fix(ai): bridge tool results for mistral family models (#45051)

packages/ai/src/protocols/openai-chat.ts

@@ -478,12 +478,22 @@ const lowerMessages = Effect.fn("OpenAIChat.lowerMessages")(function* (request:
           ]
         : [{ role: "system", content: ProviderShared.joinText(request.system) }]
   const messages = [...system]
+  const requireAssistantAfterTool =
+    request.model.compatibility?.requireAssistantAfterTool ??
+    ["mistral", "devstral", "codestral", "pixtral", "mixtral"].some((family) =>
+      request.model.id.toLowerCase().includes(family),
+    )
+  const bridgeTools = () => {
+    if (requireAssistantAfterTool && messages.at(-1)?.role === "tool") messages.push({ role: "assistant", content: "Done." })
+  }
   const pendingImages: Array<Schema.Schema.Type<typeof OpenAIChatUserContent>> = []
   const flushImages = () => {
     if (pendingImages.length === 0) return
+    bridgeTools()
     messages.push({ role: "user", content: pendingImages.splice(0) })
   }
   for (const message of request.messages) {
+    if (message.role === "user") bridgeTools()
     if (message.role === "system") {
       const part = yield* ProviderShared.wrappedSystemUpdate("OpenAI Chat", message)
       if (pendingImages.length > 0) {
@@ -526,6 +536,8 @@ const lowerMessages = Effect.fn("OpenAIChat.lowerMessages")(function* (request:
         )
       continue
     }
+    if (message.role === "assistant" && message.content.every((part) => part.type === "text" && part.text.trim() === ""))
+      continue
     if (message.role === "tool") {
       const lowered = yield* lowerToolMessages(message, options)
       messages.push(...lowered.messages)

packages/ai/src/schema/options.ts

@@ -155,6 +155,7 @@ export class LanguageModelCompatibility extends Schema.Class<LanguageModelCompat
   reasoningField: Schema.optional(Schema.String),
   maxTokensField: Schema.optional(LanguageModelMaxTokensFieldCompatibility),
   requireFinishReason: Schema.optional(Schema.Boolean),
+  requireAssistantAfterTool: Schema.optional(Schema.Boolean),
   supportsStore: Schema.optional(Schema.Boolean),
   supportsUsageInStreaming: Schema.optional(Schema.Boolean),
   supportsStrictMode: Schema.optional(Schema.Boolean),

packages/ai/test/provider/openai-chat.test.ts

@@ -85,6 +85,28 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("omits empty and whitespace-only assistant messages", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model,
+          messages: [
+            Message.user("Before."),
+            Message.assistant([]),
+            Message.assistant(""),
+            Message.assistant(" \n\t "),
+            Message.assistant("After."),
+          ],
+        }),
+      )
+
+      expect(prepared.body.messages).toEqual([
+        { role: "user", content: "Before." },
+        { role: "assistant", content: "After." },
+      ])
+    }),
+  )
+
   it.effect("replays canonical reasoning as OpenAI-compatible reasoning_content", () =>
     Effect.gen(function* () {
       const prepared = yield* compileRequest(
@@ -431,6 +453,30 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("bridges image tool results before their synthetic user message when required", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model: LanguageModel.update(model, { compatibility: { requireAssistantAfterTool: true } }),
+          messages: [
+            Message.assistant([ToolCallPart.make({ id: "call_image", name: "read", input: {} })]),
+            Message.tool({
+              id: "call_image",
+              name: "read",
+              result: {
+                type: "content",
+                value: [{ type: "file", uri: "data:image/png;base64,AAECAw==", mime: "image/png", name: "pixel.png" }],
+              },
+            }),
+          ],
+        }),
+      )
+
+      expect(prepared.body.messages.map((message) => message.role)).toEqual(["assistant", "tool", "assistant", "user"])
+      expect(prepared.body.messages[2]).toEqual({ role: "assistant", content: "Done." })
+    }),
+  )
+
   it.effect("orders parallel tool responses before one aggregated vision message", () =>
     Effect.gen(function* () {
       const prepared = yield* compileRequest(

packages/ai/test/provider/openai-compatible-chat.test.ts

@@ -238,6 +238,47 @@ describe("OpenAI-compatible Chat route", () => {
     }),
   )
 
