fix(ai): stop generating response item ids

fix(ai): generate uuidv7 item ids
fix(ai): preserve responses item ids
2026-08-07 17:49:53 -04:00 · 2026-08-07 14:26:50 -05:00 · 2026-08-07 14:04:15 -05:00 · 2026-08-07 12:57:48 -05:00
21 changed files with 709 additions and 188 deletions
@@ -90,10 +90,15 @@ const OpenResponsesFunctionCallOutput = Schema.Union([
 ])

 export const InputItem = Schema.Union([
-  Schema.Struct({ role: Schema.tag("system"), content: Schema.String }),
-  Schema.Struct({ role: Schema.tag("user"), content: Schema.Array(OpenResponsesInputContent) }),
+  Schema.Struct({ role: Schema.tag("system"), id: Schema.optionalKey(Schema.String), content: Schema.String }),
+  Schema.Struct({
+    role: Schema.tag("user"),
+    id: Schema.optionalKey(Schema.String),
+    content: Schema.Array(OpenResponsesInputContent),
+  }),
  Schema.Struct({
    role: Schema.tag("assistant"),
+    id: Schema.optionalKey(Schema.String),
    content: Schema.Array(OpenResponsesOutputText),
    phase: Schema.optionalKey(MessagePhase),
  }),
@@ -101,19 +106,23 @@ export const InputItem = Schema.Union([
  OpenResponsesItemReference,
  Schema.Struct({
    type: Schema.tag("function_call"),
+    id: Schema.optionalKey(Schema.String),
    call_id: Schema.String,
    name: Schema.String,
    arguments: Schema.String,
  }),
  Schema.Struct({
    type: Schema.tag("function_call_output"),
+    id: Schema.optionalKey(Schema.String),
    call_id: Schema.String,
    output: OpenResponsesFunctionCallOutput,
  }),
 ])
 type OpenResponsesInputItem = Schema.Schema.Type<typeof InputItem>
+type ProviderInputItem = Readonly<Record<string, unknown>> & { readonly type: string; readonly id?: string }
 type LoweredInputItem =
  | OpenResponsesInputItem
+  | ProviderInputItem
  | {
      readonly role: "assistant"
      readonly content: ReadonlyArray<{ readonly type: "output_text"; readonly text: string }>
@@ -128,7 +137,7 @@ type OpenResponsesReasoningInput = {
  summary: Array<{ type: "summary_text"; text: string }>
  encrypted_content?: string | null
 }
-type OpenResponsesReasoningReplay = Omit<OpenResponsesReasoningInput, "id">
+type OpenResponsesReasoningReplay = Omit<OpenResponsesReasoningInput, "id"> & { id?: string }

 export const Tool = Schema.Struct({
  type: Schema.tag("function"),
@@ -254,6 +263,11 @@ export interface Extension {
    readonly request: LLMRequest
  }) => MediaInput | undefined
  readonly messagePhase?: (value: unknown) => MessagePhase | null | undefined
+  readonly lowerProviderItem?: (
+    part: ToolResultPart,
+    providerMetadataKey: string,
+    store: boolean | undefined,
+  ) => ProviderInputItem | undefined
 }

 const BASE: Extension = { id: ADAPTER, name: NAME }
@@ -310,6 +324,17 @@ export const lowerToolChoice = (protocolName: string, toolChoice: NonNullable<LL
    tool: (toolName) => ({ type: "function" as const, name: toolName }),
  })

+const metadataItemID = (
+  part: { readonly itemId?: string; readonly providerMetadata?: ProviderMetadata },
+  providerMetadataKey: string,
+) => {
+  if (part.itemId) return part.itemId
+  const metadata = part.providerMetadata?.[providerMetadataKey]
+  return ProviderShared.isRecord(metadata) && typeof metadata.itemId === "string" && metadata.itemId.length > 0
+    ? metadata.itemId
+    : undefined
+}
+
 const lowerToolCall = (part: ToolCallPart): OpenResponsesInputItem => ({
  type: "function_call",
  call_id: part.id,
@@ -319,26 +344,23 @@ const lowerToolCall = (part: ToolCallPart): OpenResponsesInputItem => ({

 const lowerReasoning = (part: ReasoningPart, providerMetadataKey: string): OpenResponsesReasoningInput | undefined => {
  const metadata = part.providerMetadata?.[providerMetadataKey]
-  if (!ProviderShared.isRecord(metadata) || typeof metadata.itemId !== "string" || metadata.itemId.length === 0)
-    return undefined
+  const itemId = metadataItemID(part, providerMetadataKey)
+  if (!itemId) return undefined
  const encryptedContent =
-    typeof metadata.reasoningEncryptedContent === "string" || metadata.reasoningEncryptedContent === null
+    ProviderShared.isRecord(metadata) &&
+    (typeof metadata.reasoningEncryptedContent === "string" || metadata.reasoningEncryptedContent === null)
      ? metadata.reasoningEncryptedContent
      : undefined
  return {
    type: "reasoning",
-    id: metadata.itemId,
+    id: itemId,
    summary: part.text.length > 0 ? [{ type: "summary_text", text: part.text }] : [],
    encrypted_content: encryptedContent,
  }
 }

-const hostedToolItemID = (part: ToolResultPart, providerMetadataKey: string) => {
-  const metadata = part.providerMetadata?.[providerMetadataKey]
-  return ProviderShared.isRecord(metadata) && typeof metadata.itemId === "string" && metadata.itemId.length > 0
-    ? metadata.itemId
-    : undefined
-}
+const hostedToolItemID = (part: ToolResultPart, providerMetadataKey: string) =>
+  metadataItemID(part, providerMetadataKey)

 const lowerMedia = Effect.fn("OpenResponses.lowerMedia")(function* (
  part: MediaPart,
@@ -397,17 +419,18 @@ const lowerToolResultOutput = Effect.fn("OpenResponses.lowerToolResultOutput")(f
 })

 const lowerMessages = Effect.fn("OpenResponses.lowerMessages")(function* (request: LLMRequest, extension: Extension) {
+  const options = OpenResponsesOptions.resolve(request)
  const system: LoweredInputItem[] =
    request.system.length === 0 ? [] : [{ role: "system", content: ProviderShared.joinText(request.system) }]
  const input: LoweredInputItem[] = [...system]
-  const store = OpenResponsesOptions.resolve(request).store
+  const store = options.store
  const providerMetadataKey = request.model.route.providerMetadataKey ?? "openresponses"

  for (const message of request.messages) {
    if (message.role === "system") {
      const part = yield* ProviderShared.wrappedSystemUpdate(extension.name, message)
      const previous = input.at(-1)
-      if (previous && "role" in previous && previous.role === "user")
+      if (previous && "role" in previous && previous.role === "user" && Array.isArray(previous.content))
        input[input.length - 1] = {
          role: "user",
          content: [...previous.content, { type: "input_text", text: part.text }],
@@ -427,24 +450,24 @@ const lowerMessages = Effect.fn("OpenResponses.lowerMessages")(function* (reques
    if (message.role === "assistant") {
      const content: TextPart[] = []
      const reasoningItems: Record<string, OpenResponsesReasoningReplay> = {}
-      const reasoningReferences = new Set<string>()
-      const hostedToolReferences = new Set<string>()
+      const hostedToolItems = new Set<string>()
      const flushText = () => {
        if (content.length === 0) return
-        const groups = content.reduce<Array<{ phase: MessagePhase | null | undefined; parts: TextPart[] }>>(
-          (groups, part) => {
-            const metadata = part.providerMetadata?.[providerMetadataKey]
-            const phase = ProviderShared.isRecord(metadata) ? messagePhase(metadata.phase, extension) : undefined
-            const group = groups.at(-1)
-            if (group && group.phase === phase) group.parts.push(part)
-            else groups.push({ phase, parts: [part] })
-            return groups
-          },
-          [],
-        )
+        const groups = content.reduce<
+          Array<{ phase: MessagePhase | null | undefined; itemId: string | undefined; parts: TextPart[] }>
+        >((groups, part) => {
+          const metadata = part.providerMetadata?.[providerMetadataKey]
+          const phase = ProviderShared.isRecord(metadata) ? messagePhase(metadata.phase, extension) : undefined
+          const itemId = metadataItemID(part, providerMetadataKey)
+          const group = groups.at(-1)
+          if (group && group.phase === phase && group.itemId === itemId) group.parts.push(part)
+          else groups.push({ phase, itemId, parts: [part] })
+          return groups
+        }, [])
        input.push(
          ...groups.map((group) => ({
            role: "assistant" as const,
+            ...(group.itemId === undefined ? {} : { id: group.itemId }),
            content: group.parts.map((part) => ({ type: "output_text" as const, text: part.text })),
            ...(group.phase === undefined ? {} : { phase: group.phase }),
          })),
@@ -460,11 +483,6 @@ const lowerMessages = Effect.fn("OpenResponses.lowerMessages")(function* (reques
          flushText()
          const reasoning = lowerReasoning(part, providerMetadataKey)
          if (!reasoning) continue
-          if (store !== false) {
-            if (!reasoningReferences.has(reasoning.id)) input.push({ type: "item_reference", id: reasoning.id })
-            reasoningReferences.add(reasoning.id)
-            continue
-          }
          const existing = reasoningItems[reasoning.id]
          if (existing) {
            existing.summary.push(...reasoning.summary)
@@ -474,6 +492,7 @@ const lowerMessages = Effect.fn("OpenResponses.lowerMessages")(function* (reques
          }
          const replay = {
            type: reasoning.type,
+            id: reasoning.id,
            summary: reasoning.summary,
            encrypted_content: reasoning.encrypted_content,
          }
@@ -490,16 +509,18 @@ const lowerMessages = Effect.fn("OpenResponses.lowerMessages")(function* (reques
        if (part.type === "tool-result" && part.providerExecuted === true) {
          flushText()
          const itemID = hostedToolItemID(part, providerMetadataKey)
-          if (store !== false && itemID && !hostedToolReferences.has(itemID))
+          const providerItem = extension.lowerProviderItem?.(part, providerMetadataKey, store)
+          if (providerItem && itemID && !hostedToolItems.has(itemID)) input.push(providerItem)
+          if (!providerItem && store !== false && itemID && !hostedToolItems.has(itemID))
            input.push({ type: "item_reference", id: itemID })
-          if (store === false && part.result.type === "content") {
+          if (!providerItem && store === false && part.result.type === "content") {
            const content: ReadonlyArray<Content> = part.result.value
            input.push({
              role: "user",
              content: yield* Effect.forEach(content, (item) => lowerToolResultContentItem(item, request, extension)),
            })
          }
-          if (itemID) hostedToolReferences.add(itemID)
+          if (itemID) hostedToolItems.add(itemID)
          continue
        }
        return yield* ProviderShared.unsupportedContent(extension.name, "assistant", [
@@ -641,9 +662,9 @@ const onOutputTextDelta = (state: ParserState, event: Event, id: string): StepRe
  if (!event.delta) return [state, NO_EVENTS]
  const events: LLMEvent[] = []
  const phase = state.messagePhases[id]
-  const metadata = phase === undefined ? undefined : providerMetadata(state, { phase })
-  const lifecycle = Lifecycle.textStart(state.lifecycle, events, id, metadata)
-  return [{ ...state, lifecycle: Lifecycle.textDelta(lifecycle, events, id, event.delta) }, events]
+  const metadata = providerMetadata(state, { itemId: id, ...(phase === undefined ? {} : { phase }) })
+  const lifecycle = Lifecycle.textStart(state.lifecycle, events, id, metadata, id)
+  return [{ ...state, lifecycle: Lifecycle.textDelta(lifecycle, events, id, event.delta, metadata, id) }, events]
 }

 const onOutputTextDone = (state: ParserState, event: Event, id: string): StepResult => {
@@ -652,7 +673,13 @@ const onOutputTextDone = (state: ParserState, event: Event, id: string): StepRes
    return onOutputTextDelta(state, { ...event, delta: event.text }, id)
  }
  const events: LLMEvent[] = []
-  return [{ ...state, lifecycle: Lifecycle.textEnd(state.lifecycle, events, id) }, events]
+  return [
+    {
+      ...state,
+      lifecycle: Lifecycle.textEnd(state.lifecycle, events, id, providerMetadata(state, { itemId: id }), id),
+    },
+    events,
+  ]
 }

