fix: ensure switching anthropic models mid convo on copilot works without errors, fix issue with reasoning opaque not being picked up for gemini models (#11569)

4 files changed, 83 insertions, 6 deletions

diff --git a/packages/opencode/src/provider/sdk/copilot/chat/convert-to-openai-compatible-chat-messages.ts b/packages/opencode/src/provider/sdk/copilot/chat/convert-to-openai-compatible-chat-messages.ts
index 642d7145f..d6f7cb34b 100644
--- a/packages/opencode/src/provider/sdk/copilot/chat/convert-to-openai-compatible-chat-messages.ts
+++ b/packages/opencode/src/provider/sdk/copilot/chat/convert-to-openai-compatible-chat-messages.ts
@@ -100,7 +100,7 @@ export function convertToOpenAICompatibleChatMessages(prompt: LanguageModelV2Pro
               break
             }
             case "reasoning": {
-              reasoningText = part.text
+              if (part.text) reasoningText = part.text
               break
             }
             case "tool-call": {
@@ -122,7 +122,7 @@ export function convertToOpenAICompatibleChatMessages(prompt: LanguageModelV2Pro
           role: "assistant",
           content: text || null,
           tool_calls: toolCalls.length > 0 ? toolCalls : undefined,
-          reasoning_text: reasoningText,
+          reasoning_text: reasoningOpaque ? reasoningText : undefined,
           reasoning_opaque: reasoningOpaque,
           ...metadata,
         })
diff --git a/packages/opencode/src/provider/sdk/copilot/chat/openai-compatible-chat-language-model.ts b/packages/opencode/src/provider/sdk/copilot/chat/openai-compatible-chat-language-model.ts
index 94641e640..c85d3f3d1 100644
--- a/packages/opencode/src/provider/sdk/copilot/chat/openai-compatible-chat-language-model.ts
+++ b/packages/opencode/src/provider/sdk/copilot/chat/openai-compatible-chat-language-model.ts
@@ -219,7 +219,13 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV2 {
     // text content:
     const text = choice.message.content
     if (text != null && text.length > 0) {
-      content.push({ type: "text", text })
+      content.push({
+        type: "text",
+        text,
+        providerMetadata: choice.message.reasoning_opaque
+          ? { copilot: { reasoningOpaque: choice.message.reasoning_opaque } }
+          : undefined,
+      })
     }
 
     // reasoning content (Copilot uses reasoning_text):
@@ -243,6 +249,9 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV2 {
           toolCallId: toolCall.id ?? generateId(),
           toolName: toolCall.function.name,
           input: toolCall.function.arguments!,
+          providerMetadata: choice.message.reasoning_opaque
+            ? { copilot: { reasoningOpaque: choice.message.reasoning_opaque } }
+            : undefined,
         })
       }
     }
@@ -478,7 +487,11 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV2 {
               }
 
               if (!isActiveText) {
-                controller.enqueue({ type: "text-start", id: "txt-0" })
+                controller.enqueue({
+                  type: "text-start",
+                  id: "txt-0",
+                  providerMetadata: reasoningOpaque ? { copilot: { reasoningOpaque } } : undefined,
+                })
                 isActiveText = true
               }
 
@@ -559,6 +572,7 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV2 {
                         toolCallId: toolCall.id ?? generateId(),
                         toolName: toolCall.function.name,
                         input: toolCall.function.arguments,
+                        providerMetadata: reasoningOpaque ? { copilot: { reasoningOpaque } } : undefined,
                       })
                       toolCall.hasFinished = true
                     }
@@ -601,6 +615,7 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV2 {
                     toolCallId: toolCall.id ?? generateId(),
                     toolName: toolCall.function.name,
                     input: toolCall.function.arguments,
+                    providerMetadata: reasoningOpaque ? { copilot: { reasoningOpaque } } : undefined,
                   })
                   toolCall.hasFinished = true
                 }
diff --git a/packages/opencode/test/provider/copilot/convert-to-copilot-messages.test.ts b/packages/opencode/test/provider/copilot/convert-to-copilot-messages.test.ts
index ffc746911..9f305123a 100644
--- a/packages/opencode/test/provider/copilot/convert-to-copilot-messages.test.ts
+++ b/packages/opencode/test/provider/copilot/convert-to-copilot-messages.test.ts
@@ -354,7 +354,7 @@ describe("tool calls", () => {
 })
 
 describe("reasoning (copilot-specific)", () => {
-  test("should include reasoning_text from reasoning part", () => {
+  test("should omit reasoning_text without reasoning_opaque", () => {
     const result = convertToCopilotMessages([
       {
         role: "assistant",
@@ -370,7 +370,7 @@ describe("reasoning (copilot-specific)", () => {
         role: "assistant",
         content: "The answer is 42.",
         tool_calls: undefined,
-        reasoning_text: "Let me think about this...",
+        reasoning_text: undefined,
         reasoning_opaque: undefined,
       },
     ])
@@ -404,6 +404,33 @@ describe("reasoning (copilot-specific)", () => {
     ])
   })
 
