chore: tighten cli validation and tooling checks

src/engine/gemini.ts

@@ -1,5 +1,7 @@
 import {
   Content,
+  FinishReason,
+  GenerateContentResponse,
   GoogleGenerativeAI,
   HarmBlockThreshold,
   HarmCategory,
@@ -12,6 +14,59 @@ import { AiEngine, AiEngineConfig } from './Engine';
 
 interface GeminiConfig extends AiEngineConfig {}
 
+const GEMINI_BLOCKING_FINISH_REASONS = new Set<FinishReason>([
+  FinishReason.RECITATION,
+  FinishReason.SAFETY,
+  FinishReason.LANGUAGE
+]);
+
+const formatGeminiBlockMessage = (
+  response: GenerateContentResponse
+): string => {
+  const promptFeedback = response.promptFeedback;
+  if (promptFeedback?.blockReason) {
+    return promptFeedback.blockReasonMessage
+      ? `Gemini response was blocked due to ${promptFeedback.blockReason}: ${promptFeedback.blockReasonMessage}`
+      : `Gemini response was blocked due to ${promptFeedback.blockReason}`;
+  }
+
+  const firstCandidate = response.candidates?.[0];
+  if (firstCandidate?.finishReason) {
+    return firstCandidate.finishMessage
+      ? `Gemini response was blocked due to ${firstCandidate.finishReason}: ${firstCandidate.finishMessage}`
+      : `Gemini response was blocked due to ${firstCandidate.finishReason}`;
+  }
+
+  return 'Gemini response did not contain usable text';
+};
+
+const extractGeminiText = (response: GenerateContentResponse): string => {
+  const firstCandidate = response.candidates?.[0];
+
+  if (
+    firstCandidate?.finishReason &&
+    GEMINI_BLOCKING_FINISH_REASONS.has(firstCandidate.finishReason)
+  ) {
+    throw new Error(formatGeminiBlockMessage(response));
+  }
+
+  const text = firstCandidate?.content?.parts
+    ?.flatMap((part) =>
+      'text' in part && typeof part.text === 'string' ? [part.text] : []
+    )
+    .join('');
+
+  if (typeof text === 'string' && text.length > 0) {
+    return text;
+  }
+
+  if (response.promptFeedback?.blockReason) {
+    throw new Error(formatGeminiBlockMessage(response));
+  }
+
+  return '';
+};
+
 export class GeminiEngine implements AiEngine {
   config: GeminiConfig;
   client: GoogleGenerativeAI;
@@ -77,7 +132,7 @@ export class GeminiEngine implements AiEngine {
         }
       });
 
-      const content = result.response.text();
+      const content = extractGeminiText(result.response);
       return removeContentTags(content, 'think');
     } catch (error) {
       throw normalizeEngineError(error, 'gemini', this.config.model);