 export const onReasoningDelta = (state: ParserState, event: Event, itemID: string): StepResult => {
@@ -663,7 +690,14 @@ export const onReasoningDelta = (state: ParserState, event: Event, itemID: strin
  return [
    {
      ...state,
-      lifecycle: Lifecycle.reasoningDelta(state.lifecycle, events, id, event.delta),
+      lifecycle: Lifecycle.reasoningDelta(
+        state.lifecycle,
+        events,
+        id,
+        event.delta,
+        providerMetadata(state, { itemId: itemID }),
+        itemID,
+      ),
    },
    events,
  ]
@@ -705,7 +739,13 @@ const onOutputItemAdded = (state: ParserState, event: Event): StepResult => {
    return [
      {
        ...state,
-        lifecycle: Lifecycle.reasoningStart(state.lifecycle, events, `${item.id}:0`, reasoningMetadata(state, item)),
+        lifecycle: Lifecycle.reasoningStart(
+          state.lifecycle,
+          events,
+          `${item.id}:0`,
+          reasoningMetadata(state, item),
+          item.id,
+        ),
        reasoningItems: {
          ...state.reasoningItems,
          [item.id]: { encryptedContent: item.encrypted_content, summaryParts: { 0: "active" } },
@@ -724,6 +764,7 @@ const onOutputItemAdded = (state: ParserState, event: Event): StepResult => {
      lifecycle,
      tools: ToolStream.start(state.tools, item.id, {
        id: item.call_id ?? item.id,
+        itemId: item.id,
        name: item.name ?? "",
        input: item.arguments ?? "",
        providerMetadata: metadata,
@@ -731,7 +772,12 @@ const onOutputItemAdded = (state: ParserState, event: Event): StepResult => {
    },
    [
      ...events,
-      LLMEvent.toolInputStart({ id: item.call_id ?? item.id, name: item.name ?? "", providerMetadata: metadata }),
+      LLMEvent.toolInputStart({
+        id: item.call_id ?? item.id,
+        itemId: item.id,
+        name: item.name ?? "",
+        providerMetadata: metadata,
+      }),
    ],
  ]
 }
@@ -750,6 +796,7 @@ const onReasoningSummaryPartAdded = (state: ParserState, event: Event): StepResu
          events,
          `${event.item_id}:0`,
          providerMetadata(state, { itemId: event.item_id, reasoningEncryptedContent: null }),
+          event.item_id,
        ),
        reasoningItems: {
          ...state.reasoningItems,
@@ -770,6 +817,7 @@ const onReasoningSummaryPartAdded = (state: ParserState, event: Event): StepResu
          events,
          `${event.item_id}:${entry[0]}`,
          providerMetadata(state, { itemId: event.item_id }),
+          event.item_id,
        ),
      state.lifecycle,
    )
@@ -781,6 +829,7 @@ const onReasoningSummaryPartAdded = (state: ParserState, event: Event): StepResu
        events,
        `${event.item_id}:${event.summary_index}`,
        providerMetadata(state, { itemId: event.item_id, reasoningEncryptedContent: item.encryptedContent ?? null }),
+        event.item_id,
      ),
      reasoningItems: {
        ...state.reasoningItems,
@@ -816,6 +865,7 @@ const onReasoningSummaryPartDone = (state: ParserState, event: Event): StepResul
              events,
              `${event.item_id}:${event.summary_index}`,
              providerMetadata(state, { itemId: event.item_id }),
+              event.item_id,
            )
          : state.lifecycle,
      reasoningItems: {
@@ -870,7 +920,8 @@ const onOutputItemDone = Effect.fn("OpenResponses.onOutputItemDone")(function* (
          state.lifecycle,
          events,
          item.id,
-          phase === undefined ? undefined : providerMetadata(state, { phase }),
+          providerMetadata(state, { itemId: item.id, ...(phase === undefined ? {} : { phase }) }),
+          item.id,
        ),
        messageItems,
        messagePhases,
@@ -881,9 +932,15 @@ const onOutputItemDone = Effect.fn("OpenResponses.onOutputItemDone")(function* (

  if (item.type === "function_call") {
    if (!item.id || !item.call_id || !item.name) return [state, NO_EVENTS] satisfies StepResult
+    const metadata = providerMetadata(state, { itemId: item.id })
    const tools = state.tools[item.id]
      ? state.tools
-      : ToolStream.start(state.tools, item.id, { id: item.call_id, name: item.name })
+      : ToolStream.start(state.tools, item.id, {
+          id: item.call_id,
+          itemId: item.id,
+          name: item.name,
+          providerMetadata: metadata,
+        })
    const result =
      item.arguments === undefined
        ? yield* ToolStream.finish(state.id, tools, item.id)
@@ -913,7 +970,7 @@ const onOutputItemDone = Effect.fn("OpenResponses.onOutputItemDone")(function* (
      const lifecycle = Object.entries(reasoningItem.summaryParts)
        .filter((entry) => entry[1] === "active" || entry[1] === "can-conclude")
        .reduce(
-          (lifecycle, entry) => Lifecycle.reasoningEnd(lifecycle, events, `${item.id}:${entry[0]}`, metadata),
+          (lifecycle, entry) => Lifecycle.reasoningEnd(lifecycle, events, `${item.id}:${entry[0]}`, metadata, item.id),
          state.lifecycle,
        )
      const { [item.id]: _removed, ...reasoningItems } = state.reasoningItems
@@ -921,12 +978,12 @@ const onOutputItemDone = Effect.fn("OpenResponses.onOutputItemDone")(function* (
    }
    if (!state.lifecycle.reasoning.has(item.id)) {
      const lifecycle = Lifecycle.stepStart(state.lifecycle, events)
-      events.push(LLMEvent.reasoningStart({ id: item.id, providerMetadata: metadata }))
-      events.push(LLMEvent.reasoningEnd({ id: item.id, providerMetadata: metadata }))
+      events.push(LLMEvent.reasoningStart({ id: item.id, itemId: item.id, providerMetadata: metadata }))
+      events.push(LLMEvent.reasoningEnd({ id: item.id, itemId: item.id, providerMetadata: metadata }))
      return [{ ...state, lifecycle }, events] satisfies StepResult
    }
    return [
-      { ...state, lifecycle: Lifecycle.reasoningEnd(state.lifecycle, events, item.id, metadata) },
+      { ...state, lifecycle: Lifecycle.reasoningEnd(state.lifecycle, events, item.id, metadata, item.id) },
      events,
    ] satisfies StepResult
  }
@@ -38,10 +38,14 @@ const OpenAIResponsesToolChoice = Schema.Union([
 const OpenAIResponsesInputItem = Schema.Union([
  Schema.Struct({
    role: Schema.tag("assistant"),
+    id: Schema.optionalKey(Schema.String),
    content: Schema.Array(Schema.Struct({ type: Schema.tag("output_text"), text: Schema.String })),
    phase: Schema.optionalKey(Schema.NullOr(OpenResponses.MessagePhase)),
  }),
  OpenResponses.InputItem,
+  Schema.StructWithRest(Schema.Struct({ type: Schema.String, id: Schema.optionalKey(Schema.String) }), [
+    Schema.Record(Schema.String, Schema.Unknown),
+  ]),
 ])

 const OpenAIResponsesCoreFields = {
@@ -80,6 +84,25 @@ const extension = {
      mime_type: media.mime,
    }
  },
+  lowerProviderItem: (part, providerMetadataKey, store) => {
+    const metadata = part.providerMetadata?.[providerMetadataKey]
+    if (!ProviderShared.isRecord(metadata) || !ProviderShared.isRecord(metadata.item)) return undefined
+    if (typeof metadata.item.type !== "string") return undefined
+    const id = typeof metadata.item.id === "string" ? metadata.item.id : undefined
+    // The public API requires stored state to replay image-generation items. In
+    // stateless mode, lower the generated file through the existing user-image fallback.
+    if (metadata.item.type === "image_generation_call" && store === false) return undefined
+    if (metadata.item.type === "image_generation_call")
+      return {
+        type: metadata.item.type,
+        ...(id === undefined ? {} : { id }),
+        ...(typeof metadata.item.status === "string" ? { status: metadata.item.status } : {}),
+        ...(typeof metadata.item.revised_prompt === "string" ? { revised_prompt: metadata.item.revised_prompt } : {}),
+        ...(typeof metadata.item.result === "string" ? { result: metadata.item.result } : {}),
+      }
+    const item: Record<string, unknown> & { type: string } = { ...metadata.item, type: metadata.item.type }
+    return item
+  },
 } satisfies OpenResponses.Extension

 const nativeImageToolInput = (tool: ToolDefinition) => {
@@ -195,23 +218,29 @@ const onHostedToolDone = Effect.fn("OpenAIResponses.onHostedToolDone")(function*
  item: HostedToolItem,
 ) {
  const tool = HOSTED_TOOLS[item.type]
-  const providerMetadata = OpenResponses.providerMetadata(state, { itemId: item.id })
+  const callMetadata = OpenResponses.providerMetadata(state, { itemId: item.id })
+  const resultMetadata = OpenResponses.providerMetadata(
+    state,
+    item.type === "image_generation_call" ? { itemId: item.id } : { itemId: item.id, item },
+  )
  const events: LLMEvent[] = []
  const lifecycle = Lifecycle.stepStart(state.lifecycle, events)
  events.push(
    LLMEvent.toolCall({
      id: item.id,
+      itemId: item.id,
      name: tool.name,
      input: tool.input(item),
      providerExecuted: true,
-      providerMetadata,
+      providerMetadata: callMetadata,
    }),
    LLMEvent.toolResult({
      id: item.id,
+      itemId: item.id,
      name: tool.name,
      result: yield* hostedToolResult(item),
      providerExecuted: true,
-      providerMetadata,
+      providerMetadata: resultMetadata,
    }),
  )
  return [{ ...state, lifecycle }, events] satisfies OpenResponses.StepResult
@@ -1,4 +1,10 @@
-import { LLMEvent, type FinishReasonDetails, type ProviderMetadata, type Usage } from "../../schema"
+import {
+  LLMEvent,
+  type FinishReasonDetails,
+  type ProviderMetadata,
+  type ResponseItemID,
+  type Usage,
+} from "../../schema"

 export interface State {
  readonly stepStarted: boolean
@@ -14,16 +20,29 @@ export const stepStart = (state: State, events: LLMEvent[]): State => {
  return { ...state, stepStarted: true }
 }

-export const textStart = (state: State, events: LLMEvent[], id: string, providerMetadata?: ProviderMetadata): State => {
+export const textStart = (
+  state: State,
+  events: LLMEvent[],
+  id: string,
+  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
+): State => {
  if (state.text.has(id)) return state
  const stepped = stepStart(state, events)
-  events.push(LLMEvent.textStart({ id, providerMetadata }))
+  events.push(LLMEvent.textStart({ id, ...(itemId === undefined ? {} : { itemId }), providerMetadata }))
  return { ...stepped, text: new Set([...stepped.text, id]) }
 }

-export const textDelta = (state: State, events: LLMEvent[], id: string, text: string): State => {
-  const started = textStart(state, events, id)
-  events.push(LLMEvent.textDelta({ id, text }))
+export const textDelta = (
+  state: State,
+  events: LLMEvent[],
+  id: string,
+  text: string,
+  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
+): State => {
+  const started = textStart(state, events, id, providerMetadata, itemId)
+  events.push(LLMEvent.textDelta({ id, ...(itemId === undefined ? {} : { itemId }), text, providerMetadata }))
  return started
 }

@@ -32,10 +51,11 @@ export const reasoningStart = (
  events: LLMEvent[],
  id: string,
  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
 ): State => {
  if (state.reasoning.has(id)) return state
  const stepped = stepStart(state, events)
-  events.push(LLMEvent.reasoningStart({ id, providerMetadata }))
+  events.push(LLMEvent.reasoningStart({ id, ...(itemId === undefined ? {} : { itemId }), providerMetadata }))
  return { ...stepped, reasoning: new Set([...stepped.reasoning, id]) }
 }

@@ -45,9 +65,10 @@ export const reasoningDelta = (
  id: string,
  text: string,
  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
 ): State => {
-  const started = reasoningStart(state, events, id, providerMetadata)
-  events.push(LLMEvent.reasoningDelta({ id, text, providerMetadata }))
+  const started = reasoningStart(state, events, id, providerMetadata, itemId)
+  events.push(LLMEvent.reasoningDelta({ id, ...(itemId === undefined ? {} : { itemId }), text, providerMetadata }))
  return started
 }

