feat(ai): parse partial tool input (#44830)

packages/ai/src/protocols/utils/tool-stream.ts

@@ -1,8 +1,10 @@
-import { Effect } from "effect"
+import { Effect, Option } from "effect"
 import { AIError, LLMEvent, type ProviderMetadata, type ToolCall, type ToolInputError } from "../../schema/index.js"
 import { eventError, parseToolInput, type ToolAccumulator } from "../shared.js"
+import { parse } from "./partial-json.js"
 
 type StreamKey = string | number
+const parsePartialInput = Option.liftThrowable(parse)
 
 /**
  * One pending streamed tool call. Providers emit the tool identity and JSON
@@ -57,12 +59,15 @@ const inputStart = (tool: PendingTool) =>
     providerMetadata: tool.providerMetadata,
   })
 
-const inputDelta = (tool: PendingTool, text: string) =>
-  LLMEvent.toolInputDelta({
+const inputDelta = (tool: PendingTool, text: string) => {
+  const input = parsePartialInput(tool.input)
+  return LLMEvent.toolInputDelta({
     id: tool.id,
     name: tool.name,
     text,
+    ...(Option.isSome(input) ? { input: input.value } : {}),
   })
+}
 
 const toolCall = (route: string, tool: PendingTool, inputOverride?: string) => {
   const raw = inputOverride ?? tool.input

packages/ai/src/schema/events.ts

@@ -152,6 +152,8 @@ export const ToolInputDelta = Schema.Struct({
   id: ToolCallID,
   name: Schema.String,
   text: Schema.String,
+  /** Best-effort parse of all input fragments received through this delta. */
+  input: Schema.optional(Schema.Unknown),
 }).annotate({ identifier: "LLM.Event.ToolInputDelta" })
 export type ToolInputDelta = Schema.Schema.Type<typeof ToolInputDelta>
 

packages/ai/test/provider/anthropic-messages.test.ts

@@ -585,12 +585,11 @@ describe("Anthropic Messages route", () => {
 
   it.effect("infers empty-signature compatibility across Kimi providers", () =>
     Effect.gen(function* () {
-      const coding = AnthropicMessages.route
-        .with({
-          provider: "kimi-for-coding",
-          endpoint: { baseURL: "https://compatible.test/v1/" },
-          auth: Auth.header("x-api-key", "test"),
-        })
+      const coding = AnthropicMessages.route.with({
+        provider: "kimi-for-coding",
+        endpoint: { baseURL: "https://compatible.test/v1/" },
+        auth: Auth.header("x-api-key", "test"),
+      })
       const moonshot = AnthropicMessages.route
         .with({
           provider: "moonshotai",
@@ -1129,8 +1128,14 @@ describe("Anthropic Messages route", () => {
       expect(response.events).toEqual([
         { type: "step-start", index: 0 },
         { type: "tool-input-start", id: "call_1", name: "lookup" },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"' },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: ':"weather"}' },
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"', input: {} },
+        {
+          type: "tool-input-delta",
+          id: "call_1",
+          name: "lookup",
+          text: ':"weather"}',
+          input: { query: "weather" },
+        },
         { type: "tool-input-end", id: "call_1", name: "lookup", providerMetadata: undefined },
         {
           type: "tool-call",

packages/ai/test/provider/bedrock-converse.test.ts

@@ -475,8 +475,14 @@ describe("Bedrock Converse route", () => {
       ])
       const events = response.events.filter((event) => event.type === "tool-input-delta")
       expect(events).toEqual([
-        { type: "tool-input-delta", id: "tool_1", name: "lookup", text: '{"query"' },
-        { type: "tool-input-delta", id: "tool_1", name: "lookup", text: ':"weather"}' },
+        { type: "tool-input-delta", id: "tool_1", name: "lookup", text: '{"query"', input: {} },
+        {
+          type: "tool-input-delta",
+          id: "tool_1",
+          name: "lookup",
+          text: ':"weather"}',
+          input: { query: "weather" },
+        },
       ])
       expect(response.events.at(-1)).toMatchObject({
         type: "finish",

