fix(ai): require provider error data

packages/ai/src/protocols/anthropic-messages.ts

@@ -283,21 +283,27 @@ const AnthropicStreamDelta = Schema.Struct({
   stop_sequence: optionalNull(Schema.String),
 })
 
-const AnthropicEvent = Schema.Struct({
-  type: Schema.String,
-  index: Schema.optional(Schema.Number),
-  message: Schema.optional(Schema.Struct({ usage: Schema.optional(AnthropicUsage) })),
-  content_block: Schema.optional(AnthropicStreamBlock),
-  delta: Schema.optional(AnthropicStreamDelta),
-  usage: Schema.optional(AnthropicUsage),
-  // `type` and `message` are both required per Anthropic's spec, but
-  // OpenAI-compatible proxies and gateway translations occasionally drop one
-  // or the other; mark them optional so a partial payload still parses and
-  // the parser can fall back to whichever field is populated.
-  error: Schema.optional(
-    Schema.Struct({ type: Schema.optional(Schema.String), message: Schema.optional(Schema.String) }),
-  ),
-})
+const AnthropicEvent = Schema.StructWithRest(
+  Schema.Struct({
+    type: Schema.String,
+    index: Schema.optional(Schema.Number),
+    message: Schema.optional(Schema.Struct({ usage: Schema.optional(AnthropicUsage) })),
+    content_block: Schema.optional(AnthropicStreamBlock),
+    delta: Schema.optional(AnthropicStreamDelta),
+    usage: Schema.optional(AnthropicUsage),
+    // `type` and `message` are both required per Anthropic's spec, but
+    // OpenAI-compatible proxies and gateway translations occasionally drop one
+    // or the other; mark them optional so a partial payload still parses and
+    // the parser can fall back to whichever field is populated.
+    error: Schema.optional(
+      Schema.StructWithRest(
+        Schema.Struct({ type: Schema.optional(Schema.String), message: Schema.optional(Schema.String) }),
+        [Schema.Record(Schema.String, Schema.Unknown)],
+      ),
+    ),
+  }),
+  [Schema.Record(Schema.String, Schema.Unknown)],
+)
 type AnthropicEvent = Schema.Schema.Type<typeof AnthropicEvent>
 
 interface ParserState {
@@ -983,7 +989,11 @@ const onError = (event: AnthropicEvent) =>
   new AIError({
     module: ADAPTER,
     method: "stream",
-    reason: classifyProviderFailure({ message: providerErrorMessage(event), code: event.error?.type }),
+    reason: classifyProviderFailure({
+      message: providerErrorMessage(event),
+      code: event.error?.type,
+      data: Schema.decodeUnknownSync(Schema.Json)(event),
+    }),
   })
 
 const step = (state: ParserState, event: AnthropicEvent) => {

packages/ai/src/protocols/bedrock-converse.ts

@@ -155,69 +155,75 @@ const BedrockUsageSchema = Schema.Struct({
 })
 type BedrockUsageSchema = Schema.Schema.Type<typeof BedrockUsageSchema>
 
-const BedrockStreamException = Schema.Struct({
-  message: Schema.optional(Schema.String),
-  originalMessage: Schema.optional(Schema.String),
-  originalStatusCode: Schema.optional(Schema.Number),
-})
+const BedrockStreamException = Schema.StructWithRest(
+  Schema.Struct({
+    message: Schema.optional(Schema.String),
+    originalMessage: Schema.optional(Schema.String),
+    originalStatusCode: Schema.optional(Schema.Number),
+  }),
+  [Schema.Record(Schema.String, Schema.Unknown)],
+)
 
