diff --git a/packages/ai/src/protocols/anthropic-messages.ts b/packages/ai/src/protocols/anthropic-messages.ts
index b2d8fa70dc..3abc8e9fb9 100644
--- a/packages/ai/src/protocols/anthropic-messages.ts
+++ b/packages/ai/src/protocols/anthropic-messages.ts
@@ -316,7 +316,21 @@ const lowerServerToolResult = Effect.fn("AnthropicMessages.lowerServerToolResult
   const wireType = serverToolResultType(part.name)
   if (!wireType)
     return yield* invalid(`Anthropic Messages does not know how to round-trip server tool result for ${part.name}`)
-  return { type: wireType, tool_use_id: part.id, content: part.result.value } satisfies AnthropicServerToolResultBlock
+  const errorType = `${wireType}_error`
+  const syntheticErrorCode =
+    ProviderShared.isRecord(part.result.value) &&
+    ProviderShared.isRecord(part.result.value.error) &&
+    part.result.value.error.type === "provider.invalid-output"
+      ? "invalid_tool_input"
+      : "unavailable"
+  const content =
+    part.result.type !== "error" ||
+    (ProviderShared.isRecord(part.result.value) &&
+      part.result.value.type === errorType &&
+      typeof part.result.value.error_code === "string")
+      ? part.result.value
+      : { type: errorType, error_code: syntheticErrorCode }
+  return { type: wireType, tool_use_id: part.id, content } satisfies AnthropicServerToolResultBlock
 })
 
 const lowerImage = Effect.fn("AnthropicMessages.lowerImage")(function* (part: MediaPart) {
@@ -703,7 +717,14 @@ const onContentBlockStart = (state: ParserState, event: AnthropicEvent): StepRes
           providerExecuted: block.type === "server_tool_use",
         }),
       },
-      [...events, LLMEvent.toolInputStart({ id: block.id ?? String(event.index), name: block.name ?? "" })],
+      [
+        ...events,
+        LLMEvent.toolInputStart({
+          id: block.id ?? String(event.index),
+          name: block.name ?? "",
+          providerExecuted: block.type === "server_tool_use" ? true : undefined,
+        }),
+      ],
     ]
   }
 
diff --git a/packages/ai/src/protocols/gemini.ts b/packages/ai/src/protocols/gemini.ts
index 82a69b059e..458b2e47e7 100644
--- a/packages/ai/src/protocols/gemini.ts
+++ b/packages/ai/src/protocols/gemini.ts
@@ -441,6 +441,9 @@ const step = (state: ParserState, event: GeminiEvent) => {
     if ("functionCall" in part) {
       const input = part.functionCall.args
       const id = `tool_${nextToolCallId++}`
+      const providerMetadata = part.thoughtSignature
+        ? googleMetadata({ thoughtSignature: part.thoughtSignature })
+        : undefined
       lifecycle = Lifecycle.reasoningEnd(
         lifecycle,
         events,
@@ -448,14 +451,27 @@ const step = (state: ParserState, event: GeminiEvent) => {
         reasoningSignature ? googleMetadata({ thoughtSignature: reasoningSignature }) : undefined,
       )
       lifecycle = Lifecycle.stepStart(lifecycle, events)
+      if (typeof input === "string") {
+        events.push(
+          LLMEvent.toolInputStart({ id, name: part.functionCall.name, providerMetadata }),
+          LLMEvent.toolInputEnd({ id, name: part.functionCall.name, input, providerMetadata }),
+          LLMEvent.toolInputError({
+            id,
+            name: part.functionCall.name,
+            raw: input,
+            message: `Invalid JSON input for ${ADAPTER} tool call ${part.functionCall.name}`,
+            providerMetadata,
+          }),
+        )
+        hasToolCalls = true
+        continue
+      }
       events.push(
         LLMEvent.toolCall({
           id,
           name: part.functionCall.name,
           input,
-          providerMetadata: part.thoughtSignature
-            ? googleMetadata({ thoughtSignature: part.thoughtSignature })
-            : undefined,
+          providerMetadata,
         }),
       )
       hasToolCalls = true
diff --git a/packages/ai/src/protocols/openai-responses.ts b/packages/ai/src/protocols/openai-responses.ts
index d03cb003ff..15b930c3e0 100644
--- a/packages/ai/src/protocols/openai-responses.ts
+++ b/packages/ai/src/protocols/openai-responses.ts
@@ -820,22 +820,33 @@ const onOutputItemDone = Effect.fn("OpenAIResponses.onOutputItemDone")(function*
 
   if (item.type === "function_call") {
     if (!item.id || !item.call_id || !item.name) return [state, NO_EVENTS] satisfies StepResult
-    const tools = state.tools[item.id]
+    const existing = state.tools[item.id]
+    const providerMetadata = openaiMetadata({ itemId: item.id })
+    const tools = existing
       ? 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,
+          name: item.name,
+          providerMetadata,
+        })
     const result =
       item.arguments === undefined
         ? yield* ToolStream.finish(ADAPTER, tools, item.id)
         : yield* ToolStream.finishWithInput(ADAPTER, tools, item.id, item.arguments)
     const events: LLMEvent[] = []
-    const resultEvents = result.events ?? []
+    const resultEvents = [
+      ...(existing ? [] : [LLMEvent.toolInputStart({ id: item.call_id, name: item.name, providerMetadata })]),
+      ...(result.events ?? []),
+    ]
     const lifecycle = resultEvents.length ? Lifecycle.stepStart(state.lifecycle, events) : state.lifecycle
     events.push(...resultEvents)
     return [
       {
         ...state,
         lifecycle,
-        hasFunctionCall: resultEvents.some(LLMEvent.is.toolCall) ? true : state.hasFunctionCall,
+        hasFunctionCall:
+          state.hasFunctionCall ||
+          resultEvents.some((event) => LLMEvent.is.toolCall(event) || LLMEvent.is.toolInputError(event)),
         tools: result.tools,
       },
       events,
diff --git a/packages/ai/src/protocols/shared.ts b/packages/ai/src/protocols/shared.ts
index 3072af836f..aad8fce5f9 100644
--- a/packages/ai/src/protocols/shared.ts
+++ b/packages/ai/src/protocols/shared.ts
@@ -9,6 +9,7 @@ import {
   type ContentPart,
   type LLMRequest,
   type MediaPart,
+  type ProviderMetadata,
   type ToolFileContent,
   type TextPart,
   type ToolResultPart,
@@ -152,7 +153,16 @@ export const wrappedSystemUpdate = Effect.fn("ProviderShared.wrappedSystemUpdate
  * input deltas (e.g. zero-arg tools). The error message is uniform across
  * routes: `Invalid JSON input for <route> tool call <name>`.
  */
-export const parseToolInput = (route: string, name: string, raw: string) =>
+export const parseToolInput = (
+  route: string,
+  tool: {
+    readonly id: string
+    readonly name: string
+    readonly providerExecuted?: boolean
+    readonly providerMetadata?: ProviderMetadata
+  },
+  raw: string,
+) =>
   Effect.try({
     try: () => decodeJson(raw || "{}"),
     catch: () =>
@@ -161,10 +171,13 @@ export const parseToolInput = (route: string, name: string, raw: string) =>
         method: "stream",
         reason: new InvalidProviderOutputReason({
           route,
-          message: `Invalid JSON input for ${route} tool call ${name}`,
+          message: `Invalid JSON input for ${route} tool call ${tool.name}`,
           raw,
           source: "tool-input",
-          toolName: name,
+          toolCallID: tool.id,
+          toolName: tool.name,
+          providerExecuted: tool.providerExecuted,
+          providerMetadata: tool.providerMetadata,
         }),
       }),
   })
diff --git a/packages/ai/src/protocols/utils/tool-stream.ts b/packages/ai/src/protocols/utils/tool-stream.ts
index 8e07a64bfe..233713f0d5 100644
--- a/packages/ai/src/protocols/utils/tool-stream.ts
+++ b/packages/ai/src/protocols/utils/tool-stream.ts
@@ -53,6 +53,7 @@ const inputStart = (tool: PendingTool) =>
   LLMEvent.toolInputStart({
     id: tool.id,
     name: tool.name,
+    providerExecuted: tool.providerExecuted ? true : undefined,
     providerMetadata: tool.providerMetadata,
   })
 
