diff --git a/packages/chat-ui/src/inference-failure.test.ts b/packages/chat-ui/src/inference-failure.test.ts
index 35c4dc26..80c9326d 100644
--- a/packages/chat-ui/src/inference-failure.test.ts
+++ b/packages/chat-ui/src/inference-failure.test.ts
@@ -1,6 +1,42 @@
 import { describe, expect, test } from "bun:test";
 
-import { isClassifiedInferenceFailureText } from "./inference-failure";
+import {
+  consumerFacingInferenceText,
+  isClassifiedInferenceFailureText,
+} from "./inference-failure";
+
+describe("consumerFacingInferenceText", () => {
+  test("keeps the vendor preamble and drops [HTTP …] plus the raw provider message", () => {
+    expect(
+      consumerFacingInferenceText(
+        "This agent could not complete your request due to a credential error [HTTP 401]: API key is invalid",
+      ),
+    ).toBe(
+      "This agent could not complete your request due to a credential error",
+    );
+    expect(
+      consumerFacingInferenceText(
+        "This agent could not complete your request because the API quota has been exhausted [HTTP 429]: rate limited",
+      ),
+    ).toBe(
+      "This agent could not complete your request because the API quota has been exhausted",
+    );
+  });
+
+  test("a forced [HTTP 401] dump is not consumer copy", () => {
+    const leaked = "[HTTP 401]: API key is invalid";
+    const facing = consumerFacingInferenceText(leaked);
+    expect(facing).not.toContain("[HTTP");
+    expect(facing).not.toContain("401");
+    expect(facing).not.toContain("API key is invalid");
+  });
+
+  test("leaves cause-aware undelivered-notice copy untouched", () => {
+    const notice =
+      "I can't reach a model right now — add or check your model key in Settings, then I'll pick this up.";
+    expect(consumerFacingInferenceText(notice)).toBe(notice);
+  });
+});
 
 describe("isClassifiedInferenceFailureText", () => {
   test("matches a credential_failure reply, status code included", () => {
@@ -11,6 +47,16 @@ describe("isClassifiedInferenceFailureText", () => {
     ).toBe(true);
   });
 
+  test("matches a credential_failure reply after HTTP/raw is stripped", () => {
+    expect(
+      isClassifiedInferenceFailureText(
+        consumerFacingInferenceText(
+          "This agent could not complete your request due to a credential error [HTTP 401]: invalid api key",
+        ),
+      ),
+    ).toBe(true);
+  });
+
   test("matches a quota_exhausted reply", () => {
     expect(
       isClassifiedInferenceFailureText(
diff --git a/packages/chat-ui/src/inference-failure.ts b/packages/chat-ui/src/inference-failure.ts
index 9037d65d..0b3bb35a 100644
--- a/packages/chat-ui/src/inference-failure.ts
+++ b/packages/chat-ui/src/inference-failure.ts
@@ -29,6 +29,8 @@ export const CLASSIFIED_INFERENCE_FAILURE_PREAMBLES: readonly string[] = [
   "This agent could not complete your request because the API quota has been exhausted",
 ];
 