 // Streaming event shape — the AWS event stream wraps each JSON payload by its
 // `:event-type` header (e.g. `messageStart`, `contentBlockDelta`). We
 // reconstruct that wrapping in `decodeFrames` below so the event schema can
 // stay a plain discriminated record.
-const BedrockEvent = Schema.Struct({
-  messageStart: Schema.optional(Schema.Struct({ role: Schema.String })),
-  contentBlockStart: Schema.optional(
-    Schema.Struct({
-      contentBlockIndex: Schema.Number,
-      start: Schema.optional(
-        Schema.Struct({
-          toolUse: Schema.optional(Schema.Struct({ toolUseId: Schema.String, name: Schema.String })),
-        }),
-      ),
-    }),
-  ),
-  contentBlockDelta: Schema.optional(
-    Schema.Struct({
-      contentBlockIndex: Schema.Number,
-      delta: Schema.optional(
-        Schema.Struct({
-          text: Schema.optional(Schema.String),
-          toolUse: Schema.optional(Schema.Struct({ input: Schema.String })),
-          reasoningContent: Schema.optional(
-            Schema.Struct({
-              text: Schema.optional(Schema.String),
-              signature: Schema.optional(Schema.String),
-              // Blob fields in Bedrock's JSON event stream are base64 strings.
-              redactedContent: Schema.optional(Schema.String),
-              // Vercel's Bedrock provider exposes the same delta under
-              // Anthropic's shorter `data` spelling.
-              data: Schema.optional(Schema.String),
-            }),
-          ),
-        }),
-      ),
-    }),
-  ),
-  contentBlockStop: Schema.optional(Schema.Struct({ contentBlockIndex: Schema.Number })),
-  messageStop: Schema.optional(
-    Schema.Struct({
-      stopReason: Schema.String,
-      additionalModelResponseFields: Schema.optional(Schema.Unknown),
-    }),
-  ),
-  metadata: Schema.optional(
-    Schema.Struct({
-      usage: Schema.optional(BedrockUsageSchema),
-      metrics: Schema.optional(Schema.Unknown),
-    }),
-  ),
-  internalServerException: Schema.optional(BedrockStreamException),
-  modelStreamErrorException: Schema.optional(BedrockStreamException),
-  validationException: Schema.optional(BedrockStreamException),
-  throttlingException: Schema.optional(BedrockStreamException),
-  serviceUnavailableException: Schema.optional(BedrockStreamException),
-})
+const BedrockEvent = Schema.StructWithRest(
+  Schema.Struct({
+    messageStart: Schema.optional(Schema.Struct({ role: Schema.String })),
+    contentBlockStart: Schema.optional(
+      Schema.Struct({
+        contentBlockIndex: Schema.Number,
+        start: Schema.optional(
+          Schema.Struct({
+            toolUse: Schema.optional(Schema.Struct({ toolUseId: Schema.String, name: Schema.String })),
+          }),
+        ),
+      }),
+    ),
+    contentBlockDelta: Schema.optional(
+      Schema.Struct({
+        contentBlockIndex: Schema.Number,
+        delta: Schema.optional(
+          Schema.Struct({
+            text: Schema.optional(Schema.String),
+            toolUse: Schema.optional(Schema.Struct({ input: Schema.String })),
+            reasoningContent: Schema.optional(
+              Schema.Struct({
+                text: Schema.optional(Schema.String),
+                signature: Schema.optional(Schema.String),
+                // Blob fields in Bedrock's JSON event stream are base64 strings.
+                redactedContent: Schema.optional(Schema.String),
+                // Vercel's Bedrock provider exposes the same delta under
+                // Anthropic's shorter `data` spelling.
+                data: Schema.optional(Schema.String),
+              }),
+            ),
+          }),
+        ),
+      }),
+    ),
+    contentBlockStop: Schema.optional(Schema.Struct({ contentBlockIndex: Schema.Number })),
+    messageStop: Schema.optional(
+      Schema.Struct({
+        stopReason: Schema.String,
+        additionalModelResponseFields: Schema.optional(Schema.Unknown),
+      }),
+    ),
+    metadata: Schema.optional(
+      Schema.Struct({
+        usage: Schema.optional(BedrockUsageSchema),
+        metrics: Schema.optional(Schema.Unknown),
+      }),
+    ),
+    internalServerException: Schema.optional(BedrockStreamException),
+    modelStreamErrorException: Schema.optional(BedrockStreamException),
+    validationException: Schema.optional(BedrockStreamException),
+    throttlingException: Schema.optional(BedrockStreamException),
+    serviceUnavailableException: Schema.optional(BedrockStreamException),
+  }),
+  [Schema.Record(Schema.String, Schema.Unknown)],
+)
 type BedrockEvent = Schema.Schema.Type<typeof BedrockEvent>
 
