feat(skills): watchers skill — poll RSS / HTTP JSON / GitHub via cron no-agent (#21881)

* feat(skills): watchers skill — poll RSS / HTTP JSON / GitHub via cron no-agent Ships three reusable polling scripts plus a shared watermark helper as an optional skill. Users wire them into the existing cron (no_agent=True) mode rather than learning a new subsystem. Supersedes the closed PR #21497 (parallel watcher subsystem). Same value, zero new core surface. ## What ships - optional-skills/devops/watchers/SKILL.md: pattern + three example cron commands - optional-skills/devops/watchers/scripts/_watermark.py: shared helper (atomic state writes, bounded ID set, first-run baseline) - optional-skills/devops/watchers/scripts/watch_rss.py: RSS 2.0 + Atom - optional-skills/devops/watchers/scripts/watch_http_json.py: any JSON endpoint with configurable id_field / items_path / headers - optional-skills/devops/watchers/scripts/watch_github.py: issues / pulls / releases / commits (uses GITHUB_TOKEN if present) ## Invariants enforced by the shared helper - First run records baseline, emits nothing (never replays existing feed) - Watermark file is <state_dir>/<name>.json, atomic replace on write - Bounded to 500 IDs (configurable) - Empty stdout when no new items — cron treats that as silent delivery ## Validation - watch_rss.py against news.ycombinator.com/rss first run → empty stdout, watermark populated - Removed one seen-id, second run → emitted exactly that item - No DeprecationWarnings (ET element truth-value footgun dodged explicitly) End-user pattern: 'hermes cron create my-feed --schedule "*/15 * * * *" --no-agent --script $HERMES_HOME/skills/devops/watchers/scripts/watch_rss.py --script-args "--name hn --url https://news.ycombinator.com/rss" --deliver telegram' * docs(skills/watchers): tighten description to match peer optional skills * docs(skills/watchers): align frontmatter + structure with peer optional skills * docs(skills/watchers): gate to linux/macos (shell syntax in examples)
2026-05-09 03:11:58 +00:00 · 2026-05-08 09:27:15 -07:00 · 2026-05-08 09:27:15 -07:00 · ea8e608821
commit ea8e608821
parent 839cdd1b05
5 changed files with 680 additions and 0 deletions
--- a/optional-skills/devops/watchers/SKILL.md
+++ b/optional-skills/devops/watchers/SKILL.md
@ -0,0 +1,112 @@
+---
+name: watchers
+description: Poll RSS, JSON APIs, and GitHub with watermark dedup.
+version: 1.0.0
+author: Hermes Agent
+license: MIT
+platforms: [linux, macos]
+metadata:
+  hermes:
+    tags: [cron, polling, rss, github, http, automation, monitoring]
+    category: devops
+    requires_toolsets: [terminal]
+    related_skills: []
+---
+
+# Watchers
+
+Poll external sources on an interval and react only to new items. Three ready-made scripts plus a shared watermark helper; wire them into a cron job (or run them ad-hoc from the terminal).
+
+## When to Use
+
+- User wants to watch an RSS/Atom feed and be notified of new entries
+- User wants to watch a GitHub repo's issues / pulls / releases / commits
+- User wants to poll an arbitrary JSON endpoint and get notified on new items
+- User asks for "a watcher for X" or "notify me when X changes"
+
+## Mental model
+
+A watcher is just a script that:
+
+1. Fetches data from the external source
+2. Compares against a watermark file of previously-seen IDs
+3. Writes the new watermark back
+4. Prints new items to stdout (or nothing on no-change)
+
+The scripts below handle all three. The agent runs them via the terminal tool — from a cron job, a webhook, or an interactive chat — and reports what's new.
+
+## Ready-made scripts
+
+All three live in `$HERMES_HOME/skills/devops/watchers/scripts/` once the skill is installed. Each reads `WATCHER_STATE_DIR` (defaults to `$HERMES_HOME/watcher-state/`) for its state file, keyed by the `--name` argument.
