fix: standardize reasoning guards to truthy checks

Change `if (reasoning !== undefined)` to `if (reasoning)` in helpers.ts
and ollama.ts for consistency with the fixture-loader convention where
empty string means no reasoning.

Author: jpr5

src/helpers.ts

@@ -82,7 +82,7 @@ export function buildTextChunks(
   });
 
   // Reasoning chunks (emitted before content chunks)
-  if (reasoning !== undefined) {
+  if (reasoning) {
     for (let i = 0; i < reasoning.length; i += chunkSize) {
       const slice = reasoning.slice(i, i + chunkSize);
       chunks.push({
@@ -219,7 +219,7 @@ export function buildTextCompletion(
           role: "assistant",
           content,
           refusal: null,
-          ...(reasoning !== undefined ? { reasoning_content: reasoning } : {}),
+          ...(reasoning ? { reasoning_content: reasoning } : {}),
         },
         finish_reason: "stop",
       },

src/ollama.ts

@@ -167,7 +167,7 @@ function buildOllamaChatTextResponse(content: string, model: string, reasoning?:
     message: {
       role: "assistant",
       content,
-      ...(reasoning !== undefined ? { reasoning_content: reasoning } : {}),
+      ...(reasoning ? { reasoning_content: reasoning } : {}),
     },
     done: true,
     ...DURATION_FIELDS,
@@ -312,7 +312,7 @@ function buildOllamaGenerateTextResponse(
     model,
     created_at: new Date().toISOString(),
     response: content,
-    ...(reasoning !== undefined ? { reasoning_content: reasoning } : {}),
+    ...(reasoning ? { reasoning_content: reasoning } : {}),
     done: true,
     ...DURATION_FIELDS,
     context: [],