 // =============================================================================
@@ -666,6 +672,7 @@ const step = (state: ParserState, event: BedrockEvent) =>
         reason: classifyProviderFailure({
           message: exception[1]?.message ?? exception[1]?.originalMessage ?? "Bedrock Converse stream error",
           code: exception[0],
+          data: Schema.decodeUnknownSync(Schema.Json)(event),
         }),
       })
     }

packages/ai/src/protocols/open-responses.ts

@@ -1012,7 +1012,12 @@ export const providerFailure = (id: string, event: Event, fallback: string) => {
   return new AIError({
     module: id,
     method: "stream",
-    reason: classifyProviderFailure({ message, code, status }),
+    reason: classifyProviderFailure({
+      message,
+      code,
+      status,
+      data: Schema.decodeUnknownSync(Schema.Json)(event),
+    }),
   })
 }
 

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

@@ -209,16 +209,22 @@ const OpenAIChatChoice = Schema.Struct({
   native_finish_reason: optionalNull(Schema.String),
 })
 
-const OpenAIChatError = Schema.Struct({
-  code: optionalNull(Schema.Union([Schema.String, Schema.Number])),
-  message: Schema.String,
-})
+const OpenAIChatError = Schema.StructWithRest(
+  Schema.Struct({
+    code: optionalNull(Schema.Union([Schema.String, Schema.Number])),
+    message: Schema.String,
+  }),
+  [Schema.Record(Schema.String, Schema.Unknown)],
+)
 
-export const OpenAIChatEvent = Schema.Struct({
-  choices: optionalNull(Schema.Array(OpenAIChatChoice)),
-  usage: optionalNull(OpenAIChatUsage),
-  error: optionalNull(OpenAIChatError),
-})
+export const OpenAIChatEvent = Schema.StructWithRest(
+  Schema.Struct({
+    choices: optionalNull(Schema.Array(OpenAIChatChoice)),
+    usage: optionalNull(OpenAIChatUsage),
+    error: optionalNull(OpenAIChatError),
+  }),
+  [Schema.Record(Schema.String, Schema.Unknown)],
+)
 export type OpenAIChatEvent = Schema.Schema.Type<typeof OpenAIChatEvent>
 type OpenAIChatRequestMessage = LLMRequest["messages"][number]
 
@@ -687,6 +693,7 @@ const step = (state: ParserState, event: OpenAIChatEvent) =>
           message: event.error.message,
           code: event.error.code === undefined || event.error.code === null ? undefined : String(event.error.code),
           status: typeof event.error.code === "number" ? event.error.code : undefined,
+          data: Schema.decodeUnknownSync(Schema.Json)(event),
         }),
       })
     const events: LLMEvent[] = []

packages/ai/src/provider-error.ts

@@ -77,6 +77,7 @@ const CONTENT_POLICY_TEXT = /content[-_\s]?policy|content_filter|safety/i
 
 export interface ProviderFailure {
   readonly message: string
+  readonly data: typeof Schema.Json.Type
   readonly status?: number | undefined
   readonly code?: string | undefined
   readonly retryAfterMs?: number | undefined
@@ -93,7 +94,12 @@ export function classifyProviderFailure(input: ProviderFailure): AIError["reason
     .filter((code): code is string => code !== undefined)
     .map((code) => code.toLowerCase())
   const text = body || input.message
-  const common = { message: input.message, providerMetadata: input.providerMetadata, http: input.http }
+  const common = {
+    message: input.message,
+    data: input.data,
+    providerMetadata: input.providerMetadata,
+    http: input.http,
+  }
   const clientScoped = input.status === undefined || (input.status >= 400 && input.status < 500)
 
   if (

packages/ai/src/route/executor.ts

@@ -173,6 +173,7 @@ const statusError =
         reason: classifyProviderFailure({
           status: response.status,
           message: providerMessage(response.status, body),
+          data: body ?? null,
           retryAfterMs: retryAfter,
           rateLimit,
           http: responseHttp({
@@ -193,6 +194,7 @@ const statusError =
 // request headers are empty.
 export const classifyHttpFailure = (input: {
   readonly message: string
+  readonly data: typeof Schema.Json.Type
   readonly url: string
   readonly status?: number | undefined
   readonly code?: string | undefined
@@ -205,6 +207,7 @@ export const classifyHttpFailure = (input: {
   const details = responseBody(input.responseBody)
   return classifyProviderFailure({
     message: input.message,
+    data: input.data,
     status: input.status,
     code: input.code,
     retryAfterMs: retryAfter,