+
+| Script | What it watches | Dedup key |
+|---|---|---|
+| `watch_rss.py` | RSS 2.0 or Atom feed URL | `<guid>` / `<id>` |
+| `watch_http_json.py` | Any JSON endpoint returning a list of objects | Configurable id field |
+| `watch_github.py` | GitHub issues / pulls / releases / commits for a repo | `id` / `sha` |
+
+All three:
+
+- First run records a baseline — never replays existing feed
+- Watermark is a bounded ID set (max 500) to cap memory
+- Output format: `## <title>\n<url>\n\n<optional body>` per item
+- Empty stdout on no-new — the caller treats that as silent
+- Non-zero exit on fetch errors
+
+## Usage
+
+Run a watcher directly from the terminal tool:
+
+```bash
+python $HERMES_HOME/skills/devops/watchers/scripts/watch_rss.py \
+  --name hn --url https://news.ycombinator.com/rss --max 5
+```
+
+Watch a GitHub repo (set `GITHUB_TOKEN` in `~/.hermes/.env` to avoid the 60 req/hr anonymous rate limit):
+
+```bash
+python $HERMES_HOME/skills/devops/watchers/scripts/watch_github.py \
+  --name hermes-issues --repo NousResearch/hermes-agent --scope issues
+```
+
+Poll an arbitrary JSON API:
+
+```bash
+python $HERMES_HOME/skills/devops/watchers/scripts/watch_http_json.py \
+  --name api --url https://api.example.com/events \
+  --id-field event_id --items-path data.events
+```
+
+## Wiring into cron
+
+Ask the agent to schedule a cron job with a prompt like:
+
+> Every 15 minutes, run `watch_rss.py --name hn --url https://news.ycombinator.com/rss`. If it prints anything, summarize the headlines and deliver them. If it prints nothing, stay silent.
+
+The agent invokes the script via the terminal tool inside the cron job's agent loop; no changes to cron's built-in `--script` flag are needed.
+
+## State files
+
+Every watcher writes `$HERMES_HOME/watcher-state/<name>.json`. Inspect:
+
+```bash
+cat $HERMES_HOME/watcher-state/hn.json
+```
+
+Force a replay (next run treated as first poll):
+
+```bash
+rm $HERMES_HOME/watcher-state/hn.json
+```
+
+## Writing your own
+
+All three scripts use the same template: load watermark, fetch, diff, save, emit. `scripts/_watermark.py` is the shared helper; import it to get atomic writes + bounded ID set + first-run baseline for free. See any of the three reference scripts for how little boilerplate it takes.
+
+## Common Pitfalls
+
+1. **Printing a "no new items" header every tick.** Callers rely on empty stdout = silent. If you print anything on an empty delta, you spam the channel. The shipped scripts handle this; custom scripts must too.
+2. **Expecting the first run to emit items.** It won't — first run records a baseline. If you need an initial digest, delete the state file after the first run or add a `--prime-with-latest N` flag in your own script.
+3. **Unbounded watermark growth.** The shared helper caps at 500 IDs. Raise it for high-churn feeds; lower it on constrained filesystems.
+4. **Putting the state dir where the agent's sandbox can't write.** `$HERMES_HOME/watcher-state/` is always writable. Docker/Modal backends may not see arbitrary host paths.
+
--- a/optional-skills/devops/watchers/scripts/_watermark.py
+++ b/optional-skills/devops/watchers/scripts/_watermark.py
@ -0,0 +1,148 @@
+"""Shared watermark helper used by the three watcher scripts.
+
+A watermark is just a JSON file that records the IDs we've seen on previous
+runs, so the next run only emits items we haven't seen before.
+
+Contract:
+- First run: record all IDs from the fetched batch, emit nothing.
+- Subsequent runs: emit items whose ID isn't in the stored set.
+- Bounded: keep at most `max_seen` IDs (default 500).
+- Atomic: write to a .tmp file and rename, so a crashed script can't
+  leave a half-written state file that permanently breaks dedup.
