fix: subagent announce shows correct runtime, tokens, and output

Three fixes for subagent announce displaying "runtime 0s", "tokens n/a",
and "(no output)" even when the sub-agent completed successfully:

1. formatDurationShort: allow 0ms as valid (sub-second tasks are real),
   display as "<1s" instead of treating as invalid
2. waitForSessionUsage: increase polling from 4×200ms (800ms) to
   10×500ms (5s) so token data has time to persist
3. readLatestAssistantReply: add retry loop (5×500ms) for transcript
   readback when session data hasn't flushed yet

Fixes both copies of formatDurationShort (subagent-announce.ts and
subagents-utils.ts) for consistency.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agents/subagent-announce.ts

@@ -23,8 +23,10 @@ import { type AnnounceQueueItem, enqueueAnnounce } from "./subagent-announce-que
 import { readLatestAssistantReply } from "./tools/agent-step.js";
 
 function formatDurationShort(valueMs?: number) {
-  if (!valueMs || !Number.isFinite(valueMs) || valueMs <= 0) return undefined;
+  if (valueMs === undefined || valueMs === null || !Number.isFinite(valueMs) || valueMs < 0)
+    return undefined;
   const totalSeconds = Math.round(valueMs / 1000);
+  if (totalSeconds === 0) return "<1s";
   const hours = Math.floor(totalSeconds / 3600);
   const minutes = Math.floor((totalSeconds % 3600) / 60);
   const seconds = totalSeconds % 60;
@@ -79,8 +81,8 @@ async function waitForSessionUsage(params: { sessionKey: string }) {
       typeof entry.inputTokens === "number" ||
       typeof entry.outputTokens === "number");
   if (hasTokens()) return { entry, storePath };
-  for (let attempt = 0; attempt < 4; attempt += 1) {
-    await new Promise((resolve) => setTimeout(resolve, 200));
+  for (let attempt = 0; attempt < 10; attempt += 1) {
+    await new Promise((resolve) => setTimeout(resolve, 500));
     entry = loadSessionStore(storePath)[params.sessionKey];
     if (hasTokens()) break;
   }
@@ -359,9 +361,13 @@ export async function runSubagentAnnounceFlow(params: {
     }
 
     if (!reply) {
-      reply = await readLatestAssistantReply({
-        sessionKey: params.childSessionKey,
-      });
+      // Retry with backoff — transcript may not be flushed yet
+      for (let attempt = 0; attempt < 5 && !reply; attempt += 1) {
+        await new Promise((resolve) => setTimeout(resolve, 500));
+        reply = await readLatestAssistantReply({
+          sessionKey: params.childSessionKey,
+        });
+      }
     }
 
     if (!outcome) outcome = { status: "unknown" };

src/auto-reply/reply/subagents-utils.test.ts

@@ -59,4 +59,14 @@ describe("subagents utils", () => {
     expect(formatDurationShort(45_000)).toBe("45s");
     expect(formatDurationShort(65_000)).toBe("1m5s");
   });
+
+  it("formats zero duration as <1s instead of n/a", () => {
+    expect(formatDurationShort(0)).toBe("<1s");
+    expect(formatDurationShort(499)).toBe("<1s");
+  });
+
+  it("returns n/a for undefined/negative durations", () => {
+    expect(formatDurationShort(undefined)).toBe("n/a");
+    expect(formatDurationShort(-1)).toBe("n/a");
+  });
 });

src/auto-reply/reply/subagents-utils.ts

@@ -2,8 +2,10 @@ import type { SubagentRunRecord } from "../../agents/subagent-registry.js";
 import { truncateUtf16Safe } from "../../utils.js";
 
 export function formatDurationShort(valueMs?: number) {
-  if (!valueMs || !Number.isFinite(valueMs) || valueMs <= 0) return "n/a";
+  if (valueMs === undefined || valueMs === null || !Number.isFinite(valueMs) || valueMs < 0)
+    return "n/a";
   const totalSeconds = Math.round(valueMs / 1000);
+  if (totalSeconds === 0) return "<1s";
   const hours = Math.floor(totalSeconds / 3600);
   const minutes = Math.floor((totalSeconds % 3600) / 60);
   const seconds = totalSeconds % 60;