packages/ai/src/schema/errors.ts

@@ -35,6 +35,7 @@ export class HttpContext extends Schema.Class<HttpContext>("AI.HttpContext")({
 export class InvalidRequestReason extends Schema.Class<InvalidRequestReason>("AI.Error.InvalidRequest")({
   _tag: Schema.tag("InvalidRequest"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   parameter: Schema.optional(Schema.String),
   classification: Schema.optional(ProviderFailureClassification),
   providerMetadata: Schema.optional(ProviderMetadata),
@@ -55,6 +56,7 @@ export class NoRouteReason extends Schema.Class<NoRouteReason>("AI.Error.NoRoute
 export class AuthenticationReason extends Schema.Class<AuthenticationReason>("AI.Error.Authentication")({
   _tag: Schema.tag("Authentication"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   kind: Schema.Literals(["missing", "invalid", "expired", "insufficient-permissions", "unknown"]),
   providerMetadata: Schema.optional(ProviderMetadata),
   http: Schema.optional(HttpContext),
@@ -63,6 +65,7 @@ export class AuthenticationReason extends Schema.Class<AuthenticationReason>("AI
 export class RateLimitReason extends Schema.Class<RateLimitReason>("AI.Error.RateLimit")({
   _tag: Schema.tag("RateLimit"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   retryAfterMs: Schema.optional(Schema.Number),
   rateLimit: Schema.optional(HttpRateLimitDetails),
   providerMetadata: Schema.optional(ProviderMetadata),
@@ -72,6 +75,7 @@ export class RateLimitReason extends Schema.Class<RateLimitReason>("AI.Error.Rat
 export class QuotaExceededReason extends Schema.Class<QuotaExceededReason>("AI.Error.QuotaExceeded")({
   _tag: Schema.tag("QuotaExceeded"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   providerMetadata: Schema.optional(ProviderMetadata),
   http: Schema.optional(HttpContext),
 }) {}
@@ -79,6 +83,7 @@ export class QuotaExceededReason extends Schema.Class<QuotaExceededReason>("AI.E
 export class ContentPolicyReason extends Schema.Class<ContentPolicyReason>("AI.Error.ContentPolicy")({
   _tag: Schema.tag("ContentPolicy"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   providerMetadata: Schema.optional(ProviderMetadata),
   http: Schema.optional(HttpContext),
 }) {}
@@ -86,6 +91,7 @@ export class ContentPolicyReason extends Schema.Class<ContentPolicyReason>("AI.E
 export class ProviderInternalReason extends Schema.Class<ProviderInternalReason>("AI.Error.ProviderInternal")({
   _tag: Schema.tag("ProviderInternal"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   status: Schema.optional(Schema.Number),
   retryAfterMs: Schema.optional(Schema.Number),
   providerMetadata: Schema.optional(ProviderMetadata),
@@ -129,6 +135,7 @@ export class InvalidProviderOutputReason extends Schema.Class<InvalidProviderOut
 export class UnknownProviderReason extends Schema.Class<UnknownProviderReason>("AI.Error.UnknownProvider")({
   _tag: Schema.tag("UnknownProvider"),
   message: Schema.String,
+  data: Schema.optional(Schema.Json),
   status: Schema.optional(Schema.Number),
   providerMetadata: Schema.optional(ProviderMetadata),
   http: Schema.optional(HttpContext),

packages/ai/src/schema/events.ts

@@ -216,6 +216,7 @@ export type Finish = Schema.Schema.Type<typeof Finish>
 export const ProviderErrorEvent = Schema.Struct({
   type: Schema.tag("provider-error"),
   message: Schema.String,
+  data: Schema.Json,
   classification: Schema.optional(ProviderFailureClassification),
   providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.ProviderError" })