+export { consumerFacingInferenceText } from "@corbits/chat/consumer-inference-text";
+
 export function isClassifiedInferenceFailureText(text: string): boolean {
   return CLASSIFIED_INFERENCE_FAILURE_PREAMBLES.some((preamble) =>
     text.startsWith(preamble),
diff --git a/packages/chat-ui/src/timeline.tsx b/packages/chat-ui/src/timeline.tsx
index 26160143..cd99cfd0 100644
--- a/packages/chat-ui/src/timeline.tsx
+++ b/packages/chat-ui/src/timeline.tsx
@@ -57,7 +57,10 @@ import type { BlockResponseActions } from "./blocks/block-responses";
 import type { ConnectGithubActions } from "./blocks/connect-github-actions";
 import type { ConnectServiceActions } from "./blocks/connect-service-actions";
 import { BlockPartView } from "./blocks/registry";
-import { isClassifiedInferenceFailureText } from "./inference-failure";
+import {
+  consumerFacingInferenceText,
+  isClassifiedInferenceFailureText,
+} from "./inference-failure";
 import { WorkbenchLoadingState } from "./loading-state";
 import { Markdown } from "./markdown";
 import type { ProfileSubject } from "./profile-subject";
@@ -455,6 +458,7 @@ function TextBubble({
   pendingNonce?: string;
   pendingActions?: PendingActions;
 }) {
+  const consumerText = consumerFacingInferenceText(text);
   const display = senderDisplay(sender, participants, currentUser);
   const isOwn =
     currentUser !== undefined &&
@@ -545,10 +549,10 @@ function TextBubble({
           </>
         )}
         <div className="chat-bubble-text">
-          <Markdown text={text} />
+          <Markdown text={consumerText} />
         </div>
         {onFixConnection !== undefined &&
-          isClassifiedInferenceFailureText(text) && (
+          isClassifiedInferenceFailureText(consumerText) && (
             <Button
               type="button"
               variant="outline"
@@ -710,6 +714,7 @@ function FailedTurnStrip({
 }) {
   const display = senderDisplay(item.sender, participants, currentUser);
   const sender = display?.label ?? CHAT_STRINGS.senderFallbackMember;
+  const consumerDetail = consumerFacingInferenceText(detailText);
   const [expanded, setExpanded] = useState(false);
   // Guards the resend itself against a double-click firing two sends —
   // not composer state, since Retry never touches the composer any more.
@@ -748,7 +753,9 @@ function FailedTurnStrip({
       </button>
       {expanded ? (
         <span className="chat-turn-failed-detail">
-          {detailText.length > 0 ? detailText : CHAT_STRINGS.turnFailedSub}
+          {consumerDetail.length > 0
+            ? consumerDetail
+            : CHAT_STRINGS.turnFailedSub}
         </span>
       ) : null}
     </div>
diff --git a/packages/chat-ui/test/components.test.tsx b/packages/chat-ui/test/components.test.tsx
index 48b12446..99bec22e 100644
--- a/packages/chat-ui/test/components.test.tsx
+++ b/packages/chat-ui/test/components.test.tsx
@@ -498,6 +498,22 @@ describe("WorkbenchTimeline", () => {
     expect(markup).toContain("Fix this connection");
   });
 
+  test("never renders HTTP status or the raw provider message on a classified failure reply", () => {
+    const markup = renderToStaticMarkup(
+      <WorkbenchTimeline
+        items={classifiedFailureItems}
+        onFixConnection={() => {}}
+      />,
+    );
+    expect(markup).not.toMatch(/\[HTTP/);
+    expect(markup).not.toContain("401");
+    expect(markup).not.toContain("invalid api key");
+    expect(markup).toContain(
+      "This agent could not complete your request due to a credential error",
+    );
+    expect(markup).toContain("Fix this connection");
+  });
+
   test("renders Fix this connection as a react-ui outline button, not a bare link", () => {
     const markup = renderToStaticMarkup(
       <WorkbenchTimeline
diff --git a/packages/chat-ui/test/failed-turn-strip.test.tsx b/packages/chat-ui/test/failed-turn-strip.test.tsx
index 1eea25d4..5c219327 100644
--- a/packages/chat-ui/test/failed-turn-strip.test.tsx
+++ b/packages/chat-ui/test/failed-turn-strip.test.tsx
@@ -5,6 +5,7 @@
 // row (`.chat-turn-failed`, CL-6376) instead of an ordinary text bubble —
 // or, before the CL-6376 redesign, `PrFailedTurnStrip`'s bordered banner.
 import { afterEach, describe, expect, test } from "bun:test";
+import { GlobalRegistrator } from "@happy-dom/global-registrator";
 import { act } from "react";
 import { createRoot } from "react-dom/client";
 import type { Root } from "react-dom/client";
@@ -12,6 +13,15 @@ import type { Root } from "react-dom/client";
 import type { MessageItem } from "../src/api";
 import { WorkbenchTimeline } from "../src/timeline";
 
