fix: show model response errors in chat

.changeset/show-model-response-errors.md

@@ -0,0 +1,5 @@
+---
+"@jmfederico/pi-web": patch
+---
+
+Show model response errors in the chat transcript instead of leaving the conversation blank.

src/client/src/chatMessages.test.ts

@@ -29,6 +29,19 @@ describe("chat message normalization", () => {
     ]);
   });
 
+  it("shows assistant model errors as system chat messages", () => {
+    expect(normalizeMessage({ role: "assistant", content: [], stopReason: "error", errorMessage: "429 rate limit", timestamp: "2026-05-09T12:00:00.000Z", provider: "openai", model: "gpt-4.1" })).toEqual([
+      { role: "system", parts: [{ type: "text", text: "Model response failed: 429 rate limit" }], meta: { timestamp: "2026-05-09T12:00:00.000Z", model: { provider: "openai", id: "gpt-4.1" } } },
+    ]);
+  });
+
+  it("keeps partial assistant content and adds a visible error line", () => {
+    expect(normalizeMessage({ role: "assistant", content: [{ type: "text", text: "partial answer" }], stopReason: "error", errorMessage: "connection lost" })).toEqual([
+      textMessage("assistant", "partial answer"),
+      textMessage("system", "Model response failed: connection lost"),
+    ]);
+  });
+
   it("extracts skill invocation blocks into dedicated skill and user messages", () => {
     expect(normalizeMessage({ role: "user", content: "<skill name=\"playwright\" location=\"/skills/playwright\">\nUse browser\n</skill>\n\nNow test the UI" })).toEqual([
       { role: "user", parts: [{ type: "skillInvocation", name: "playwright", location: "/skills/playwright", content: "Use browser" }] },

src/client/src/chatMessages.ts

@@ -53,7 +53,16 @@ export function normalizeMessage(message: unknown): ChatLine[] {
 
   const visible = parts.filter((part) => part.type !== "empty");
   const displayRole = role === "assistant" && visible.length > 0 && visible.every((part) => part.type === "skillRead") ? "skill" : role;
-  return visible.length > 0 ? [withMessageMeta({ role: displayRole, parts: visible, ...(source === undefined ? {} : { source }) }, message)] : [];
+  const lines = visible.length > 0 ? [withMessageMeta({ role: displayRole, parts: visible, ...(source === undefined ? {} : { source }) }, message)] : [];
+  const errorLine = assistantErrorLine(message);
+  return errorLine === undefined ? lines : [...lines, withMessageMeta(errorLine, message)];
+}
+
+function assistantErrorLine(message: unknown): ChatLine | undefined {
+  if (getString(message, "role") !== "assistant" || getString(message, "stopReason") !== "error") return undefined;
+  const errorMessage = getString(message, "errorMessage")?.trim();
+  const detail = errorMessage === undefined || errorMessage === "" ? "The model returned an error." : errorMessage;
+  return textMessage("system", `Model response failed: ${detail}`);
 }
 
 function isChatLine(message: unknown): message is ChatLine {

src/client/src/chatTranscript.test.ts

@@ -61,6 +61,46 @@ describe("applyTranscriptEvent", () => {
     ]);
   });
 
+  it("appends finalized assistant errors that have no displayable content", () => {
+    expect(applyTranscriptEvent([textMessage("user", "question")], {
+      type: "message.end",
+      message: {
+        role: "assistant",
+        content: [],
+        stopReason: "error",
+        errorMessage: "provider returned 500",
+        timestamp: "2026-05-09T12:00:00.000Z",
+        provider: "anthropic",
+        model: "claude-sonnet",
+      },
+    })).toEqual([
+      textMessage("user", "question"),
+      { role: "system", parts: [{ type: "text", text: "Model response failed: provider returned 500" }], meta: { timestamp: "2026-05-09T12:00:00.000Z", model: { provider: "anthropic", id: "claude-sonnet" } } },
+    ]);
+  });
+
+  it("replaces streamed assistant text and keeps the finalized error line", () => {
+    const streamed: ChatLine[] = [
+      textMessage("user", "question"),
+      textMessage("assistant", "partial"),
+    ];
+
+    expect(applyTranscriptEvent(streamed, {
+      type: "message.end",
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "partial answer" }],
+        stopReason: "error",
+        errorMessage: "connection lost",
+        timestamp: "2026-05-09T12:00:00.000Z",
+      },
+    })).toEqual([
+      textMessage("user", "question"),
+      { ...textMessage("assistant", "partial answer"), meta: { timestamp: "2026-05-09T12:00:00.000Z" } },
+      { role: "system", parts: [{ type: "text", text: "Model response failed: connection lost" }], meta: { timestamp: "2026-05-09T12:00:00.000Z" } },
+    ]);
+  });
+
   it("replaces streamed skill reads when the finalized assistant message includes thinking", () => {
     const streamed: ChatLine[] = [
       { role: "skill", parts: [{ type: "skillRead", name: "playwright", path: "/skills/playwright/SKILL.md" }] },

src/client/src/chatTranscript.ts

@@ -25,10 +25,16 @@ function applyFinalMessage(messages: ChatLine[], rawMessage: unknown): ChatLine[
     return finalizeToolExecution(messages, rawToolResult.toolCallId, rawToolResult.toolName, summarizeArgs(rawToolResult.content), rawToolResult.text, rawToolResult.isError, rawToolResult.content, rawToolResult.details);
   }
 
-  const ended = normalizeMessage(rawMessage)[0];
-  if (ended === undefined) return undefined;
-  const displayEnded = ended.role === "assistant" ? withoutToolCalls(ended) : ended;
-  if (displayEnded.parts.length === 0) return messages;
+  const ended = normalizeMessage(rawMessage);
+  if (ended.length === 0) return undefined;
+  const displayEnded = ended
+    .map((line) => line.role === "assistant" ? withoutToolCalls(line) : line)
+    .filter((line) => line.parts.length > 0);
+  if (displayEnded.length === 0) return messages;
+  return displayEnded.reduce((next, line) => applyFinalLine(next, line), messages);
+}
+
+function applyFinalLine(messages: ChatLine[], displayEnded: ChatLine): ChatLine[] {
   const skillReadIndex = findMatchingSkillRead(messages, displayEnded);
   if (skillReadIndex >= 0) return [...messages.slice(0, skillReadIndex), displayEnded, ...messages.slice(skillReadIndex + 1)];
   const last = messages.at(-1);