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

@@ -1031,12 +1031,24 @@ describe("Anthropic Messages route", () => {
     Effect.gen(function* () {
       const error = yield* LLMClient.generate(request).pipe(
         Effect.provide(
-          fixedResponse(sseEvents({ type: "error", error: { type: "overloaded_error", message: "Overloaded" } })),
+          fixedResponse(
+            sseEvents({
+              type: "error",
+              error: { type: "overloaded_error", message: "Overloaded", request_id: "req_123" },
+            }),
+          ),
         ),
         Effect.flip,
       )
 
-      expect(error.reason).toMatchObject({ _tag: "ProviderInternal", message: "overloaded_error: Overloaded" })
+      expect(error.reason).toMatchObject({
+        _tag: "ProviderInternal",
+        message: "overloaded_error: Overloaded",
+        data: {
+          type: "error",
+          error: { type: "overloaded_error", message: "Overloaded", request_id: "req_123" },
+        },
+      })
     }),
   )
 

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

@@ -714,11 +714,15 @@ describe("Bedrock Converse route", () => {
     Effect.gen(function* () {
       const body = concat([
         eventFrame("messageStart", { role: "assistant" }),
-        exceptionFrame("throttlingException", { message: "Slow down" }),
+        exceptionFrame("throttlingException", { message: "Slow down", requestId: "req_123" }),
       ])
       const error = yield* LLMClient.generate(baseRequest).pipe(Effect.provide(fixedBytes(body)), Effect.flip)
 
-      expect(error.reason).toMatchObject({ _tag: "RateLimit", message: "Slow down" })
+      expect(error.reason).toMatchObject({
+        _tag: "RateLimit",
+        message: "Slow down",
+        data: { throttlingException: { message: "Slow down", requestId: "req_123" } },
+      })
     }),
   )
 

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

@@ -2592,13 +2592,25 @@ describe("OpenAI Responses route", () => {
               message: "Something went wrong",
               param: null,
               sequence_number: 1,
+              diagnostic: { region: "us-east" },
             }),
           ),
         ),
         Effect.flip,
       )
 
-      expect(error.reason).toMatchObject({ _tag: "UnknownProvider", message: "Something went wrong" })
+      expect(error.reason).toMatchObject({
+        _tag: "UnknownProvider",
+        message: "Something went wrong",
+        data: {
+          type: "error",
+          code: null,
+          message: "Something went wrong",
+          param: null,
+          sequence_number: 1,
+          diagnostic: { region: "us-east" },
+        },
+      })
     }),
   )
 

packages/ai/test/provider/openrouter.test.ts

@@ -253,14 +253,17 @@ describe("OpenRouter", () => {
         Effect.provide(
           fixedResponse(
             sseEvents({
-              error: { code: 502, message: "Provider disconnected" },
+              error: { code: 502, message: "Provider disconnected", upstream: "openai" },
             }),
           ),
         ),
         Effect.flip,
       )
 
-      expect(error.reason).toMatchObject({ _tag: "ProviderInternal" })
+      expect(error.reason).toMatchObject({
+        _tag: "ProviderInternal",
+        data: { error: { code: 502, message: "Provider disconnected", upstream: "openai" } },
+      })
       expect(error.message).toContain("Provider disconnected")
     }),
   )

packages/client/src/effect/api/api.ts

@@ -478,7 +478,12 @@ export type Endpoint5_31Output =
           readonly location?: Location.Ref | undefined
           readonly data: {
             readonly sessionID: Session.ID
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number | undefined }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number | undefined
+              readonly data?: Schema.Json | undefined
+            }
           }
         }
       | {
@@ -605,7 +610,12 @@ export type Endpoint5_31Output =
           readonly data: {
             readonly sessionID: Session.ID
             readonly assistantMessageID: SessionMessage.ID
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number | undefined }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number | undefined
+              readonly data?: Schema.Json | undefined
+            }
             readonly cost?: (number & Brand.Brand<"Money.USD">) | undefined
             readonly tokens?:
               | {
@@ -767,7 +777,12 @@ export type Endpoint5_31Output =
             readonly sessionID: Session.ID
             readonly assistantMessageID: SessionMessage.ID
             readonly id: string
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number | undefined }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number | undefined
+              readonly data?: Schema.Json | undefined
+            }
             readonly content?:
               | readonly [
                   (
@@ -807,7 +822,12 @@ export type Endpoint5_31Output =
             readonly assistantMessageID: SessionMessage.ID
             readonly attempt: number
             readonly at: number
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number | undefined }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number | undefined
+              readonly data?: Schema.Json | undefined
+            }
           }
         }
       | {
@@ -848,7 +868,12 @@ export type Endpoint5_31Output =
           readonly data: {
             readonly sessionID: Session.ID
             readonly reason: "auto" | "manual"
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number | undefined }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number | undefined
+              readonly data?: Schema.Json | undefined
+            }
             readonly inputID?: SessionMessage.ID | undefined
           }
         }