+if (typeof document === "undefined") {
+  GlobalRegistrator.register();
+}
+
+declare global {
+  var IS_REACT_ACT_ENVIRONMENT: boolean;
+}
+globalThis.IS_REACT_ACT_ENVIRONMENT = true;
+
 let container: HTMLDivElement | null = null;
 let root: Root | null = null;
 
@@ -187,6 +197,56 @@ describe("the failed-turn notice renders through PrFailedTurnStrip", () => {
     );
   });
 
+  test("the expanded detail never shows HTTP status or a raw provider dump", async () => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+    const items: MessageItem[] = [
+      {
+        id: "msg_ok",
+        createdAt: "2026-01-01T00:00:00.000Z",
+        parts: [{ kind: "text", text: "hi @echo" }],
+        sender: { name: null, address: "prn_alice@agents.example" },
+      },
+      {
+        id: "msg_notice",
+        createdAt: "2026-01-01T00:00:05.000Z",
+        parts: [
+          {
+            kind: "text",
+            text: "This agent could not complete your request due to a credential error [HTTP 401]: API key is invalid.",
+            turnFailed: true,
+          },
+        ],
+        sender: { name: null, address: "ins_echo1@agents.example" },
+      },
+    ];
+    await act(async () => {
+      root?.render(
+        <WorkbenchTimeline
+          items={items}
+          participants={[
+            { address: "ins_echo1@agents.example", handle: "echo" },
+          ]}
+        />,
+      );
+    });
+
+    act(() => {
+      container
+        ?.querySelector(".chat-turn-failed-disclosure")
+        ?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+
+    const detail = container.querySelector(".chat-turn-failed-detail");
+    expect(detail?.textContent).toBe(
+      "This agent could not complete your request due to a credential error",
+    );
+    expect(detail?.textContent).not.toMatch(/\[HTTP/);
+    expect(detail?.textContent).not.toContain("401");
+    expect(detail?.textContent).not.toContain("API key is invalid");
+  });
+
   test("Retry auto-resends the recovered request text — no composer round trip", async () => {
     container = document.createElement("div");
     document.body.appendChild(container);
diff --git a/packages/chat/package.json b/packages/chat/package.json
index b600582f..4596e789 100644
--- a/packages/chat/package.json
+++ b/packages/chat/package.json
@@ -15,6 +15,7 @@
     "./stream-events": "./src/stream-events.ts",
     "./blocks": "./src/blocks.ts",
     "./agent-address": "./src/agent-address.ts",
+    "./consumer-inference-text": "./src/consumer-inference-text.ts",
     "./workbench-host-naming": "./src/workbench-host-naming.ts",
     "./display-name": "./src/display-name.ts",
     "./id-leak-guard": "./src/id-leak-guard.ts"
diff --git a/packages/chat/src/consumer-inference-text.test.ts b/packages/chat/src/consumer-inference-text.test.ts
new file mode 100644
index 00000000..d604a001
--- /dev/null
+++ b/packages/chat/src/consumer-inference-text.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, test } from "bun:test";
+
+import {
+  CONSUMER_INFERENCE_FAILURE_NOTICE,
+  consumerFacingInferenceText,
+} from "./consumer-inference-text";
+
+describe("consumerFacingInferenceText", () => {
+  test("leaves ordinary replies unchanged", () => {
+    expect(consumerFacingInferenceText("Hello there.")).toBe("Hello there.");