@@ -63,8 +64,9 @@ const inputDelta = (tool: PendingTool, text: string) =>
     text,
   })
 
-const toolCall = (route: string, tool: PendingTool, inputOverride?: string) =>
-  parseToolInput(route, tool.name, inputOverride ?? tool.input).pipe(
+const toolCall = (route: string, tool: PendingTool, inputOverride?: string) => {
+  const raw = inputOverride ?? tool.input
+  return parseToolInput(route, tool, raw).pipe(
     Effect.map(
       (input): ToolCall =>
         LLMEvent.toolCall({
@@ -75,7 +77,20 @@ const toolCall = (route: string, tool: PendingTool, inputOverride?: string) =>
           providerMetadata: tool.providerMetadata,
         }),
     ),
+    Effect.match({
+      onFailure: (error) =>
+        LLMEvent.toolInputError({
+          id: tool.id,
+          name: tool.name,
+          raw,
+          message: error.reason.message,
+          providerExecuted: tool.providerExecuted ? true : undefined,
+          providerMetadata: tool.providerMetadata,
+        }),
+      onSuccess: (event) => event,
+    }),
   )
+}
 
 /** Store the updated tool and produce the optional public delta event. */
 const appendTool = <K extends StreamKey>(
@@ -158,8 +173,8 @@ export const appendExisting = <K extends StreamKey>(
 
 /**
  * Finalize one pending tool call: parse the accumulated raw JSON, remove it
- * from state, and return the optional public `tool-call` event. Missing keys are
- * a no-op because some providers emit stop events for non-tool content blocks.
+ * from state, and emit either `tool-call` or `tool-input-error`. Missing keys
+ * are a no-op because some providers emit stop events for non-tool blocks.
  */
 export const finish = <K extends StreamKey>(route: string, tools: State<K>, key: K) =>
   Effect.gen(function* () {
@@ -186,7 +201,12 @@ export const finishWithInput = <K extends StreamKey>(route: string, tools: State
     return {
       tools: withoutTool(tools, key),
       events: [
-        LLMEvent.toolInputEnd({ id: tool.id, name: tool.name, providerMetadata: tool.providerMetadata }),
+        LLMEvent.toolInputEnd({
+          id: tool.id,
+          name: tool.name,
+          input,
+          providerMetadata: tool.providerMetadata,
+        }),
         yield* toolCall(route, tool, input),
       ],
     }
diff --git a/packages/ai/src/schema/errors.ts b/packages/ai/src/schema/errors.ts
index d4bb693a32..39b185726b 100644
--- a/packages/ai/src/schema/errors.ts
+++ b/packages/ai/src/schema/errors.ts
@@ -107,7 +107,9 @@ export class InvalidProviderOutputReason extends Schema.Class<InvalidProviderOut
   route: Schema.optional(Schema.String),
   raw: Schema.optional(Schema.String),
   source: Schema.optional(Schema.Literal("tool-input")),
+  toolCallID: Schema.optional(Schema.String),
   toolName: Schema.optional(Schema.String),
+  providerExecuted: Schema.optional(Schema.Boolean),
   providerMetadata: Schema.optional(ProviderMetadata),
 }) {}
 
diff --git a/packages/ai/src/schema/events.ts b/packages/ai/src/schema/events.ts
index f43251f670..49b409a61b 100644
--- a/packages/ai/src/schema/events.ts
+++ b/packages/ai/src/schema/events.ts
@@ -129,6 +129,7 @@ export const ToolInputStart = Schema.Struct({
   type: Schema.tag("tool-input-start"),
   id: ToolCallID,
   name: Schema.String,
+  providerExecuted: Schema.optional(Schema.Boolean),
   providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ToolInputStart" })
 export type ToolInputStart = Schema.Schema.Type<typeof ToolInputStart>
@@ -145,10 +146,22 @@ export const ToolInputEnd = Schema.Struct({
   type: Schema.tag("tool-input-end"),
   id: ToolCallID,
   name: Schema.String,
+  input: Schema.optional(Schema.String),
   providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ToolInputEnd" })
 export type ToolInputEnd = Schema.Schema.Type<typeof ToolInputEnd>
 
+export const ToolInputError = Schema.Struct({
+  type: Schema.tag("tool-input-error"),
+  id: ToolCallID,
+  name: Schema.String,
+  raw: Schema.String,
+  message: Schema.String,
+  providerExecuted: Schema.optional(Schema.Boolean),
+  providerMetadata: Schema.optional(ProviderMetadata),
+}).annotate({ identifier: "LLM.Event.ToolInputError" })
+export type ToolInputError = Schema.Schema.Type<typeof ToolInputError>
+
 export const ToolCall = Schema.Struct({
   type: Schema.tag("tool-call"),
   id: ToolCallID,
@@ -216,6 +229,7 @@ const llmEventTagged = Schema.Union([
   ToolInputStart,
   ToolInputDelta,
   ToolInputEnd,
+  ToolInputError,
   ToolCall,
   ToolResult,
   ToolError,
@@ -253,6 +267,8 @@ export const LLMEvent = Object.assign(llmEventTagged, {
   toolInputDelta: (input: WithID<ToolInputDelta, ToolCallID>) =>
     ToolInputDelta.make({ ...input, id: toolCallID(input.id) }),
   toolInputEnd: (input: WithID<ToolInputEnd, ToolCallID>) => ToolInputEnd.make({ ...input, id: toolCallID(input.id) }),
+  toolInputError: (input: WithID<ToolInputError, ToolCallID>) =>
+    ToolInputError.make({ ...input, id: toolCallID(input.id) }),
   toolCall: (input: WithID<ToolCall, ToolCallID>) => ToolCall.make({ ...input, id: toolCallID(input.id) }),
   toolResult: (input: WithID<ToolResult, ToolCallID>) =>
     ToolResult.make({
@@ -283,6 +299,7 @@ export const LLMEvent = Object.assign(llmEventTagged, {
     toolInputStart: llmEventTagged.guards["tool-input-start"],
     toolInputDelta: llmEventTagged.guards["tool-input-delta"],
     toolInputEnd: llmEventTagged.guards["tool-input-end"],
+    toolInputError: llmEventTagged.guards["tool-input-error"],
     toolCall: llmEventTagged.guards["tool-call"],
     toolResult: llmEventTagged.guards["tool-result"],
     toolError: llmEventTagged.guards["tool-error"],
@@ -498,6 +515,7 @@ const reduceToolInputEnd = (state: ResponseState, event: ToolInputEnd): Response
       [event.id]: {
         ...current,
         name: event.name,
+        text: event.input ?? current.text,
         providerMetadata: event.providerMetadata ?? current.providerMetadata,
       },
     },
@@ -548,6 +566,8 @@ const reduceResponseState = (state: ResponseState, event: LLMEvent): ResponseSta
       return reduceToolInputDelta(next, event)
     case "tool-input-end":
       return reduceToolInputEnd(next, event)
+    case "tool-input-error":
+      return next
     case "tool-call":
       return reduceToolCall(next, event)
     case "tool-result":
diff --git a/packages/ai/test/provider/anthropic-messages.test.ts b/packages/ai/test/provider/anthropic-messages.test.ts
index dcb20aa0ae..2fd0628593 100644
--- a/packages/ai/test/provider/anthropic-messages.test.ts
+++ b/packages/ai/test/provider/anthropic-messages.test.ts
@@ -617,6 +617,43 @@ describe("Anthropic Messages route", () => {
     }),
   )
 
