diff --git a/src/cli/helpers/accumulator.ts b/src/cli/helpers/accumulator.ts
index 93f056b..a5ae960 100644
--- a/src/cli/helpers/accumulator.ts
+++ b/src/cli/helpers/accumulator.ts
@@ -451,6 +451,13 @@ function extractTextPart(v: unknown): string {
   return "";
 }
 
+function markCompactionCompleted(ctx?: ContextTracker): void {
+  if (!ctx) return;
+  ctx.pendingCompaction = true;
+  ctx.pendingSkillsReinject = true;
+  ctx.pendingReflectionTrigger = true;
+}
+
 function resolveLineIdForKind(
   b: Buffers,
   canonicalId: string,
@@ -787,6 +794,9 @@ export function onChunk(
           phase: "finished",
           summary: compactionSummary,
         }));
+        // Legacy servers may emit compaction completion as a user_message
+        // system alert instead of summary_message.
+        markCompactionCompleted(ctx);
       }
       // If not a summary, ignore it (user messages aren't rendered during streaming)
       break;
@@ -1131,11 +1141,7 @@ export function onChunk(
         // Set here (not in event_message) because summary_message arrives after
         // compaction completes, guaranteeing the next usage_statistics has the
         // reduced token count.
-        if (ctx) {
-          ctx.pendingCompaction = true;
-          ctx.pendingSkillsReinject = true;
-          ctx.pendingReflectionTrigger = true;
-        }
+        markCompactionCompleted(ctx);
         break;
       }
 
diff --git a/src/tests/cli/accumulator-usage.test.ts b/src/tests/cli/accumulator-usage.test.ts
index 9a514ca..10c1753 100644
--- a/src/tests/cli/accumulator-usage.test.ts
+++ b/src/tests/cli/accumulator-usage.test.ts
@@ -106,6 +106,30 @@ describe("accumulator usage statistics", () => {
     expect(tracker.pendingReflectionTrigger).toBe(true);
   });
 
+  test("sets reflection trigger for legacy compaction summary user_message", () => {
+    const buffers = createBuffers("agent-1");
+    const tracker = createContextTracker();
+    const legacySummary = JSON.stringify({
+      type: "system_alert",
+      message:
+        "The following prior messages have been hidden due to the conversation context window being reached.\nThe following is a summary of the previous messages: compact summary",
+    });
+
+    onChunk(
+      buffers,
+      {
+        message_type: "user_message",
+        id: "legacy-compaction-1",
+        content: legacySummary,
+      } as unknown as LettaStreamingResponse,
+      tracker,
+    );
+
+    expect(tracker.pendingCompaction).toBe(true);
+    expect(tracker.pendingSkillsReinject).toBe(true);
+    expect(tracker.pendingReflectionTrigger).toBe(true);
+  });
+
   test("accumulates assistant messages when otid is missing but id is present", () => {
     const buffers = createBuffers();