+  });
+
+  test("keeps a classified preamble and drops a trailing HTTP dump", () => {
+    expect(
+      consumerFacingInferenceText(
+        "This agent could not complete your request due to a credential error [HTTP 401]: API key is invalid.",
+      ),
+    ).toBe(
+      "This agent could not complete your request due to a credential error",
+    );
+  });
+
+  test("a forced HTTP dump is not consumer copy", () => {
+    const text = consumerFacingInferenceText("[HTTP 401]: API key is invalid.");
+    expect(text).toBe(CONSUMER_INFERENCE_FAILURE_NOTICE);
+    expect(text).not.toMatch(/\[HTTP/i);
+    expect(text).not.toMatch(/401/);
+    expect(text.toLowerCase()).not.toContain("api key is invalid");
+  });
+
+  test("a JSON provider-error object is not consumer copy", () => {
+    const text = consumerFacingInferenceText(
+      '{"error":{"message":"Incorrect API key provided","type":"invalid_request_error","code":"invalid_api_key"}}',
+    );
+    expect(text).toBe(CONSUMER_INFERENCE_FAILURE_NOTICE);
+    expect(text.toLowerCase()).not.toContain("invalid_api_key");
+  });
+});
diff --git a/packages/chat/src/consumer-inference-text.ts b/packages/chat/src/consumer-inference-text.ts
new file mode 100644
index 00000000..da999311
--- /dev/null
+++ b/packages/chat/src/consumer-inference-text.ts
@@ -0,0 +1,29 @@
+/**
+ * Person-facing inference copy. HTTP status, raw provider dumps, and
+ * JSON error objects never belong on the timeline, in a sidebar preview,
+ * or next to the composer — DESIGN.md Honesty is one consumer sentence.
+ */
+
+const HTTP_STATUS_MARK = /\[HTTP\s+\d+\]/i;
+const TRAILING_HTTP_DUMP = /\s*\[HTTP\s+\d+\]:[\s\S]*$/i;
+
+export const CONSUMER_INFERENCE_FAILURE_NOTICE =
+  "This didn't go through. Try again, or check the connection in Settings.";
+
+function isProviderJsonDump(raw: string): boolean {
+  const trimmed = raw.trim();
+  if (!(trimmed.startsWith("{") || trimmed.startsWith("["))) return false;
+  return /"error"/i.test(trimmed);
+}
+
+function needsSanitization(raw: string): boolean {
+  return HTTP_STATUS_MARK.test(raw) || isProviderJsonDump(raw);
+}
+
+/** Drop HTTP status and raw provider text; keep a classified preamble when present. */
+export function consumerFacingInferenceText(raw: string): string {
+  if (!needsSanitization(raw)) return raw;
+  const stripped = raw.replace(TRAILING_HTTP_DUMP, "").trim();
+  if (stripped.length > 0 && !needsSanitization(stripped)) return stripped;
+  return CONSUMER_INFERENCE_FAILURE_NOTICE;
+}
diff --git a/packages/chat/src/index.ts b/packages/chat/src/index.ts
index 128c15ad..43198575 100644
--- a/packages/chat/src/index.ts
+++ b/packages/chat/src/index.ts
@@ -33,6 +33,10 @@ export type {
   SettleConnectedServiceInput,
 } from "./connect-pending";
 export { encodeParts, decodeParts, decodeMail, senderOf } from "./codec";
+export {
+  CONSUMER_INFERENCE_FAILURE_NOTICE,
+  consumerFacingInferenceText,
+} from "./consumer-inference-text";
 export type {
   MailContent,
   MailReadContent,
diff --git a/packages/chat/src/room-messages.test.ts b/packages/chat/src/room-messages.test.ts
index 00ef3ae5..10c62adb 100644
--- a/packages/chat/src/room-messages.test.ts
+++ b/packages/chat/src/room-messages.test.ts
@@ -58,6 +58,43 @@ describe("postRoomMessage", () => {
     ]);
   });
 
