diff --git a/docs/.generated/config-baseline.sha256 b/docs/.generated/config-baseline.sha256
index fb3a8eddf13..c71fd66d5b9 100644
--- a/docs/.generated/config-baseline.sha256
+++ b/docs/.generated/config-baseline.sha256
@@ -1,4 +1,4 @@
-747a24d0acf12f95ec75feabb47dad8f03ff0e3a7173b4d277c648f75d956ce5  config-baseline.json
-cbb9a6ee1cb69068d5eb63f00f95512ba19778415ea5b2eabe056aaea38978b5  config-baseline.core.json
-e239cc20f20f8d0172812bc0ad3ee6df52da88e2e2702e3d03a47e01561132ae  config-baseline.channel.json
-b695cb31b4c0cf1d31f842f2892e99cc3ff8d84263ae72b72977cae844b81d6e  config-baseline.plugin.json
+12639f02b5283d35fb01136164f68301c22b8ac6786e69662142ec484924bdd8  config-baseline.json
+ada810ee23e23ad739f1b652891adffb34988d455638d5e4ea3cb8ac15197304  config-baseline.core.json
+99bb34fcf83ba6bb50a3fc11f170bd379bee5728b0938707fc39ebd7638e12eb  config-baseline.channel.json
+5f5d4e850df6e9854a85b5d008236854ce185c707fdbb566efcf00f8c08b36e3  config-baseline.plugin.json
diff --git a/src/auto-reply/reply/agent-runner-execution.test.ts b/src/auto-reply/reply/agent-runner-execution.test.ts
index c7e11f74516..ed1e46c86c5 100644
--- a/src/auto-reply/reply/agent-runner-execution.test.ts
+++ b/src/auto-reply/reply/agent-runner-execution.test.ts
@@ -931,6 +931,131 @@ describe("runAgentTurnWithFallback", () => {
     );
   });
 
+  it("prefers onCompactionEnd callback over default notice when notifyUser is enabled", async () => {
+    const onBlockReply = vi.fn();
+    const onCompactionEnd = vi.fn();
+    state.runEmbeddedPiAgentMock.mockImplementationOnce(async (params: EmbeddedAgentParams) => {
+      await params.onAgentEvent?.({ stream: "compaction", data: { phase: "start" } });
+      await params.onAgentEvent?.({
+        stream: "compaction",
+        data: { phase: "end", completed: true },
+      });
+      return { payloads: [{ text: "final" }], meta: {} };
+    });
+
+    const followupRun = createFollowupRun();
+    followupRun.run.config = {
+      agents: {
+        defaults: {
+          compaction: {
+            notifyUser: true,
+          },
+        },
+      },
+    };
+
+    const runAgentTurnWithFallback = await getRunAgentTurnWithFallback();
+    const result = await runAgentTurnWithFallback({
+      commandBody: "hello",
+      followupRun,
+      sessionCtx: {
+        Provider: "whatsapp",
+        MessageSid: "msg",
+      } as unknown as TemplateContext,
+      opts: { onBlockReply, onCompactionEnd },
+      typingSignals: createMockTypingSignaler(),
+      blockReplyPipeline: null,
+      blockStreamingEnabled: false,
+      resolvedBlockStreamingBreak: "message_end",
+      applyReplyToMode: (payload) => payload,
+      shouldEmitToolResult: () => true,
+      shouldEmitToolOutput: () => false,
+      pendingToolTasks: new Set(),
+      resetSessionAfterCompactionFailure: async () => false,
+      resetSessionAfterRoleOrderingConflict: async () => false,
+      isHeartbeat: false,
+      sessionKey: "main",
+      getActiveSessionEntry: () => undefined,
+      resolvedVerboseLevel: "off",
+    });
+
+    expect(result.kind).toBe("success");
+    expect(onCompactionEnd).toHaveBeenCalledTimes(1);
+    // The start notice still fires (no onCompactionStart callback provided),
+    // but the completion notice is suppressed in favor of the callback.
