped lines already acked before restart"
+
+
+@pytest.mark.asyncio
+async def test_impostor_worker_rejected_at_tls(
+    tmp_path: pathlib.Path, _pki_env: dict
+) -> None:
+    port = _free_port()
+    master_log = tmp_path / "master.log"
+    master_json = tmp_path / "master.json"
+    listener_cfg = lst.ListenerConfig(
+        log_path=master_log,
+        json_path=master_json,
+        bind_host="127.0.0.1",
+        bind_port=port,
+        ca_dir=_pki_env["ca_dir"],
+    )
+    stop = asyncio.Event()
+    listener_task = asyncio.create_task(lst.run_listener(listener_cfg, stop_event=stop))
+    await asyncio.sleep(0.2)
+
+    try:
+        # Build a forwarder SSL context from a DIFFERENT CA — should be rejected.
+        evil_ca = pki.generate_ca("Evil CA")
+        evil_dir = tmp_path / "evil"
+        pki.write_worker_bundle(
+            pki.issue_worker_cert(evil_ca, "evil-worker", ["127.0.0.1"]), evil_dir
+        )
+
+        ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+        ctx.load_cert_chain(str(evil_dir / "worker.crt"), str(evil_dir / "worker.key"))
+        ctx.load_verify_locations(cafile=str(evil_dir / "ca.crt"))
+        ctx.verify_mode = ssl.CERT_REQUIRED
+        ctx.check_hostname = False
+
+        rejected = False
+        try:
+            r, w = await asyncio.open_connection("127.0.0.1", port, ssl=ctx)
+            # If TLS somehow succeeded, push a byte and expect the server to drop.
+            w.write(b"5 hello")
+            await w.drain()
+            # If the server accepted this from an unknown CA, that's a failure.
+            await asyncio.sleep(0.2)
+            w.close()
+            try:
+                await w.wait_closed()
+            except Exception:
+                pass
+        except (ssl.SSLError, OSError, ConnectionError):
+            rejected = True
+
+        assert rejected or master_log.stat().st_size == 0, (
+            "impostor connection must be rejected or produce no log lines"
+        )
+    finally:
+        stop.set()
+        try:
+            await asyncio.wait_for(listener_task, timeout=5)
+        except asyncio.TimeoutError:
+            listener_task.cancel()