+  it.effect("preserves provider execution identity for malformed server tool input", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        { type: "message_start", message: { usage: { input_tokens: 5 } } },
+        {
+          type: "content_block_start",
+          index: 0,
+          content_block: { type: "server_tool_use", id: "srvtoolu_malformed", name: "web_search" },
+        },
+        {
+          type: "content_block_delta",
+          index: 0,
+          delta: { type: "input_json_delta", partial_json: '{"query":"partial' },
+        },
+        { type: "content_block_stop", index: 0 },
+        { type: "message_delta", delta: { stop_reason: "end_turn" }, usage: { output_tokens: 1 } },
+      )
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(request, {
+          tools: [{ name: "web_search", description: "Web search", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.events.find((event) => event.type === "tool-input-start")).toMatchObject({
+        type: "tool-input-start",
+        id: "srvtoolu_malformed",
+        providerExecuted: true,
+      })
+      expect(response.events.find((event) => event.type === "tool-input-error")).toMatchObject({
+        type: "tool-input-error",
+        id: "srvtoolu_malformed",
+        raw: '{"query":"partial',
+        providerExecuted: true,
+      })
+    }),
+  )
+
   it.effect("decodes web_search_tool_result_error as provider-executed error result", () =>
     Effect.gen(function* () {
       const body = sseEvents(
@@ -708,6 +745,55 @@ describe("Anthropic Messages route", () => {
     }),
   )
 
+  it.effect("lowers synthetic server tool failures to valid Anthropic error payloads", () =>
+    Effect.gen(function* () {
+      const prepared = yield* LLMClient.prepare<AnthropicMessages.AnthropicBody>(
+        LLM.request({
+          id: "req_server_tool_input_error",
+          model,
+          messages: [
+            Message.assistant([
+              {
+                type: "tool-call",
+                id: "srvtoolu_malformed",
+                name: "web_search",
+                input: {},
+                providerExecuted: true,
+              },
+              {
+                type: "tool-result",
+                id: "srvtoolu_malformed",
+                name: "web_search",
+                result: {
+                  type: "error",
+                  value: {
+                    error: { type: "provider.invalid-output" },
+                    raw: '{"query":"partial',
+                  },
+                },
+                providerExecuted: true,
+              },
+            ]),
+          ],
+        }),
+      )
+
+      expect(prepared.body.messages).toMatchObject([
+        {
+          role: "assistant",
+          content: [
+            { type: "server_tool_use", id: "srvtoolu_malformed", name: "web_search", input: {} },
+            {
+              type: "web_search_tool_result",
+              tool_use_id: "srvtoolu_malformed",
+              content: { type: "web_search_tool_result_error", error_code: "invalid_tool_input" },
+            },
+          ],
+        },
+      ])
+    }),
+  )
+
   it.effect("rejects round-trip for unknown server tool names", () =>
     Effect.gen(function* () {
       const error = yield* LLMClient.prepare(
diff --git a/packages/ai/test/provider/bedrock-converse.test.ts b/packages/ai/test/provider/bedrock-converse.test.ts
index c7b519d368..222981bb99 100644
--- a/packages/ai/test/provider/bedrock-converse.test.ts
+++ b/packages/ai/test/provider/bedrock-converse.test.ts
@@ -303,6 +303,36 @@ describe("Bedrock Converse route", () => {
     }),
   )
 
+  it.effect("emits malformed streamed tool input without a tool call", () =>
+    Effect.gen(function* () {
+      const body = eventStreamBody(
+        ["messageStart", { role: "assistant" }],
+        [
+          "contentBlockStart",
+          {
+            contentBlockIndex: 0,
+            start: { toolUse: { toolUseId: "tool_malformed", name: "lookup" } },
+          },
+        ],
+        ["contentBlockDelta", { contentBlockIndex: 0, delta: { toolUse: { input: '{"query":"partial' } } }],
+        ["contentBlockStop", { contentBlockIndex: 0 }],
+        ["messageStop", { stopReason: "tool_use" }],
+      )
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(baseRequest, {
+          tools: [{ name: "lookup", description: "Lookup", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedBytes(body)))
+
+      expect(response.toolCalls).toEqual([])
+      expect(response.events.find((event) => event.type === "tool-input-error")).toMatchObject({
+        type: "tool-input-error",
+        id: "tool_malformed",
+        raw: '{"query":"partial',
+      })
+    }),
+  )
+
   it.effect("decodes reasoning deltas", () =>
     Effect.gen(function* () {
       const body = eventStreamBody(
diff --git a/packages/ai/test/provider/gemini.test.ts b/packages/ai/test/provider/gemini.test.ts
index 1dc253c0ea..ff38a7aaa5 100644
--- a/packages/ai/test/provider/gemini.test.ts
+++ b/packages/ai/test/provider/gemini.test.ts
@@ -490,6 +490,35 @@ describe("Gemini route", () => {
     }),
   )
 
+  it.effect("reports string-encoded function arguments without repairing them", () =>
+    Effect.gen(function* () {
+      const body = sseEvents({
+        candidates: [
+          {
+            content: {
+              role: "model",
+              parts: [{ functionCall: { name: "lookup", args: '{"query":"partial' } }],
+            },
+            finishReason: "STOP",
+          },
+        ],
+      })
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(request, {
+          tools: [{ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.toolCalls).toEqual([])
+      expect(response.events.find((event) => event.type === "tool-input-error")).toMatchObject({
+        type: "tool-input-error",
+        id: "tool_0",
+        name: "lookup",
+        raw: '{"query":"partial',
+      })
+    }),
+  )
+
   it.effect("assigns unique ids to multiple streamed tool calls", () =>
     Effect.gen(function* () {
       const body = sseEvents({
diff --git a/packages/ai/test/provider/openai-chat.test.ts b/packages/ai/test/provider/openai-chat.test.ts
index e2efa1717d..64f6456445 100644
--- a/packages/ai/test/provider/openai-chat.test.ts
+++ b/packages/ai/test/provider/openai-chat.test.ts
@@ -606,6 +606,33 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("preserves a valid parallel call when another call is malformed", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        deltaChunk({
+          role: "assistant",
+          tool_calls: [
+            { index: 0, id: "call_valid", function: { name: "lookup", arguments: '{"query":"weather"}' } },
+            { index: 1, id: "call_malformed", function: { name: "lookup", arguments: '{"query":"partial' } },
+          ],
+        }),
+        deltaChunk({}, "tool_calls"),
+      )
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(request, {
+          tools: [{ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(
+        response.events.filter((event) => event.type === "tool-call" || event.type === "tool-input-error"),
+      ).toMatchObject([
+        { type: "tool-call", id: "call_valid", input: { query: "weather" } },
+        { type: "tool-input-error", id: "call_malformed", raw: '{"query":"partial' },
+      ])
+    }),
+  )
+
   it.effect("fails a streamed tool call when the provider ends without a finish reason", () =>
     Effect.gen(function* () {
       const body = sseEvents(
diff --git a/packages/ai/test/provider/openai-responses.test.ts b/packages/ai/test/provider/openai-responses.test.ts
index 7548340690..b3bc39128c 100644
--- a/packages/ai/test/provider/openai-responses.test.ts
+++ b/packages/ai/test/provider/openai-responses.test.ts
@@ -1238,6 +1238,7 @@ describe("OpenAI Responses route", () => {
           type: "tool-input-end",
           id: "call_1",
           name: "lookup",
+          input: '{"query":"weather"}',
           providerMetadata: { openai: { itemId: "item_1" } },
         },
         {
@@ -1259,6 +1260,87 @@ describe("OpenAI Responses route", () => {
     }),
   )
 