+
+Import and use from any custom watcher script:
+
+    from _watermark import Watermark
+
+    wm = Watermark.load("my-feed-name")
+    new_items = wm.filter_new(fetched_items, id_key="id")
+    wm.save()
+"""
+
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+from typing import Any, Dict, Iterable, List, Optional
+
+
+def _state_dir() -> Path:
+    """Where watermark files live — respects WATCHER_STATE_DIR override."""
+    override = os.environ.get("WATCHER_STATE_DIR")
+    if override:
+        return Path(override)
+    # Default: $HERMES_HOME/watcher-state/, falling back to ~/.hermes/watcher-state/.
+    hermes_home = os.environ.get("HERMES_HOME") or str(Path.home() / ".hermes")
+    return Path(hermes_home) / "watcher-state"
+
+
+class Watermark:
+    """Per-watcher state. Persisted to <state_dir>/<name>.json."""
+
+    def __init__(self, name: str, *, max_seen: int = 500) -> None:
+        if not name or not name.replace("-", "").replace("_", "").isalnum():
+            raise ValueError(
+                f"watermark name must be alphanumeric + '-'/'_' (got {name!r})"
+            )
+        self.name = name
+        self.max_seen = max_seen
+        self._path = _state_dir() / f"{name}.json"
+        self._data: Dict[str, Any] = {"seen_ids": [], "first_run": True}
+
+    @classmethod
+    def load(cls, name: str, *, max_seen: int = 500) -> "Watermark":
+        wm = cls(name, max_seen=max_seen)
+        if wm._path.exists():
+            try:
+                wm._data = json.loads(wm._path.read_text(encoding="utf-8"))
+                wm._data.setdefault("seen_ids", [])
+                wm._data["first_run"] = False
+            except (OSError, json.JSONDecodeError):
+                # Corrupt state file — treat as a first run but don't crash.
+                wm._data = {"seen_ids": [], "first_run": True}
+        return wm
+
+    @property
+    def is_first_run(self) -> bool:
+        return bool(self._data.get("first_run", True))
+
+    @property
+    def seen(self) -> List[str]:
+        return list(self._data.get("seen_ids", []))
+
+    def filter_new(
+        self, items: Iterable[Dict[str, Any]], *, id_key: str = "id"
+    ) -> List[Dict[str, Any]]:
+        """Return items whose id isn't in the stored set.
+
+        Side effect: updates the in-memory seen set with every id in the
+        batch (so save() persists the full new watermark).  On first run,
+        records every id but returns an empty list (baseline, no replay).
+        """
+        existing = set(str(x) for x in self._data.get("seen_ids", []))
+        was_first_run = self.is_first_run
+
+        new_items: List[Dict[str, Any]] = []
+        batch_ids: List[str] = []
+        for item in items:
+            ident = item.get(id_key)
+            if ident is None:
+                continue
+            ident_str = str(ident)
+            batch_ids.append(ident_str)
+            if ident_str in existing:
+                continue
+            if was_first_run:
+                continue  # record but don't emit
+            new_items.append(item)
+
+        combined = list(existing) + [i for i in batch_ids if i not in existing]
+        if len(combined) > self.max_seen:
+            combined = combined[-self.max_seen:]
+        self._data["seen_ids"] = combined
+        self._data["first_run"] = False
+        return new_items
+
+    def save(self) -> None:
+        self._path.parent.mkdir(parents=True, exist_ok=True)
+        tmp = self._path.with_suffix(".tmp")
+        tmp.write_text(
+            json.dumps(self._data, indent=2, sort_keys=True),
+            encoding="utf-8",
+        )
+        os.replace(tmp, self._path)
+
+
+def format_items_as_markdown(
+    items: List[Dict[str, Any]],
+    *,
+    title_key: str = "title",
+    url_key: str = "url",
+    body_key: Optional[str] = None,
+    max_body_chars: int = 500,
+) -> str:
+    """Render a list of items as Markdown for cron delivery.
+
+    One heading per item + its URL + optional snippet of body.  Output is
+    empty string when items is empty — cron will then treat stdout as
+    silent and skip delivery (existing behavior).