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

@@ -104,7 +104,7 @@ export type ToolTextContent = { type: "text"; text: string }
 
 export type ToolFileContent = { type: "file"; uri: string; mime: string; name?: string | null }
 
-export type SessionStructuredError = { type: string; message: string; status?: number }
+export type SessionStructuredError = { type: string; message: string; status?: number; data?: JsonValue }
 
 export type SessionMessageCompactionRunning = {
   type: "compaction"
@@ -2647,7 +2647,12 @@ export type SessionImportInput = {
                   | {
                       readonly status: "error"
                       readonly input: { readonly [x: string]: JsonValue }
-                      readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+                      readonly error: {
+                        readonly type: string
+                        readonly message: string
+                        readonly status?: number
+                        readonly data?: JsonValue
+                      }
                       readonly content?: readonly [
                         (
                           | { readonly type: "text"; readonly text: string }
@@ -2682,11 +2687,21 @@ export type SessionImportInput = {
             readonly reasoning: number
             readonly cache: { readonly read: number; readonly write: number }
           }
-          readonly error?: { readonly type: string; readonly message: string; readonly status?: number }
+          readonly error?: {
+            readonly type: string
+            readonly message: string
+            readonly status?: number
+            readonly data?: JsonValue
+          }
           readonly retry?: {
             readonly attempt: number
             readonly at: number
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number
+              readonly data?: JsonValue
+            }
           }
         }
       | (
@@ -2717,7 +2732,12 @@ export type SessionImportInput = {
               readonly time: { readonly created: number }
               readonly status: "failed"
               readonly reason: "auto" | "manual"
-              readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+              readonly error: {
+                readonly type: string
+                readonly message: string
+                readonly status?: number
+                readonly data?: JsonValue
+              }
             }
         )
     >
@@ -2914,7 +2934,12 @@ export type SessionImportInput = {
                   | {
                       readonly status: "error"
                       readonly input: { readonly [x: string]: JsonValue }
-                      readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+                      readonly error: {
+                        readonly type: string
+                        readonly message: string
+                        readonly status?: number
+                        readonly data?: JsonValue
+                      }
                       readonly content?: readonly [
                         (
                           | { readonly type: "text"; readonly text: string }
@@ -2949,11 +2974,21 @@ export type SessionImportInput = {
             readonly reasoning: number
             readonly cache: { readonly read: number; readonly write: number }
           }
-          readonly error?: { readonly type: string; readonly message: string; readonly status?: number }
+          readonly error?: {
+            readonly type: string
+            readonly message: string
+            readonly status?: number
+            readonly data?: JsonValue
+          }
           readonly retry?: {
             readonly attempt: number
             readonly at: number
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number
+              readonly data?: JsonValue
+            }
           }
         }
       | (
@@ -2984,7 +3019,12 @@ export type SessionImportInput = {
               readonly time: { readonly created: number }
               readonly status: "failed"
               readonly reason: "auto" | "manual"
-              readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+              readonly error: {
+                readonly type: string
+                readonly message: string
+                readonly status?: number
+                readonly data?: JsonValue
+              }
             }
         )
     >
@@ -3181,7 +3221,12 @@ export type SessionImportInput = {
                   | {
                       readonly status: "error"
                       readonly input: { readonly [x: string]: JsonValue }
-                      readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+                      readonly error: {
+                        readonly type: string
+                        readonly message: string
+                        readonly status?: number
+                        readonly data?: JsonValue
+                      }
                       readonly content?: readonly [
                         (
                           | { readonly type: "text"; readonly text: string }
@@ -3216,11 +3261,21 @@ export type SessionImportInput = {
             readonly reasoning: number
             readonly cache: { readonly read: number; readonly write: number }
           }
-          readonly error?: { readonly type: string; readonly message: string; readonly status?: number }
+          readonly error?: {
+            readonly type: string
+            readonly message: string
+            readonly status?: number
+            readonly data?: JsonValue
+          }
           readonly retry?: {
             readonly attempt: number
             readonly at: number
-            readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+            readonly error: {
+              readonly type: string
+              readonly message: string
+              readonly status?: number
+              readonly data?: JsonValue
+            }
           }
         }
       | (
@@ -3251,7 +3306,12 @@ export type SessionImportInput = {
               readonly time: { readonly created: number }
               readonly status: "failed"
               readonly reason: "auto" | "manual"
-              readonly error: { readonly type: string; readonly message: string; readonly status?: number }
+              readonly error: {
+                readonly type: string
+                readonly message: string
+                readonly status?: number
+                readonly data?: JsonValue
+              }
             }
         )
     >

