diff --git a/.changeset/vscode-busy-error-message.md b/.changeset/vscode-busy-error-message.md
new file mode 100644
index 0000000000..b361b449cb
--- /dev/null
+++ b/.changeset/vscode-busy-error-message.md
@@ -0,0 +1,5 @@
+---
+"kimi-code": patch
+---
+
+Stop reporting a busy chat session as "Internal error occurred." A prompt sent while a response is still being generated now surfaces as "A message is being sent. Please wait." (code `turn.agent_busy`) with the original detail attached, instead of the generic internal-error message that the plain `Error` was mapped to.
diff --git a/apps/vscode/src/runtime/session-runtime.ts b/apps/vscode/src/runtime/session-runtime.ts
index a3bd2b4615..4b1db8ff36 100644
--- a/apps/vscode/src/runtime/session-runtime.ts
+++ b/apps/vscode/src/runtime/session-runtime.ts
@@ -1,5 +1,6 @@
 import {
   isKimiError,
+  KimiError,
   type ContentPart as SdkContentPart,
   type Event,
   type PromptInput,
@@ -188,7 +189,7 @@ export class SessionRuntime {
       // such terminal event, so reject terminally: the caller's composer must
       // unlock rather than hang until the handshake timeout.
       this.emitError(
-        new Error(ALREADY_GENERATING_MESSAGE),
+        new KimiError("turn.agent_busy", ALREADY_GENERATING_MESSAGE),
         "runtime",
         { terminal: this.hasActiveWork ? false : undefined },
       );
@@ -225,7 +226,7 @@ export class SessionRuntime {
   beginHostAction(input: string | LegacyContentPart[], forkable = false): number {
     this.ensureOpen();
     if (this.isBusy) {
-      throw new Error(ALREADY_GENERATING_MESSAGE);
+      throw new KimiError("turn.agent_busy", ALREADY_GENERATING_MESSAGE);
     }
     const actionId = ++this.hostActionSequence;
     this.hostActionActive = true;
diff --git a/apps/vscode/test/kimi-runtime.test.ts b/apps/vscode/test/kimi-runtime.test.ts
index 6a86f7f2d1..a5cfdc856e 100644
--- a/apps/vscode/test/kimi-runtime.test.ts
+++ b/apps/vscode/test/kimi-runtime.test.ts
@@ -599,6 +599,8 @@ describe("Kimi runtime (owns shared SDK sessions for Webviews)", () => {
     const busyWarning = broadcasts.find(({ data }) => (data as { type?: string }).type === "error");
     expect(busyWarning?.data).toMatchObject({
       type: "error",
+      code: "turn.agent_busy",
+      message: "A message is being sent. Please wait.",
       phase: "runtime",
       detail: "A response is already being generated for this session.",
       terminal: false,
diff --git a/apps/vscode/test/settings-store.test.ts b/apps/vscode/test/settings-store.test.ts
index 93d0decad8..b26590a29e 100644
--- a/apps/vscode/test/settings-store.test.ts
+++ b/apps/vscode/test/settings-store.test.ts
@@ -426,15 +426,15 @@ describe("Webview mid-turn warnings", () => {
 
     useChatStore.getState().processEvent({
       type: "error",
-      code: "internal",
-      message: "Internal error occurred.",
+      code: "turn.agent_busy",
+      message: "A message is being sent. Please wait.",
       detail: "A response is already being generated for this session.",
       phase: "runtime",
       terminal: false,
     });
 
     // The turn is still running: nothing unlocks, nothing flushes, nothing is retried.
-    expect(boundary.toastWarning).toHaveBeenCalledWith("Internal error occurred.");
+    expect(boundary.toastWarning).toHaveBeenCalledWith("A message is being sent. Please wait.");
     const state = useChatStore.getState();
     expect(state.isStreaming).toBe(true);
     expect(state.queue).toHaveLength(1);