diff --git a/CHANGELOG.md b/CHANGELOG.md
index 276dc3526c5..a5dfdbd71e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -123,6 +123,7 @@ Docs: https://docs.openclaw.ai
 - Gateway/exec approvals: surface requested env override keys in gateway-host approval prompts so operators can review surviving env context without inheriting noisy base host env.
 - Telegram/network: preserve sticky IPv4 fallback state across polling restarts so hosts with unstable IPv6 to `api.telegram.org` stop re-triggering repeated Telegram timeouts after each restart. (#48282) Thanks @yassinebkr.
 - Plugins/subagents: forward per-run provider and model overrides through gateway plugin subagent dispatch so plugin-launched agent delegations honor explicit model selection again. (#48277) Thanks @jalehman.
+- Agents/compaction: write minimal boundary summaries for empty preparations while keeping split-turn prefixes on the normal path, so no-summarizable-message sessions stop retriggering the safeguard loop. (#42215) thanks @lml2468.
 
 ### Fixes
 
diff --git a/extensions/discord/src/monitor/message-handler.preflight.test.ts b/extensions/discord/src/monitor/message-handler.preflight.test.ts
index 0067de03c4e..bd55cd2ead2 100644
--- a/extensions/discord/src/monitor/message-handler.preflight.test.ts
+++ b/extensions/discord/src/monitor/message-handler.preflight.test.ts
@@ -389,7 +389,6 @@ describe("preflightDiscordMessage", () => {
       id: "m-webhook-hydrated-1",
       channelId: threadId,
       content: "",
-      webhookId: undefined,
       author: {
         id: "relay-bot-1",
         bot: true,
diff --git a/src/agents/pi-extensions/compaction-safeguard.test.ts b/src/agents/pi-extensions/compaction-safeguard.test.ts
index 882099f3569..509bbdd25b2 100644
--- a/src/agents/pi-extensions/compaction-safeguard.test.ts
+++ b/src/agents/pi-extensions/compaction-safeguard.test.ts
@@ -138,10 +138,31 @@ async function runCompactionScenario(params: {
   });
   const result = (await compactionHandler(params.event, mockContext)) as {
     cancel?: boolean;
+    compaction?: {
+      summary: string;
+      firstKeptEntryId: string;
+      tokensBefore: number;
+    };
   };
   return { result, getApiKeyMock };
 }
 
+function expectCompactionResult(result: {
+  cancel?: boolean;
+  compaction?: {
+    summary: string;
+    firstKeptEntryId: string;
+    tokensBefore: number;
+  };
+}) {
+  expect(result.cancel).not.toBe(true);
+  expect(result.compaction).toBeDefined();
+  if (!result.compaction) {
+    throw new Error("Expected compaction result");
+  }
+  return result.compaction;
+}
+
 describe("compaction-safeguard tool failures", () => {
   it("formats tool failures with meta and summary", () => {
     const messages: AgentMessage[] = [
@@ -1524,10 +1545,117 @@ describe("compaction-safeguard double-compaction guard", () => {
       event: mockEvent,
       apiKey: "sk-test", // pragma: allowlist secret
     });
-    expect(result).toEqual({ cancel: true });
+    const compaction = expectCompactionResult(result);
+    // After fix for #41981: returns a compaction result (not cancel) to write
+    // a boundary entry and break the re-trigger loop.
+    // buildStructuredFallbackSummary(undefined) produces a minimal structured summary
+    expect(compaction.summary).toContain("## Decisions");
+    expect(compaction.summary).toContain("No prior history.");
+    expect(compaction.summary).toContain("## Open TODOs");
+    expect(compaction.firstKeptEntryId).toBe("entry-1");
+    expect(compaction.tokensBefore).toBe(1500);
     expect(getApiKeyMock).not.toHaveBeenCalled();
   });
 
