fix: context overflow compaction and subagent announce improvements (#11664) (thanks @tyler6204)

* initial commit

* feat: implement deriveSessionTotalTokens function and update usage tests

* Added deriveSessionTotalTokens function to calculate total tokens based on usage and context tokens.
* Updated usage tests to include cases for derived session total tokens.
* Refactored session usage calculations in multiple files to utilize the new function for improved accuracy.

* fix: restore overflow truncation fallback + changelog/test hardening (#11551) (thanks @tyler6204)

src/agents/pi-embedded-subscribe.ts

@@ -16,6 +16,7 @@ import {
 } from "./pi-embedded-helpers.js";
 import { createEmbeddedPiSessionEventHandler } from "./pi-embedded-subscribe.handlers.js";
 import { formatReasoningMessage } from "./pi-embedded-utils.js";
+import { hasNonzeroUsage, normalizeUsage, type UsageLike } from "./usage.js";
 
 const THINKING_TAG_SCAN_RE = /<\s*(\/?)\s*(?:think(?:ing)?|thought|antthinking)\s*>/gi;
 const FINAL_TAG_SCAN_RE = /<\s*(\/?)\s*final\s*>/gi;
@@ -69,6 +70,14 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
     pendingMessagingTexts: new Map(),
     pendingMessagingTargets: new Map(),
   };
+  const usageTotals = {
+    input: 0,
+    output: 0,
+    cacheRead: 0,
+    cacheWrite: 0,
+    total: 0,
+  };
+  let compactionCount = 0;
 
   const assistantTexts = state.assistantTexts;
   const toolMetas = state.toolMetas;
@@ -222,6 +231,43 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
       state.compactionRetryPromise = null;
     }
   };
+  const recordAssistantUsage = (usageLike: unknown) => {
+    const usage = normalizeUsage((usageLike ?? undefined) as UsageLike | undefined);
+    if (!hasNonzeroUsage(usage)) {
+      return;
+    }
+    usageTotals.input += usage.input ?? 0;
+    usageTotals.output += usage.output ?? 0;
+    usageTotals.cacheRead += usage.cacheRead ?? 0;
+    usageTotals.cacheWrite += usage.cacheWrite ?? 0;
+    const usageTotal =
+      usage.total ??
+      (usage.input ?? 0) + (usage.output ?? 0) + (usage.cacheRead ?? 0) + (usage.cacheWrite ?? 0);
+    usageTotals.total += usageTotal;
+  };
+  const getUsageTotals = () => {
+    const hasUsage =
+      usageTotals.input > 0 ||
+      usageTotals.output > 0 ||
+      usageTotals.cacheRead > 0 ||
+      usageTotals.cacheWrite > 0 ||
+      usageTotals.total > 0;
+    if (!hasUsage) {
+      return undefined;
+    }
+    const derivedTotal =
+      usageTotals.input + usageTotals.output + usageTotals.cacheRead + usageTotals.cacheWrite;
+    return {
+      input: usageTotals.input || undefined,
+      output: usageTotals.output || undefined,
+      cacheRead: usageTotals.cacheRead || undefined,
+      cacheWrite: usageTotals.cacheWrite || undefined,
+      total: usageTotals.total || derivedTotal || undefined,
+    };
+  };
+  const incrementCompactionCount = () => {
+    compactionCount += 1;
+  };
 
   const blockChunking = params.blockReplyChunking;
   const blockChunker = blockChunking ? new EmbeddedBlockChunker(blockChunking) : null;
@@ -530,6 +576,10 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
     noteCompactionRetry,
     resolveCompactionRetry,
     maybeResolveCompactionWait,
+    recordAssistantUsage,
+    incrementCompactionCount,
+    getUsageTotals,
+    getCompactionCount: () => compactionCount,
   };
 
   const unsubscribe = params.session.subscribe(createEmbeddedPiSessionEventHandler(ctx));
@@ -546,6 +596,8 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
     // which is generated AFTER the tool sends the actual answer.
     didSendViaMessagingTool: () => messagingToolSentTexts.length > 0,
     getLastToolError: () => (state.lastToolError ? { ...state.lastToolError } : undefined),
+    getUsageTotals,
+    getCompactionCount: () => compactionCount,
     waitForCompactionRetry: () => {
       if (state.compactionInFlight || state.pendingCompactionRetry > 0) {
         ensureCompactionPromise();