frontend: a status-bar widget, and evidence the data plane is the product

Omarchy 4 runs one long-running Quickshell process and its bar accepts
command modules that print {"text", "tooltip", "class"}. That is the
cheapest native frontend Vitals can have: no QML, no websocket, no plugin
manifest, just a command the bar runs on an interval.

bar_widget.py prints that shape from the existing JSON API, with a
workload selector and a tooltip that carries the verdict line. It also
fails soft, because a status bar should never make a session look broken
when the monitor is down.

This is the point of splitting sampling from presentation: a native UI on
another distro is a new frontend, not a rewrite.

Signed-off-by: Christian Sass <csass@binaryranch.com>

tools/bar_widget.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+"""
+bar_widget.py — one line of JSON for a status bar.
+
+Omarchy's shell, Waybar, and anything else that speaks the same convention can
+run this on an interval and render the result. It is the cheapest possible
+frontend for Vitals: no QML, no websocket, no plugin manifest.
+
+  {"text": "97%", "tooltip": "6.9 cores in leaked browsers...", "class": "hot"}
+
+Usage:
+  python3 tools/bar_widget.py                  # machine total
+  python3 tools/bar_widget.py --workload brave # one workload
+  python3 tools/bar_widget.py --url http://127.0.0.1:8791
+"""
+
+import argparse
+import json
+import sys
+import urllib.error
+import urllib.request
+
+
+def fetch(url):
+    with urllib.request.urlopen(url + "/api/snapshot", timeout=3) as r:
+        return json.load(r)
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--url", default="http://127.0.0.1:8791")
+    ap.add_argument("--workload", default="", help="substring of a workload name")
+    args = ap.parse_args()
+
+    try:
+        snap = fetch(args.url)
+    except (urllib.error.URLError, OSError, ValueError):
+        # a bar widget must never be the reason a session looks broken
+        print(json.dumps({"text": "vitals ?", "tooltip": "Vitals is not responding", "class": "offline"}))
+        return 0
+
+    if args.workload:
+        match = [w for w in snap["workloads"] if args.workload.lower() in w["name"].lower()]
+        if not match:
+            print(json.dumps({"text": "?", "tooltip": f"no workload matching {args.workload}",
+                              "class": "offline"}))
+            return 0
+        w = max(match, key=lambda x: x["cpu"])
+        text = f'{w["cpu"]:.1f}c'
+        tip = [f'{w["name"]}: {w["cpu"]:.2f} cores ({w["pct"]:.0f}%), {w["procs"]} procs']
+        if w.get("verdict"):
+            tip.append(w["verdict"])
+        for t in (w.get("tabs") or [])[:3]:
+            tip.append(f'  {t["title"][:40]} — {t["task_pct"]:.1f}% page work')
+        klass = "hot" if w["pct"] > 40 else "warn" if w["pct"] > 15 else "ok"
+        if "leaked" in (w.get("flags") or []):
+            klass = "leaked"
+        print(json.dumps({"text": text, "tooltip": "\n".join(tip), "class": klass}))
+        return 0
+
+    pct = snap["total_pct"]
+    klass = "hot" if pct > 80 else "warn" if pct > 50 else "ok"
+    tip = [f'{snap["total_busy"]:.2f} of {snap["cores"]} cores ({pct}%)']
+    for w in snap["workloads"][:5]:
+        tip.append(f'  {w["name"][:28]} {w["cpu"]:.2f}c')
+    flagged = [w for w in snap["workloads"] if w.get("flags")]
+    for w in flagged:
+        tip.append(f'  ! {w["name"]}: {", ".join(w["flags"])}')
+    print(json.dumps({"text": f"{pct}%", "tooltip": "\n".join(tip), "class": klass}))
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())