experiment(confidence-engine): add openai provider apparatus

lib/llm/provider.js

@@ -12,6 +12,14 @@ export function getProvider() {
   return new OllamaLlmProvider();
 }
 
+/**
+ * Experiment-only construction seam. Production provider selection remains Ollama.
+ * @param {{ apiKey?: string, fetchImpl?: typeof fetch }} [options]
+ */
+export function createOpenAIReconstructionProvider(options = {}) {
+  return new OpenAIReconstructionProvider(options);
+}
+
 function recoverJson(raw) {
   if (typeof raw !== "string") return raw;
   const trimmed = raw.trim();
@@ -294,3 +302,56 @@ class OllamaLlmProvider {
     }
   }
 }
+
+class OpenAIReconstructionProvider {
+  constructor({ apiKey = process.env.OPENAI_API_KEY, fetchImpl = fetch } = {}) {
+    this.apiKey = apiKey;
+    this.fetchImpl = fetchImpl;
+  }
+
+  async generateReconstruction(prompt, modelName = "gpt-5.6-terra") {
+    if (!this.apiKey) throw new Error("OPENAI_API_KEY is not set");
+
+    const response = await this.fetchImpl("https://api.openai.com/v1/responses", {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${this.apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        model: modelName,
+        input: prompt,
+        text: {
+          format: {
+            type: "json_schema",
+            name: "reconstruction",
+            strict: true,
+            schema: reconstructionJsonSchema,
+          },
+        },
+      }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      const error = new Error(
+        `OpenAI Responses API returned ${response.status}: ${body}`,
+      );
+      error.providerApiPath = "/v1/responses";
+      throw error;
+    }
+
+    const data = await response.json();
+    const outputText = data.output_text;
+    if (typeof outputText !== "string") {
+      const error = new Error("OpenAI Responses API returned no output_text");
+      error.providerApiPath = "/v1/responses";
+      throw error;
+    }
+
+    return {
+      response: recoverJson(outputText),
+      providerApiPath: "/v1/responses",
+    };
+  }
+}