refactor: move chat error kinds into codersdk (#24955)

Moves the chat error kind taxonomy from `coderd/x/chatd/chaterror` into
`codersdk.ChatErrorKind` and types `ChatError.Kind` /
`ChatStreamRetry.Kind` so generated TypeScript exposes an SDK-owned
union, including `usage_limit`. Backend chat classification now
references the SDK constants directly while preserving the existing JSON
string values.

Keeps chat usage-limit admission failures on their existing 409 response
shape. The frontend maps structured usage-limit responses to the
SDK-owned `usage_limit` kind, uses generated `TypesGen.ChatErrorKind`
directly, and removes the local string union and alias.

codersdk/chats.go

@@ -1442,6 +1442,33 @@ type ChatStreamStatus struct {
 	Status ChatStatus `json:"status"`
 }
 
+// ChatErrorKind classifies chat errors for consistent client rendering.
+type ChatErrorKind string
+
+const (
+	ChatErrorKindGeneric        ChatErrorKind = "generic"
+	ChatErrorKindOverloaded     ChatErrorKind = "overloaded"
+	ChatErrorKindRateLimit      ChatErrorKind = "rate_limit"
+	ChatErrorKindTimeout        ChatErrorKind = "timeout"
+	ChatErrorKindStartupTimeout ChatErrorKind = "startup_timeout"
+	ChatErrorKindAuth           ChatErrorKind = "auth"
+	ChatErrorKindConfig         ChatErrorKind = "config"
+	ChatErrorKindUsageLimit     ChatErrorKind = "usage_limit"
+)
+
+// AllChatErrorKinds contains every ChatErrorKind value.
+// Update this when adding new constants above.
+var AllChatErrorKinds = []ChatErrorKind{
+	ChatErrorKindGeneric,
+	ChatErrorKindOverloaded,
+	ChatErrorKindRateLimit,
+	ChatErrorKindTimeout,
+	ChatErrorKindStartupTimeout,
+	ChatErrorKindAuth,
+	ChatErrorKindConfig,
+	ChatErrorKindUsageLimit,
+}
+
 // ChatError represents a terminal chat error in persisted chat state or the
 // live stream.
 type ChatError struct {
@@ -1451,7 +1478,7 @@ type ChatError struct {
 	// normalized error message when available.
 	Detail string `json:"detail,omitempty"`
 	// Kind classifies the error for consistent client rendering.
-	Kind string `json:"kind,omitempty"`
+	Kind ChatErrorKind `json:"kind,omitempty"`
 	// Provider identifies the upstream model provider when known.
 	Provider string `json:"provider,omitempty"`
 	// Retryable reports whether the underlying error is transient.
@@ -1470,7 +1497,7 @@ type ChatStreamRetry struct {
 	// Error is the normalized error message from the failed attempt.
 	Error string `json:"error"`
 	// Kind classifies the retry reason for consistent client rendering.
-	Kind string `json:"kind,omitempty"`
+	Kind ChatErrorKind `json:"kind,omitempty"`
 	// Provider identifies the upstream model provider when known.
 	Provider string `json:"provider,omitempty"`
 	// StatusCode is the best-effort upstream HTTP status code.

codersdk/chats_test.go

@@ -137,6 +137,35 @@ func TestChatUsageLimitExceededFrom(t *testing.T) {
 	})
 }
 
+func TestChatErrorKind_JSONRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	terminal := codersdk.ChatError{
+		Message: "limit reached",
+		Kind:    codersdk.ChatErrorKindUsageLimit,
+	}
+	data, err := json.Marshal(terminal)
+	require.NoError(t, err)
+	require.Contains(t, string(data), `"kind":"usage_limit"`)
+
+	var decodedTerminal codersdk.ChatError
+	require.NoError(t, json.Unmarshal(data, &decodedTerminal))
+	require.Equal(t, codersdk.ChatErrorKindUsageLimit, decodedTerminal.Kind)
+
+	retry := codersdk.ChatStreamRetry{
+		Attempt: 1,
+		Error:   "retrying",
+		Kind:    codersdk.ChatErrorKindUsageLimit,
+	}
+	data, err = json.Marshal(retry)
+	require.NoError(t, err)
+	require.Contains(t, string(data), `"kind":"usage_limit"`)
+
+	var decodedRetry codersdk.ChatStreamRetry
+	require.NoError(t, json.Unmarshal(data, &decodedRetry))
+	require.Equal(t, codersdk.ChatErrorKindUsageLimit, decodedRetry.Kind)
+}
+
 func TestChatMessagePart_StripInternal(t *testing.T) {
 	t.Parallel()
 
@@ -450,7 +479,7 @@ func TestChat_JSONRoundTrip(t *testing.T) {
 	lastError := &codersdk.ChatError{
 		Message:    "boom",
 		Detail:     "provider detail",
-		Kind:       "generic",
+		Kind:       codersdk.ChatErrorKindGeneric,
 		Provider:   "openai",
 		Retryable:  true,
 		StatusCode: 503,