fix(openai-shim): preserve tool result images and local token caps (#659)

Keep tool-result images as real image_url parts for OpenAI-compatible requests and use max_tokens for local providers like Ollama and LM Studio.

src/services/api/openaiShim.test.ts

@@ -403,6 +403,97 @@ test('preserves usage from final OpenAI stream chunk with empty choices', async
   expect(usageEvent?.usage?.output_tokens).toBe(45)
 })
 
+test('uses max_tokens instead of max_completion_tokens for local providers', async () => {
+  process.env.OPENAI_BASE_URL = 'http://localhost:11434/v1'
+
+  globalThis.fetch = (async (_input, init) => {
+    const body = JSON.parse(String(init?.body))
+    expect(body.max_tokens).toBe(64)
+    expect(body.max_completion_tokens).toBeUndefined()
+    expect(body.stream_options).toBeUndefined()
+
+    return new Response(
+      JSON.stringify({
+        id: 'chatcmpl-1',
+        model: 'llama3.1:8b',
+        choices: [
+          {
+            message: {
+              role: 'assistant',
+              content: 'hello',
+            },
+            finish_reason: 'stop',
+          },
+        ],
+        usage: {
+          prompt_tokens: 5,
+          completion_tokens: 1,
+          total_tokens: 6,
+        },
+      }),
+      {
+        headers: {
+          'Content-Type': 'application/json',
+        },
+      },
+    )
+  }) as FetchType
+
+  const client = createOpenAIShimClient({}) as OpenAIShimClient
+
+  await client.beta.messages.create({
+    model: 'llama3.1:8b',
+    messages: [{ role: 'user', content: 'hello' }],
+    max_tokens: 64,
+    stream: false,
+  })
+})
+
+test('keeps max_completion_tokens for non-local non-github providers', async () => {
+  process.env.OPENAI_BASE_URL = 'https://api.openai.com/v1'
+
+  globalThis.fetch = (async (_input, init) => {
+    const body = JSON.parse(String(init?.body))
+    expect(body.max_completion_tokens).toBe(64)
+    expect(body.max_tokens).toBeUndefined()
+
+    return new Response(
+      JSON.stringify({
+        id: 'chatcmpl-1',
+        model: 'gpt-4o',
+        choices: [
+          {
+            message: {
+              role: 'assistant',
+              content: 'hello',
+            },
+            finish_reason: 'stop',
+          },
+        ],
+        usage: {
+          prompt_tokens: 5,
+          completion_tokens: 1,
+          total_tokens: 6,
+        },
+      }),
+      {
+        headers: {
+          'Content-Type': 'application/json',
+        },
+      },
+    )
+  }) as FetchType
+
+  const client = createOpenAIShimClient({}) as OpenAIShimClient
+
+  await client.beta.messages.create({
+    model: 'gpt-4o',
+    messages: [{ role: 'user', content: 'hello' }],
+    max_tokens: 64,
+    stream: false,
+  })
+})
+
 test('preserves Gemini tool call extra_content in follow-up requests', async () => {
   let requestBody: Record<string, unknown> | undefined
 
@@ -689,9 +780,117 @@ test('preserves image tool results as placeholders in follow-up requests', async
 
   const toolMessage = (requestBody?.messages as Array<Record<string, unknown>>).find(
     message => message.role === 'tool',
-  ) as { content?: string } | undefined
+  ) as {
+    content?: Array<{
+      type: string
+      text?: string
+      image_url?: { url: string }
+    }> | string
+  } | undefined
 
-  expect(toolMessage?.content).toContain('[image:image/png]')
+  expect(Array.isArray(toolMessage?.content)).toBe(true)
+  const parts = toolMessage?.content as Array<{
+    type: string
+    text?: string
+    image_url?: { url: string }
+  }>
+  const imagePart = parts.find(part => part.type === 'image_url')
+  expect(imagePart?.image_url?.url).toBe('data:image/png;base64,ZmFrZQ==')
+})
+
+test('preserves mixed text and image tool results as multipart content', async () => {
+  let requestBody: Record<string, unknown> | undefined
+
+  globalThis.fetch = (async (_input, init) => {
+    requestBody = JSON.parse(String(init?.body))
+
+    return new Response(
+      JSON.stringify({
+        id: 'chatcmpl-1',
+        model: 'gpt-4o',
+        choices: [
+          {
+            message: {
+              role: 'assistant',
+              content: 'done',
+            },
+            finish_reason: 'stop',
+          },
+        ],
+        usage: {
+          prompt_tokens: 12,
+          completion_tokens: 4,
+          total_tokens: 16,
+        },
+      }),
+      {
+        headers: {
+          'Content-Type': 'application/json',
+        },
+      },
+    )
+  }) as FetchType
+
+  const client = createOpenAIShimClient({}) as OpenAIShimClient
+
+  await client.beta.messages.create({
+    model: 'gpt-4o',
+    system: 'test system',
+    messages: [
+      { role: 'user', content: 'Read this screenshot' },
+      {
+        role: 'assistant',
+        content: [
+          {
+            type: 'tool_use',
+            id: 'call_image_2',
+            name: 'Read',
+            input: { file_path: 'C:\\temp\\screenshot.png' },
+          },
+        ],
+      },
+      {
+        role: 'user',
+        content: [
+          {
+            type: 'tool_result',
+            tool_use_id: 'call_image_2',
+            content: [
+              { type: 'text', text: 'Screenshot captured' },
+              {
+                type: 'image',
+                source: {
+                  type: 'base64',
+                  media_type: 'image/png',
+                  data: 'ZmFrZQ==',
+                },
+              },
+            ],
+          },
+        ],
+      },
+    ],
+    max_tokens: 64,
+    stream: false,
+  })
+
+  const toolMessage = (requestBody?.messages as Array<Record<string, unknown>>).find(
+    message => message.role === 'tool',
+  ) as {
+    content?: Array<{
+      type: string
+      text?: string
+      image_url?: { url: string }
+    }>
+  } | undefined
+
+  expect(Array.isArray(toolMessage?.content)).toBe(true)
+  const parts = toolMessage?.content ?? []
+  expect(parts[0]).toEqual({ type: 'text', text: 'Screenshot captured' })
+  expect(parts[1]).toEqual({
+    type: 'image_url',
+    image_url: { url: 'data:image/png;base64,ZmFrZQ==' },
+  })
 })
 