+  it.effect("emits malformed function input when output_item.done arrives without added", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        {
+          type: "response.output_item.done",
+          item: {
+            type: "function_call",
+            id: "item_malformed",
+            call_id: "call_malformed",
+            name: "lookup",
+            arguments: '{"query":"partial',
+          },
+        },
+        { type: "response.completed", response: { usage: { input_tokens: 5, output_tokens: 1 } } },
+      )
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(request, {
+          tools: [{ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(
+        response.events.filter(
+          (event) =>
+            event.type === "tool-input-start" || event.type === "tool-input-end" || event.type === "tool-input-error",
+        ),
+      ).toMatchObject([
+        { type: "tool-input-start", id: "call_malformed", name: "lookup" },
+        {
+          type: "tool-input-end",
+          id: "call_malformed",
+          name: "lookup",
+          input: '{"query":"partial',
+        },
+        {
+          type: "tool-input-error",
+          id: "call_malformed",
+          name: "lookup",
+          raw: '{"query":"partial',
+        },
+      ])
+    }),
+  )
+
+  it.effect("uses malformed final function input instead of valid streamed deltas", () =>
+    Effect.gen(function* () {
+      const body = sseEvents(
+        {
+          type: "response.output_item.added",
+          item: { type: "function_call", id: "item_1", call_id: "call_1", name: "lookup", arguments: "" },
+        },
+        { type: "response.function_call_arguments.delta", item_id: "item_1", delta: '{"query":"valid"}' },
+        {
+          type: "response.output_item.done",
+          item: {
+            type: "function_call",
+            id: "item_1",
+            call_id: "call_1",
+            name: "lookup",
+            arguments: '{"query":"partial',
+          },
+        },
+        { type: "response.completed", response: { usage: { input_tokens: 5, output_tokens: 1 } } },
+      )
+      const response = yield* LLMClient.generate(
+        LLM.updateRequest(request, {
+          tools: [{ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } }],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.events.find((event) => event.type === "tool-input-end")).toMatchObject({
+        type: "tool-input-end",
+        input: '{"query":"partial',
+      })
+      expect(response.events.find((event) => event.type === "tool-input-error")).toMatchObject({
+        type: "tool-input-error",
+        raw: '{"query":"partial',
+      })
+    }),
+  )
+
   it.effect("decodes web_search_call as provider-executed tool-call + tool-result", () =>
     Effect.gen(function* () {
       const item = {
diff --git a/packages/ai/test/tool-stream.test.ts b/packages/ai/test/tool-stream.test.ts
index 487bc9624c..27721952fe 100644
--- a/packages/ai/test/tool-stream.test.ts
+++ b/packages/ai/test/tool-stream.test.ts
@@ -57,32 +57,61 @@ describe("ToolStream", () => {
       expect(finished).toEqual({
         tools: {},
         events: [
-          { type: "tool-input-end", id: "call_1", name: "lookup" },
+          { type: "tool-input-end", id: "call_1", name: "lookup", input: '{"query":"final"}' },
           { type: "tool-call", id: "call_1", name: "lookup", input: { query: "final" } },
         ],
       })
     }),
   )
 
-  it.effect("classifies malformed tool input with its raw arguments", () =>
+  it.effect("emits malformed tool input with stable identity and raw arguments", () =>
     Effect.gen(function* () {
       const tools = ToolStream.start(ToolStream.empty<number>(), 0, {
         id: "call_1",
         name: "lookup",
         input: '{"query":"partial',
       })
-      const error = yield* ToolStream.finish(ADAPTER, tools, 0).pipe(Effect.flip)
+      const finished = yield* ToolStream.finish(ADAPTER, tools, 0)
 
-      expect(error).toBeInstanceOf(LLMError)
-      expect(error.reason).toMatchObject({
-        _tag: "InvalidProviderOutput",
-        source: "tool-input",
-        toolName: "lookup",
-        raw: '{"query":"partial',
+      expect(finished).toMatchObject({
+        tools: {},
+        events: [
+          { type: "tool-input-end", id: "call_1", name: "lookup" },
+          {
+            type: "tool-input-error",
+            id: "call_1",
+            name: "lookup",
+            raw: '{"query":"partial',
+            message: "Invalid JSON input for test-route tool call lookup",
+          },
+        ],
       })
     }),
   )
 
+  it.effect("preserves valid sibling calls when one input is malformed", () =>
+    Effect.gen(function* () {
+      const first = ToolStream.start(ToolStream.empty<number>(), 0, {
+        id: "call_valid",
+        name: "lookup",
+        input: '{"query":"weather"}',
+      })
+      const tools = ToolStream.start(first, 1, {
+        id: "call_malformed",
+        name: "lookup",
+        input: '{"query":"partial',
+      })
+      const finished = yield* ToolStream.finishAll(ADAPTER, tools)
+
+      expect(
+        finished.events.filter((event) => event.type === "tool-call" || event.type === "tool-input-error"),
+      ).toMatchObject([
+        { type: "tool-call", id: "call_valid", input: { query: "weather" } },
+        { type: "tool-input-error", id: "call_malformed", raw: '{"query":"partial' },
+      ])
+    }),
+  )
+
   it.effect("preserves providerExecuted and clears all tools", () =>
     Effect.gen(function* () {
       const first: ToolStream.State<number> = ToolStream.start(ToolStream.empty<number>(), 0, {
diff --git a/packages/client/src/promise/generated/types.ts b/packages/client/src/promise/generated/types.ts
index fc8720d212..3ae799a87e 100644
--- a/packages/client/src/promise/generated/types.ts
+++ b/packages/client/src/promise/generated/types.ts
@@ -161,6 +161,8 @@ export type SessionMessageProviderState6 = { [x: string]: any }
 
 export type SessionMessageProviderState7 = { [x: string]: any }
 
+export type SessionMessageProviderState8 = { [x: string]: any }
+
 export type EventLogSynced = { type: "log.synced"; aggregateID: string; seq?: number }
 
 export type ModelCapabilities = { tools: boolean; input: Array<string>; output: Array<string> }
@@ -735,16 +737,6 @@ export type SessionTextEnded = {
   data: { sessionID: string; assistantMessageID: string; ordinal: number; text: string }
 }
 
-export type SessionToolInputStarted = {
-  id: string
-  created: number
-  metadata?: { [x: string]: any }
-  type: "session.tool.input.started"
-  durable: { aggregateID: string; seq: number; version: 1 }
-  location?: LocationRef
-  data: { sessionID: string; assistantMessageID: string; callID: string; name: string }
-}
-
 export type SessionToolInputEnded = {
   id: string
   created: number
@@ -1366,6 +1358,23 @@ export type SessionReasoningEnded = {
   }
 }
 
+export type SessionToolInputStarted = {
+  id: string
+  created: number
+  metadata?: { [x: string]: any }
+  type: "session.tool.input.started"
+  durable: { aggregateID: string; seq: number; version: 1 }
+  location?: LocationRef
+  data: {
+    sessionID: string
+    assistantMessageID: string
+    callID: string
+    name: string
+    executed?: boolean
+    state?: SessionMessageProviderState5
+  }
+}
+
 export type SessionToolCalled = {
   id: string
   created: number
@@ -1379,7 +1388,7 @@ export type SessionToolCalled = {
     callID: string
     input: { [x: string]: any }
     executed: boolean
-    state?: SessionMessageProviderState5
+    state?: SessionMessageProviderState6
   }
 }
 
@@ -1395,9 +1404,10 @@ export type SessionToolFailed = {
     assistantMessageID: string
     callID: string
     error: SessionStructuredError
+    raw?: string
     result?: any
     executed: boolean
-    resultState?: SessionMessageProviderState7
+    resultState?: SessionMessageProviderState8
   }
 }
 
