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-runner/run/attempt.ts

@@ -650,6 +650,8 @@ export async function runEmbeddedAttempt(
         getMessagingToolSentTargets,
         didSendViaMessagingTool,
         getLastToolError,
+        getUsageTotals,
+        getCompactionCount,
       } = subscription;
 
       const queueHandle: EmbeddedPiQueueHandle = {
@@ -908,6 +910,8 @@ export async function runEmbeddedAttempt(
         cloudCodeAssistFormatError: Boolean(
           lastAssistant?.errorMessage && isCloudCodeAssistFormatError(lastAssistant.errorMessage),
         ),
+        attemptUsage: getUsageTotals(),
+        compactionCount: getCompactionCount(),
         // Client tool call detected (OpenResponses hosted tools)
         clientToolCall: clientToolCallDetected ?? undefined,
       };