Truth strip review fixes: all-offline is not Listening, hearing bounded (#232)

- Every configured node offline now degrades the Radio stage ("all N nodes
  offline") so the wall no longer shows "Listening" with nothing up.
- nodes-hearing only counts configured nodes, so it can't exceed N/N.
- AI chip copy: "no incident writes in the recent window" instead of
  "last incident write none in window".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/lib/usePipelineHealth.ts

@@ -182,14 +182,21 @@ export function derivePipelineHealth(
   // ── Radio ────────────────────────────────────────────────────────────────
   const newestCallAt = maxDate(calls.map((c) => ms(c.started_at)));
   const anyNodeUp = nodes.some((n) => n.status !== "offline");
+  // Every configured node offline is not "Listening" — nothing can be heard.
+  const allNodesOffline = nodes.length > 0 && !anyNodeUp;
   const radioDry = anyNodeUp && (!newestCallAt || now - newestCallAt.getTime() > absenceMs);
   const radio: PipelineStage = {
     key: "radio", label: "Radio", lastAt: newestCallAt,
-    state: nodes.length === 0 ? "unknown" : radioDry ? "degraded" : "ok",
+    state: nodes.length === 0 ? "unknown" : radioDry || allNodesOffline ? "degraded" : "ok",
-    detail: newestCallAt ? `last call heard ${agoText(newestCallAt, now)}` : "no calls in the recent window",
+    detail: allNodesOffline
+      ? `all ${nodes.length} node${nodes.length === 1 ? "" : "s"} offline`
+      : newestCallAt ? `last call heard ${agoText(newestCallAt, now)}` : "no calls in the recent window",
   };
+  // Bounded to configured nodes so a call from a since-removed node can't push
+  // the KPI past N/N.
+  const knownNodes = new Set(nodes.map((n) => n.node_id));
   const nodesHearing = new Set(
-    calls.filter((c) => now - ms(c.started_at) <= staleMs).map((c) => c.node_id),
+    calls.filter((c) => now - ms(c.started_at) <= staleMs && knownNodes.has(c.node_id)).map((c) => c.node_id),
   ).size;
 
   // ── STT: radio heard, nothing transcribed ────────────────────────────────
@@ -225,7 +232,7 @@ export function derivePipelineHealth(
     state: aiDry || aiTiers.length ? "degraded" : reachable === false && !newestAiAt ? "unknown" : "ok",
     detail: aiDry
       ? `transcribed, no incident written since ${newestAiAt ? clockTime(newestAiAt) : clockTime(new Date(oldestUncorrelated))}`
-      : `last incident write ${agoText(newestAiAt, now)}${reachable === false ? " · /health/ai unreachable" : ""}`,
+      : `${newestAiAt ? `last incident write ${agoText(newestAiAt, now)}` : "no incident writes in the recent window"}${reachable === false ? " · /health/ai unreachable" : ""}`,
   };
 
   // ── Context feeds (chip only — a dead camera feed doesn't blind the pipeline) ──
@@ -244,7 +251,8 @@ export function derivePipelineHealth(
 
   // ── Verdict ─────────────────────────────────────────────────────────────
   const parts: string[] = [];
-  if (radio.state === "degraded") parts.push(`nodes checking in, no radio heard since ${newestCallAt ? clockTime(newestCallAt) : "—"}`);
+  if (allNodesOffline) parts.push(`${radio.detail}${newestCallAt ? `, last call heard ${clockTime(newestCallAt)}` : ""}`);
+  else if (radioDry) parts.push(`nodes checking in, no radio heard since ${newestCallAt ? clockTime(newestCallAt) : "—"}`);
   if (sttDry) parts.push(stt.detail);
   if (aiDry) parts.push(ai_.detail);
   for (const t of degradedTiers) parts.push(tierText(t.tier, t.state));