@@ -1877,7 +1887,7 @@ export type SessionToolSuccess = {
     content: Array<LLMToolContent>
     result?: any
     executed: boolean
-    resultState?: SessionMessageProviderState6
+    resultState?: SessionMessageProviderState7
   }
 }
 
diff --git a/packages/core/src/session/message-updater.ts b/packages/core/src/session/message-updater.ts
index 4b463e872e..6b85b7fd56 100644
--- a/packages/core/src/session/message-updater.ts
+++ b/packages/core/src/session/message-updater.ts
@@ -324,6 +324,8 @@ export function update(adapter: Adapter, event: SessionEvent.Event) {
                 type: "tool",
                 id: event.data.callID,
                 name: event.data.name,
+                executed: event.data.executed,
+                providerState: event.data.state,
                 time: { created: event.created },
                 state: SessionMessage.ToolStateStreaming.make({ status: "streaming", input: "" }),
               }),
@@ -396,7 +398,7 @@ export function update(adapter: Adapter, event: SessionEvent.Event) {
                 status: "error",
                 error: event.data.error,
                 input: typeof match.state.input === "string" ? {} : match.state.input,
-                raw: typeof match.state.input === "string" ? match.state.input : undefined,
+                raw: event.data.raw ?? (typeof match.state.input === "string" ? match.state.input : undefined),
                 structured: match.state.status === "running" ? match.state.structured : {},
                 content: match.state.status === "running" ? match.state.content : [],
                 result: event.data.result,
diff --git a/packages/core/src/session/runner/llm.ts b/packages/core/src/session/runner/llm.ts
index 96155ef06e..62c80554f1 100644
--- a/packages/core/src/session/runner/llm.ts
+++ b/packages/core/src/session/runner/llm.ts
@@ -28,6 +28,8 @@ import { toSessionError } from "../to-session-error"
 import { SessionRunnerRetry } from "./retry"
 import { SessionUsage } from "../usage"
 
+const MAX_MALFORMED_TOOL_RETRIES = 4
+
 const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
@@ -80,6 +82,7 @@ const layer = Layer.effect(
       sessionID: SessionSchema.ID,
       promotion: SessionPending.Delivery | undefined,
       step: number,
+      recoverMalformedToolInput: boolean,
       recoverOverflow?: typeof compaction.compact,
       assistantMessageID?: SessionMessage.ID,
     ) {
@@ -143,7 +146,7 @@ const layer = Layer.effect(
               }
             }
             yield* publish(event)
-            if (event.type !== "tool-call" || event.providerExecuted) return
+            if (event.type !== "tool-call" || publisher.isProviderExecuted(event.id)) return
             const tool = prepared.resolveToolCall(event.name)
             if (tool.type === "reject") {
               yield* serialized(publisher.failUnsettledTools(tool.error))
@@ -244,13 +247,35 @@ const layer = Layer.effect(
           if (overflowFailure) yield* publish(overflowFailure)
           const llmFailure = streamFailure instanceof LLMError ? streamFailure : undefined
           const malformedToolInput =
-            llmFailure?.reason._tag === "InvalidProviderOutput" && llmFailure.reason.source === "tool-input"
-          const recoveredMalformedToolInput = malformedToolInput
+            llmFailure?.reason._tag === "InvalidProviderOutput" &&
+            llmFailure.reason.source === "tool-input" &&
+            llmFailure.reason.toolCallID !== undefined &&
+            llmFailure.reason.toolName !== undefined &&
+            llmFailure.reason.raw !== undefined
+              ? {
+                  id: llmFailure.reason.toolCallID,
+                  name: llmFailure.reason.toolName,
+                  raw: llmFailure.reason.raw,
+                  providerExecuted: llmFailure.reason.providerExecuted,
+                  providerMetadata: llmFailure.reason.providerMetadata,
+                }
+              : undefined
+          const failedMalformedToolInput = malformedToolInput
             ? yield* serialized(
-                publisher.failUnsettledTools({
-                  type: "provider.invalid-output",
-                  message: "Tool call arguments were malformed JSON and were not executed. Retry with valid JSON.",
-                }),
+                publisher.failMalformedToolInput(
+                  {
+                    id: malformedToolInput.id,
+                    name: malformedToolInput.name,
+                    raw: malformedToolInput.raw,
+                    providerExecuted: malformedToolInput.providerExecuted,
+                    providerMetadata: malformedToolInput.providerMetadata,
+                  },
+                  {
+                    type: "provider.invalid-output",
+                    message: "Tool call arguments were malformed JSON and were not executed. Retry with valid JSON.",
+                  },
+                  toSessionError(llmFailure),
+                ),
               )
             : false
           if (llmFailure && !publisher.hasProviderError()) {
@@ -267,6 +292,11 @@ const layer = Layer.effect(
           }
           // Provider error events only arrive from the stream, so the flag is final here.
           const providerFailed = publisher.hasProviderError()
+          const recoveredMalformedToolInput =
+            recoverMalformedToolInput &&
+            !providerFailed &&
+            !streamInterrupted &&
+            (failedMalformedToolInput || (stream._tag === "Success" && publisher.hasMalformedToolInput()))
 
           // Settle every owned tool fiber. FiberSet.join returns on the first failure, so retain
           // the individual fibers and await all exits before publishing the terminal step event.
@@ -346,6 +376,7 @@ const layer = Layer.effect(
           return {
             _tag: "Completed",
             needsContinuation: needsContinuation || recoveredMalformedToolInput,
+            malformedToolInput: recoveredMalformedToolInput,
             step: currentStep,
           } as const
         }),
@@ -356,6 +387,7 @@ const layer = Layer.effect(
       sessionID: SessionSchema.ID,
       promotion: SessionPending.Delivery | undefined,
       step: number,
+      recoverMalformedToolInput: boolean,
     ) {
       // Compaction restarts rebuild the request from compacted history without re-promoting.
       // Overflow recovery is one-shot: a post-compaction attempt must not recover another
@@ -366,7 +398,14 @@ const layer = Layer.effect(
       let assistantMessageID: SessionMessage.ID | undefined
       while (true) {
         const attempt = yield* Effect.suspend(() =>
-          attemptStep(sessionID, currentPromotion, currentStep, recoverOverflow, assistantMessageID),
+          attemptStep(
+            sessionID,
+            currentPromotion,
+            currentStep,
+            recoverMalformedToolInput,
+            recoverOverflow,
+            assistantMessageID,
+          ),
         ).pipe(
           Effect.tapError((error) =>
             error instanceof SessionRunnerRetry.RetryableFailure
@@ -388,7 +427,12 @@ const layer = Layer.effect(
               .pipe(Effect.andThen(Effect.fail(error.cause)))
           }),
         )
-        if (attempt._tag === "Completed") return { needsContinuation: attempt.needsContinuation, step: attempt.step }
+        if (attempt._tag === "Completed")
+          return {
+            needsContinuation: attempt.needsContinuation,
+            malformedToolInput: attempt.malformedToolInput,
+            step: attempt.step,
+          }
         if (attempt._tag === "RestartAfterOverflowCompaction") recoverOverflow = undefined
         yield* Effect.yieldNow
         currentPromotion = undefined
@@ -446,12 +490,19 @@ const layer = Layer.effect(
       while (shouldRun) {
         let needsContinuation = true
         let step = 1
+        let malformedToolRetries = 0
         // Repeat steps while continuation is needed. A step needs continuation only
         // when it recorded local tool calls whose results the model has not yet seen;
-        // a provider error suppresses it. Pending steers also continue the loop so
-        // interjections are answered before the session goes idle.
+        // malformed tool input can also continue within its bounded recovery budget.
+        // A provider error suppresses continuation. Pending steers also continue the
+        // loop so interjections are answered before the session goes idle.
         while (needsContinuation) {
-          const result = yield* runStep(input.sessionID, promotion, step)
+          const result = yield* runStep(
+            input.sessionID,
+            promotion,
+            step,
+            malformedToolRetries < MAX_MALFORMED_TOOL_RETRIES,
+          )
           // Steer/queue promotion inside runStep has already made the pending input a visible
           // user message by this point, so the first-user-message check below is reliable.
           if (!titleAttempted.has(input.sessionID)) {
@@ -459,6 +510,7 @@ const layer = Layer.effect(
             forkTitle(title.generateForFirstPrompt(yield* getSession(input.sessionID)).pipe(Effect.ignore))
           }
           needsContinuation = result.needsContinuation
+          malformedToolRetries = result.malformedToolInput ? malformedToolRetries + 1 : 0
           step = result.step + 1
           if (needsContinuation) {
             yield* runPendingCompaction(input.sessionID)
diff --git a/packages/core/src/session/runner/publish-llm-event.ts b/packages/core/src/session/runner/publish-llm-event.ts
index 6a71f5d888..711853ff65 100644
--- a/packages/core/src/session/runner/publish-llm-event.ts
+++ b/packages/core/src/session/runner/publish-llm-event.ts
@@ -53,6 +53,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
       called: boolean
       settled: boolean
       providerExecuted: boolean
+      rawInput: string
     }
   >()
   let assistantMessageID = input.assistantMessageID
@@ -60,6 +61,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
   let stepFailed = false
   let providerFailed = false
   let retryEvidence = false
+  let malformedToolInput = false
   let stepFailure: SessionError.Error | undefined
   let stepSettlement:
     | {
@@ -112,12 +114,12 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
         if (state !== undefined) current.state = { ...current.state, ...state }
         return Effect.succeed(current.ordinal)
       })
-    const end = Effect.fnUntraced(function* (id: string, state?: Record<string, unknown>) {
+    const end = Effect.fnUntraced(function* (id: string, state?: Record<string, unknown>, value?: string) {
       const current = chunks.get(id)
       if (!current) return yield* Effect.die(new Error(`${name} end before start: ${id}`))
       yield* ended(
         id,
-        current.values.join(""),
+        value ?? current.values.join(""),
         current.ordinal,
         state === undefined ? current.state : { ...current.state, ...state },
       )
@@ -175,7 +177,12 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
     yield* toolInput.flush()
   })
 