+    """
+    if not items:
+        return ""
+    lines: List[str] = []
+    for item in items:
+        title = (item.get(title_key) or "(no title)").strip()
+        url = (item.get(url_key) or "").strip()
+        lines.append(f"## {title}")
+        if url:
+            lines.append(url)
+        if body_key:
+            body = (item.get(body_key) or "").strip()
+            if body:
+                if len(body) > max_body_chars:
+                    body = body[:max_body_chars].rstrip() + "…"
+                lines.append("")
+                lines.append(body)
+        lines.append("")
+    return "\n".join(lines).rstrip() + "\n"
--- a/optional-skills/devops/watchers/scripts/watch_github.py
+++ b/optional-skills/devops/watchers/scripts/watch_github.py
@ -0,0 +1,168 @@
+#!/usr/bin/env python3
+"""Watch GitHub activity — issues, pulls, releases, or commits — with dedup.
+
+Usage (via cron with --no-agent):
+
+    hermes cron create hermes-issues \\
+      --schedule "*/5 * * * *" --no-agent \\
+      --script "$HERMES_HOME/skills/devops/watchers/scripts/watch_github.py" \\
+      --script-args "--name hermes-issues --repo NousResearch/hermes-agent --scope issues"
+
+Set GITHUB_TOKEN (or GH_TOKEN) in ~/.hermes/.env to avoid the 60 req/hr
+anonymous rate limit.
+
+Scopes: issues | pulls | releases | commits.  Or pass --search QUERY to
+use the /search/issues endpoint instead of /repos/:owner/:repo/:scope.
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import re
+import sys
+import urllib.error
+import urllib.parse
+import urllib.request
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+from _watermark import Watermark, format_items_as_markdown  # type: ignore
+
+
+VALID_SCOPES = ("issues", "pulls", "releases", "commits")
+
+
+def _flatten_commit(item):
+    """Commit objects nest title/author/date under 'commit' — flatten for rendering."""
+    commit = item.get("commit") or {}
+    msg = (commit.get("message") or "").strip().splitlines()
+    title = msg[0] if msg else ""
+    body = "\n".join(msg[1:]).strip() if len(msg) > 1 else ""
+    author = (item.get("author") or {}).get("login") or (commit.get("author") or {}).get("name", "")
+    date = (commit.get("author") or {}).get("date", "")
+    return {
+        "id": item.get("sha", ""),
+        "title": f"{title}  ({author})" if author else title,
+        "url": item.get("html_url"),
+        "body": body,
+        "created_at": date,
+    }
+
+
+def _flatten_issue_or_release(item):
+    return {
+        "id": str(item.get("id", "")),
+        "title": item.get("title") or item.get("name") or "",
+        "url": item.get("html_url") or item.get("url"),
+        "body": (item.get("body") or "").strip(),
+        "state": item.get("state"),
+        "author": (item.get("user") or {}).get("login")
+        or (item.get("author") or {}).get("login"),
+        "created_at": item.get("created_at"),
+    }
+
+
+def main() -> int:
+    p = argparse.ArgumentParser(description="Watch GitHub issues / pulls / releases / commits.")
+    p.add_argument("--name", required=True, help="Watcher name (used for state file)")
+    p.add_argument("--repo", default="",
+                   help="owner/name of the repo (one of --repo or --search is required)")
+    p.add_argument("--scope", default="issues", choices=VALID_SCOPES,
+                   help="What to poll (default: issues)")
+    p.add_argument("--search", default="",
+                   help="GitHub issues search query (alternative to --repo/--scope)")
+    p.add_argument("--per-page", type=int, default=30,
+                   help="Results per page (default: 30, max: 100)")
+    p.add_argument("--max", type=int, default=20,
+                   help="Max new items to emit per tick (default: 20)")
+    p.add_argument("--with-body", action="store_true",
+                   help="Include issue/commit body as a snippet under each item")
+    p.add_argument("--timeout", type=float, default=30.0,
+                   help="HTTP timeout in seconds (default: 30)")
+    args = p.parse_args()
+
+    if not args.repo and not args.search:
+        print("watch_github: one of --repo or --search is required", file=sys.stderr)
+        return 2
+    if args.repo and not re.fullmatch(r"[A-Za-z0-9._-]+/[A-Za-z0-9._-]+", args.repo):
+        print(f"watch_github: --repo must be owner/name (got {args.repo!r})", file=sys.stderr)
+        return 2
+
+    # URL + flattening strategy.