packages/core/src/aisdk.ts

@@ -780,7 +780,10 @@ function llmError(method: string, error: unknown) {
       ? new InvalidProviderOutputReason({ message: error.message })
       : APICallError.isInstance(error)
         ? apiCallErrorReason(error)
-        : new UnknownProviderReason({ message: unknownErrorMessage(error) })
+        : new UnknownProviderReason({
+            message: unknownErrorMessage(error),
+            data: Schema.decodeUnknownSync(Schema.Json)(jsonValue(error)),
+          })
   return new AIError({
     module: "AISDK",
     method,
@@ -792,6 +795,7 @@ function apiCallErrorReason(error: APICallError) {
   const details = providerErrorDetails(error)
   const reason = RequestExecutor.classifyHttpFailure({
     message: details.message,
+    data: Schema.decodeUnknownSync(Schema.Json)(jsonValue(error.data ?? error.responseBody ?? null)),
     url: error.url,
     status: error.statusCode,
     code: details.code,

packages/core/src/session/runner/publish-llm-event.ts

@@ -528,7 +528,7 @@ export const createLLMEventPublisher = (bus: Pick<Bus.Interface, "publish">, inp
         return
       case "provider-error":
         providerFailed = true
-        yield* failAssistant({ type: "provider.unknown", message: event.message })
+        yield* failAssistant({ type: "provider.unknown", message: event.message, data: event.data })
         return
     }
   })

packages/core/src/session/to-session-error.ts

@@ -61,5 +61,11 @@ export function toSessionError(cause: unknown): SessionError.Error {
 function providerError(type: string, reason: AIError["reason"]): SessionError.Error {
   const status =
     ("http" in reason ? reason.http?.response?.status : undefined) ?? ("status" in reason ? reason.status : undefined)
-  return { type, message: reason.message, ...(status === undefined ? {} : { status }) }
+  const data = "data" in reason ? reason.data : reason._tag === "InvalidProviderOutput" ? reason.raw : undefined
+  return {
+    type,
+    message: reason.message,
+    ...(status === undefined ? {} : { status }),
+    ...(data === undefined ? {} : { data }),
+  }
 }

packages/core/test/aisdk.test.ts

@@ -487,6 +487,7 @@ it.effect("derives status and code when the AI SDK error message is empty", () =
     expect(projected.type).toBe("provider.invalid-request")
     expect(projected.status).toBe(404)
     expect(projected.message).not.toBe("")
+    expect(projected.data).toEqual({ error: { message: "", code: "not_found" } })
   }),
 )
 