-  const startToolInput = Effect.fnUntraced(function* (event: { readonly id: string; readonly name: string }) {
+  const startToolInput = Effect.fnUntraced(function* (event: {
+    readonly id: string
+    readonly name: string
+    readonly providerExecuted?: boolean
+    readonly providerMetadata?: ProviderMetadata
+  }) {
     if (tools.has(event.id)) return yield* Effect.die(new Error(`Duplicate tool input start: ${event.id}`))
     const assistantMessageID = yield* startAssistant()
     tools.set(event.id, {
@@ -183,7 +190,8 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
       name: event.name,
       called: false,
       settled: false,
-      providerExecuted: false,
+      providerExecuted: event.providerExecuted === true,
+      rawInput: "",
     })
     yield* toolInput.start(event.id)
     yield* events.publish(SessionEvent.Tool.Input.Started, {
@@ -191,16 +199,60 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
       assistantMessageID,
       callID: event.id,
       name: event.name,
+      executed: event.providerExecuted,
+      state: providerState(event.providerMetadata),
     })
   })
 
-  const endToolInput = Effect.fnUntraced(function* (event: { readonly id: string; readonly name: string }) {
+  const endToolInput = Effect.fnUntraced(function* (event: {
+    readonly id: string
+    readonly name: string
+    readonly input?: string
+  }) {
     const tool = tools.get(event.id)
     if (!tool) return yield* Effect.die(new Error(`Tool input end before start: ${event.id}`))
     if (tool.name !== event.name)
       return yield* Effect.die(new Error(`Tool input name changed for ${event.id}: ${tool.name} -> ${event.name}`))
     if (!toolInput.has(event.id)) return yield* Effect.die(new Error(`Duplicate tool input end: ${event.id}`))
-    yield* toolInput.end(event.id)
+    tool.rawInput = event.input ?? tool.rawInput
+    yield* toolInput.end(event.id, undefined, event.input)
+  })
+
+  const failMalformedToolInput = Effect.fnUntraced(function* (
+    event: {
+      readonly id: string
+      readonly name: string
+      readonly raw: string
+      readonly providerExecuted?: boolean
+      readonly providerMetadata?: ProviderMetadata
+    },
+    error: SessionError.Error,
+    assistantError: SessionError.Error,
+  ) {
+    if (!tools.has(event.id)) yield* startToolInput(event)
+    const tool = tools.get(event.id)
+    if (!tool || tool.called || tool.settled) return false
+    if (tool.name !== event.name)
+      return yield* Effect.die(new Error(`Tool input name changed for ${event.id}: ${tool.name} -> ${event.name}`))
+    tool.providerExecuted = event.providerExecuted === true || tool.providerExecuted
+    const correctedRaw = !toolInput.has(event.id) && tool.rawInput !== event.raw ? event.raw : undefined
+    if (toolInput.has(event.id)) {
+      tool.rawInput = event.raw
+      yield* toolInput.end(event.id, undefined, event.raw)
+    }
+    tool.settled = true
+    malformedToolInput = true
+    yield* events.publish(SessionEvent.Tool.Failed, {
+      sessionID: input.sessionID,
+      assistantMessageID: tool.assistantMessageID,
+      callID: event.id,
+      error,
+      raw: correctedRaw,
+      executed: tool.providerExecuted,
+    })
+    yield* startAssistant()
+    if (stepFailure === undefined) stepFailure = assistantError
+    return true
   })
 
   const flush = Effect.fn("SessionRunner.flush")(function* () {
@@ -210,11 +262,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
   const failTools = Effect.fnUntraced(function* (error: SessionError.Error, mode: "all" | "hosted" | "uncalled") {
     let failed = false
     for (const [callID, tool] of tools) {
-      if (
-        tool.settled ||
-        (mode === "hosted" && !tool.providerExecuted) ||
-        (mode === "uncalled" && tool.called)
-      )
+      if (tool.settled || (mode === "hosted" && !tool.providerExecuted) || (mode === "uncalled" && tool.called))
         continue
       tool.settled = true
       failed = true
@@ -325,6 +373,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
         if (tool.name !== event.name)
           return yield* Effect.die(new Error(`Tool input name changed for ${event.id}: ${tool.name} -> ${event.name}`))
         if (!toolInput.has(event.id)) return yield* Effect.die(new Error(`Tool input delta after end: ${event.id}`))
+        tool.rawInput += event.text
         yield* toolInput.append(event.id, event.text)
         yield* events.publish(SessionEvent.Tool.Input.Delta, {
           sessionID: input.sessionID,
@@ -337,16 +386,30 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
       case "tool-input-end":
         yield* endToolInput(event)
         return
+      case "tool-input-error":
+        retryEvidence = true
+        if (
+          !(yield* failMalformedToolInput(
+            event,
+            {
+              type: "provider.invalid-output",
+              message: "Tool call arguments were malformed JSON and were not executed. Retry with valid JSON.",
+            },
+            { type: "provider.invalid-output", message: event.message },
+          ))
+        )
+          return yield* Effect.die(new Error(`Malformed tool input after call settlement: ${event.id}`))
+        return
       case "tool-call": {
         retryEvidence = true
         if (!tools.has(event.id)) yield* startToolInput(event)
         const tool = tools.get(event.id)!
-        if (toolInput.has(event.id)) yield* endToolInput(event)
+        if (toolInput.has(event.id)) yield* endToolInput({ id: event.id, name: event.name })
         if (tool.name !== event.name)
           return yield* Effect.die(new Error(`Tool call name changed for ${event.id}: ${tool.name} -> ${event.name}`))
         if (tool.called) return yield* Effect.die(new Error(`Duplicate tool call: ${event.id}`))
         tool.called = true
-        tool.providerExecuted = event.providerExecuted === true
+        tool.providerExecuted = event.providerExecuted === true || tool.providerExecuted
         yield* events.publish(SessionEvent.Tool.Called, {
           sessionID: input.sessionID,
           assistantMessageID: tool.assistantMessageID,
@@ -436,10 +499,13 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
     publish,
     flush,
     failAssistant,
+    failMalformedToolInput,
     publishStepFailure,
     failUnsettledTools,
     hasProviderError: () => providerFailed,
+    hasMalformedToolInput: () => malformedToolInput,
     hasRetryEvidence: () => retryEvidence,
+    isProviderExecuted: (callID: string) => tools.get(callID)?.providerExecuted === true,
     stepFailure: () => stepFailure,
     stepSettlement: () => stepSettlement,
     startAssistant,
diff --git a/packages/core/src/session/runner/to-llm-message.ts b/packages/core/src/session/runner/to-llm-message.ts
index e91eef2c28..5fe57b611e 100644
--- a/packages/core/src/session/runner/to-llm-message.ts
+++ b/packages/core/src/session/runner/to-llm-message.ts
@@ -110,7 +110,12 @@ const toolResult = (tool: SessionMessage.AssistantTool, providerMetadata: Provid
       result:
         tool.executed === true && tool.state.result !== undefined
           ? tool.state.result
-          : { error: tool.state.error, content: tool.state.content, structured: tool.state.structured },
+          : {
+              error: tool.state.error,
+              content: tool.state.content,
+              structured: tool.state.structured,
+              ...(tool.state.raw === undefined ? {} : { raw: tool.state.raw }),
+            },
       resultType: "error",
       providerExecuted: tool.executed,
       providerMetadata,
diff --git a/packages/core/test/session-runner.test.ts b/packages/core/test/session-runner.test.ts
index da67e9e0c1..fd7039b554 100644
--- a/packages/core/test/session-runner.test.ts
+++ b/packages/core/test/session-runner.test.ts
@@ -4134,8 +4134,9 @@ describe("SessionRunnerLLM", () => {
         method: "stream",
         reason: new InvalidProviderOutputReason({
           message: "Invalid JSON input for tool call echo",
-          raw: '{"text":"partial',
+          raw: '{"text":"authoritative',
           source: "tool-input",
+          toolCallID: "call-malformed",
           toolName: "echo",
         }),
       })
@@ -4160,7 +4161,7 @@ describe("SessionRunnerLLM", () => {
           state: {
             status: "error",
             input: {},
-            raw: '{"text":"partial',
+            raw: '{"text":"authoritative',
             error: {
               message: "Tool call arguments were malformed JSON and were not executed. Retry with valid JSON.",
             },
@@ -4182,6 +4183,7 @@ describe("SessionRunnerLLM", () => {
                   error: {
                     message: "Tool call arguments were malformed JSON and were not executed. Retry with valid JSON.",
                   },
+                  raw: '{"text":"authoritative',
                 },
               },
             },
@@ -4209,6 +4211,219 @@ describe("SessionRunnerLLM", () => {
     }),
   )
 
