Enforce JSON schema for Gemini responses

Add responseMimeType and a responseSchema to the Gemini provider's generationConfig to force structured JSON output. With this, it should be usable with gemini-2.5-flash

Author: JoaoPauloSPloger

lib/llm/gemini.mjs

@@ -23,6 +23,25 @@ export class GeminiProvider extends LLMProvider {
         contents: [{ parts: [{ text: userMessage }] }],
         generationConfig: {
           maxOutputTokens: opts.maxTokens || 4096,
+          // Trava estrutural para garantir o JSON nativo
+          responseMimeType: "application/json",
+          responseSchema: {
+            type: "ARRAY",
+            items: {
+              type: "OBJECT",
+              properties: {
+                title: { type: "STRING", description: "Short title (max 10 words)" },
+                type: { type: "STRING", enum: ["LONG", "SHORT", "HEDGE", "WATCH", "AVOID"] },
+                ticker: { type: "STRING", description: "Primary instrument" },
+                confidence: { type: "STRING", enum: ["HIGH", "MEDIUM", "LOW"] },
+                rationale: { type: "STRING", description: "2-3 sentence explanation citing specific data" },
+                risk: { type: "STRING", description: "Key risk factor" },
+                horizon: { type: "STRING", description: "Intraday, Days, Weeks, or Months" },
+                signals: { type: "ARRAY", items: { type: "STRING" } }
+              },
+              required: ["title", "type", "ticker", "confidence", "rationale", "risk", "horizon", "signals"]
+            }
+          }
         },
       }),
       signal: AbortSignal.timeout(opts.timeout || 60000),
@@ -45,4 +64,4 @@ export class GeminiProvider extends LLMProvider {
       model: this.model,
     };
   }
-}
+}