diff --git a/src/server/routes/proxy/responsesWebsocket.ts b/src/server/routes/proxy/responsesWebsocket.ts
index 74ec6c7..ab8ed84 100644
--- a/src/server/routes/proxy/responsesWebsocket.ts
+++ b/src/server/routes/proxy/responsesWebsocket.ts
@@ -552,8 +552,8 @@ async function handleResponsesWebsocketConnection(
   request: IncomingMessage,
   authContext: ResponsesWebsocketAuthContext,
 ) {
-  const websocketSessionId = headerValueToTrimmedString(request.headers['session_id'])
-    || headerValueToTrimmedString(request.headers['session-id'])
+  const websocketSessionId = headerValueToTrimmedString(request.headers['session-id'])
+    || headerValueToTrimmedString(request.headers['session_id'])
     || headerValueToTrimmedString(request.headers['conversation-id'])
     || headerValueToTrimmedString(request.headers['conversation_id'])
     || randomUUID();
diff --git a/src/server/transformers/gemini/generate-content/requestBridge.test.ts b/src/server/transformers/gemini/generate-content/requestBridge.test.ts
index c2ef3f7..de3ac8a 100644
--- a/src/server/transformers/gemini/generate-content/requestBridge.test.ts
+++ b/src/server/transformers/gemini/generate-content/requestBridge.test.ts
@@ -262,4 +262,57 @@ describe('gemini generate-content request bridge', () => {
     expect(functionCallCount).toBe(2);
     expect(functionResponseCount).toBe(2);
   });
+
+  it('uses canonical tool-call names for Gemini functionResponse parts', () => {
+    const body = buildCanonicalRequestToGeminiGenerateContentBody({
+      operation: 'generate',
+      surface: 'gemini-generate-content',
+      cliProfile: 'generic',
+      requestedModel: 'gemini-2.5-pro',
+      stream: false,
+      messages: [
+        {
+          role: 'assistant',
+          parts: [{
+            type: 'tool_call',
+            id: 'call_weather',
+            name: 'lookup_weather',
+            argumentsJson: '{"city":"Paris"}',
+          }],
+        },
+        {
+          role: 'tool',
+          parts: [{
+            type: 'tool_result',
+            toolCallId: 'call_weather',
+            resultJson: { temperature: '22C' },
+          }],
+        },
+      ],
+    });
+
+    expect(body.contents).toEqual([
+      {
+        role: 'model',
+        parts: [{
+          functionCall: {
+            id: 'call_weather',
+            name: 'lookup_weather',
+            args: { city: 'Paris' },
+          },
+        }],
+      },
+      {
+        role: 'user',
+        parts: [{
+          functionResponse: {
+            name: 'lookup_weather',
+            response: {
+              result: { temperature: '22C' },
+            },
+          },
+        }],
+      },
+    ]);
+  });
 });
diff --git a/src/server/transformers/gemini/generate-content/requestBridge.ts b/src/server/transformers/gemini/generate-content/requestBridge.ts
index 4839096..d88dcd7 100644
--- a/src/server/transformers/gemini/generate-content/requestBridge.ts
+++ b/src/server/transformers/gemini/generate-content/requestBridge.ts
@@ -328,7 +328,10 @@ export function buildGeminiGenerateContentRequestFromOpenAi(input: {
   return request;
 }
 
-function canonicalPartToGeminiPart(part: CanonicalContentPart): Record<string, unknown> | null {
+function canonicalPartToGeminiPart(
+  part: CanonicalContentPart,
+  toolNameById?: ReadonlyMap<string, string>,
+): Record<string, unknown> | null {
   if (part.type === 'text') {
     return {
       text: part.text,
@@ -391,10 +394,13 @@ function canonicalPartToGeminiPart(part: CanonicalContentPart): Record<string, u
   }
 
   if (part.type === 'tool_result') {
+    const response = part.resultJson ?? parseJsonString(part.resultText ?? '');
     return {
       functionResponse: {
-        name: part.toolCallId,
-        response: part.resultJson ?? parseJsonString(part.resultText ?? ''),
+        name: toolNameById?.get(part.toolCallId) || 'unknown',
+        response: {
+          result: response,
+        },
       },
     };
   }
@@ -407,19 +413,26 @@ export function buildCanonicalRequestToGeminiGenerateContentBody(
 ): Record<string, unknown> {
   const contents: Array<Record<string, unknown>> = [];
   const systemParts: Array<Record<string, unknown>> = [];
+  const toolNameById = new Map<string, string>();
 
   for (const message of request.messages) {
     if (message.role === 'system' || message.role === 'developer') {
       systemParts.push(
         ...message.parts
-          .map((part) => canonicalPartToGeminiPart(part))
+          .map((part) => canonicalPartToGeminiPart(part, toolNameById))
           .filter((part): part is Record<string, unknown> => !!part),
       );
       continue;
     }
 
+    for (const part of message.parts) {
+      if (part.type === 'tool_call') {
+        toolNameById.set(part.id, part.name);
+      }
+    }
+
     const parts = message.parts
-      .map((part) => canonicalPartToGeminiPart(part))
+      .map((part) => canonicalPartToGeminiPart(part, toolNameById))
       .filter((part): part is Record<string, unknown> => !!part);
 
     if (parts.length <= 0) continue;