@@ -56,19 +77,26 @@ export const reasoningEnd = (
  events: LLMEvent[],
  id: string,
  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
 ): State => {
  if (!state.reasoning.has(id)) return state
  const stepped = stepStart(state, events)
-  events.push(LLMEvent.reasoningEnd({ id, providerMetadata }))
+  events.push(LLMEvent.reasoningEnd({ id, ...(itemId === undefined ? {} : { itemId }), providerMetadata }))
  const reasoning = new Set(stepped.reasoning)
  reasoning.delete(id)
  return { ...stepped, reasoning }
 }

-export const textEnd = (state: State, events: LLMEvent[], id: string, providerMetadata?: ProviderMetadata): State => {
+export const textEnd = (
+  state: State,
+  events: LLMEvent[],
+  id: string,
+  providerMetadata?: ProviderMetadata,
+  itemId?: ResponseItemID,
+): State => {
  if (!state.text.has(id)) return state
  const stepped = stepStart(state, events)
-  events.push(LLMEvent.textEnd({ id, providerMetadata }))
+  events.push(LLMEvent.textEnd({ id, ...(itemId === undefined ? {} : { itemId }), providerMetadata }))
  const text = new Set(stepped.text)
  text.delete(id)
  return { ...stepped, text }
@@ -1,5 +1,12 @@
 import { Effect } from "effect"
-import { AIError, LLMEvent, type ProviderMetadata, type ToolCall, type ToolInputError } from "../../schema"
+import {
+  AIError,
+  LLMEvent,
+  type ProviderMetadata,
+  type ResponseItemID,
+  type ToolCall,
+  type ToolInputError,
+} from "../../schema"
 import { eventError, parseToolInput, type ToolAccumulator } from "../shared"

 type StreamKey = string | number
@@ -10,6 +17,7 @@ type StreamKey = string | number
 * so far, not the parsed object.
 */
 export interface PendingTool extends ToolAccumulator {
+  readonly itemId?: ResponseItemID
  readonly providerExecuted?: boolean
  readonly providerMetadata?: ProviderMetadata
 }
@@ -52,6 +60,7 @@ const withoutTool = <K extends StreamKey>(tools: State<K>, key: K): State<K> =>
 const inputStart = (tool: PendingTool) =>
  LLMEvent.toolInputStart({
    id: tool.id,
+    ...(tool.itemId === undefined ? {} : { itemId: tool.itemId }),
    name: tool.name,
    providerExecuted: tool.providerExecuted ? true : undefined,
    providerMetadata: tool.providerMetadata,
@@ -60,6 +69,7 @@ const inputStart = (tool: PendingTool) =>
 const inputDelta = (tool: PendingTool, text: string) =>
  LLMEvent.toolInputDelta({
    id: tool.id,
+    ...(tool.itemId === undefined ? {} : { itemId: tool.itemId }),
    name: tool.name,
    text,
  })
@@ -70,6 +80,7 @@ const toolCall = (route: string, tool: PendingTool, inputOverride?: string) => {
    Effect.map((input): ToolCall | ToolInputError =>
      LLMEvent.toolCall({
        id: tool.id,
+        ...(tool.itemId === undefined ? {} : { itemId: tool.itemId }),
        name: tool.name,
        input,
        providerExecuted: tool.providerExecuted ? true : undefined,
@@ -82,6 +93,7 @@ const toolCall = (route: string, tool: PendingTool, inputOverride?: string) => {
        : Effect.succeed(
            LLMEvent.toolInputError({
              id: tool.id,
+              ...(tool.itemId === undefined ? {} : { itemId: tool.itemId }),
              name: tool.name,
              raw,
            }),
@@ -93,7 +105,15 @@ const toolCall = (route: string, tool: PendingTool, inputOverride?: string) => {
 const finishEvents = (tool: PendingTool, event: ToolCall | ToolInputError): ReadonlyArray<LLMEvent> =>
  event.type === "tool-input-error"
    ? [event]
-    : [LLMEvent.toolInputEnd({ id: tool.id, name: tool.name, providerMetadata: tool.providerMetadata }), event]
+    : [
+        LLMEvent.toolInputEnd({
+          id: tool.id,
+          ...(tool.itemId === undefined ? {} : { itemId: tool.itemId }),
+          name: tool.name,
+          providerMetadata: tool.providerMetadata,
+        }),
+        event,
+      ]

 /** Store the updated tool and produce the optional public delta event. */
 const appendTool = <K extends StreamKey>(
@@ -148,6 +168,7 @@ export const appendOrStart = <K extends StreamKey>(
    id,
    name,
    input: `${current?.input ?? ""}${delta.text}`,
+    itemId: current?.itemId,
    providerExecuted: current?.providerExecuted,
    providerMetadata: current?.providerMetadata,
  }
@@ -1,5 +1,5 @@
 import { Schema } from "effect"
-import { ContentBlockID, FinishReason, ProviderMetadata, ToolCallID } from "./ids"
+import { ContentBlockID, FinishReason, ProviderMetadata, ResponseItemID, ToolCallID } from "./ids"
 import { Message, ToolCallPart, ToolOutput, ToolResultPart, ToolResultValue, type ContentPart } from "./messages"
 import { ProviderFailureClassification } from "./errors"

@@ -84,6 +84,7 @@ export type StepStart = Schema.Schema.Type<typeof StepStart>
 export const TextStart = Schema.Struct({
  type: Schema.tag("text-start"),
  id: ContentBlockID,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.TextStart" })
 export type TextStart = Schema.Schema.Type<typeof TextStart>
@@ -92,6 +93,7 @@ export const TextDelta = Schema.Struct({
  type: Schema.tag("text-delta"),
  id: ContentBlockID,
  text: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.TextDelta" })
 export type TextDelta = Schema.Schema.Type<typeof TextDelta>
@@ -99,6 +101,7 @@ export type TextDelta = Schema.Schema.Type<typeof TextDelta>
 export const TextEnd = Schema.Struct({
  type: Schema.tag("text-end"),
  id: ContentBlockID,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.TextEnd" })
 export type TextEnd = Schema.Schema.Type<typeof TextEnd>
@@ -106,6 +109,7 @@ export type TextEnd = Schema.Schema.Type<typeof TextEnd>
 export const ReasoningStart = Schema.Struct({
  type: Schema.tag("reasoning-start"),
  id: ContentBlockID,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ReasoningStart" })
 export type ReasoningStart = Schema.Schema.Type<typeof ReasoningStart>
@@ -114,6 +118,7 @@ export const ReasoningDelta = Schema.Struct({
  type: Schema.tag("reasoning-delta"),
  id: ContentBlockID,
  text: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ReasoningDelta" })
 export type ReasoningDelta = Schema.Schema.Type<typeof ReasoningDelta>
@@ -121,6 +126,7 @@ export type ReasoningDelta = Schema.Schema.Type<typeof ReasoningDelta>
 export const ReasoningEnd = Schema.Struct({
  type: Schema.tag("reasoning-end"),
  id: ContentBlockID,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ReasoningEnd" })
 export type ReasoningEnd = Schema.Schema.Type<typeof ReasoningEnd>
@@ -129,6 +135,7 @@ export const ToolInputStart = Schema.Struct({
  type: Schema.tag("tool-input-start"),
  id: ToolCallID,
  name: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  providerExecuted: Schema.optional(Schema.Boolean),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ToolInputStart" })
@@ -137,6 +144,7 @@ export type ToolInputStart = Schema.Schema.Type<typeof ToolInputStart>
 export const ToolInputDelta = Schema.Struct({
  type: Schema.tag("tool-input-delta"),
  id: ToolCallID,
+  itemId: Schema.optional(ResponseItemID),
  name: Schema.String,
  text: Schema.String,
 }).annotate({ identifier: "LLM.Event.ToolInputDelta" })
@@ -146,6 +154,7 @@ export const ToolInputEnd = Schema.Struct({
  type: Schema.tag("tool-input-end"),
  id: ToolCallID,
  name: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ToolInputEnd" })
 export type ToolInputEnd = Schema.Schema.Type<typeof ToolInputEnd>
@@ -154,6 +163,7 @@ export type ToolInputEnd = Schema.Schema.Type<typeof ToolInputEnd>
 export const ToolInputError = Schema.Struct({
  type: Schema.tag("tool-input-error"),
  id: ToolCallID,
+  itemId: Schema.optional(ResponseItemID),
  name: Schema.String,
  raw: Schema.String,
 }).annotate({ identifier: "LLM.Event.ToolInputError" })
@@ -162,6 +172,7 @@ export type ToolInputError = Schema.Schema.Type<typeof ToolInputError>
 export const ToolCall = Schema.Struct({
  type: Schema.tag("tool-call"),
  id: ToolCallID,
+  itemId: Schema.optional(ResponseItemID),
  name: Schema.String,
  input: Schema.Unknown,
  providerExecuted: Schema.optional(Schema.Boolean),
@@ -172,6 +183,7 @@ export type ToolCall = Schema.Schema.Type<typeof ToolCall>
 export const ToolResult = Schema.Struct({
  type: Schema.tag("tool-result"),
  id: ToolCallID,
+  itemId: Schema.optional(ResponseItemID),
  name: Schema.String,
  result: ToolResultValue,
  output: Schema.optional(ToolOutput),
@@ -183,6 +195,7 @@ export type ToolResult = Schema.Schema.Type<typeof ToolResult>
 export const ToolError = Schema.Struct({
  type: Schema.tag("tool-error"),
  id: ToolCallID,
+  itemId: Schema.optional(ResponseItemID),
  name: Schema.String,
  message: Schema.String,
  error: Schema.optional(Schema.Defect()),
@@ -334,12 +347,14 @@ const responseUsage = (events: ReadonlyArray<LLMEvent>) =>
 interface ContentAssembly {
  readonly contentIndex: number
  readonly text: string
+  readonly itemId?: ResponseItemID
  readonly providerMetadata?: ProviderMetadata
 }

 interface ToolInputAssembly {
  readonly name: string
  readonly text: string
+  readonly itemId?: ResponseItemID
  readonly providerMetadata?: ProviderMetadata
 }

@@ -385,11 +400,27 @@ const appendEvent = (state: ResponseState, event: LLMEvent): ResponseState => {
  }
 }

-const textContent = (text: string, providerMetadata: ProviderMetadata | undefined): ContentPart =>
-  providerMetadata === undefined ? { type: "text", text } : { type: "text", text, providerMetadata }
+const textContent = (
+  text: string,
+  itemId: ResponseItemID | undefined,
+  providerMetadata: ProviderMetadata | undefined,
+): ContentPart => ({
+  type: "text",
+  text,
+  ...(itemId === undefined ? {} : { itemId }),
+  ...(providerMetadata === undefined ? {} : { providerMetadata }),
+})

-const reasoningContent = (text: string, providerMetadata: ProviderMetadata | undefined): ContentPart =>
-  providerMetadata === undefined ? { type: "reasoning", text } : { type: "reasoning", text, providerMetadata }
+const reasoningContent = (
+  text: string,
+  itemId: ResponseItemID | undefined,
+  providerMetadata: ProviderMetadata | undefined,
+): ContentPart => ({
+  type: "reasoning",
+  text,
+  ...(itemId === undefined ? {} : { itemId }),
+  ...(providerMetadata === undefined ? {} : { providerMetadata }),
+})

 const contentWith = (state: ResponseState, content: ReadonlyArray<ContentPart>): ResponseState => ({
  ...state,
@@ -404,26 +435,32 @@ const replaceContent = (state: ResponseState, index: number, part: ContentPart)
    state.message.content.map((item, itemIndex) => (itemIndex === index ? part : item)),
  )

-const ensureText = (state: ResponseState, id: string, providerMetadata?: ProviderMetadata): ResponseState => {
+const ensureText = (
+  state: ResponseState,
+  id: string,
+  itemId?: ResponseItemID,
+  providerMetadata?: ProviderMetadata,
+): ResponseState => {
  if (state.textParts[id]) return state
  return {
-    ...appendContent(state, textContent("", providerMetadata)),
+    ...appendContent(state, textContent("", itemId, providerMetadata)),
    textParts: {
      ...state.textParts,
-      [id]: { contentIndex: state.message.content.length, text: "", providerMetadata },
+      [id]: { contentIndex: state.message.content.length, text: "", itemId, providerMetadata },
    },
  }
 }

 const reduceTextDelta = (state: ResponseState, event: TextDelta): ResponseState => {
-  const started = ensureText(state, event.id, event.providerMetadata)
+  const started = ensureText(state, event.id, event.itemId, event.providerMetadata)
  const current = started.textParts[event.id]
  if (!current) return started
  const text = current.text + event.text
+  const itemId = event.itemId ?? current.itemId
  const providerMetadata = event.providerMetadata ?? current.providerMetadata
  return {
-    ...replaceContent(started, current.contentIndex, textContent(text, providerMetadata)),
-    textParts: { ...started.textParts, [event.id]: { ...current, text, providerMetadata } },
+    ...replaceContent(started, current.contentIndex, textContent(text, itemId, providerMetadata)),
+    textParts: { ...started.textParts, [event.id]: { ...current, text, itemId, providerMetadata } },
  }
 }