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

@@ -1164,8 +1164,14 @@ describe("OpenAI Chat route", () => {
       expect(response.events).toEqual([
         { type: "step-start", index: 0 },
         { type: "tool-input-start", id: "call_1", name: "lookup", providerMetadata: undefined },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"' },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: ':"weather"}' },
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"', input: {} },
+        {
+          type: "tool-input-delta",
+          id: "call_1",
+          name: "lookup",
+          text: ':"weather"}',
+          input: { query: "weather" },
+        },
         { type: "tool-input-end", id: "call_1", name: "lookup", providerMetadata: undefined },
         {
           type: "tool-call",
@@ -1265,8 +1271,14 @@ describe("OpenAI Chat route", () => {
       expect(response.events).toEqual([
         { type: "step-start", index: 0 },
         { type: "tool-input-start", id: "call_1", name: "lookup", providerMetadata: undefined },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"' },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: ':"weather"}' },
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"', input: {} },
+        {
+          type: "tool-input-delta",
+          id: "call_1",
+          name: "lookup",
+          text: ':"weather"}',
+          input: { query: "weather" },
+        },
         { type: "tool-input-end", id: "call_1", name: "lookup", providerMetadata: undefined },
         {
           type: "tool-call",

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

@@ -2806,12 +2806,14 @@ describe("OpenAI Responses route", () => {
           id: "call_1",
           name: "lookup",
           text: '{"query"',
+          input: {},
         },
         {
           type: "tool-input-delta",
           id: "call_1",
           name: "lookup",
           text: ':"weather"}',
+          input: { query: "weather" },
         },
         {
           type: "tool-input-end",

packages/ai/test/tool-stream.test.ts

@@ -23,9 +23,11 @@ describe("ToolStream", () => {
 
       expect(first.events).toEqual([
         { type: "tool-input-start", id: "call_1", name: "lookup" },
-        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"' },
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: '{"query"', input: {} },
+      ])
+      expect(second.events).toEqual([
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: ':"weather"}', input: { query: "weather" } },
       ])
-      expect(second.events).toEqual([{ type: "tool-input-delta", id: "call_1", name: "lookup", text: ':"weather"}' }])
       expect(finished).toEqual({
         tools: {},
         events: [
@@ -36,6 +38,45 @@ describe("ToolStream", () => {
     }),
   )
 
+  it.effect("exposes cumulative partial string values", () =>
+    Effect.gen(function* () {
+      const result = ToolStream.appendOrStart(
+        ADAPTER,
+        ToolStream.empty<number>(),
+        0,
+        { id: "call_1", name: "lookup", text: '{"query":"wea' },
+        "missing tool",
+      )
+      if (ToolStream.isError(result)) return yield* result
+
+      expect(result.events.at(-1)).toEqual({
+        type: "tool-input-delta",
+        id: "call_1",
+        name: "lookup",
+        text: '{"query":"wea',
+        input: { query: "wea" },
+      })
+    }),
+  )
+
+  it.effect("omits partial input when the accumulated value cannot be parsed", () =>
+    Effect.gen(function* () {
+      const result = ToolStream.appendOrStart(
+        ADAPTER,
+        ToolStream.empty<number>(),
+        0,
+        { id: "call_1", name: "lookup", text: "x" },
+        "missing tool",
+      )
+      if (ToolStream.isError(result)) return yield* result
+
+      expect(result.events).toEqual([
+        { type: "tool-input-start", id: "call_1", name: "lookup" },
+        { type: "tool-input-delta", id: "call_1", name: "lookup", text: "x" },
+      ])
+    }),
+  )
+
   it.effect("keeps accumulated identity when later deltas contain empty strings", () =>
     Effect.gen(function* () {
       const first = ToolStream.appendOrStart(