+    if args.search:
+        url = (
+            "https://api.github.com/search/issues"
+            f"?q={urllib.parse.quote(args.search)}&per_page={args.per_page}"
+        )
+        flatten = _flatten_issue_or_release
+        items_path = "items"
+    elif args.scope == "commits":
+        url = f"https://api.github.com/repos/{args.repo}/commits?per_page={args.per_page}"
+        flatten = _flatten_commit
+        items_path = ""
+    else:
+        url = (
+            f"https://api.github.com/repos/{args.repo}/{args.scope}"
+            f"?per_page={args.per_page}&state=all"
+        )
+        flatten = _flatten_issue_or_release
+        items_path = ""
+
+    headers = {
+        "Accept": "application/vnd.github+json",
+        "User-Agent": "Hermes-Watcher/1.0",
+    }
+    token = os.environ.get("GITHUB_TOKEN") or os.environ.get("GH_TOKEN")
+    if token:
+        headers["Authorization"] = f"Bearer {token}"
+
+    req = urllib.request.Request(url)
+    for k, v in headers.items():
+        req.add_header(k, v)
+
+    try:
+        with urllib.request.urlopen(req, timeout=args.timeout) as resp:
+            raw = resp.read()
+    except urllib.error.HTTPError as e:
+        print(f"watch_github: HTTP {e.code} from {url}", file=sys.stderr)
+        return 2
+    except (urllib.error.URLError, TimeoutError, OSError) as e:
+        print(f"watch_github: network error: {e}", file=sys.stderr)
+        return 2
+
+    try:
+        data = json.loads(raw.decode("utf-8"))
+    except (UnicodeDecodeError, json.JSONDecodeError) as e:
+        print(f"watch_github: response is not valid JSON: {e}", file=sys.stderr)
+        return 2
+
+    # Drill into items_path if needed (search endpoint returns {"items":[...]}).
+    if items_path:
+        data = data.get(items_path) if isinstance(data, dict) else None
+    if not isinstance(data, list):
+        print(f"watch_github: expected a list of items; got {type(data).__name__}",
+              file=sys.stderr)
+        return 2
+
+    items = [flatten(i) for i in data if isinstance(i, dict)]
+    # Drop any items that flattened without an ID (defensive).
+    items = [i for i in items if i.get("id")]
+
+    wm = Watermark.load(args.name)
+    new_items = wm.filter_new(items, id_key="id")
+    wm.save()
+
+    if args.max > 0:
+        new_items = new_items[: args.max]
+
+    body_key = "body" if args.with_body else None
+    output = format_items_as_markdown(new_items, body_key=body_key)
+    if output:
+        sys.stdout.write(output)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
--- a/optional-skills/devops/watchers/scripts/watch_http_json.py
+++ b/optional-skills/devops/watchers/scripts/watch_http_json.py
@ -0,0 +1,131 @@
+#!/usr/bin/env python3
+"""Watch any JSON endpoint that returns a list of objects; dedup by ID field.
+
+Usage (via cron with --no-agent):
+
+    hermes cron create api-events \\
+      --schedule "*/1 * * * *" --no-agent \\
+      --script "$HERMES_HOME/skills/devops/watchers/scripts/watch_http_json.py" \\
+      --script-args "--name api --url https://api.example.com/events \\
+                     --id-field event_id --items-path data.events"
+
+The response can be:
+  - a top-level JSON list (default), or
+  - a JSON object with a dotted ``--items-path`` pointing to the list.
+
+Each item is deduped by ``--id-field`` (default "id").
+
+Optional ``--header KEY:VALUE`` flags pass HTTP headers (repeatable).
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import sys
+import urllib.error
+import urllib.request
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+from _watermark import Watermark, format_items_as_markdown  # type: ignore
+
+
+def _dig(obj, path: str):
+    """Dotted-path lookup: _dig({'a':{'b':[1,2]}}, 'a.b') → [1,2]."""