+  it.effect("does not recover malformed tool input from an interrupted stream", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      yield* admit(session, "Interrupt malformed tool input")
+      const failure = new LLMError({
+        module: "test",
+        method: "stream",
+        reason: new InvalidProviderOutputReason({
+          message: "Invalid JSON input for tool call echo",
+          raw: '{"text":"partial',
+          source: "tool-input",
+          toolCallID: "call-malformed-interrupted",
+          toolName: "echo",
+        }),
+      })
+      responseStream = Stream.fromIterable([
+        LLMEvent.stepStart({ index: 0 }),
+        LLMEvent.toolInputStart({ id: "call-malformed-interrupted", name: "echo" }),
+        LLMEvent.toolInputDelta({
+          id: "call-malformed-interrupted",
+          name: "echo",
+          text: '{"text":"partial',
+        }),
+      ]).pipe(
+        Stream.concat(
+          Stream.failCause(
+            Cause.fromReasons([Cause.makeFailReason(failure), Cause.makeInterruptReason(1)]),
+          ),
+        ),
+      )
+
+      const exit = yield* session.resume(sessionID).pipe(Effect.exit)
+
+      expect(Exit.isFailure(exit)).toBe(true)
+      expect(requests).toHaveLength(1)
+    }),
+  )
+
+  it.effect("settles a valid sibling tool before recovering malformed input", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      yield* admit(session, "Run one valid and one malformed tool")
+      toolExecutionGate = yield* Deferred.make<void>()
+      toolExecutionsStarted = yield* Deferred.make<void>()
+      toolExecutionsReady = 1
+      responses = [
+        [
+          LLMEvent.stepStart({ index: 0 }),
+          LLMEvent.toolCall({ id: "call-valid", name: "echo", input: { text: "valid" } }),
+          LLMEvent.toolInputStart({ id: "call-malformed-sibling", name: "echo" }),
+          LLMEvent.toolInputDelta({
+            id: "call-malformed-sibling",
+            name: "echo",
+            text: '{"text":"partial',
+          }),
+          LLMEvent.toolInputEnd({ id: "call-malformed-sibling", name: "echo" }),
+          LLMEvent.toolInputError({
+            id: "call-malformed-sibling",
+            name: "echo",
+            raw: '{"text":"partial',
+            message: "Invalid JSON input for tool call echo",
+          }),
+          LLMEvent.stepFinish({ index: 0, reason: "tool-calls" }),
+          LLMEvent.finish({ reason: "tool-calls" }),
+        ],
+        reply.stop(),
+      ]
+
+      const run = yield* session.resume(sessionID).pipe(Effect.forkChild)
+      yield* Deferred.await(toolExecutionsStarted)
+      yield* Deferred.succeed(toolExecutionGate, undefined)
+      yield* Fiber.join(run)
+      toolExecutionGate = undefined
+      toolExecutionsStarted = undefined
+
+      expect(requests).toHaveLength(2)
+      expect(executions).toEqual(["valid"])
+      expect(requireAssistant(yield* session.context(sessionID)).content).toMatchObject([
+        { id: "call-valid", state: { status: "completed", input: { text: "valid" } } },
+        {
+          id: "call-malformed-sibling",
+          state: { status: "error", raw: '{"text":"partial' },
+        },
+      ])
+    }),
+  )
+
+  it.effect("limits malformed tool input recovery to four retries", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      yield* admit(session, "Keep calling malformed tools")
+      responses = Array.from({ length: 5 }, (_, index) => {
+        const id = `call-malformed-${index}`
+        return [
+          LLMEvent.stepStart({ index: 0 }),
+          LLMEvent.toolInputStart({ id, name: "echo" }),
+          LLMEvent.toolInputDelta({ id, name: "echo", text: '{"text":"partial' }),
+          LLMEvent.toolInputEnd({ id, name: "echo" }),
+          LLMEvent.toolInputError({
+            id,
+            name: "echo",
+            raw: '{"text":"partial',
+            message: "Invalid JSON input for tool call echo",
+          }),
+          LLMEvent.stepFinish({ index: 0, reason: "tool-calls" }),
+          LLMEvent.finish({ reason: "tool-calls" }),
+        ]
+      })
+
+      expect(yield* session.resume(sessionID).pipe(Effect.flip)).toMatchObject({
+        _tag: "Session.StepFailedError",
+        error: { type: "provider.invalid-output", message: "Invalid JSON input for tool call echo" },
+      })
+      expect(requests).toHaveLength(5)
+      expect(executions).toEqual([])
+    }),
+  )
+
+  it.effect("replays malformed hosted tool input as provider-executed", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      yield* admit(session, "Recover a malformed hosted tool")
+      responses = [
+        [
+          LLMEvent.stepStart({ index: 0 }),
+          LLMEvent.toolInputStart({
+            id: "call-hosted-malformed",
+            name: "web_search",
+            providerExecuted: true,
+          }),
+          LLMEvent.toolInputDelta({
+            id: "call-hosted-malformed",
+            name: "web_search",
+            text: '{"query":"partial',
+          }),
+          LLMEvent.toolInputEnd({ id: "call-hosted-malformed", name: "web_search" }),
+          LLMEvent.toolInputError({
+            id: "call-hosted-malformed",
+            name: "web_search",
+            raw: '{"query":"partial',
+            message: "Invalid JSON input for Anthropic Messages tool call web_search",
+            providerExecuted: true,
+          }),
+          LLMEvent.stepFinish({ index: 0, reason: "tool-calls" }),
+          LLMEvent.finish({ reason: "tool-calls" }),
+        ],
+        reply.stop(),
+      ]
+
+      yield* session.resume(sessionID)
+
+      expect(requests).toHaveLength(2)
+      expect(requests[1].messages).toMatchObject([
+        { role: "user" },
+        {
+          role: "assistant",
+          content: [
+            {
+              type: "tool-call",
+              id: "call-hosted-malformed",
+              providerExecuted: true,
+            },
+            {
+              type: "tool-result",
+              id: "call-hosted-malformed",
+              providerExecuted: true,
+            },
+          ],
+        },
+      ])
+      expect(requireAssistant(yield* session.context(sessionID)).content).toMatchObject([
+        { id: "call-hosted-malformed", executed: true, state: { status: "error" } },
+      ])
+      yield* replaySessionProjection(sessionID)
+      expect(requireAssistant(yield* session.context(sessionID)).content).toMatchObject([
+        { id: "call-hosted-malformed", executed: true, state: { status: "error" } },
+      ])
+    }),
+  )
+
+  it.effect("preserves provider execution identity when the final tool events omit it", () =>
+    Effect.gen(function* () {
+      const session = yield* setup
+      yield* admit(session, "Keep hosted tool identity")
+      response = [
+        LLMEvent.stepStart({ index: 0 }),
+        LLMEvent.toolInputStart({ id: "call-hosted-start-only", name: "echo", providerExecuted: true }),
+        LLMEvent.toolInputDelta({ id: "call-hosted-start-only", name: "echo", text: '{"text":"hosted"}' }),
+        LLMEvent.toolInputEnd({ id: "call-hosted-start-only", name: "echo" }),
+        LLMEvent.toolCall({ id: "call-hosted-start-only", name: "echo", input: { text: "hosted" } }),
+        LLMEvent.toolResult({
+          id: "call-hosted-start-only",
+          name: "echo",
+          result: { type: "json", value: { text: "hosted" } },
+        }),
+        LLMEvent.stepFinish({ index: 0, reason: "tool-calls" }),
+        LLMEvent.finish({ reason: "tool-calls" }),
+      ]
+
+      yield* session.resume(sessionID)
+
+      expect(requests).toHaveLength(1)
+      expect(executions).toEqual([])
+      expect(requireAssistant(yield* session.context(sessionID)).content).toMatchObject([
+        {
+          id: "call-hosted-start-only",
+          executed: true,
+          state: { status: "completed", input: { text: "hosted" } },
+        },
+      ])
+    }),
+  )
+
   it.effect("does not continue automatically after a provider error follows a local tool call", () =>
     Effect.gen(function* () {
       const session = yield* setup
diff --git a/packages/schema/src/session-event.ts b/packages/schema/src/session-event.ts
index aaeb6565c3..e22f7bc09b 100644
--- a/packages/schema/src/session-event.ts
+++ b/packages/schema/src/session-event.ts
@@ -371,6 +371,8 @@ export namespace Tool {
       schema: {
         ...ToolBase,
         name: Schema.String,
+        executed: Schema.Boolean.pipe(optional),
+        state: SessionMessage.ProviderState.pipe(optional),
       },
     })
     export type Started = typeof Started.Type
@@ -443,6 +445,7 @@ export namespace Tool {
     schema: {
       ...ToolBase,
       error: SessionError.Error,
+      raw: Schema.String.pipe(optional),
       result: Schema.Unknown.pipe(optional),
       executed: Schema.Boolean,
       resultState: SessionMessage.ProviderState.pipe(optional),
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index b742ed2f40..760ea5c700 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -1020,6 +1020,8 @@ export type GlobalEvent = {
           assistantMessageID: string
           callID: string
           name: string
+          executed?: boolean
+          state?: SessionMessageProviderState
         }
       }
     | {
@@ -1093,6 +1095,7 @@ export type GlobalEvent = {
           assistantMessageID: string
           callID: string
           error: SessionStructuredError
+          raw?: string
           result?: unknown
           executed: boolean
           resultState?: SessionMessageProviderState
@@ -4117,6 +4120,8 @@ export type SyncEventSessionToolInputStarted = {
       assistantMessageID: string
       callID: string
       name: string
+      executed?: boolean
+      state?: SessionMessageProviderState
     }
   }
 }
@@ -4215,6 +4220,7 @@ export type SyncEventSessionToolFailed = {
       assistantMessageID: string
       callID: string
       error: SessionStructuredError
+      raw?: string
       result?: unknown
       executed: boolean
       resultState?: SessionMessageProviderState
@@ -4639,6 +4645,7 @@ export type SessionMessageToolStateError = {
   input: {
     [key: string]: unknown
   }
+  raw?: string
   content: Array<LlmToolContent>
   structured: {
     [key: string]: unknown
@@ -5275,6 +5282,8 @@ export type SessionToolInputStarted = {
     assistantMessageID: string
     callID: string
     name: string
+    executed?: boolean
+    state?: SessionMessageProviderState
   }
 }
 