@@ -431,32 +468,39 @@ const reduceTextEnd = (state: ResponseState, event: TextEnd): ResponseState => {
  const current = state.textParts[event.id]
  if (!current) return state
  const providerMetadata = event.providerMetadata ?? current.providerMetadata
+  const itemId = event.itemId ?? current.itemId
  return {
-    ...replaceContent(state, current.contentIndex, textContent(current.text, providerMetadata)),
-    textParts: { ...state.textParts, [event.id]: { ...current, providerMetadata } },
+    ...replaceContent(state, current.contentIndex, textContent(current.text, itemId, providerMetadata)),
+    textParts: { ...state.textParts, [event.id]: { ...current, itemId, providerMetadata } },
  }
 }

-const ensureReasoning = (state: ResponseState, id: string, providerMetadata?: ProviderMetadata): ResponseState => {
+const ensureReasoning = (
+  state: ResponseState,
+  id: string,
+  itemId?: ResponseItemID,
+  providerMetadata?: ProviderMetadata,
+): ResponseState => {
  if (state.reasoningParts[id]) return state
  return {
-    ...appendContent(state, reasoningContent("", providerMetadata)),
+    ...appendContent(state, reasoningContent("", itemId, providerMetadata)),
    reasoningParts: {
      ...state.reasoningParts,
-      [id]: { contentIndex: state.message.content.length, text: "", providerMetadata },
+      [id]: { contentIndex: state.message.content.length, text: "", itemId, providerMetadata },
    },
  }
 }

 const reduceReasoningDelta = (state: ResponseState, event: ReasoningDelta): ResponseState => {
-  const started = ensureReasoning(state, event.id, event.providerMetadata)
+  const started = ensureReasoning(state, event.id, event.itemId, event.providerMetadata)
  const current = started.reasoningParts[event.id]
  if (!current) return started
  const text = current.text + event.text
+  const itemId = event.itemId ?? current.itemId
  const providerMetadata = event.providerMetadata ?? current.providerMetadata
  return {
-    ...replaceContent(started, current.contentIndex, reasoningContent(text, providerMetadata)),
-    reasoningParts: { ...started.reasoningParts, [event.id]: { ...current, text, providerMetadata } },
+    ...replaceContent(started, current.contentIndex, reasoningContent(text, itemId, providerMetadata)),
+    reasoningParts: { ...started.reasoningParts, [event.id]: { ...current, text, itemId, providerMetadata } },
  }
 }

@@ -464,9 +508,10 @@ const reduceReasoningEnd = (state: ResponseState, event: ReasoningEnd): Response
  const current = state.reasoningParts[event.id]
  if (!current) return state
  const providerMetadata = event.providerMetadata ?? current.providerMetadata
+  const itemId = event.itemId ?? current.itemId
  return {
-    ...replaceContent(state, current.contentIndex, reasoningContent(current.text, providerMetadata)),
-    reasoningParts: { ...state.reasoningParts, [event.id]: { ...current, providerMetadata } },
+    ...replaceContent(state, current.contentIndex, reasoningContent(current.text, itemId, providerMetadata)),
+    reasoningParts: { ...state.reasoningParts, [event.id]: { ...current, itemId, providerMetadata } },
  }
 }

@@ -474,7 +519,7 @@ const reduceToolInputStart = (state: ResponseState, event: ToolInputStart): Resp
  ...state,
  toolInputs: {
    ...state.toolInputs,
-    [event.id]: { name: event.name, text: "", providerMetadata: event.providerMetadata },
+    [event.id]: { name: event.name, text: "", itemId: event.itemId, providerMetadata: event.providerMetadata },
  },
 })

@@ -495,6 +540,7 @@ const reduceToolInputEnd = (state: ResponseState, event: ToolInputEnd): Response
      [event.id]: {
        ...current,
        name: event.name,
+        itemId: event.itemId ?? current.itemId,
        providerMetadata: event.providerMetadata ?? current.providerMetadata,
      },
    },
@@ -504,6 +550,7 @@ const reduceToolInputEnd = (state: ResponseState, event: ToolInputEnd): Response
 const toolCallContent = (event: ToolCall): ContentPart =>
  ToolCallPart.make({
    id: event.id,
+    ...(event.itemId === undefined ? {} : { itemId: event.itemId }),
    name: event.name,
    input: event.input,
    ...(event.providerExecuted === undefined ? {} : { providerExecuted: event.providerExecuted }),
@@ -513,6 +560,7 @@ const toolCallContent = (event: ToolCall): ContentPart =>
 const toolResultContent = (event: ToolResult): ContentPart =>
  ToolResultPart.make({
    id: event.id,
+    ...(event.itemId === undefined ? {} : { itemId: event.itemId }),
    name: event.name,
    result: event.result,
    ...(event.providerExecuted === undefined ? {} : { providerExecuted: event.providerExecuted }),
@@ -528,13 +576,13 @@ const reduceResponseState = (state: ResponseState, event: LLMEvent): ResponseSta
  const next = appendEvent(state, event)
  switch (event.type) {
    case "text-start":
-      return ensureText(next, event.id, event.providerMetadata)
+      return ensureText(next, event.id, event.itemId, event.providerMetadata)
    case "text-delta":
      return reduceTextDelta(next, event)
    case "text-end":
      return reduceTextEnd(next, event)
    case "reasoning-start":
-      return ensureReasoning(next, event.id, event.providerMetadata)
+      return ensureReasoning(next, event.id, event.itemId, event.providerMetadata)
    case "reasoning-delta":
      return reduceReasoningDelta(next, event)
    case "reasoning-end":
@@ -21,6 +21,9 @@ export type ProviderID = typeof ProviderID.Type
 export const ResponseID = Schema.String
 export type ResponseID = Schema.Schema.Type<typeof ResponseID>

+export const ResponseItemID = Schema.String
+export type ResponseItemID = Schema.Schema.Type<typeof ResponseItemID>
+
 export const ContentBlockID = Schema.String
 export type ContentBlockID = Schema.Schema.Type<typeof ContentBlockID>

@@ -1,6 +1,6 @@
 import { Schema } from "effect"
 import { Tool } from "@opencode-ai/schema/tool"
-import { JsonSchema, MessageRole, ProviderMetadata } from "./ids"
+import { JsonSchema, MessageRole, ProviderMetadata, ResponseItemID } from "./ids"
 import { CacheHint, CachePolicy, GenerationOptions, HttpOptions, LanguageModelSchema, ProviderOptions } from "./options"
 import { isRecord } from "../utils/record"

@@ -25,6 +25,7 @@ export const SystemPart = Object.assign(systemPartSchema, {
 export const TextPart = Schema.Struct({
  type: Schema.Literal("text"),
  text: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  cache: Schema.optional(CacheHint),
  metadata: Schema.optional(Schema.Record(Schema.String, Schema.Unknown)),
  providerMetadata: Schema.optional(ProviderMetadata),
@@ -121,6 +122,7 @@ export const ToolCallPart = Object.assign(
  Schema.Struct({
    type: Schema.Literal("tool-call"),
    id: Schema.String,
+    itemId: Schema.optional(ResponseItemID),
    name: Schema.String,
    input: Schema.Unknown,
    providerExecuted: Schema.optional(Schema.Boolean),
@@ -138,6 +140,7 @@ export const ToolResultPart = Object.assign(
  Schema.Struct({
    type: Schema.Literal("tool-result"),
    id: Schema.String,
+    itemId: Schema.optional(ResponseItemID),
    name: Schema.String,
    result: ToolResultValue,
    providerExecuted: Schema.optional(Schema.Boolean),
@@ -154,6 +157,7 @@ export const ToolResultPart = Object.assign(
    ): ToolResultPart => ({
      type: "tool-result",
      id: input.id,
+      ...(input.itemId === undefined ? {} : { itemId: input.itemId }),
      name: input.name,
      result: ToolResultValue.make(input.result, input.resultType),
      providerExecuted: input.providerExecuted,
@@ -168,6 +172,7 @@ export type ToolResultPart = Schema.Schema.Type<typeof ToolResultPart>
 export const ReasoningPart = Schema.Struct({
  type: Schema.Literal("reasoning"),
  text: Schema.String,
+  itemId: Schema.optional(ResponseItemID),
  encrypted: Schema.optional(Schema.String),
  cache: Schema.optional(CacheHint),
  metadata: Schema.optional(Schema.Record(Schema.String, Schema.Unknown)),
@@ -181,7 +186,7 @@ export const ContentPart = Schema.Union([TextPart, MediaPart, ToolCallPart, Tool
 export type ContentPart = Schema.Schema.Type<typeof ContentPart>