+  it.effect("bridges tool results for Mistral-family models and honors compatibility overrides", () =>
+    Effect.gen(function* () {
+      const cases = [
+        { id: "mistral-small", bridge: true },
+        { id: "devstral-small", bridge: true },
+        { id: "codestral-latest", bridge: true },
+        { id: "pixtral-large", bridge: true },
+        { id: "open-mixtral-8x22b", bridge: true },
+        { id: "ordinary-model", bridge: false },
+        { id: "ordinary-model", override: true, bridge: true },
+        { id: "mistral-small", override: false, bridge: false },
+      ] as const
+
+      yield* Effect.forEach(cases, (item) =>
+        Effect.gen(function* () {
+          const selected = OpenAICompatibleChat.route
+            .with({ provider: "custom", endpoint: { baseURL: "https://api.custom.test/v1" } })
+            .model({
+              id: item.id,
+              compatibility: "override" in item ? { requireAssistantAfterTool: item.override } : undefined,
+            })
+          const prepared = yield* compileRequest(
+            LLM.request({
+              model: selected,
+              messages: [
+                Message.assistant([ToolCallPart.make({ id: "call_1", name: "lookup", input: {} })]),
+                Message.tool({ id: "call_1", name: "lookup", result: "Sunny" }),
+                Message.user("What next?"),
+              ],
+            }),
+          )
+
+          expect(prepared.body.messages.map((message) => message.role)).toEqual(
+            item.bridge ? ["assistant", "tool", "assistant", "user"] : ["assistant", "tool", "user"],
+          )
+          if (item.bridge) expect(prepared.body.messages[2]).toEqual({ role: "assistant", content: "Done." })
+        }),
+      )
+    }),
+  )
+
   it.effect("posts to the configured compatible endpoint and parses text usage", () =>
     Effect.gen(function* () {
       const response = yield* LLMClient.generate(request).pipe(

packages/client/src/promise/generated/types.ts

@@ -1312,6 +1312,7 @@ export type ModelCompatibility = {
   reasoningField?: ModelReasoningField
   maxTokensField?: ModelMaxTokensField
   requireFinishReason?: boolean
+  requireAssistantAfterTool?: boolean
 }
 
 export type ModelCost = {

packages/core/test/model-resolver.test.ts

@@ -392,6 +392,7 @@ describe("ModelResolver", () => {
             reasoningField: "vendor_reasoning",
             maxTokensField: "max_completion_tokens",
             requireFinishReason: false,
+            requireAssistantAfterTool: true,
           },
           settings: {
             apiKey: "settings-secret",
@@ -417,6 +418,7 @@ describe("ModelResolver", () => {
       expect(resolved.compatibility?.reasoningField).toBe("vendor_reasoning")
       expect(resolved.compatibility?.maxTokensField).toBe("max_completion_tokens")
       expect(resolved.compatibility?.requireFinishReason).toBe(false)
+      expect(resolved.compatibility?.requireAssistantAfterTool).toBe(true)
       expect(prepared.body).toMatchObject({ max_completion_tokens: 10 })
       expect(prepared.body).not.toHaveProperty("max_tokens")
       expect(resolved.route.endpoint.baseURL).toBe("https://compatible.example/v1")

packages/schema/src/model.ts

@@ -57,6 +57,7 @@ export const Compatibility = Schema.Struct({
   reasoningField: ReasoningField.pipe(optional),
   maxTokensField: MaxTokensField.pipe(optional),
   requireFinishReason: Schema.Boolean.pipe(optional),
+  requireAssistantAfterTool: Schema.Boolean.pipe(optional),
 }).annotate({ identifier: "Model.Compatibility" })
 
 export interface Capabilities extends Schema.Schema.Type<typeof Capabilities> {}

packages/schema/test/model.test.ts

@@ -42,11 +42,13 @@ describe("Model.Compatibility", () => {
         reasoningField: "vendor_reasoning",
         maxTokensField: "max_completion_tokens",
         requireFinishReason: false,
+        requireAssistantAfterTool: true,
       }),
     ).toEqual({
       reasoningField: "vendor_reasoning",
       maxTokensField: "max_completion_tokens",
       requireFinishReason: false,
+      requireAssistantAfterTool: true,
     })
   })
 })