 test('uses GEMINI_ACCESS_TOKEN for Gemini OpenAI-compatible requests', async () => {

src/services/api/openaiShim.ts

@@ -176,35 +176,61 @@ function convertSystemPrompt(
   return String(system)
 }
 
-function convertToolResultContent(content: unknown): string {
+function convertToolResultContent(
-  if (typeof content === 'string') return content
+  content: unknown,
-  if (!Array.isArray(content)) return JSON.stringify(content ?? '')
+  isError?: boolean,
+): string | Array<{ type: string; text?: string; image_url?: { url: string } }> {
+  if (typeof content === 'string') {
+    return isError ? `Error: ${content}` : content
+  }
+  if (!Array.isArray(content)) {
+    const text = JSON.stringify(content ?? '')
+    return isError ? `Error: ${text}` : text
+  }
 
-  const chunks: string[] = []
+  const parts: Array<{
+    type: string
+    text?: string
+    image_url?: { url: string }
+  }> = []
   for (const block of content) {
     if (block?.type === 'text' && typeof block.text === 'string') {
-      chunks.push(block.text)
+      parts.push({ type: 'text', text: block.text })
       continue
     }
 
     if (block?.type === 'image') {
       const source = block.source
       if (source?.type === 'url' && source.url) {
-        chunks.push(`[Image](${source.url})`)
+        parts.push({ type: 'image_url', image_url: { url: source.url } })
-      } else if (source?.type === 'base64') {
+      } else if (source?.type === 'base64' && source.media_type && source.data) {
-        chunks.push(`[image:${source.media_type ?? 'unknown'}]`)
+        parts.push({
-      } else {
+          type: 'image_url',
-        chunks.push('[image]')
+          image_url: {
+            url: `data:${source.media_type};base64,${source.data}`,
+          },
+        })
       }
       continue
     }
 
     if (typeof block?.text === 'string') {
-      chunks.push(block.text)
+      parts.push({ type: 'text', text: block.text })
     }
   }
 
-  return chunks.join('\n')
+  if (parts.length === 0) return ''
+  if (parts.length === 1 && parts[0].type === 'text') {
+    const text = parts[0].text ?? ''
+    return isError ? `Error: ${text}` : text
+  }
+  if (isError && parts[0]?.type === 'text') {
+    parts[0] = { ...parts[0], text: `Error: ${parts[0].text ?? ''}` }
+  } else if (isError) {
+    parts.unshift({ type: 'text', text: 'Error:' })
+  }
+
+  return parts
 }
 
 function convertContentBlocks(
@@ -292,11 +318,10 @@ function convertMessages(
 
         // Emit tool results as tool messages
         for (const tr of toolResults) {
-          const trContent = convertToolResultContent(tr.content)
           result.push({
             role: 'tool',
             tool_call_id: tr.tool_use_id ?? 'unknown',
-            content: tr.is_error ? `Error: ${trContent}` : trContent,
+            content: convertToolResultContent(tr.content, tr.is_error),
           })
         }
 
@@ -1216,12 +1241,13 @@ class OpenAIShimMessages {
 
     const isGithub = isGithubModelsMode()
     const isMistral = isMistralMode()
+    const isLocal = isLocalProviderUrl(request.baseUrl)
 
     const githubEndpointType = getGithubEndpointType(request.baseUrl)
     const isGithubCopilot = isGithub && githubEndpointType === 'copilot'
     const isGithubModels = isGithub && (githubEndpointType === 'models' || githubEndpointType === 'custom')
 
-    if ((isGithub || isMistral) && body.max_completion_tokens !== undefined) {
+    if ((isGithub || isMistral || isLocal) && body.max_completion_tokens !== undefined) {
       body.max_tokens = body.max_completion_tokens
       delete body.max_completion_tokens
     }