+  it("returns compaction result with structured fallback summary sections", async () => {
+    const sessionManager = stubSessionManager();
+    const model = createAnthropicModelFixture();
+    setCompactionSafeguardRuntime(sessionManager, { model });
+
+    const mockEvent = {
+      preparation: {
+        messagesToSummarize: [] as AgentMessage[],
+        turnPrefixMessages: [] as AgentMessage[],
+        firstKeptEntryId: "entry-2",
+        tokensBefore: 2000,
+        previousSummary: "## Decisions\nUsed approach A.",
+        fileOps: { read: [], edited: [], written: [] },
+        settings: { reserveTokens: 16384 },
+      },
+      customInstructions: "",
+      signal: new AbortController().signal,
+    };
+    const { result } = await runCompactionScenario({
+      sessionManager,
+      event: mockEvent,
+      apiKey: "sk-test", // pragma: allowlist secret
+    });
+    const compaction = expectCompactionResult(result);
+    // Fallback preserves previous summary when it has required sections
+    expect(compaction.summary).toContain("## Decisions");
+    expect(compaction.summary).toContain("## Open TODOs");
+    expect(compaction.firstKeptEntryId).toBe("entry-2");
+  });
+
+  it("writes boundary again on repeated empty preparation (no cancel loop after new assistant message)", async () => {
+    const sessionManager = stubSessionManager();
+    const model = createAnthropicModelFixture();
+    setCompactionSafeguardRuntime(sessionManager, { model });
+
+    const mockEvent = {
+      preparation: {
+        messagesToSummarize: [] as AgentMessage[],
+        turnPrefixMessages: [] as AgentMessage[],
+        firstKeptEntryId: "entry-3",
+        tokensBefore: 1000,
+        fileOps: { read: [], edited: [], written: [] },
+      },
+      customInstructions: "",
+      signal: new AbortController().signal,
+    };
+
+    // First call — writes boundary
+    const { result: result1 } = await runCompactionScenario({
+      sessionManager,
+      event: mockEvent,
+      apiKey: "sk-test", // pragma: allowlist secret
+    });
+    const compaction1 = expectCompactionResult(result1);
+    expect(compaction1.summary).toContain("## Decisions");
+
+    // Simulate: after the boundary, a new assistant message arrives, SDK
+    // triggers compaction again with another empty preparation. The safeguard
+    // must write another boundary (not cancel) to avoid re-entering the
+    // cancel loop described in the maintainer review.
+    const { result: result2 } = await runCompactionScenario({
+      sessionManager,
+      event: mockEvent,
+      apiKey: "sk-test", // pragma: allowlist secret
+    });
+    const compaction2 = expectCompactionResult(result2);
+    expect(compaction2.summary).toContain("## Decisions");
+    expect(compaction2.firstKeptEntryId).toBe("entry-3");
+  });
+
+  it("does not write boundary when turnPrefixMessages has real content (split-turn)", async () => {
+    const sessionManager = stubSessionManager();
+    const model = createAnthropicModelFixture();
+    setCompactionSafeguardRuntime(sessionManager, { model });
+
+    const mockEvent = {
+      preparation: {
+        messagesToSummarize: [] as AgentMessage[],
+        turnPrefixMessages: [
+          { role: "user" as const, content: "real turn prefix content" },
+        ] as AgentMessage[],
+        firstKeptEntryId: "entry-4",
+        tokensBefore: 2000,
+        fileOps: { read: [], edited: [], written: [] },
+        isSplitTurn: true,
+      },
+      customInstructions: "",
+      signal: new AbortController().signal,
+    };
+    const { result } = await runCompactionScenario({
+      sessionManager,
+      event: mockEvent,
+      apiKey: null,
+    });
+    // Should NOT take the boundary fast-path — falls through to normal compaction
+    // (which cancels due to no API key, but that's the expected normal path)
+    expect(result).toEqual({ cancel: true });
+  });
+
   it("continues when messages include real conversation content", async () => {
     const sessionManager = stubSessionManager();
     const model = createAnthropicModelFixture();
diff --git a/src/agents/pi-extensions/compaction-safeguard.ts b/src/agents/pi-extensions/compaction-safeguard.ts
index 4461b97d3e0..92332140656 100644
--- a/src/agents/pi-extensions/compaction-safeguard.ts
+++ b/src/agents/pi-extensions/compaction-safeguard.ts
@@ -702,11 +702,32 @@ async function readWorkspaceContextForSummary(): Promise<string> {
 export default function compactionSafeguardExtension(api: ExtensionAPI): void {
   api.on("session_before_compact", async (event, ctx) => {
     const { preparation, customInstructions: eventInstructions, signal } = event;
-    if (!preparation.messagesToSummarize.some(isRealConversationMessage)) {
-      log.warn(
-        "Compaction safeguard: cancelling compaction with no real conversation messages to summarize.",
+    const hasRealSummarizable = preparation.messagesToSummarize.some(isRealConversationMessage);
+    const hasRealTurnPrefix = preparation.turnPrefixMessages.some(isRealConversationMessage);
+    if (!hasRealSummarizable && !hasRealTurnPrefix) {
+      // When there are no summarizable messages AND no real turn-prefix content,
+      // cancelling compaction leaves context unchanged but the SDK re-triggers
+      // _checkCompaction after every assistant response — creating a cancel loop
+      // that blocks cron lanes (#41981).
+      //
+      // Strategy: always return a minimal compaction result so the SDK writes a
+      // boundary entry. The SDK's prepareCompaction() returns undefined when the
+      // last entry is a compaction, which blocks immediate re-triggering within
+      // the same turn. After a new assistant message arrives, if the SDK triggers
+      // compaction again with an empty preparation, we write another boundary —
+      // this is bounded to at most one boundary per LLM round-trip, not a tight
+      // loop.
+      log.info(
+        "Compaction safeguard: no real conversation messages to summarize; writing compaction boundary to suppress re-trigger loop.",
       );
-      return { cancel: true };
+      const fallbackSummary = buildStructuredFallbackSummary(preparation.previousSummary);
+      return {
+        compaction: {
+          summary: fallbackSummary,
+          firstKeptEntryId: preparation.firstKeptEntryId,
+          tokensBefore: preparation.tokensBefore,
+        },
+      };
     }
     const { readFiles, modifiedFiles } = computeFileLists(preparation.fileOps);
     const fileOpsSummary = formatFileOperations(readFiles, modifiedFiles);