fix: surface llm workflow errors

src/lib/llm/client.ts

@@ -28,6 +28,16 @@ export interface LlmProviderStatus {
   reason?: string;
 }
 
+export class LlmValidationError extends Error {
+  constructor(
+    message: string,
+    public readonly task: LlmTaskName,
+  ) {
+    super(message);
+    this.name = "LlmValidationError";
+  }
+}
+
 function getProvider() {
   return (process.env.LLM_PROVIDER || "deepseek").toLowerCase();
 }
@@ -80,8 +90,8 @@ export function setChatCompletionForTesting(
   chatCompletionForTesting = handler;
 }
 
-function getTask(input: GenerateInput) {
-  return input.task?.trim() || "unknown";
+function getTask(input: GenerateInput): LlmTaskName {
+  return input.task || "unknown";
 }
 
 function getRawLogLimit() {
@@ -204,11 +214,14 @@ export function setGenerateJsonForValidation(
 export async function generateValidatedJson<T>({
   schema,
   ...input
-}: GenerateValidatedJsonInput<T>): Promise<T | null> {
+}: GenerateValidatedJsonInput<T>): Promise<T> {
   const task = getTask(input);
   if (!isLlmConfigured()) {
     console.info(`[llm:validated] task=${task} ok=false reason=not_configured`);
-    return null;
+    throw new LlmValidationError(
+      getLlmProviderStatus().reason ?? "LLM provider is not configured",
+      task,
+    );
   }
 
   const status = getLlmProviderStatus();
@@ -230,14 +243,20 @@ export async function generateValidatedJson<T>({
     console.warn(
       `[llm:validated] task=${task} ok=false zod_error=${quoteLogValue(summarizeZodError(parsed.error))}`,
     );
-    return null;
+    throw new LlmValidationError(
+      `LLM response failed schema validation: ${summarizeZodError(parsed.error)}`,
+      task,
+    );
   } catch (error) {
+    if (error instanceof LlmValidationError) {
+      throw error;
+    }
     console.info(`[llm:validated] task=${task} ok=false reason=provider_error`);
     const message = error instanceof Error ? error.message : String(error);
     console.warn(
       `[llm:error] task=${task} duration_ms=${Date.now() - startedAt} message=${quoteLogValue(message)}`,
     );
-    return null;
+    throw error instanceof Error ? error : new Error(message);
   }
 }