+    expect(onBlockReply).toHaveBeenCalledTimes(1);
+    expect(onBlockReply).toHaveBeenCalledWith(
+      expect.objectContaining({
+        text: "🧹 Compacting context...",
+        isCompactionNotice: true,
+      }),
+    );
+  });
+
+  it("emits an incomplete compaction notice when compaction ends without completing", async () => {
+    const onBlockReply = vi.fn();
+    state.runEmbeddedPiAgentMock.mockImplementationOnce(async (params: EmbeddedAgentParams) => {
+      await params.onAgentEvent?.({ stream: "compaction", data: { phase: "start" } });
+      await params.onAgentEvent?.({
+        stream: "compaction",
+        data: { phase: "end", completed: false },
+      });
+      return { payloads: [{ text: "final" }], meta: {} };
+    });
+
+    const followupRun = createFollowupRun();
+    followupRun.run.config = {
+      agents: {
+        defaults: {
+          compaction: {
+            notifyUser: true,
+          },
+        },
+      },
+    };
+
+    const runAgentTurnWithFallback = await getRunAgentTurnWithFallback();
+    const result = await runAgentTurnWithFallback({
+      commandBody: "hello",
+      followupRun,
+      sessionCtx: {
+        Provider: "whatsapp",
+        MessageSid: "msg",
+      } as unknown as TemplateContext,
+      opts: { onBlockReply },
+      typingSignals: createMockTypingSignaler(),
+      blockReplyPipeline: null,
+      blockStreamingEnabled: false,
+      resolvedBlockStreamingBreak: "message_end",
+      applyReplyToMode: (payload) => payload,
+      shouldEmitToolResult: () => true,
+      shouldEmitToolOutput: () => false,
+      pendingToolTasks: new Set(),
+      resetSessionAfterCompactionFailure: async () => false,
+      resetSessionAfterRoleOrderingConflict: async () => false,
+      isHeartbeat: false,
+      sessionKey: "main",
+      getActiveSessionEntry: () => undefined,
+      resolvedVerboseLevel: "off",
+    });
+
+    expect(result.kind).toBe("success");
+    expect(onBlockReply).toHaveBeenNthCalledWith(
+      1,
+      expect.objectContaining({
+        text: "🧹 Compacting context...",
+        isCompactionNotice: true,
+      }),
+    );
+    expect(onBlockReply).toHaveBeenNthCalledWith(
+      2,
+      expect.objectContaining({
+        text: "🧹 Compaction incomplete",
+        isCompactionNotice: true,
+      }),
+    );
+  });
+
   it("does not show a rate-limit countdown for mixed-cause fallback exhaustion", async () => {
     state.runWithModelFallbackMock.mockRejectedValueOnce(
       Object.assign(
diff --git a/src/auto-reply/reply/agent-runner-execution.ts b/src/auto-reply/reply/agent-runner-execution.ts
index 28f1387bd4a..2f9f6aa34bf 100644
--- a/src/auto-reply/reply/agent-runner-execution.ts
+++ b/src/auto-reply/reply/agent-runner-execution.ts
@@ -626,12 +626,18 @@ export async function runAgentTurnWithFallback(params: {
   const currentMessageId = params.sessionCtx.MessageSidFull ?? params.sessionCtx.MessageSid;
   const shouldNotifyUserAboutCompaction =
     runtimeConfig?.agents?.defaults?.compaction?.notifyUser === true;
-  const sendCompactionNotice = async (phase: "start" | "end") => {
+  const sendCompactionNotice = async (phase: "start" | "end" | "incomplete") => {
     if (!params.opts?.onBlockReply) {
       return;
     }
+    const text =
+      phase === "start"
+        ? "🧹 Compacting context..."
+        : phase === "end"
+          ? "🧹 Compaction complete"
+          : "🧹 Compaction incomplete";
     const noticePayload = params.applyReplyToMode({
-      text: phase === "start" ? "🧹 Compacting context..." : "🧹 Compaction complete",
+      text,
       replyToId: currentMessageId,
       replyToCurrent: true,
       isCompactionNotice: true,
@@ -1172,13 +1178,17 @@ export async function runAgentTurnWithFallback(params: {
                         await sendCompactionNotice("start");
                       }
                     }
-                    const completed = evt.data?.completed === true;
-                    if (phase === "end" && completed) {
-                      attemptCompactionCount += 1;
-                      if (params.opts?.onCompactionEnd) {
-                        await params.opts.onCompactionEnd();
+                    if (phase === "end") {
+                      const completed = evt.data?.completed === true;
+                      if (completed) {
+                        attemptCompactionCount += 1;
+                        if (params.opts?.onCompactionEnd) {
+                          await params.opts.onCompactionEnd();
+                        } else if (shouldNotifyUserAboutCompaction) {
+                          await sendCompactionNotice("end");
+                        }
                       } else if (shouldNotifyUserAboutCompaction) {
-                        await sendCompactionNotice("end");
+                        await sendCompactionNotice("incomplete");
                       }
                     }
                   }