+  test("persists a consumer sentence, not HTTP status or a raw provider dump", async () => {
+    const roomMessages = createInMemoryRoomMessageStore();
+    const publisher = recordingPublisher();
+
+    const posted = await postRoomMessage(
+      { roomMessages, publish: publisher.publish },
+      {
+        tenantId: TENANT,
+        workbenchId: WORKBENCH,
+        sender: { name: null, address: "run_myra@acme.example" },
+        runId: "run_myra",
+        parts: [
+          {
+            kind: "text",
+            text: "This agent could not complete your request due to a credential error [HTTP 401]: API key is invalid.",
+          },
+        ],
+      },
+    );
+
+    expect(posted.parts).toEqual([
+      {
+        kind: "text",
+        text: "This agent could not complete your request due to a credential error",
+      },
+    ]);
+    const listed = await roomMessages.listMessages({
+      tenantId: TENANT,
+      workbenchId: WORKBENCH,
+    });
+    expect(listed.items[0]?.parts).toEqual(posted.parts);
+    expect(JSON.stringify(publisher.published)).not.toMatch(/\[HTTP/);
+    expect(JSON.stringify(publisher.published)).not.toContain(
+      "API key is invalid",
+    );
+  });
+
   test("an agent's message carries its run, a human's carries its principal", async () => {
     const roomMessages = createInMemoryRoomMessageStore();
     const publisher = recordingPublisher();
@@ -202,4 +239,17 @@ describe("previewOf", () => {
       ]),
     ).toBe("");
   });
+
+  test("does not preview HTTP status or raw provider dumps", () => {
+    expect(
+      previewOf([
+        {
+          kind: "text",
+          text: "This agent could not complete your request due to a credential error [HTTP 401]: API key is invalid.",
+        },
+      ]),
+    ).toBe(
+      "This agent could not complete your request due to a credential error",
+    );
+  });
 });
diff --git a/packages/chat/src/room-messages.ts b/packages/chat/src/room-messages.ts
index 9d27f3e3..afba9755 100644
--- a/packages/chat/src/room-messages.ts
+++ b/packages/chat/src/room-messages.ts
@@ -14,6 +14,7 @@ import { and, asc, count, desc, eq, gt, inArray, lt, or } from "drizzle-orm";
 import type { Part } from "./parts";
 import { workbenchMessages } from "./schema";
 import type { ChatDb } from "./store";
+import { consumerFacingInferenceText } from "./consumer-inference-text";
 import { ChatMessageEventData } from "./stream-events";
 import type { WorkbenchSubscriberRegistry } from "./workbench-events";
 
@@ -130,14 +131,16 @@ function newMessageId(): string {
  * previews as nothing rather than a fabricated placeholder.
  */
 export function previewOf(parts: readonly Part[]): string {
-  const text = parts
-    .filter((part): part is Extract<Part, { kind: "text" }> => {
-      return part.kind === "text";
-    })
-    .map((part) => part.text)
-    .join(" ")
-    .replace(/\s+/g, " ")
-    .trim();
+  const text = consumerFacingInferenceText(
+    parts
+      .filter((part): part is Extract<Part, { kind: "text" }> => {
+        return part.kind === "text";
+      })
+      .map((part) => part.text)
+      .join(" ")
+      .replace(/\s+/g, " ")
+      .trim(),
+  );
   return text.length > PREVIEW_MAX_LENGTH
     ? `${text.slice(0, PREVIEW_MAX_LENGTH).trimEnd()}…`
     : text;
@@ -155,6 +158,15 @@ export function previewOf(parts: readonly Part[]): string {
  * `ChatMessageEventData` is the wire contract this shape is asserted
  * against before it ever reaches `publish`.
  */
+function consumerFacingParts(parts: readonly Part[]): Part[] {
+  return parts.map((part) => {
+    if (part.kind !== "text") return part;
+    const text = consumerFacingInferenceText(part.text);
+    if (text === part.text) return part;
+    return { ...part, text };
+  });
+}
+
 export async function postRoomMessage(
   deps: {
     readonly roomMessages: RoomMessageStore;
@@ -162,8 +174,10 @@ export async function postRoomMessage(
   },
   input: PostRoomMessageInput,
 ): Promise<RoomMessage> {
+  const parts = consumerFacingParts(input.parts);
   const message = await deps.roomMessages.insertMessage({
     ...input,
+    parts,
     id: newMessageId(),
   });
   const data = ChatMessageEventData.assert({