fix!: persist structured chat errors (#24919)

**Breaking change for changelog:**

> `codersdk.Chat.last_error` now returns a structured `ChatError` object
(`{message, kind, provider, retryable, status_code, detail}`) instead of
a plain string. The chats API is experimental
(`/api/experimental/chats`), so this ships without a deprecation cycle;
consumers reading `chat.last_error` as a string must update to read
`chat.last_error.message`. SDK/generated TypeScript terminal error
payloads now use the single `ChatError` type; the live stream error
payload type is renamed from `ChatStreamError` to `ChatError`.

Persisted chat errors now carry the same provider-specific detail (kind,
provider, retryable, HTTP status, optional detail) as the live stream,
so refreshing a failed chat rehydrates with the full structured error
instead of a one-line headline.

Existing rows are migrated in place: legacy text errors are wrapped into
`{message, kind: "generic"}` so already-errored chats still render, and
rows with `last_error IS NULL` stay NULL. Internally, persisted fallback
decoding now reuses the existing `chaterror.KindGeneric` constant, with
no JSON value change.

Closes CODAGT-239

cli/agents_chat.go

@@ -1287,7 +1287,7 @@ func (m chatViewModel) handleStreamEvent(event codersdk.ChatStreamEvent) (chatVi
 						chatID:     m.activeChatID,
 						event: codersdk.ChatStreamEvent{
 							Type: codersdk.ChatStreamEventTypeError,
-							Error: &codersdk.ChatStreamError{
+							Error: &codersdk.ChatError{
 								Message: fmt.Sprintf(
 									"failed to parse ask_user_question: %v",
 									err,

cli/agents_list.go

@@ -78,7 +78,7 @@ func (m chatListModel) filteredChats() []codersdk.Chat {
 			filtered = append(filtered, chat)
 			continue
 		}
-		if chat.LastError != nil && strings.Contains(strings.ToLower(*chat.LastError), query) {
+		if chat.LastError != nil && strings.Contains(strings.ToLower(chat.LastError.Message), query) {
 			filtered = append(filtered, chat)
 		}
 	}
@@ -445,13 +445,14 @@ func (m chatListModel) View() string {
 		rowText := fmt.Sprintf("%s%s %s %s%s", rowPrefix, rowStyle.Render(title), status, m.styles.dimmedText.Render(timeAgo(row.chat.UpdatedAt)), extra)
 		lines = append(lines, rowText)
 
-		if row.chat.Status == codersdk.ChatStatusError && row.chat.LastError != nil {
+		if row.chat.Status == codersdk.ChatStatusError && row.chat.LastError != nil && row.chat.LastError.Message != "" {
+			lastError := row.chat.LastError.Message
 			errWidth := max(m.width-4, 20)
 			errPrefix := "    "
 			if row.depth > 0 {
 				errPrefix += strings.Repeat("  ", row.depth)
 			}
-			lines = append(lines, errPrefix+m.styles.dimmedText.Render(m.styles.truncate(sanitizeTerminalRenderableText(*row.chat.LastError), errWidth)))
+			lines = append(lines, errPrefix+m.styles.dimmedText.Render(m.styles.truncate(sanitizeTerminalRenderableText(lastError), errWidth)))
 		}
 	}
 

cli/agents_stream_test.go

@@ -116,7 +116,7 @@ func TestConsumeChatStreamText(t *testing.T) {
 		{Type: codersdk.ChatStreamEventTypeMessage, Message: &codersdk.ChatMessage{ID: 1, ChatID: uuid.New(), Role: codersdk.ChatMessageRoleAssistant, Content: []codersdk.ChatMessagePart{{Type: codersdk.ChatMessagePartTypeText, Text: "Hello world"}}}},
 		{Type: codersdk.ChatStreamEventTypeStatus, Status: &codersdk.ChatStreamStatus{Status: codersdk.ChatStatusRunning}},
 		{Type: codersdk.ChatStreamEventTypeRetry, Retry: &codersdk.ChatStreamRetry{Attempt: 2, Error: "rate limited"}},
-		{Type: codersdk.ChatStreamEventTypeError, Error: &codersdk.ChatStreamError{Message: "boom"}},
+		{Type: codersdk.ChatStreamEventTypeError, Error: &codersdk.ChatError{Message: "boom"}},
 	} {
 		events <- event
 	}

cli/agents_test.go

@@ -1070,7 +1070,7 @@ func TestAgents(t *testing.T) {
 			t.Parallel()
 			updated, cmd := applyStream(newTestChatViewModel(nil), codersdk.ChatStreamEvent{
 				Type:  codersdk.ChatStreamEventTypeError,
-				Error: &codersdk.ChatStreamError{Message: "stream blew up"},
+				Error: &codersdk.ChatError{Message: "stream blew up"},
 			})
 			require.Nil(t, cmd)
 			require.Equal(t, "stream error: stream blew up", updated.err.Error())