fix(compaction): preserve summary diagnostics on cancellation

packages/compaction/compaction-basic/src/region.ts

@@ -400,7 +400,7 @@ async function summarizeCompaction(
       summaryResult = await dependencies.summarize(prepared.input, agent, signal)
       break
     } catch (error: unknown) {
-      signal?.throwIfAborted()
+      if (signal?.aborted === true) throw error
       assertStable(dependencies, agent.session, prepared)
       if (!dependencies.recover(error, agent, prepared.shadowedSeqs, signal)) throw error
       prepared = prepareCompaction(dependencies, agent.session,

packages/compaction/compaction-image-offload/tests/image-offload.spec.ts

@@ -364,6 +364,12 @@ describe('compaction-image-offload', () => {
     await agent.whenIdle()
     expect(adapter.requests).toHaveLength(1)
     expect(decisions(agent.session)).toEqual([])
+    expect(ctx.waterfall('compaction/summary-error', {
+      session: agent.session,
+      sourceEventSeqs: agent.session.surface.nodes,
+      error: new LlmError('summary budget exceeded', IMAGE_OFFLOAD_REQUIRED_CODE, { offloadImages: 1 }),
+    }, () => false)).toBe(false)
+    expect(decisions(agent.session)).toEqual([])
   })
 
   it('leaves every other failure to downstream recovery', async () => {