fix: prefer result over output in Gemini Interactions function_result parsing

Author: jpr5

docs/gemini-interactions/index.html

@@ -134,7 +134,7 @@ <h3>Content[] with Function Result (Tool Response)</h3>
     {
       <span class="prop">"role"</span>: <span class="str">"user"</span>,
       <span class="prop">"parts"</span>: [
-        { <span class="prop">"type"</span>: <span class="str">"function_result"</span>, <span class="prop">"name"</span>: <span class="str">"get_weather"</span>, <span class="prop">"call_id"</span>: <span class="str">"call_abc123"</span>, <span class="prop">"output"</span>: <span class="str">"72F sunny"</span> }
+        { <span class="prop">"type"</span>: <span class="str">"function_result"</span>, <span class="prop">"name"</span>: <span class="str">"get_weather"</span>, <span class="prop">"call_id"</span>: <span class="str">"call_abc123"</span>, <span class="prop">"result"</span>: <span class="str">"72F sunny"</span> }
       ]
     }
   ],

src/__tests__/gemini-interactions.test.ts

@@ -251,7 +251,7 @@ describe("geminiInteractionsToCompletionRequest", () => {
             {
               type: "function_result",
               call_id: "call_abc",
-              output: { temperature: 72 },
+              result: { temperature: 72 },
             },
           ],
         },
@@ -393,7 +393,7 @@ describe("geminiInteractionsToCompletionRequest", () => {
     expect(result.messages).toEqual([{ role: "user", content: "hi" }]);
   });
 
-  it("converts function_result with string output (passes through as-is)", () => {
+  it("converts function_result with string result (passes through as-is)", () => {
     const result = geminiInteractionsToCompletionRequest({
       model: "gemini-2.5-flash",
       input: [
@@ -403,7 +403,7 @@ describe("geminiInteractionsToCompletionRequest", () => {
             {
               type: "function_result",
               call_id: "call_str",
-              output: "plain string result",
+              result: "plain string result",
             },
           ],
         },
@@ -465,7 +465,7 @@ describe("geminiInteractionsToCompletionRequest", () => {
             {
               type: "function_result",
               call_id: "call_legacy_result",
-              output: { status: "ok" },
+              result: { status: "ok" },
             },
           ],
         },
@@ -477,6 +477,53 @@ describe("geminiInteractionsToCompletionRequest", () => {
     expect(result.messages[0].tool_call_id).toBe("call_legacy_result");
   });
 
+  // ─── result vs output preference tests ────────────────────────────────
+
+  it("falls back to output when result is not present (backwards compat)", () => {
+    const result = geminiInteractionsToCompletionRequest({
+      model: "gemini-2.5-flash",
+      input: [
+        {
+          role: "user",
+          content: [
+            {
+              type: "function_result",
+              call_id: "call_old",
+              output: { legacy: true },
+            },
+          ],
+        },
+      ],
+    });
+    expect(result.messages).toHaveLength(1);
+    expect(result.messages[0].role).toBe("tool");
+    expect(result.messages[0].content).toBe('{"legacy":true}');
+    expect(result.messages[0].tool_call_id).toBe("call_old");
+  });
+
+  it("prefers result over output when both are present on a function_result", () => {
+    const result = geminiInteractionsToCompletionRequest({
+      model: "gemini-2.5-flash",
+      input: [
+        {
+          role: "user",
+          content: [
+            {
+              type: "function_result",
+              call_id: "call_both",
+              result: { from: "result" },
+              output: { from: "output" },
+            },
+          ],
+        },
+      ],
+    });
+    expect(result.messages).toHaveLength(1);
+    expect(result.messages[0].role).toBe("tool");
+    expect(result.messages[0].content).toBe('{"from":"result"}');
+    expect(result.messages[0].tool_call_id).toBe("call_both");
+  });
+
   // ─── content vs parts preference test ─────────────────────────────────
 
   it("prefers content over parts when both are present on a Turn", () => {
@@ -1011,7 +1058,7 @@ describe("Gemini Interactions — fixture matching", () => {
             {
               type: "function_result",
               call_id: "call_abc",
-              output: "result",
+              result: "result",
             },
           ],
         },
@@ -1179,4 +1226,23 @@ describe("Gemini Interactions — edge cases", () => {
     expect(deltas).toHaveLength(1);
     expect((deltas[0].delta as Record<string, unknown>).text).toBe("");
   });
+
+  it("returns 500 for unrecognized fixture response type", async () => {
+    instance = await createServer([
+      {
+        match: { userMessage: "bad-shape" },
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        response: { unknownField: true } as any,
+      },
+    ]);
+    const res = await post(`${instance.url}/v1beta/interactions`, {
+      model: "gemini-2.5-flash",
+      input: "bad-shape",
+      stream: false,
+    });
+    expect(res.status).toBe(500);
+    const body = JSON.parse(res.body);
+    expect(body.error.code).toBe("INTERNAL");
+    expect(body.error.message).toBe("Fixture response did not match any known type");
+  });
 });

src/gemini-interactions.ts

@@ -46,6 +46,7 @@ interface InteractionsContentBlock {
   id?: string;
   arguments?: Record<string, unknown>;
   output?: unknown;
+  result?: unknown;
 }
 
 interface InteractionsTurn {
@@ -132,10 +133,11 @@ export function geminiInteractionsToCompletionRequest(
           } else if (funcResultParts.length > 0) {
             // Tool response messages
             for (const part of funcResultParts) {
+              const resultValue = part.result ?? part.output;
               messages.push({
                 role: "tool",
                 content:
-                  typeof part.output === "string" ? part.output : JSON.stringify(part.output ?? ""),
+                  typeof resultValue === "string" ? resultValue : JSON.stringify(resultValue ?? ""),
                 tool_call_id: part.call_id ?? part.id ?? "",
               });
             }