diff --git a/CHANGELOG.md b/CHANGELOG.md
index ccd9a3ba663..60d5a147112 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@ Docs: https://docs.openclaw.ai
 - Agents/sandbox: preserve existing workspace file modes when sandbox edits atomically replace files, so 0644 files do not collapse to 0600 after Write/Edit/apply_patch. Fixes #44077. Thanks @patosullivan.
 - Agents/models: keep legacy CLI runtime model refs such as `claude-cli/*` in the configured allowlist after canonical runtime migration, so cron `payload.model` overrides keep working. Fixes #75753. Thanks @RyanSandoval.
 - Gateway/watch: keep colored subsystem log prefixes in the managed tmux pane even when the parent shell exports `NO_COLOR`, while preserving explicit `FORCE_COLOR=0` opt-out. Thanks @vincentkoc.
+- Agents/compaction: submit a non-empty runtime-event marker for pre-compaction memory flush turns, so strict Anthropic providers no longer reject the silent flush as an empty user message. Fixes #75305. Thanks @sableassistant3777-source.
 - Plugin SDK: re-export `isPrivateIpAddress` from `plugin-sdk/ssrf-runtime`, restoring source-checkout builds for SearXNG and Firecrawl private-network guards. Thanks @vincentkoc.
 - CLI/directory: report unsupported directory operations for installed channel plugins instead of prompting to reinstall the plugin when it lacks a directory adapter. Fixes #75770. Thanks @lawong888.
 - Web search/SearXNG: show the JSON API `search.formats` prerequisite during SearXNG setup before prompting for the base URL. Supersedes #65592. Thanks @evanpaul14.
diff --git a/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.test.ts b/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.test.ts
index 6a6c5241eee..eca6a3d8969 100644
--- a/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.test.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.test.ts
@@ -111,7 +111,7 @@ describe("resolvePromptSubmissionSkipReason", () => {
     ).toBeNull();
   });
 
-  it("allows blank prompt on runtimeOnly turns", () => {
+  it("skips blank prompt on runtimeOnly turns", () => {
     expect(
       resolvePromptSubmissionSkipReason({
         prompt: "",
@@ -119,7 +119,7 @@ describe("resolvePromptSubmissionSkipReason", () => {
         runtimeOnly: true,
         imageCount: 0,
       }),
-    ).toBeNull();
+    ).toBe("empty_prompt_history_images");
   });
 
   it("treats undefined runtimeOnly as a visible user submission", () => {
diff --git a/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.ts b/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.ts
index ef04a02d180..ce77c5388fa 100644
--- a/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.prompt-helpers.ts
@@ -244,9 +244,6 @@ export function resolvePromptSubmissionSkipReason(params: {
   imageCount: number;
   runtimeOnly?: boolean;
 }): PromptSubmissionSkipReason | null {
-  if (params.runtimeOnly) {
-    return null;
-  }
   if (params.prompt.trim().length > 0 || params.imageCount > 0) {
     return null;
   }
diff --git a/src/agents/pi-embedded-runner/run/runtime-context-prompt.test.ts b/src/agents/pi-embedded-runner/run/runtime-context-prompt.test.ts
index 736169527b8..d3a02204d31 100644
--- a/src/agents/pi-embedded-runner/run/runtime-context-prompt.test.ts
+++ b/src/agents/pi-embedded-runner/run/runtime-context-prompt.test.ts
@@ -55,7 +55,7 @@ describe("runtime context prompt submission", () => {
         transcriptPrompt: "",
       }),
     ).toEqual({
-      prompt: "",
+      prompt: "Continue the OpenClaw runtime event.",
       runtimeContext: "internal event",
       runtimeOnly: true,
       runtimeSystemContext: expect.stringContaining("internal event"),
diff --git a/src/agents/pi-embedded-runner/run/runtime-context-prompt.ts b/src/agents/pi-embedded-runner/run/runtime-context-prompt.ts
index 218c777a304..8111214eaef 100644
--- a/src/agents/pi-embedded-runner/run/runtime-context-prompt.ts
+++ b/src/agents/pi-embedded-runner/run/runtime-context-prompt.ts
@@ -6,6 +6,8 @@ import {
 } from "../../internal-runtime-context.js";
 export { OPENCLAW_RUNTIME_CONTEXT_CUSTOM_TYPE };
 
+const OPENCLAW_RUNTIME_EVENT_USER_PROMPT = "Continue the OpenClaw runtime event.";
+
 type RuntimeContextSession = {
   sendCustomMessage: (
     message: {
@@ -54,7 +56,7 @@ export function resolveRuntimeContextPromptParts(params: {
   if (!prompt) {
     return runtimeContext
       ? {
-          prompt: "",
+          prompt: OPENCLAW_RUNTIME_EVENT_USER_PROMPT,
           runtimeContext,
           runtimeOnly: true,
           runtimeSystemContext: buildRuntimeEventSystemContext(runtimeContext),
diff --git a/src/auto-reply/reply/agent-runner-memory.test.ts b/src/auto-reply/reply/agent-runner-memory.test.ts
index 223e03900a0..04f35fcc42b 100644
--- a/src/auto-reply/reply/agent-runner-memory.test.ts
+++ b/src/auto-reply/reply/agent-runner-memory.test.ts
@@ -160,6 +160,7 @@ describe("runMemoryFlushIfNeeded", () => {
     };
     expect(flushCall.prompt).toContain("Pre-compaction memory flush.");
     expect(flushCall.transcriptPrompt).toBe("");
+    expect(flushCall.prompt).not.toBe(flushCall.transcriptPrompt);
     expect(flushCall.memoryFlushWritePath).toMatch(/^memory\/\d{4}-\d{2}-\d{2}\.md$/);
     expect(flushCall.silentExpected).toBe(true);
     expect(refreshQueuedFollowupSessionMock).toHaveBeenCalledWith({