feat(experiments): support freeform provider responses

lib/llm/provider.js

@@ -352,6 +352,9 @@ class OllamaLlmProvider {
     const baseUrl = process.env.OLLAMA_BASE_URL;
     if (!baseUrl) throw new Error("OLLAMA_BASE_URL is not set");
 
+    // Explicit null signals "freeform text" — no JSON-schema constraint.
+    const useFreeformText = outputSchema === null;
+
     let apiUsed = null;
     let chatSupported = false;
     let rawResponse = null;
@@ -382,15 +385,19 @@ class OllamaLlmProvider {
       try {
         apiUsed = "/api/chat";
         providerExecution.chatRequestAttempted = true;
+        const body = {
+          model: modelName,
+          messages: [{ role: "user", content: prompt }],
+          stream: false,
+        };
+        // Explicit null → omit format constraint entirely.
+        if (outputSchema !== null) {
+          body.format = outputSchema ?? reconstructionJsonSchema;
+        }
         const res = await fetch(`${baseUrl}/api/chat`, {
           method: "POST",
           headers: { "Content-Type": "application/json" },
-          body: JSON.stringify({
-            model: modelName,
-            messages: [{ role: "user", content: prompt }],
-            stream: false,
-            format: outputSchema ?? reconstructionJsonSchema,
-          }),
+          body: JSON.stringify(body),
           signal: requestAbort.signal,
         });
 
@@ -445,6 +452,11 @@ class OllamaLlmProvider {
           ? fullResponseData.response
           : JSON.stringify(fullResponseData);
 
+        // generate has no format constraint — treat freeform input as freeform output.
+        if (useFreeformText) {
+          apiUsed = "/api/generate";
+        }
+
       } catch (e) {
         if (apiUsed === "/api/generate") {
           const error = new Error(
@@ -476,11 +488,11 @@ class OllamaLlmProvider {
     // ================================================================
     if (rawResponse === "") {
       let diagInfo = "";
-      
+
       if (fullResponseData) {
         const keys = Object.keys(fullResponseData);
         diagInfo = "Keys in response: " + keys.join(", ") + "\n";
-        
+
         for (const key of keys) {
           const val = fullResponseData[key];
           if (typeof val === "string") {
@@ -501,6 +513,7 @@ class OllamaLlmProvider {
         "\nPossible causes:\n" +
         "- Check 'ollama list' — make sure the model name matches exactly what's installed\n" +
         "- The model may be corrupted. Try: ollama pull " + modelName + "\n" +
+        (useFreeformText ? "- No format constraint was sent — the model may not support freeform output.\n" : "") +
         "- This Ollama version does not support format:json — using prompt instructions only (reliability varies)\n" +
         "- If your model is very small (e.g., tinyllama, phi), try a larger one like llama3.1 or mistral"
       );
@@ -512,6 +525,14 @@ class OllamaLlmProvider {
     // ================================================================
     // Step 5: Parse and return
     // ================================================================
+    if (useFreeformText) {
+      return {
+        response: rawResponse,
+        providerApiPath: apiUsed,
+        providerExecution,
+      };
+    }
+
     try {
       return {
         response: recoverJson(rawResponse),
@@ -553,17 +574,27 @@ class OpenAIReconstructionProvider {
     { signal, outputZodSchema } = {},
   ) {
     if (!this.apiKey) throw new Error("OPENAI_API_KEY is not set");
-    const structuredOutputSchema = outputSchema
-      ? createOpenAIStrictSchema(outputSchema, outputZodSchema ?? null)
-      : openAIReconstructionJsonSchema;
 
-    const format = {
-      type: "json_schema",
-      name: "reconstruction",
-      strict: true,
-      schema: structuredOutputSchema,
-    };
-    traceOpenAISchema({ model: modelName, format, schema: structuredOutputSchema });
+    // Explicit null → freeform text output (no JSON-schema constraint).
+    const useFreeformText = outputSchema === null;
+
+    let format;
+    if (useFreeformText) {
+      format = { type: "text" };
+    } else {
+      const structuredOutputSchema = outputSchema
+        ? createOpenAIStrictSchema(outputSchema, outputZodSchema ?? null)
+        : openAIReconstructionJsonSchema;
+      format = {
+        type: "json_schema",
+        name: "reconstruction",
+        strict: true,
+        schema: structuredOutputSchema,
+      };
+
+      traceOpenAISchema({ model: modelName, format, schema: structuredOutputSchema });
+    }
+
     const response = await this.fetchImpl("https://api.openai.com/v1/responses", {
       method: "POST",
       headers: {
@@ -599,6 +630,14 @@ class OpenAIReconstructionProvider {
       throw error;
     }
 
+    // Freeform mode — return raw text without JSON recovery or transformation.
+    if (useFreeformText) {
+      return {
+        response: outputText,
+        providerApiPath: "/v1/responses",
+      };
+    }
+
     const recoveredResponse = recoverJson(outputText);
     const normalisedResponse = outputSchema && !outputZodSchema
       ? recoveredResponse