fix: for anthropic compat ensure empty msgs and empty reasoning is filtered out

2 files changed, 194 insertions, 0 deletions

diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 48011c81a..ae236285c 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -17,6 +17,25 @@ function mimeToModality(mime: string): Modality | undefined {
 
 export namespace ProviderTransform {
   function normalizeMessages(msgs: ModelMessage[], model: Provider.Model): ModelMessage[] {
+    // Anthropic rejects messages with empty content - filter out empty string messages
+    // and remove empty text/reasoning parts from array content
+    if (model.api.npm === "@ai-sdk/anthropic") {
+      msgs = msgs
+        .map((msg) => {
+          if (typeof msg.content === "string") return msg
+          if (!Array.isArray(msg.content)) return msg
+          const filtered = msg.content.filter((part) => {
+            if (part.type === "text" || part.type === "reasoning") {
+              return part.text !== ""
+            }
+            return true
+          })
+          if (filtered.length === 0) return undefined
+          return { ...msg, content: filtered }
+        })
+        .filter((msg): msg is ModelMessage => msg !== undefined && msg.content !== "")
+    }
+
     if (model.api.id.includes("claude")) {
       return msgs.map((msg) => {
         if ((msg.role === "assistant" || msg.role === "tool") && Array.isArray(msg.content)) {
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 287015c4d..32b1ecb24 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -410,6 +410,181 @@ describe("ProviderTransform.message - empty image handling", () => {
   })
 })
 
+describe("ProviderTransform.message - anthropic empty content filtering", () => {
+  const anthropicModel = {
+    id: "anthropic/claude-3-5-sonnet",
+    providerID: "anthropic",
+    api: {
+      id: "claude-3-5-sonnet-20241022",
+      url: "https://api.anthropic.com",
+      npm: "@ai-sdk/anthropic",
+    },
+    name: "Claude 3.5 Sonnet",
+    capabilities: {
+      temperature: true,
+      reasoning: false,
+      attachment: true,
+      toolcall: true,
+      input: { text: true, audio: false, image: true, video: false, pdf: true },
+      output: { text: true, audio: false, image: false, video: false, pdf: false },
+      interleaved: false,
+    },
+    cost: {
+      input: 0.003,
+      output: 0.015,
+      cache: { read: 0.0003, write: 0.00375 },
+    },
+    limit: {
+      context: 200000,
+      output: 8192,
+    },
+    status: "active",
+    options: {},
+    headers: {},
+  } as any
+
+  test("filters out messages with empty string content", () => {
+    const msgs = [
+      { role: "user", content: "Hello" },
+      { role: "assistant", content: "" },
+      { role: "user", content: "World" },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe("Hello")
+    expect(result[1].content).toBe("World")
+  })
+
+  test("filters out empty text parts from array content", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "" },
+          { type: "text", text: "Hello" },
+          { type: "text", text: "" },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toHaveLength(1)
+    expect(result[0].content[0]).toEqual({ type: "text", text: "Hello" })
+  })
+
+  test("filters out empty reasoning parts from array content", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "reasoning", text: "" },
+          { type: "text", text: "Answer" },
+          { type: "reasoning", text: "" },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toHaveLength(1)
+    expect(result[0].content[0]).toEqual({ type: "text", text: "Answer" })
+  })
+
+  test("removes entire message when all parts are empty", () => {
+    const msgs = [
+      { role: "user", content: "Hello" },
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "" },
+          { type: "reasoning", text: "" },
+        ],
+      },
+      { role: "user", content: "World" },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe("Hello")
+    expect(result[1].content).toBe("World")
+  })
+
+  test("keeps non-text/reasoning parts even if text parts are empty", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "" },
+          { type: "tool-call", toolCallId: "123", toolName: "bash", input: { command: "ls" } },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toHaveLength(1)
+    expect(result[0].content[0]).toEqual({
+      type: "tool-call",
+      toolCallId: "123",
+      toolName: "bash",
+      input: { command: "ls" },
+    })
+  })
+
+  test("keeps messages with valid text alongside empty parts", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "reasoning", text: "Thinking..." },
+          { type: "text", text: "" },
+          { type: "text", text: "Result" },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, anthropicModel)
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toHaveLength(2)
+    expect(result[0].content[0]).toEqual({ type: "reasoning", text: "Thinking..." })
+    expect(result[0].content[1]).toEqual({ type: "text", text: "Result" })
+  })
+
+  test("does not filter for non-anthropic providers", () => {
+    const openaiModel = {
+      ...anthropicModel,
+      providerID: "openai",
+      api: {
+        id: "gpt-4",
+        url: "https://api.openai.com",
+        npm: "@ai-sdk/openai",
+      },
+    }
+
+    const msgs = [
+      { role: "assistant", content: "" },
+      {
+        role: "assistant",
+        content: [{ type: "text", text: "" }],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, openaiModel)
+
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe("")
+    expect(result[1].content).toHaveLength(1)
+  })
+})
+
 describe("ProviderTransform.variants", () => {
   const createMockModel = (overrides: Partial<any> = {}): any => ({
     id: "test/test-model",