+  test("should include reasoning_opaque from text part providerOptions", () => {
+    const result = convertToCopilotMessages([
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "text",
+            text: "Done!",
+            providerOptions: {
+              copilot: { reasoningOpaque: "opaque-text-456" },
+            },
+          },
+        ],
+      },
+    ])
+
+    expect(result).toEqual([
+      {
+        role: "assistant",
+        content: "Done!",
+        tool_calls: undefined,
+        reasoning_text: undefined,
+        reasoning_opaque: "opaque-text-456",
+      },
+    ])
+  })
+
   test("should handle reasoning-only assistant message", () => {
     const result = convertToCopilotMessages([
       {
diff --git a/packages/opencode/test/provider/copilot/copilot-chat-model.test.ts b/packages/opencode/test/provider/copilot/copilot-chat-model.test.ts
index 0b82c1868..562da4507 100644
--- a/packages/opencode/test/provider/copilot/copilot-chat-model.test.ts
+++ b/packages/opencode/test/provider/copilot/copilot-chat-model.test.ts
@@ -65,6 +65,12 @@ const FIXTURES = {
     `data: {"choices":[{"finish_reason":"tool_calls","index":0,"delta":{"content":null,"role":"assistant","tool_calls":[{"function":{"arguments":"{\\"code\\":\\"1 + 1\\"}","name":"project_eval"},"id":"call_MHw3RDhmT1J5Z3B6WlhpVjlveTc","index":0,"type":"function"}],"reasoning_opaque":"ytGNWFf2doK38peANDvm7whkLPKrd+Fv6/k34zEPBF6Qwitj4bTZT0FBXleydLb6"}}],"created":1766068644,"id":"oBFEaafzD9DVlOoPkY3l4Qs","usage":{"completion_tokens":12,"prompt_tokens":8677,"prompt_tokens_details":{"cached_tokens":3692},"total_tokens":8768,"reasoning_tokens":79},"model":"gemini-3-pro-preview"}`,
     `data: [DONE]`,
   ],
+
+  reasoningOpaqueWithToolCallsNoReasoningText: [
+    `data: {"choices":[{"index":0,"delta":{"content":null,"role":"assistant","tool_calls":[{"function":{"arguments":"{}","name":"read_file"},"id":"call_reasoning_only","index":0,"type":"function"}],"reasoning_opaque":"opaque-xyz"}}],"created":1769917420,"id":"opaque-only","usage":{"completion_tokens":0,"prompt_tokens":0,"prompt_tokens_details":{"cached_tokens":0},"total_tokens":0,"reasoning_tokens":0},"model":"gemini-3-flash-preview"}`,
+    `data: {"choices":[{"finish_reason":"tool_calls","index":0,"delta":{"content":null,"role":"assistant","tool_calls":[{"function":{"arguments":"{}","name":"read_file"},"id":"call_reasoning_only_2","index":1,"type":"function"}]}}],"created":1769917420,"id":"opaque-only","usage":{"completion_tokens":12,"prompt_tokens":123,"prompt_tokens_details":{"cached_tokens":0},"total_tokens":135,"reasoning_tokens":0},"model":"gemini-3-flash-preview"}`,
+    `data: [DONE]`,
+  ],
 }
 
 function createMockFetch(chunks: string[]) {
@@ -447,6 +453,35 @@ describe("doStream", () => {
     })
   })
 
+  test("should attach reasoning_opaque to tool calls without reasoning_text", async () => {
+    const mockFetch = createMockFetch(FIXTURES.reasoningOpaqueWithToolCallsNoReasoningText)
+    const model = createModel(mockFetch)
+
+    const { stream } = await model.doStream({
+      prompt: TEST_PROMPT,
+      includeRawChunks: false,
+    })
+
+    const parts = await convertReadableStreamToArray(stream)
+    const reasoningParts = parts.filter(
+      (p) => p.type === "reasoning-start" || p.type === "reasoning-delta" || p.type === "reasoning-end",
+    )
+
+    expect(reasoningParts).toHaveLength(0)
+
+    const toolCall = parts.find((p) => p.type === "tool-call" && p.toolCallId === "call_reasoning_only")
+    expect(toolCall).toMatchObject({
+      type: "tool-call",
+      toolCallId: "call_reasoning_only",
+      toolName: "read_file",
+      providerMetadata: {
+        copilot: {
+          reasoningOpaque: "opaque-xyz",
+        },
+      },
+    })
+  })
+
   test("should include response metadata from first chunk", async () => {
     const mockFetch = createMockFetch(FIXTURES.basicText)
     const model = createModel(mockFetch)