feat: wrap compaction generateSummary in retryAsync

Integrate retry logic with abort-classifier for /compact endpoint:
- Wrap generateSummary calls in retryAsync with exponential backoff
- Auto-skip retry on user cancellation and gateway restart (AbortError)
- Config: 3 attempts, 500ms-5s delay, 20% jitter
- Add comprehensive Vitest tests (5/5 passed)

Related: #16809, #5744, #17143

src/agents/compaction.ts

@@ -1,6 +1,7 @@
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import type { ExtensionContext } from "@mariozechner/pi-coding-agent";
 import { estimateTokens, generateSummary } from "@mariozechner/pi-coding-agent";
+import { retryAsync } from "../infra/retry.js";
 import { DEFAULT_CONTEXT_TOKENS } from "./defaults.js";
 import { repairToolUseResultPairing, stripToolResultDetails } from "./session-transcript-repair.js";
 
@@ -159,14 +160,25 @@ async function summarizeChunks(params: {
   let summary = params.previousSummary;
 
   for (const chunk of chunks) {
-    summary = await generateSummary(
-      chunk,
-      params.model,
-      params.reserveTokens,
-      params.apiKey,
-      params.signal,
-      params.customInstructions,
-      summary,
+    summary = await retryAsync(
+      () =>
+        generateSummary(
+          chunk,
+          params.model,
+          params.reserveTokens,
+          params.apiKey,
+          params.signal,
+          params.customInstructions,
+          summary,
+        ),
+      {
+        attempts: 3,
+        minDelayMs: 500,
+        maxDelayMs: 5000,
+        jitter: 0.2,
+        label: "compaction/generateSummary",
+        shouldRetry: (err) => !(err instanceof Error && err.name === "AbortError"),
+      },
     );
   }