+    if not path:
+        return obj
+    cur = obj
+    for part in path.split("."):
+        if isinstance(cur, dict) and part in cur:
+            cur = cur[part]
+        else:
+            return None
+    return cur
+
+
+def _parse_header(s: str):
+    if ":" not in s:
+        raise argparse.ArgumentTypeError(
+            f"--header expects 'KEY: VALUE' (got {s!r})"
+        )
+    k, v = s.split(":", 1)
+    return (k.strip(), v.strip())
+
+
+def main() -> int:
+    p = argparse.ArgumentParser(description="Poll a JSON endpoint.")
+    p.add_argument("--name", required=True, help="Watcher name (used for state file)")
+    p.add_argument("--url", required=True, help="JSON endpoint URL")
+    p.add_argument("--id-field", default="id",
+                   help="Field used to dedup items (default: 'id')")
+    p.add_argument("--items-path", default="",
+                   help="Dotted path to the list inside the JSON response (e.g. 'data.events')")
+    p.add_argument("--title-field", default="title",
+                   help="Field used as the item title in the rendered output (default: 'title')")
+    p.add_argument("--url-field", default="url",
+                   help="Field used as the item URL in the rendered output (default: 'url')")
+    p.add_argument("--body-field", default="",
+                   help="Optional body field to include as a snippet under each item")
+    p.add_argument("--max", type=int, default=20,
+                   help="Max new items to emit per tick (default: 20)")
+    p.add_argument("--header", action="append", type=_parse_header, default=[],
+                   metavar="KEY: VALUE",
+                   help="HTTP header (repeatable)")
+    p.add_argument("--timeout", type=float, default=20.0,
+                   help="HTTP timeout in seconds (default: 20)")
+    args = p.parse_args()
+
+    req = urllib.request.Request(args.url, headers={"User-Agent": "Hermes-Watcher/1.0"})
+    for k, v in args.header:
+        req.add_header(k, v)
+
+    try:
+        with urllib.request.urlopen(req, timeout=args.timeout) as resp:
+            raw = resp.read()
+    except urllib.error.HTTPError as e:
+        print(f"watch_http_json: HTTP {e.code} from {args.url}", file=sys.stderr)
+        return 2
+    except (urllib.error.URLError, TimeoutError, OSError) as e:
+        print(f"watch_http_json: network error: {e}", file=sys.stderr)
+        return 2
+
+    try:
+        data = json.loads(raw.decode("utf-8"))
+    except (UnicodeDecodeError, json.JSONDecodeError) as e:
+        print(f"watch_http_json: response is not valid JSON: {e}", file=sys.stderr)
+        return 2
+
+    items = _dig(data, args.items_path) if args.items_path else data
+    if not isinstance(items, list):
+        print(
+            f"watch_http_json: items_path={args.items_path!r} did not resolve to a list "
+            f"(got {type(items).__name__})",
+            file=sys.stderr,
+        )
+        return 2
+
+    # Keep only dicts — skip any bare strings / numbers so filter_new doesn't crash.
+    items = [i for i in items if isinstance(i, dict)]
+
+    wm = Watermark.load(args.name)
+    new_items = wm.filter_new(items, id_key=args.id_field)
+    wm.save()
+
+    if args.max > 0:
+        new_items = new_items[: args.max]
+
+    body_key = args.body_field or None
+    output = format_items_as_markdown(
+        new_items,
+        title_key=args.title_field,
+        url_key=args.url_field,
+        body_key=body_key,
+    )
+    if output:
+        sys.stdout.write(output)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
--- a/optional-skills/devops/watchers/scripts/watch_rss.py
+++ b/optional-skills/devops/watchers/scripts/watch_rss.py
@ -0,0 +1,121 @@
+#!/usr/bin/env python3
+"""Watch an RSS 2.0 or Atom feed; print new items to stdout, silent on empty.
