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.

coderd/database/db2sdk/db2sdk.go

@@ -28,7 +28,6 @@ import (
 	"github.com/coder/coder/v2/coderd/util/ptr"
 	"github.com/coder/coder/v2/coderd/util/slice"
 	"github.com/coder/coder/v2/coderd/workspaceapps/appurl"
-	"github.com/coder/coder/v2/coderd/x/chatd/chaterror"
 	"github.com/coder/coder/v2/coderd/x/chatd/chatprompt"
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/provisionersdk/proto"
@@ -1619,16 +1618,16 @@ func decodeChatLastError(raw pqtype.NullRawMessage) *codersdk.ChatError {
 	if err := json.Unmarshal(raw.RawMessage, &payload); err != nil {
 		return &codersdk.ChatError{
 			Message: fallbackChatLastErrorMessage,
-			Kind:    chaterror.KindGeneric,
+			Kind:    codersdk.ChatErrorKindGeneric,
 		}
 	}
 
 	payload.Message = strings.TrimSpace(payload.Message)
 	payload.Detail = strings.TrimSpace(payload.Detail)
-	payload.Kind = strings.TrimSpace(payload.Kind)
+	payload.Kind = codersdk.ChatErrorKind(strings.TrimSpace(string(payload.Kind)))
 	payload.Provider = strings.TrimSpace(payload.Provider)
 	if payload.Kind == "" {
-		payload.Kind = chaterror.KindGeneric
+		payload.Kind = codersdk.ChatErrorKindGeneric
 	}
 	if payload.Message == "" {
 		payload.Message = fallbackChatLastErrorMessage

coderd/database/db2sdk/db2sdk_test.go

@@ -19,7 +19,6 @@ import (
 	"github.com/coder/coder/v2/coderd/database/dbgen"
 	"github.com/coder/coder/v2/coderd/database/dbtestutil"
 	"github.com/coder/coder/v2/coderd/database/dbtime"
-	"github.com/coder/coder/v2/coderd/x/chatd/chaterror"
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/provisionersdk/proto"
 )
@@ -920,7 +919,7 @@ func TestChat_AllFieldsPopulated(t *testing.T) {
 	lastErrorPayload := codersdk.ChatError{
 		Message:    "boom",
 		Detail:     "provider detail",
-		Kind:       chaterror.KindGeneric,
+		Kind:       codersdk.ChatErrorKindGeneric,
 		Provider:   "openai",
 		Retryable:  true,
 		StatusCode: 503,
@@ -1082,7 +1081,7 @@ func TestChat_LastErrorFallback(t *testing.T) {
 			raw:  json.RawMessage(`{`),
 			expectPayload: &codersdk.ChatError{
 				Message:   fallbackMessage,
-				Kind:      chaterror.KindGeneric,
+				Kind:      codersdk.ChatErrorKindGeneric,
 				Retryable: false,
 			},
 		},
@@ -1091,7 +1090,7 @@ func TestChat_LastErrorFallback(t *testing.T) {
 			raw:  json.RawMessage(`{"kind":"timeout","provider":"openai","status_code":504}`),
 			expectPayload: &codersdk.ChatError{
 				Message:    fallbackMessage,
-				Kind:       "timeout",
+				Kind:       codersdk.ChatErrorKindTimeout,
 				Provider:   "openai",
 				Retryable:  false,
 				StatusCode: 504,
@@ -1102,7 +1101,7 @@ func TestChat_LastErrorFallback(t *testing.T) {
 			raw:  json.RawMessage(`{"message":"  ","provider":"openai"}`),
 			expectPayload: &codersdk.ChatError{
 				Message:   fallbackMessage,
-				Kind:      chaterror.KindGeneric,
+				Kind:      codersdk.ChatErrorKindGeneric,
 				Provider:  "openai",
 				Retryable: false,
 			},
@@ -1112,12 +1111,21 @@ func TestChat_LastErrorFallback(t *testing.T) {
 			raw:  json.RawMessage(`{"message":"OpenAI returned an unexpected error.","provider":"openai","status_code":502}`),
 			expectPayload: &codersdk.ChatError{
 				Message:    "OpenAI returned an unexpected error.",
-				Kind:       chaterror.KindGeneric,
+				Kind:       codersdk.ChatErrorKindGeneric,
 				Provider:   "openai",
 				Retryable:  false,
 				StatusCode: 502,
 			},
 		},
+		{
+			name: "UsageLimitKindRoundTrips",
+			raw:  json.RawMessage(`{"message":"Usage limit reached.","kind":"usage_limit"}`),
+			expectPayload: &codersdk.ChatError{
+				Message:   "Usage limit reached.",
+				Kind:      codersdk.ChatErrorKindUsageLimit,
+				Retryable: false,
+			},
+		},
 	}
 
 	for _, tc := range tests {