 export class Message extends Schema.Class<Message>("LLM.Message")({
-  id: Schema.optional(Schema.String),
+  id: Schema.optional(ResponseItemID),
  role: MessageRole,
  content: Schema.Array(ContentPart),
  metadata: Schema.optional(Schema.Record(Schema.String, Schema.Unknown)),
@@ -79,7 +79,7 @@ const result = (call: ToolCallPart, value: ToolResultValueType | ToolSettlement,
              id: call.id,
              name: call.name,
              result: settlement.result,
-              providerMetadata: call.providerMetadata,
+              ...(call.providerMetadata === undefined ? {} : { providerMetadata: call.providerMetadata }),
            }),
          ]
        : [
@@ -88,7 +88,7 @@ const result = (call: ToolCallPart, value: ToolResultValueType | ToolSettlement,
              name: call.name,
              result: settlement.result,
              output: settlement.output,
-              providerMetadata: call.providerMetadata,
+              ...(call.providerMetadata === undefined ? {} : { providerMetadata: call.providerMetadata }),
            }),
          ],
  }
@@ -44,7 +44,7 @@
        "headers": {
          "content-type": "application/json"
        },
-        "body": "{\"model\":\"gpt-5.5\",\"input\":[{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"Think briefly, then reply exactly with: Hello!\"}]},{\"type\":\"reasoning\",\"summary\":[],\"encrypted_content\":\"gAAAAABqEjXoGMCw3WDXpoD9151PEr2Lt8raW7KBKefQhZJGWx5f8jy152bApO6oE-Mr1BhUtfZNq3OPBVfSL4ioQ9bHREfujIBXgk9LUDBAz2Sle7KjOr9HaUV16A4HBiaFIRFjsHPS9G8yEySp1m6F1CD_WR6apyUGgugRh_y39EcOJmxPOzmiac5DVM6fraA1VpcGbqrZ1x2ANHFDOfnYTycPtPNTgzE7LjkYjDDWbT03uN1YxfP4pqjDVRzY14pA8bSZ8ys-pDv5kUFCAsw-OlU4jYKUXp-M8_6KTaRQP71LPwppt__zG_NJPfy-qUil4pOU8_NoxtxerHgLLXbfExZdzfpoGinoEjn7nj7BJDEtl-LNeNEb5c-1ZymNfVMp-Cs3fLEPkAV8rtHFtZ0MhE_07GKbGo7hTrOmkM4DydxmHsdWGNbXAG35cprslEA5P7p3GHFKnRs5hGs2eq-XcZ3yki64ZBOU_Tv6UR7nUH09gF1rdrJo3dpre6M00COwwdZ02zUP5KxCuI8FKu2jsZu9zgMVXDALsdtM5orTCVLXsn4rddWd111zE-vMjNmMMmktW2cHMjH7j1ooA-9P083koNVYiLi4UhMA64gTqgyl8MxkZekl7eFSMa7qk295NaHOKtFxzYYcZ9jdioCwSPSZ0ZZWLoNgrK7SWfRh0uaTHNcMZ3wq8ae6CguktIeVTCPTQAqJLQqd7AU0oOCKCJ7BWnC-L8UC6m7Pm9ZS958uUVeWBhgKHzMAGq9UeQB7IEeAcbMn3EDgOSfd8qCb8iwU9iG9dcu9axQwWU7pd7kd-T-He61W7z5wWgpx1KehWCxrN6kuKSo6p-uUfwVnJukreOn8BJNAzADQgz68bhmN9VGih7YcKVnLgwDwKditrjSd6-tfE0Baarj3jWENvT6ohY17R9FDrKS-2v8IIX6tGjoKJw8SRhaWLNv4vWlmxRgR0gdac3qumd0GKqsWSveNz01naA==\"},{\"role\":\"assistant\",\"content\":[{\"type\":\"output_text\",\"text\":\"Hello!\"}]},{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"Now reply exactly with: Done.\"}]}],\"store\":false,\"include\":[\"reasoning.encrypted_content\"],\"reasoning\":{\"effort\":\"low\",\"summary\":\"auto\"},\"text\":{\"verbosity\":\"low\"},\"max_output_tokens\":40,\"stream\":true}"
+        "body": "{\"model\":\"gpt-5.5\",\"input\":[{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"Think briefly, then reply exactly with: Hello!\"}]},{\"type\":\"reasoning\",\"summary\":[],\"encrypted_content\":\"gAAAAABqEjXoGMCw3WDXpoD9151PEr2Lt8raW7KBKefQhZJGWx5f8jy152bApO6oE-Mr1BhUtfZNq3OPBVfSL4ioQ9bHREfujIBXgk9LUDBAz2Sle7KjOr9HaUV16A4HBiaFIRFjsHPS9G8yEySp1m6F1CD_WR6apyUGgugRh_y39EcOJmxPOzmiac5DVM6fraA1VpcGbqrZ1x2ANHFDOfnYTycPtPNTgzE7LjkYjDDWbT03uN1YxfP4pqjDVRzY14pA8bSZ8ys-pDv5kUFCAsw-OlU4jYKUXp-M8_6KTaRQP71LPwppt__zG_NJPfy-qUil4pOU8_NoxtxerHgLLXbfExZdzfpoGinoEjn7nj7BJDEtl-LNeNEb5c-1ZymNfVMp-Cs3fLEPkAV8rtHFtZ0MhE_07GKbGo7hTrOmkM4DydxmHsdWGNbXAG35cprslEA5P7p3GHFKnRs5hGs2eq-XcZ3yki64ZBOU_Tv6UR7nUH09gF1rdrJo3dpre6M00COwwdZ02zUP5KxCuI8FKu2jsZu9zgMVXDALsdtM5orTCVLXsn4rddWd111zE-vMjNmMMmktW2cHMjH7j1ooA-9P083koNVYiLi4UhMA64gTqgyl8MxkZekl7eFSMa7qk295NaHOKtFxzYYcZ9jdioCwSPSZ0ZZWLoNgrK7SWfRh0uaTHNcMZ3wq8ae6CguktIeVTCPTQAqJLQqd7AU0oOCKCJ7BWnC-L8UC6m7Pm9ZS958uUVeWBhgKHzMAGq9UeQB7IEeAcbMn3EDgOSfd8qCb8iwU9iG9dcu9axQwWU7pd7kd-T-He61W7z5wWgpx1KehWCxrN6kuKSo6p-uUfwVnJukreOn8BJNAzADQgz68bhmN9VGih7YcKVnLgwDwKditrjSd6-tfE0Baarj3jWENvT6ohY17R9FDrKS-2v8IIX6tGjoKJw8SRhaWLNv4vWlmxRgR0gdac3qumd0GKqsWSveNz01naA==\",\"id\":\"rs_0a0794dab3b8ec7d016a1235e7ce3881958a5eca32a36a14c5\"},{\"role\":\"assistant\",\"content\":[{\"type\":\"output_text\",\"text\":\"Hello!\"}]},{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"Now reply exactly with: Done.\"}]}],\"store\":false,\"include\":[\"reasoning.encrypted_content\"],\"reasoning\":{\"effort\":\"low\",\"summary\":\"auto\"},\"text\":{\"verbosity\":\"low\"},\"max_output_tokens\":40,\"stream\":true}"
      },
      "response": {
        "status": 200,
@@ -8,7 +8,6 @@ import {
  type ProviderMetadata,
  type ToolCallPart,
  ToolResultPart,
-  type ToolResultValue,
  type Usage,
 } from "../../src/schema"
 import { type Tools, toDefinitions } from "../../src/tool"
@@ -61,9 +60,10 @@ export const runTools = <T extends Tools>(options: RunOptions<T>) =>
            ...dispatched.map(([call, dispatched]) =>
              Message.tool({
                id: call.id,
+                itemId: dispatched.events.find(LLMEvent.is.toolResult)?.itemId,
                name: call.name,
                result: dispatched.result,
-                providerMetadata: call.providerMetadata,
+                providerMetadata: dispatched.events.find(LLMEvent.is.toolResult)?.providerMetadata,
              }),
            ),
          ],
@@ -89,9 +89,15 @@ const stepState = (events: ReadonlyArray<LLMEvent>) => {

  for (const event of events) {
    if (event.type === "text-delta" || event.type === "reasoning-delta") {
-      appendText(assistantContent, event.type === "text-delta" ? "text" : "reasoning", event.text)
+      appendText(assistantContent, event.type === "text-delta" ? "text" : "reasoning", event.text, event.itemId)
    } else if (event.type === "text-end" || event.type === "reasoning-end") {
-      appendText(assistantContent, event.type === "text-end" ? "text" : "reasoning", "", event.providerMetadata)
+      appendText(
+        assistantContent,
+        event.type === "text-end" ? "text" : "reasoning",
+        "",
+        event.itemId,
+        event.providerMetadata,
+      )
    } else if (event.type === "tool-call") {
      assistantContent.push(event)
      if (!event.providerExecuted) toolCalls.push(event)
@@ -99,6 +105,7 @@ const stepState = (events: ReadonlyArray<LLMEvent>) => {
      assistantContent.push(
        ToolResultPart.make({
          id: event.id,
+          itemId: event.itemId,
          name: event.name,
          result: event.result,
          providerExecuted: true,
@@ -118,6 +125,7 @@ const appendText = (
  content: ContentPart[],
  type: "text" | "reasoning",
  text: string,
+  itemId?: string,
  providerMetadata?: ProviderMetadata,
 ) => {
  const last = content.at(-1)
@@ -125,11 +133,12 @@ const appendText = (
    content[content.length - 1] = {
      ...last,
      text: `${last.text}${text}`,
+      itemId: itemId ?? last.itemId,
      providerMetadata: providerMetadata ?? last.providerMetadata,
    }
    return
  }
-  content.push({ type, text, providerMetadata })
+  content.push({ type, text, itemId, providerMetadata })
 }

 const addUsage = (left: Usage | undefined, right: Usage | undefined): Usage | undefined => {
@@ -45,7 +45,7 @@ describe("Open Responses-compatible route", () => {
          },
        },
      })
-      expect(prepared.body).toEqual({
+      expect(prepared.body).toMatchObject({
        model: "example-model",
        input: [
          { role: "system", content: "You are concise." },
@@ -53,6 +53,8 @@ describe("Open Responses-compatible route", () => {
        ],
        stream: true,
      })
+      expect(prepared.body.input[0]).not.toHaveProperty("id")
+      expect(prepared.body.input[1]).not.toHaveProperty("id")
    }),
  )

@@ -69,6 +69,9 @@ describe("OpenAI Responses route", () => {
        stream: true,
        max_output_tokens: 20,
        temperature: 0,
+        tool_choice: undefined,
+        tools: undefined,
+        top_p: undefined,
      })
    }),
  )
@@ -329,7 +332,7 @@ describe("OpenAI Responses route", () => {
      yield* LLMClient.generate(
        LLMRequest.update(request, {
          model: Azure.configure({
-            baseURL: "https://opencode-test.openai.azure.com/openai/v1/",
+            baseURL: "https://opencode-test.openai.azure.com/openai/",
            apiKey: "azure-key",
            headers: { authorization: "Bearer stale" },
          }).responses("gpt-4.1-mini"),
@@ -410,7 +413,7 @@ describe("OpenAI Responses route", () => {
        }),
      )

-      expect(prepared.body).toEqual({
+      expect(prepared.body).toMatchObject({
        model: "gpt-4.1-mini",
        input: [
          { role: "user", content: [{ type: "input_text", text: "What is the weather?" }] },
@@ -425,6 +428,60 @@ describe("OpenAI Responses route", () => {
        tools: undefined,
        top_p: undefined,
      })
+      const call = prepared.body.input.find((item) => "type" in item && item.type === "function_call")
+      const output = prepared.body.input.find((item) => "type" in item && item.type === "function_call_output")
+      expect(call?.id).toBeUndefined()
+      expect(output?.id).toBeUndefined()
+    }),
+  )
+
+  it.effect("does not generate response item ids for client-created history", () =>
+    Effect.sync(() => {
+      const canonical = LLM.request({
+        model,
+        messages: [
+          Message.assistant([
+            { type: "text", text: "Working." },
+            { type: "reasoning", text: "Thinking." },
+            ToolCallPart.make({ id: "call_1", name: "lookup", input: {} }),
+          ]),
+          Message.tool({ id: "call_1", name: "lookup", result: "done" }),
+        ],
+      })
+
+      expect(canonical.messages[0]?.id).toBeUndefined()
+      expect(canonical.messages[1]?.id).toBeUndefined()
+      expect(canonical.messages[0]?.content.every((part) => part.type === "media" || part.itemId === undefined)).toBe(
+        true,
+      )
+      expect(canonical.messages[1]?.content[0]).not.toHaveProperty("itemId")
+    }),
+  )
+
+  it.effect("preserves opaque assistant item ids without assigning ids to function items", () =>
+    Effect.gen(function* () {
+      const canonical = LLM.request({
+        model,
+        messages: [
+          Message.assistant([
+            { type: "text", text: "Calling.", itemId: "plain-text" },
+            ToolCallPart.make({ id: "call_1", itemId: "plain-call", name: "lookup", input: {} }),
+          ]),
+          Message.tool({ id: "call_1", itemId: "plain-output", name: "lookup", result: "done" }),
+        ],
+      })
+      const prepared = yield* compileRequest(canonical)
+
+      expect(canonical.messages[0]?.content.map((part) => (part.type === "media" ? undefined : part.itemId))).toEqual([
+        "plain-text",
+        "plain-call",
+      ])
+      expect(canonical.messages[1]?.content[0]).toMatchObject({ itemId: "plain-output" })
+      expect(prepared.body.input).toEqual([
+        { role: "assistant", id: "plain-text", content: [{ type: "output_text", text: "Calling." }] },
+        { type: "function_call", call_id: "call_1", name: "lookup", arguments: "{}" },
+        { type: "function_call_output", call_id: "call_1", output: '"done"' },
+      ])
    }),
  )

@@ -864,9 +921,21 @@ describe("OpenAI Responses route", () => {
      expect(response.text).toBe("Hello!")
      expect(response.events).toEqual([
        { type: "step-start", index: 0 },
-        { type: "text-start", id: "msg_1" },
-        { type: "text-delta", id: "msg_1", text: "Hello" },
-        { type: "text-delta", id: "msg_1", text: "!" },
+        { type: "text-start", id: "msg_1", itemId: "msg_1", providerMetadata: { openai: { itemId: "msg_1" } } },
+        {
+          type: "text-delta",
+          id: "msg_1",
+          itemId: "msg_1",
+          text: "Hello",
+          providerMetadata: { openai: { itemId: "msg_1" } },
+        },
+        {
+          type: "text-delta",
+          id: "msg_1",
+          itemId: "msg_1",
+          text: "!",
+          providerMetadata: { openai: { itemId: "msg_1" } },
+        },
        { type: "text-end", id: "msg_1" },
        {
          type: "step-finish",
@@ -923,17 +992,20 @@ describe("OpenAI Responses route", () => {
        {
          type: "text",
          text: "Checking.",
-          providerMetadata: { openai: { phase: "commentary" } },
+          itemId: "msg_commentary",
+          providerMetadata: { openai: { itemId: "msg_commentary", phase: "commentary" } },
        },
        {
          type: "text",
          text: "Finished.",
-          providerMetadata: { openai: { phase: "final_answer" } },
+          itemId: "msg_final",
+          providerMetadata: { openai: { itemId: "msg_final", phase: "final_answer" } },
        },
        {
          type: "text",
          text: "Unclassified.",
-          providerMetadata: { openai: { phase: null } },
+          itemId: "msg_null",
+          providerMetadata: { openai: { itemId: "msg_null", phase: null } },
        },
      ])