+
+Usage (via cron with --no-agent):
+
+    hermes cron create my-feed \\
+      --schedule "*/15 * * * *" --no-agent \\
+      --script "$HERMES_HOME/skills/devops/watchers/scripts/watch_rss.py" \\
+      --script-args "--name hn --url https://news.ycombinator.com/rss"
+
+First run records a baseline (emits nothing).  Subsequent runs emit only
+items whose <guid> / <id> isn't in the watermark.
+"""
+
+from __future__ import annotations
+
+import argparse
+import sys
+import urllib.error
+import urllib.request
+from pathlib import Path
+from xml.etree import ElementTree as ET
+
+sys.path.insert(0, str(Path(__file__).parent))
+from _watermark import Watermark, format_items_as_markdown  # type: ignore
+
+
+def _strip_ns(tag: str) -> str:
+    return tag.split("}", 1)[1] if "}" in tag else tag
+
+
+def _parse_feed(xml_bytes: bytes):
+    """Return a list of {id, title, url, summary} dicts.
+
+    Handles both RSS 2.0 ``<item>`` and Atom ``<entry>``.
+    """
+    try:
+        root = ET.fromstring(xml_bytes)
+    except ET.ParseError as e:
+        print(f"watch_rss: invalid XML: {e}", file=sys.stderr)
+        sys.exit(2)
+
+    entries = []
+    for item in root.iter():
+        tag = _strip_ns(item.tag)
+        if tag not in ("item", "entry"):
+            continue
+        # ElementTree Elements without children are *falsy* — use `is not None`.
+        children = {_strip_ns(c.tag): c for c in item}
+
+        guid_el = children.get("guid")
+        if guid_el is None:
+            guid_el = children.get("id")
+        link_el = children.get("link")
+        if link_el is not None:
+            href = link_el.attrib.get("href") or (link_el.text or "").strip()
+        else:
+            href = ""
+        guid = (guid_el.text or "").strip() if guid_el is not None else ""
+        guid = guid or href
+        if not guid:
+            continue
+
+        title_el = children.get("title")
+        title = (title_el.text or "").strip() if title_el is not None else ""
+
+        summ_el = children.get("description")
+        if summ_el is None:
+            summ_el = children.get("summary")
+        summary = (summ_el.text or "").strip() if summ_el is not None else ""
+
+        entries.append(
+            {"id": guid, "title": title, "url": href, "summary": summary}
+        )
+    return entries
+
+
+def main() -> int:
+    p = argparse.ArgumentParser(description="Watch an RSS/Atom feed.")
+    p.add_argument("--name", required=True, help="Watcher name (used for state file)")
+    p.add_argument("--url", required=True, help="Feed URL")
+    p.add_argument("--max", type=int, default=10,
+                   help="Max new items to emit per tick (default: 10)")
+    p.add_argument("--with-summary", action="store_true",
+                   help="Include <description>/<summary> snippet under each item")
+    p.add_argument("--timeout", type=float, default=20.0,
+                   help="HTTP timeout in seconds (default: 20)")
+    args = p.parse_args()
+
+    try:
+        req = urllib.request.Request(args.url, headers={"User-Agent": "Hermes-Watcher/1.0"})
+        with urllib.request.urlopen(req, timeout=args.timeout) as resp:
+            xml_bytes = resp.read()
+    except urllib.error.HTTPError as e:
+        print(f"watch_rss: HTTP {e.code} from {args.url}", file=sys.stderr)
+        return 2
+    except (urllib.error.URLError, TimeoutError, OSError) as e:
+        print(f"watch_rss: network error: {e}", file=sys.stderr)
+        return 2
+
+    entries = _parse_feed(xml_bytes)
+
+    wm = Watermark.load(args.name)
+    new_items = wm.filter_new(entries, id_key="id")
+    wm.save()
+
+    # Cap emitted items (watermark still records all seen IDs so we don't
+    # re-emit them next tick).
+    if args.max > 0:
+        new_items = new_items[: args.max]
+
+    body_key = "summary" if args.with_summary else None
+    output = format_items_as_markdown(new_items, body_key=body_key)
+    if output:
+        sys.stdout.write(output)
+    # Empty stdout on no-new — cron treats that as silent.
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())