@@ -5393,6 +5402,7 @@ export type SessionToolFailed = {
     assistantMessageID: string
     callID: string
     error: SessionStructuredError
+    raw?: string
     result?: unknown
     executed: boolean
     resultState?: SessionMessageProviderState
@@ -7479,6 +7489,8 @@ export type EventSessionToolInputStarted = {
     assistantMessageID: string
     callID: string
     name: string
+    executed?: boolean
+    state?: SessionMessageProviderState
   }
 }
 
@@ -7558,6 +7570,7 @@ export type EventSessionToolFailed = {
     assistantMessageID: string
     callID: string
     error: SessionStructuredError
+    raw?: string
     result?: unknown
     executed: boolean
     resultState?: SessionMessageProviderState
@@ -9607,6 +9620,10 @@ export type SessionReasoningEndedV2 = {
   }
 }
 
+export type SessionMessageProviderState5 = {
+  [key: string]: unknown
+}
+
 export type SessionToolInputStartedV2 = {
   id: string
   created: number
@@ -9625,6 +9642,8 @@ export type SessionToolInputStartedV2 = {
     assistantMessageID: string
     callID: string
     name: string
+    executed?: boolean
+    state?: SessionMessageProviderState5
   }
 }
 
@@ -9649,7 +9668,7 @@ export type SessionToolInputEndedV2 = {
   }
 }
 
-export type SessionMessageProviderState5 = {
+export type SessionMessageProviderState6 = {
   [key: string]: unknown
 }
 
@@ -9674,7 +9693,7 @@ export type SessionToolCalledV2 = {
       [key: string]: unknown
     }
     executed: boolean
-    state?: SessionMessageProviderState5
+    state?: SessionMessageProviderState6
   }
 }
 
@@ -9702,7 +9721,7 @@ export type SessionToolProgressV2 = {
   }
 }
 
-export type SessionMessageProviderState6 = {
+export type SessionMessageProviderState7 = {
   [key: string]: unknown
 }
 
@@ -9729,11 +9748,11 @@ export type SessionToolSuccessV2 = {
     content: Array<LlmToolContent>
     result?: unknown
     executed: boolean
-    resultState?: SessionMessageProviderState6
+    resultState?: SessionMessageProviderState7
   }
 }
 
-export type SessionMessageProviderState7 = {
+export type SessionMessageProviderState8 = {
   [key: string]: unknown
 }
 
@@ -9755,9 +9774,10 @@ export type SessionToolFailedV2 = {
     assistantMessageID: string
     callID: string
     error: SessionStructuredError
+    raw?: string
     result?: unknown
     executed: boolean
-    resultState?: SessionMessageProviderState7
+    resultState?: SessionMessageProviderState8
   }
 }