@@ -941,16 +1013,19 @@ describe("OpenAI Responses route", () => {
      expect(prepared.body.input).toEqual([
        {
          role: "assistant",
+          id: "msg_commentary",
          content: [{ type: "output_text", text: "Checking." }],
          phase: "commentary",
        },
        {
          role: "assistant",
+          id: "msg_final",
          content: [{ type: "output_text", text: "Finished." }],
          phase: "final_answer",
        },
        {
          role: "assistant",
+          id: "msg_null",
          content: [{ type: "output_text", text: "Unclassified." }],
          phase: null,
        },
@@ -1043,12 +1118,24 @@ describe("OpenAI Responses route", () => {
      )

      expect(response.events.filter((event) => event.type.startsWith("text-"))).toEqual([
-        { type: "text-start", id: "msg_1" },
-        { type: "text-delta", id: "msg_1", text: "First" },
-        { type: "text-end", id: "msg_1" },
-        { type: "text-start", id: "msg_2" },
-        { type: "text-delta", id: "msg_2", text: "Second" },
-        { type: "text-end", id: "msg_2" },
+        { type: "text-start", id: "msg_1", itemId: "msg_1", providerMetadata: { openai: { itemId: "msg_1" } } },
+        {
+          type: "text-delta",
+          id: "msg_1",
+          itemId: "msg_1",
+          text: "First",
+          providerMetadata: { openai: { itemId: "msg_1" } },
+        },
+        { type: "text-end", id: "msg_1", itemId: "msg_1", providerMetadata: { openai: { itemId: "msg_1" } } },
+        { type: "text-start", id: "msg_2", itemId: "msg_2", providerMetadata: { openai: { itemId: "msg_2" } } },
+        {
+          type: "text-delta",
+          id: "msg_2",
+          itemId: "msg_2",
+          text: "Second",
+          providerMetadata: { openai: { itemId: "msg_2" } },
+        },
+        { type: "text-end", id: "msg_2", itemId: "msg_2", providerMetadata: { openai: { itemId: "msg_2" } } },
      ])
    }),
  )
@@ -1068,9 +1155,15 @@ describe("OpenAI Responses route", () => {
      expect(response.text).toBe("Hello")
      expect(response.events).toMatchObject([
        { type: "step-start", index: 0 },
-        { type: "reasoning-start", id: "rs_1" },
-        { type: "reasoning-delta", id: "rs_1", text: "thinking" },
-        { type: "text-start", id: "msg_1" },
+        { type: "reasoning-start", id: "rs_1", itemId: "rs_1", providerMetadata: { openai: { itemId: "rs_1" } } },
+        {
+          type: "reasoning-delta",
+          id: "rs_1",
+          itemId: "rs_1",
+          text: "thinking",
+          providerMetadata: { openai: { itemId: "rs_1" } },
+        },
+        { type: "text-start", id: "msg_1", itemId: "msg_1", providerMetadata: { openai: { itemId: "msg_1" } } },
        { type: "text-delta", id: "msg_1", text: "Hello" },
        { type: "reasoning-end", id: "rs_1" },
        { type: "text-end", id: "msg_1" },
@@ -1079,8 +1172,8 @@ describe("OpenAI Responses route", () => {
      ])
      expect(response.events.filter((event) => event.type === "finish")).toHaveLength(1)
      expect(response.message.content).toEqual([
-        { type: "reasoning", text: "thinking" },
-        { type: "text", text: "Hello" },
+        { type: "reasoning", text: "thinking", itemId: "rs_1", providerMetadata: { openai: { itemId: "rs_1" } } },
+        { type: "text", text: "Hello", itemId: "msg_1", providerMetadata: { openai: { itemId: "msg_1" } } },
      ])
    }),
  )
@@ -1111,6 +1204,7 @@ describe("OpenAI Responses route", () => {
        expect.objectContaining({
          type: "reasoning-end",
          id: "rs_1",
+          itemId: "rs_1",
          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: "encrypted-state" } },
        }),
      )
@@ -1151,19 +1245,34 @@ describe("OpenAI Responses route", () => {
        {
          type: "reasoning-start",
          id: "rs_1:0",
+          itemId: "rs_1",
          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: null } },
        },
-        { type: "reasoning-delta", id: "rs_1:0", text: "First" },
-        { type: "reasoning-end", id: "rs_1:0", providerMetadata: { openai: { itemId: "rs_1" } } },
+        {
+          type: "reasoning-delta",
+          id: "rs_1:0",
+          itemId: "rs_1",
+          text: "First",
+          providerMetadata: { openai: { itemId: "rs_1" } },
+        },
+        { type: "reasoning-end", id: "rs_1:0", itemId: "rs_1", providerMetadata: { openai: { itemId: "rs_1" } } },
        {
          type: "reasoning-start",
          id: "rs_1:1",
+          itemId: "rs_1",
          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: null } },
        },
-        { type: "reasoning-delta", id: "rs_1:1", text: "Second" },
+        {
+          type: "reasoning-delta",
+          id: "rs_1:1",
+          itemId: "rs_1",
+          text: "Second",
+          providerMetadata: { openai: { itemId: "rs_1" } },
+        },
        {
          type: "reasoning-end",
          id: "rs_1:1",
+          itemId: "rs_1",
          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: "encrypted-state" } },
        },
        { type: "step-finish", index: 0, reason: { normalized: "stop", raw: undefined } },
@@ -1201,8 +1310,8 @@ describe("OpenAI Responses route", () => {
      )

      expect(response.events.filter((event) => event.type === "reasoning-end")).toEqual([
-        { type: "reasoning-end", id: "rs_1:0", providerMetadata: { openai: { itemId: "rs_1" } } },
-        { type: "reasoning-end", id: "rs_1:1", providerMetadata: { openai: { itemId: "rs_1" } } },
+        { type: "reasoning-end", id: "rs_1:0", itemId: "rs_1", providerMetadata: { openai: { itemId: "rs_1" } } },
+        { type: "reasoning-end", id: "rs_1:1", itemId: "rs_1", providerMetadata: { openai: { itemId: "rs_1" } } },
      ])
    }),
  )
@@ -1250,7 +1359,7 @@ describe("OpenAI Responses route", () => {
                  { role: "user", content: [{ type: "input_text", text: "Summarize it." }] },
                ],
              })
-              expect(body.input[1]).not.toHaveProperty("id")
+              expect(body.input[1]).toHaveProperty("id", "rs_1")
              return input.respond(
                sseEvents(
                  { type: "response.output_text.delta", item_id: "msg_1", delta: "Parser now round-trips reasoning." },
@@ -1297,6 +1406,7 @@ describe("OpenAI Responses route", () => {
        { role: "assistant", content: [{ type: "output_text", text: "Before." }] },
        {
          type: "reasoning",
+          id: "rs_1",
          encrypted_content: "encrypted-state",
          summary: [{ type: "summary_text", text: "Checked order." }],
        },
@@ -1305,7 +1415,7 @@ describe("OpenAI Responses route", () => {
    }),
  )

-  it.effect("references stored reasoning items by id", () =>
+  it.effect("replays complete stored reasoning items with their id", () =>
    Effect.gen(function* () {
      const prepared = yield* compileRequest(
        LLM.request({
@@ -1323,7 +1433,14 @@ describe("OpenAI Responses route", () => {
        }),
      )

-      expect(prepared.body.input).toEqual([{ type: "item_reference", id: "rs_1" }])
+      expect(prepared.body.input).toEqual([
+        {
+          type: "reasoning",
+          id: "rs_1",
+          summary: [{ type: "summary_text", text: "Checked the previous diff." }],
+          encrypted_content: undefined,
+        },
+      ])
    }),
  )

@@ -1432,6 +1549,7 @@ describe("OpenAI Responses route", () => {
      expect(prepared.body.input).toEqual([
        {
          type: "reasoning",
+          id: "rs_1",
          encrypted_content: "encrypted-state",
          summary: [
            { type: "summary_text", text: "First" },
@@ -1511,6 +1629,7 @@ describe("OpenAI Responses route", () => {
        outputTokens: 1,
        nonCachedInputTokens: 5,
        cacheReadInputTokens: undefined,
+        cacheWriteInputTokens: undefined,
        reasoningTokens: undefined,
        totalTokens: 6,
        providerMetadata: { openai: { input_tokens: 5, output_tokens: 1 } },
@@ -1521,30 +1640,35 @@ describe("OpenAI Responses route", () => {
        {
          type: "tool-input-start",
          id: "call_1",
+          itemId: "item_1",
          name: "lookup",
          providerMetadata: { openai: { itemId: "item_1" } },
        },
        {
          type: "tool-input-delta",
          id: "call_1",
+          itemId: "item_1",
          name: "lookup",
          text: '{"query"',
        },
        {
          type: "tool-input-delta",
          id: "call_1",
+          itemId: "item_1",
          name: "lookup",
          text: ':"weather"}',
        },
        {
          type: "tool-input-end",
          id: "call_1",
+          itemId: "item_1",
          name: "lookup",
          providerMetadata: { openai: { itemId: "item_1" } },
        },
        {
          type: "tool-call",
          id: "call_1",
+          itemId: "item_1",
          name: "lookup",
          input: { query: "weather" },
          providerExecuted: undefined,
@@ -1564,6 +1688,17 @@ describe("OpenAI Responses route", () => {
          usage,
        },
      ])
+      expect(response.message.content).toEqual([
+        {
+          type: "tool-call",
+          id: "call_1",
+          itemId: "item_1",
+          name: "lookup",
+          input: { query: "weather" },
+          providerExecuted: undefined,
+          providerMetadata: { openai: { itemId: "item_1" } },
+        },
+      ])
    }),
  )

@@ -1596,6 +1731,7 @@ describe("OpenAI Responses route", () => {
      expect(response.events.find(LLMEvent.is.toolInputError)).toEqual({
        type: "tool-input-error",
        id: "call_1",
+        itemId: "item_1",
        name: "lookup",
        raw: '{"query":"partial',
      })
@@ -1652,6 +1788,7 @@ describe("OpenAI Responses route", () => {
        {
          type: "tool-call",
          id: "ws_1",
+          itemId: "ws_1",
          name: "web_search",
          input: { type: "search", query: "effect 4" },
          providerExecuted: true,
@@ -1660,11 +1797,35 @@ describe("OpenAI Responses route", () => {
        {
          type: "tool-result",
          id: "ws_1",
+          itemId: "ws_1",
          name: "web_search",
          result: { type: "json", value: item },
          providerExecuted: true,
+          providerMetadata: { openai: { itemId: "ws_1", item } },
+          output: undefined,
+        },
+      ])
+      expect(response.message.content).toEqual([
+        {
+          type: "tool-call",
+          id: "ws_1",
+          itemId: "ws_1",
+          name: "web_search",
+          input: { type: "search", query: "effect 4" },
+          providerExecuted: true,
          providerMetadata: { openai: { itemId: "ws_1" } },
        },
+        {
+          type: "tool-result",
+          id: "ws_1",
+          itemId: "ws_1",
+          name: "web_search",
+          result: { type: "json", value: item },
+          providerExecuted: true,
+          providerMetadata: { openai: { itemId: "ws_1", item } },
+          metadata: undefined,
+          cache: undefined,
+        },
      ])
    }),
  )
@@ -1742,6 +1903,7 @@ describe("OpenAI Responses route", () => {
      expect(toolCall).toEqual({
        type: "tool-call",
        id: "ci_1",
+        itemId: "ci_1",
        name: "code_interpreter",
        input: { code: "print(1+1)", container_id: "cnt_xyz" },
        providerExecuted: true,
@@ -1751,10 +1913,12 @@ describe("OpenAI Responses route", () => {
      expect(toolResult).toEqual({
        type: "tool-result",
        id: "ci_1",
+        itemId: "ci_1",
        name: "code_interpreter",
        result: { type: "json", value: item },
        providerExecuted: true,
-        providerMetadata: { openai: { itemId: "ci_1" } },
+        providerMetadata: { openai: { itemId: "ci_1", item } },
+        output: undefined,
      })
    }),
  )
@@ -49,6 +49,43 @@ describe("LLMResponse reducer", () => {
    expect(state.message.content).toEqual([{ type: "text", text: "partial" }])
  })

+  test("assembles response item identity and provider metadata", () => {
+    const response = LLMResponse.fromEvents([
+      LLMEvent.textStart({ id: "text-block", itemId: "msg_existing" }),
+      LLMEvent.textDelta({
+        id: "text-block",
+        itemId: "msg_existing",
+        text: "Answer",
+        providerMetadata: { openai: { itemId: "msg_existing" } },
+      }),
+      LLMEvent.textEnd({ id: "text-block", itemId: "msg_existing" }),
+      LLMEvent.reasoningStart({ id: "reasoning-block", itemId: "rs_existing" }),
+      LLMEvent.reasoningDelta({
+        id: "reasoning-block",
+        itemId: "rs_existing",
+        text: "Thought",
+        providerMetadata: { openai: { itemId: "rs_existing" } },
+      }),
+      LLMEvent.reasoningEnd({ id: "reasoning-block", itemId: "rs_existing" }),
+      LLMEvent.finish({ reason: { normalized: "stop" } }),
+    ])
+
+    expect(response?.message.content).toEqual([
+      {
+        type: "text",
+        text: "Answer",
+        itemId: "msg_existing",
+        providerMetadata: { openai: { itemId: "msg_existing" } },
+      },
+      {
+        type: "reasoning",
+        text: "Thought",
+        itemId: "rs_existing",
+        providerMetadata: { openai: { itemId: "rs_existing" } },
+      },
+    ])
+  })
+
  test("does not complete ended content without a terminal finish", () => {
    const state = reduce([
      LLMEvent.textStart({ id: "t1" }),
@@ -172,7 +172,7 @@ describe("LLMClient tools", () => {
      expect(calls).toEqual([{ id: "call_projected", parameters: { prefix: "count" }, output: { count: "2" } }])
      expect(dispatched.result).toEqual({ type: "text", value: "count:2" })
      expect(dispatched.output).toEqual({ structured: { count: "2" }, content: [{ type: "text", text: "count:2" }] })
-      expect(dispatched.events).toEqual([
+      expect(dispatched.events).toMatchObject([
        LLMEvent.toolResult({
          id: "call_projected",
          name: "projected",
@@ -180,6 +180,7 @@ describe("LLMClient tools", () => {
          output: { structured: { count: "2" }, content: [{ type: "text", text: "count:2" }] },
        }),
      ])
+      expect(dispatched.events[0]?.itemId).toBeUndefined()
    }),
  )

@@ -197,7 +198,7 @@ describe("LLMClient tools", () => {
        LLMEvent.toolCall({ id: "call_1", name: "tool", input: {}, providerMetadata }),
      )

-      expect(dispatched.events).toEqual([
+      expect(dispatched.events).toMatchObject([
        LLMEvent.toolResult({
          id: "call_1",
          name: "tool",
@@ -206,12 +207,13 @@ describe("LLMClient tools", () => {
          providerMetadata,
        }),
      ])
+      expect(dispatched.events[0]?.itemId).toBeUndefined()

      const failed = yield* ToolRuntime.dispatch(
        {},
-        LLMEvent.toolCall({ id: "call_2", name: "missing", input: {}, providerMetadata }),
+        LLMEvent.toolCall({ id: "call_2", itemId: "fc_failed", name: "missing", input: {}, providerMetadata }),
      )
-      expect(failed.events).toEqual([
+      expect(failed.events).toMatchObject([
        LLMEvent.toolError({
          id: "call_2",
          name: "missing",
@@ -225,6 +227,27 @@ describe("LLMClient tools", () => {
          providerMetadata,
        }),
      ])
+      const errorItemID = failed.events.find(LLMEvent.is.toolError)?.itemId
+      const resultItemID = failed.events.find(LLMEvent.is.toolResult)?.itemId
+      expect(errorItemID).toBeUndefined()
+      expect(resultItemID).toBeUndefined()
+    }),
+  )
+
+  it.effect("does not derive a function output item id from the function call item id", () =>
+    Effect.gen(function* () {
+      const tool = Tool.make({
+        description: "Return text.",
+        parameters: Schema.Struct({}),
+        success: Schema.String,
+        execute: () => Effect.succeed("hello"),
+      })
+      const dispatched = yield* ToolRuntime.dispatch(
+        { tool },
+        LLMEvent.toolCall({ id: "call_1", itemId: "fc_existing", name: "tool", input: {} }),
+      )
+
+      expect(dispatched.events.find(LLMEvent.is.toolResult)?.itemId).toBeUndefined()
    }),
  )

@@ -437,7 +460,7 @@ describe("LLMClient tools", () => {
      )

      expect(dispatched.result).toEqual(callerOwned)
-      expect(dispatched.events).toEqual([
+      expect(dispatched.events).toMatchObject([
        LLMEvent.toolResult({
          id: "call_1",
          name: "eventful",
@@ -445,6 +468,7 @@ describe("LLMClient tools", () => {
          output: { structured: { ok: true }, content: [] },
        }),
      ])
+      expect(dispatched.events[0]?.itemId).toBeUndefined()
    }),
  )

@@ -116,7 +116,11 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
  })
  const currentAssistantMessageID = () =>
    stepStarted ? Effect.succeed(assistantMessageID) : Effect.die(new Error("Tool event before assistant step start"))
-  const providerState = (metadata: ProviderMetadata | undefined) => metadata?.[input.providerMetadataKey]
+  const providerState = (metadata: ProviderMetadata | undefined, itemId?: string) => {
+    const state = metadata?.[input.providerMetadataKey]
+    if (itemId === undefined) return state
+    return { ...(typeof state === "object" && state !== null && !Array.isArray(state) ? state : {}), itemId }
+  }
  const fragments = (
    name: string,
    ended: (id: string, value: string, ordinal: number, state?: Record<string, unknown>) => Effect.Effect<void>,
@@ -340,7 +344,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
        return
      case "text-start":
        outputStarted = true
-        const startedTextOrdinal = yield* text.start(event.id, providerState(event.providerMetadata))
+        const startedTextOrdinal = yield* text.start(event.id, providerState(event.providerMetadata, event.itemId))
        yield* bus.publish(SessionEvent.Text.Started, {
          sessionID: input.sessionID,
          assistantMessageID: yield* startAssistant(),
@@ -348,7 +352,11 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
        })
        return
      case "text-delta":
-        const deltaTextOrdinal = yield* text.append(event.id, event.text, providerState(event.providerMetadata))
+        const deltaTextOrdinal = yield* text.append(
+          event.id,
+          event.text,
+          providerState(event.providerMetadata, event.itemId),
+        )
        yield* bus.publish(SessionEvent.Text.Delta, {
          sessionID: input.sessionID,
          assistantMessageID: yield* currentAssistantMessageID(),
@@ -357,23 +365,26 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
        })
        return
      case "text-end":
-        yield* text.end(event.id, providerState(event.providerMetadata))
+        yield* text.end(event.id, providerState(event.providerMetadata, event.itemId))
        return
      case "reasoning-start":
        outputStarted = true
-        const startedReasoningOrdinal = yield* reasoning.start(event.id, providerState(event.providerMetadata))
+        const startedReasoningOrdinal = yield* reasoning.start(
+          event.id,
+          providerState(event.providerMetadata, event.itemId),
+        )
        yield* bus.publish(SessionEvent.Reasoning.Started, {
          sessionID: input.sessionID,
          assistantMessageID: yield* startAssistant(),
          ordinal: startedReasoningOrdinal,
-          state: providerState(event.providerMetadata),
+          state: providerState(event.providerMetadata, event.itemId),
        })
        return
      case "reasoning-delta":
        const deltaReasoningOrdinal = yield* reasoning.append(
          event.id,
          event.text,
-          providerState(event.providerMetadata),
+          providerState(event.providerMetadata, event.itemId),
        )
        yield* bus.publish(SessionEvent.Reasoning.Delta, {
          sessionID: input.sessionID,
@@ -383,7 +394,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
        })
        return
      case "reasoning-end":
-        yield* reasoning.end(event.id, providerState(event.providerMetadata))
+        yield* reasoning.end(event.id, providerState(event.providerMetadata, event.itemId))
        return
      case "tool-input-start":
        outputStarted = true
@@ -427,7 +438,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
          id: event.id,
          input: asRecord(event.input),
          executed: tool.providerExecuted,
-          state: providerState(event.providerMetadata),
+          state: providerState(event.providerMetadata, event.itemId),
        })
        return
      }
@@ -445,7 +456,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
        }
        tool.settled = true
        const executed = event.providerExecuted === true || tool.providerExecuted
-        const resultState = providerState(event.providerMetadata)
+        const resultState = providerState(event.providerMetadata, event.itemId)
        if (event.result.type === "error") {
          yield* bus.publish(SessionEvent.Tool.Failed, {
            sessionID: input.sessionID,
@@ -485,7 +496,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
              : { type: "tool.execution", message: event.message },
          ...failureSnapshot(tool),
          executed: tool.providerExecuted,
-          resultState: providerState(event.providerMetadata),
+          resultState: providerState(event.providerMetadata, event.itemId),
        })
        return
      }
@@ -510,8 +521,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp

  const progress = Effect.fnUntraced(function* (id: string, update: Tool.Metadata) {
    const tool = tools.get(id)
-    if (!tool?.called || tool.settled)
-      return yield* Effect.die(new Error(`Tool progress outside running call: ${id}`))
+    if (!tool?.called || tool.settled) return yield* Effect.die(new Error(`Tool progress outside running call: ${id}`))
    tool.progress = update
    yield* bus.publish(SessionEvent.Tool.Progress, {
      sessionID: input.sessionID,
@@ -522,11 +532,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
  })

  /** Publishes one canonical terminal event for a locally executed tool call. */
-  const toolExecution = Effect.fnUntraced(function* (
-    id: string,
-    name: string,
-    result: Tool.Result,
-  ) {
+  const toolExecution = Effect.fnUntraced(function* (id: string, name: string, result: Tool.Result) {
    const tool = tools.get(id)
    if (!tool?.called) return yield* Effect.die(new Error(`Tool execution before call: ${id}`))
    if (tool.name !== name)
@@ -1,4 +1,10 @@
-import { Message, ToolCallPart, ToolResultPart, type ContentPart, type ProviderMetadata } from "@opencode-ai/ai"
+import {
+  Message,
+  ToolCallPart,
+  ToolResultPart,
+  type ContentPart,
+  type ProviderMetadata,
+} from "@opencode-ai/ai"
 import { Option, Schema } from "effect"
 import type { Model } from "../../model"
 import { SessionMessage } from "../message"
@@ -66,27 +72,46 @@ const providerMetadata = (
  state: Record<string, unknown> | undefined,
 ): ProviderMetadata | undefined => (state === undefined ? undefined : { [provider]: state })

+const responseItemID = (state: Record<string, unknown> | undefined) =>
+  typeof state?.itemId === "string" ? state.itemId : undefined
+
+const portableProviderState = (state: Record<string, unknown> | undefined) => {
+  if (state === undefined || !("itemId" in state)) return state
+  const { itemId: _itemId, ...portable } = state
+  return portable
+}
+
 const toolInput = (tool: SessionMessage.AssistantTool) =>
  tool.state.status === "streaming"
    ? Option.getOrElse(decodeToolInput(tool.state.input), () => tool.state.input)
    : tool.state.input

-const toolCall = (tool: SessionMessage.AssistantTool, providerMetadata: ProviderMetadata | undefined): ContentPart =>
+const toolCall = (
+  tool: SessionMessage.AssistantTool,
+  itemId: string | undefined,
+  providerMetadata: ProviderMetadata | undefined,
+): ContentPart =>
  ToolCallPart.make({
    id: tool.id,
+    ...(itemId === undefined ? {} : { itemId }),
    name: tool.name,
    input: toolInput(tool),
    providerExecuted: tool.executed,
    providerMetadata,
  })

-const toolResult = (tool: SessionMessage.AssistantTool, providerMetadata: ProviderMetadata | undefined) => {
+const toolResult = (
+  tool: SessionMessage.AssistantTool,
+  itemId: string | undefined,
+  providerMetadata: ProviderMetadata | undefined,
+) => {
  if (tool.state.status === "completed") {
    // TODO: Materialize remote and managed URIs before provider-history lowering.
    const content = tool.state.content
    const single = content.length === 1 ? content[0] : undefined
    return ToolResultPart.make({
      id: tool.id,
+      ...(itemId === undefined ? {} : { itemId }),
      name: tool.name,
      result:
        single?.type === "text"
@@ -99,6 +124,7 @@ const toolResult = (tool: SessionMessage.AssistantTool, providerMetadata: Provid
  if (tool.state.status === "error") {
    return ToolResultPart.make({
      id: tool.id,
+      ...(itemId === undefined ? {} : { itemId }),
      name: tool.name,
      result: { error: tool.state.error, content: tool.state.content ?? [] },
      resultType: "error",
@@ -118,7 +144,13 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
        {
          type: "text",
          text: item.text,
-          providerMetadata: sameProvider ? providerMetadata(providerMetadataKey, item.state) : undefined,
+          itemId: reuseProviderMetadata ? responseItemID(item.state) : undefined,
+          providerMetadata: sameProvider
+            ? providerMetadata(
+                providerMetadataKey,
+                reuseProviderMetadata ? item.state : portableProviderState(item.state),
+              )
+            : undefined,
        },
      ]
    if (item.type === "reasoning")
@@ -127,6 +159,7 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
            {
              type: "reasoning",
              text: item.text,
+              itemId: responseItemID(item.state),
              providerMetadata: providerMetadata(providerMetadataKey, item.state),
            },
          ]
@@ -138,6 +171,7 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
      (sameModel && item.executed === true && (item.state.status === "completed" || item.state.status === "error"))
    const call = toolCall(
      item,
+      reuseToolProviderMetadata ? responseItemID(item.providerState) : undefined,
      reuseToolProviderMetadata ? providerMetadata(providerMetadataKey, item.providerState) : undefined,
    )
    if (item.executed !== true) return [call]
@@ -145,6 +179,11 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
    // replay must survive a model switch within the same provider.
    const result = toolResult(
      item,
+      reuseToolProviderMetadata
+        ? responseItemID(item.providerResultState ?? (item.executed === true ? item.providerState : undefined))
+        : sameProvider && item.executed === true
+          ? responseItemID(item.providerResultState)
+          : undefined,
      reuseToolProviderMetadata
        ? providerMetadata(providerMetadataKey, item.providerResultState ?? item.providerState)
        : sameProvider && item.executed === true && item.providerResultState !== undefined
@@ -163,9 +202,8 @@ const assistant = (message: SessionMessage.Assistant, model: Model.Ref, provider
    .map((item) =>
      toolResult(
        item,
-        reuseProviderMetadata
-          ? providerMetadata(providerMetadataKey, item.providerResultState ?? item.providerState)
-          : undefined,
+        responseItemID(item.providerResultState) ?? `fco_${item.id}`,
+        reuseProviderMetadata ? providerMetadata(providerMetadataKey, item.providerResultState) : undefined,
      ),
    )
    .filter((message) => message !== undefined)
@@ -204,7 +242,7 @@ function toLLMMessage(message: SessionMessage.Info, model: Model.Ref, providerMe
    case "skill":
      return [Message.make({ id: message.id, role: "user", content: message.text, metadata: message.metadata })]
    case "system":
-      return [Message.system(message.text)]
+      return [Message.make({ id: message.id, role: "system", content: message.text })]
    case "shell":
      return [
        Message.make({
@@ -110,7 +110,13 @@ describe("toLLMMessages", () => {
    )

    expect(messages.map((message) => message.role)).toEqual(["system", "user", "user", "user", "user"])
-    expect(messages[0]).toEqual(Message.system("Updated context\n\nOther context"))
+    expect(messages[0]).toEqual(
+      Message.make({
+        id: "msg_system",
+        role: "system",
+        content: [{ type: "text", text: "Updated context\n\nOther context" }],
+      }),
+    )
    expect(messages[1]).toEqual(
      Message.make({
        id: id("user"),
@@ -476,6 +482,7 @@ Recent work
      {
        type: "tool-result",
        id: "completed",
+        itemId: "fco_completed",
        name: "read",
        result: {
          type: "content",
@@ -513,6 +520,7 @@ Recent work
      {
        type: "reasoning",
        text: "Think",
+        itemId: "rs_1",
        providerMetadata: { provider: { itemId: "rs_1", reasoningEncryptedContent: "encrypted-state" } },
      },
    ])
@@ -602,6 +610,7 @@ Recent work
      {
        type: "tool-call",
        id: "hosted-completed",
+        itemId: "call_completed",
        name: "web_search",
        input: { query: "Effect" },
        providerExecuted: true,
@@ -610,6 +619,7 @@ Recent work
      {
        type: "tool-result",
        id: "hosted-completed",
+        itemId: "result_completed",
        name: "web_search",
        result: { type: "text", value: '{"found":true}' },
        providerExecuted: true,
@@ -620,6 +630,7 @@ Recent work
      {
        type: "tool-call",
        id: "hosted-failed",
+        itemId: "call_failed",
        name: "web_search",
        input: { query: "Effect" },
        providerExecuted: true,
@@ -628,6 +639,7 @@ Recent work
      {
        type: "tool-result",
        id: "hosted-failed",
+        itemId: "result_failed",
        name: "web_search",
        result: {
          type: "error",
@@ -698,6 +710,7 @@ Recent work
      {
        type: "tool-call",
        id: "hosted-old-model",
+        itemId: undefined,
        name: "web_search",
        input: { query: "Effect" },
        providerExecuted: true,
@@ -706,6 +719,7 @@ Recent work
      {
        type: "tool-result",
        id: "hosted-old-model",
+        itemId: "hosted-old-model",
        name: "web_search",
        result: { type: "text", value: '{"status":"completed"}' },
        providerExecuted: true,
@@ -718,6 +732,7 @@ Recent work
      {
        type: "tool-call",
        id: "local-old-model",
+        itemId: undefined,
        name: "read",
        input: { path: "README.md" },
        providerExecuted: false,
@@ -728,6 +743,7 @@ Recent work
      {
        type: "tool-result",
        id: "local-old-model",
+        itemId: "fco_local-old-model",
        name: "read",
        result: { type: "text", value: "Hello" },
        providerExecuted: false,
@@ -24,9 +24,7 @@ const capture = (providerMetadataKey = "anthropic", options?: { readonly interru
      const publish = Effect.sync(() => {
        const event = { id: Event.ID.create(), type: definition.type, data } as Event.Payload<typeof definition>
        published.push({
-          type: definition.durable
-            ? Bus.versionedType(definition.type, definition.durable.version)
-            : definition.type,
+          type: definition.durable ? Bus.versionedType(definition.type, definition.durable.version) : definition.type,
          data,
        })
        return event
@@ -66,9 +64,10 @@ const hostedResult = LLMEvent.toolResult({

 test("local tool success serializes media base64 once through canonical content", async () => {
  const { published, publisher } = capture()
-  await Effect.runPromise(publisher.publish(call))
+  const localCall = LLMEvent.toolCall({ ...call, itemId: "fc_call-image" })
+  await Effect.runPromise(publisher.publish(localCall))
  await Effect.runPromise(
-    publisher.toolExecution(call.id, call.name, {
+    publisher.toolExecution(localCall.id, localCall.name, {
      output: { type: "media", mime: "image/png" },
      content: [
        { type: "text", text: "Image read successfully" },
@@ -84,6 +83,11 @@ test("local tool success serializes media base64 once through canonical content"
  expect(success?.data).not.toHaveProperty("result")
  expect(success?.data).not.toHaveProperty("output")

+  const called = published.find((event) => event.type === "session.tool.called.1")?.data
+  expect(called).toMatchObject({ state: { itemId: "fc_call-image" } })
+  expect(success?.data).not.toHaveProperty("resultState")
+  expect(JSON.stringify(success?.data)).not.toContain('"itemId":"fc_call-image"')
+
  expect(success?.data).toMatchObject({
    content: [
      { type: "text", text: "Image read successfully" },
@@ -226,9 +230,7 @@ test("provider-executed tool metadata is flattened using the route key", async (
 test("binary failure emits no success event", async () => {
  const { published, publisher } = capture()
  await Effect.runPromise(publisher.publish(call))
-  await Effect.runPromise(
-    publisher.failTool(call.id, { type: "tool.execution", message: "Cannot read binary file" }),
-  )
+  await Effect.runPromise(publisher.failTool(call.id, { type: "tool.execution", message: "Cannot read binary file" }))
  expect(published.some((event) => event.type === "session.tool.success.2")).toBe(false)
  expect(published.some((event) => event.type === "session.tool.failed.2")).toBe(true)
 })
@@ -558,6 +558,15 @@ const messageTexts = (request: LLMRequest, role: "user" | "system") =>
 const userTexts = (request: LLMRequest) => messageTexts(request, "user")
 const systemTexts = (request: LLMRequest) => messageTexts(request, "system")
 const messageRoles = (request: LLMRequest | undefined) => request?.messages.map((message) => message.role)
+const withoutItemIDs = (messages: LLMRequest["messages"]) =>
+  messages.map((message) => ({
+    role: message.role,
+    content: message.content.map((part) => {
+      if (!("itemId" in part)) return part
+      const { itemId: _itemId, ...content } = part
+      return content
+    }),
+  }))

 const recordedEventTypes = (id: Session.ID) =>
  Effect.gen(function* () {
@@ -856,8 +865,8 @@ describe("SessionRunnerLLM", () => {
      yield* Fiber.join(renamed)

      expect(requests).toHaveLength(5)
-      expect(requests[2]?.messages).toContainEqual(Message.user("First prompt"))
-      expect(requests[4]?.messages).toContainEqual(Message.user("First prompt"))
+      expect(withoutItemIDs(requests[2]!.messages)).toContainEqual(withoutItemIDs([Message.user("First prompt")])[0])
+      expect(withoutItemIDs(requests[4]!.messages)).toContainEqual(withoutItemIDs([Message.user("First prompt")])[0])
      expect((yield* session.get(sessionID)).title).toBe("Generated title")
    }),
  )
@@ -882,7 +891,7 @@ describe("SessionRunnerLLM", () => {
      // A hook-removed call fails independently and continues while step allowance remains.
      expect(requests).toHaveLength(2)
      expect(requests[0]?.system.map((part) => part.text)).toEqual(["Hooked system"])
-      expect(requests[0]?.messages).toEqual([Message.user("Hooked message")])
+      expect(withoutItemIDs(requests[0]!.messages)).toEqual(withoutItemIDs([Message.user("Hooked message")]))
      expect(requests[0]?.tools.map((tool) => tool.name)).not.toContain("echo")
      expect(requests[0]?.tools.map((tool) => tool.name)).not.toContain("unregistered")
      expect(executions).toEqual([])
@@ -1307,12 +1316,14 @@ describe("SessionRunnerLLM", () => {
      systemBaseline = "Changed context"
      yield* runPrompt(session, "Second")

-      expect(
-        PromptCacheDiagnostics.compare(
-          PromptCacheDiagnostics.snapshot(requests[0]),
-          PromptCacheDiagnostics.snapshot(requests[1]),
-        ),
-      ).toEqual({ status: "append-only", previousMessages: 1, currentMessages: 3 })
+      const firstSnapshot = PromptCacheDiagnostics.snapshot(requests[0]!)
+      const secondSnapshot = PromptCacheDiagnostics.snapshot(requests[1]!)
+      expect(PromptCacheDiagnostics.compare(firstSnapshot, secondSnapshot)).toEqual({
+        status: "append-only",
+        previousMessages: 1,
+        currentMessages: 3,
+      })
+      expect(secondSnapshot.messages[0]).toEqual(firstSnapshot.messages[0])
      expect(requests.map((request) => request.system.map((part) => part.text))).toEqual([
        [defaultSystem, "Initial context"],
        [defaultSystem, "Initial context"],
@@ -2532,9 +2543,24 @@ describe("SessionRunnerLLM", () => {
        {
          type: "reasoning",
          text: "Encrypted thought",
+          itemId: "rs_1",
          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: "encrypted-state" } },
        },
      ])
+
+      yield* admit(session, "Continue again")
+      yield* TestLLM.push([])
+      yield* session.resume(sessionID)
+
+      expect(requests[2]?.messages[1]?.content.map((part) => ("itemId" in part ? part.itemId : undefined))).toEqual(
+        requests[1]?.messages[1]?.content.map((part) => ("itemId" in part ? part.itemId : undefined)),
+      )
+      expect(
+        PromptCacheDiagnostics.compare(
+          PromptCacheDiagnostics.snapshot(requests[1]!),
+          PromptCacheDiagnostics.snapshot(requests[2]!),
+        ),
+      ).toEqual({ status: "append-only", previousMessages: 3, currentMessages: 4 })
    }),
  )

@@ -2613,6 +2639,7 @@ describe("SessionRunnerLLM", () => {
        {
          type: "tool-call",
          id: "hosted-search",
+          itemId: "hosted-search",
          name: "web_search",
          input: { query: "Effect" },
          providerExecuted: true,
Author	SHA1	Message	Date
Aiden Cline	0657dcbad2	fix(ai): stop generating response item ids	2026-08-07 14:26:50 -05:00
Aiden Cline	82afcfd4e0	fix(ai): generate uuidv7 item ids	2026-08-07 14:04:15 -05:00
Aiden Cline	a1cbcc8641	fix(ai): preserve responses item ids	2026-08-07 12:57:48 -05:00