@@ -504,6 +505,7 @@ it.effect("preserves complete HTTP context on AI SDK call errors", () =>
     expect(http?.response?.status).toBe(404)
     expect(http?.response?.headers["authorization"]).toBe("Bearer secret-token")
     expect(http?.body).toBe('{"error":{"message":"","code":"not_found"}}')
+    expect(error.reason).toMatchObject({ data: '{"error":{"message":"","code":"not_found"}}' })
   }),
 )
 

packages/core/test/session-error.test.ts

@@ -61,6 +61,24 @@ describe("toSessionError", () => {
       ).type,
     ).toBe("provider.no-route")
     expect(toSessionError(llm(new UnknownProviderReason({ message: "unknown" }))).type).toBe("provider.unknown")
+    expect(toSessionError(llm(new InvalidProviderOutputReason({ message: "malformed", raw: "not-json" })))).toEqual({
+      type: "provider.invalid-output",
+      message: "malformed",
+      data: "not-json",
+    })
+  })
+
+  test("preserves provider error data", () => {
+    const data = {
+      type: "error",
+      sequence_number: 2,
+      error: { type: "server_error", code: null, message: null },
+    }
+    expect(toSessionError(llm(new UnknownProviderReason({ message: "stream error", data })))).toEqual({
+      type: "provider.unknown",
+      message: "stream error",
+      data,
+    })
   })
 
   test("preserves the permission rejection type without exposing internal fields", () => {

packages/core/test/session-runner.test.ts

@@ -925,7 +925,7 @@ describe("SessionRunnerLLM", () => {
       yield* admit(session, "Second prompt")
       const titleFailed = yield* Deferred.make<void>()
       yield* TestLLM.push(
-        Stream.make(LLMEvent.providerError({ message: "Title provider unavailable" })).pipe(
+        Stream.make(LLMEvent.providerError({ message: "Title provider unavailable", data: {} })).pipe(
           Stream.ensuring(Deferred.succeed(titleFailed, undefined)),
         ),
         TestLLM.text("Recovered", "text-recovered"),
@@ -2179,7 +2179,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push(TestLLM.text("Earlier answer", "text-manual-provider-history"))
       yield* runPrompt(session, "Earlier question")
 
-      yield* TestLLM.push([LLMEvent.providerError({ message: "summary unavailable" })])
+      yield* TestLLM.push([LLMEvent.providerError({ message: "summary unavailable", data: {} })])
       const compaction = yield* session.compact({ sessionID })
       yield* session.resume(sessionID)
 
@@ -2337,7 +2337,7 @@ describe("SessionRunnerLLM", () => {
       currentModel = compactModel
       requests.length = 0
       yield* TestLLM.push(
-        [LLMEvent.providerError({ message: "Unsupported parameter: max_output_tokens" })],
+        [LLMEvent.providerError({ message: "Unsupported parameter: max_output_tokens", data: {} })],
         TestLLM.text("Must not run", "text-after-failed-compaction"),
       )
       yield* admit(session, "Recent exact request ".repeat(180))
@@ -2362,7 +2362,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push(
         [
           LLMEvent.stepStart({ index: 0 }),
-          LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" }),
+          LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" }),
         ],
         TestLLM.text("## Objective\n- Recover overflow", "text-summary"),
         TestLLM.text("Recovered", "text-final"),
@@ -2389,7 +2389,7 @@ describe("SessionRunnerLLM", () => {
       const session = yield* setupOverflowRecovery
       currentModel = model
       yield* TestLLM.push(
-        [LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" })],
+        [LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" })],
         TestLLM.text("## Objective\n- Recover unknown limit", "text-summary-unknown-limit"),
         TestLLM.text("Recovered", "text-final-unknown-limit"),
       )
@@ -2408,7 +2408,7 @@ describe("SessionRunnerLLM", () => {
       const session = yield* setupOverflowRecovery
       currentModel = undersizedContextModel
       yield* TestLLM.push(
-        [LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" })],
+        [LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" })],
         TestLLM.text("## Objective\n- Recover undersized limit", "text-summary-undersized-limit"),
         TestLLM.text("Recovered", "text-final-undersized-limit"),
       )
@@ -2427,7 +2427,7 @@ describe("SessionRunnerLLM", () => {
       const session = yield* setupOverflowRecovery
       const overflow = () => [
         LLMEvent.stepStart({ index: 0 }),
-        LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" }),
+        LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" }),
       ]
       yield* TestLLM.push(overflow(), TestLLM.text("## Objective\n- Recover once", "text-summary"), overflow())
       yield* admit(session, "Continue")
@@ -2474,8 +2474,8 @@ describe("SessionRunnerLLM", () => {
     Effect.gen(function* () {
       const session = yield* setupOverflowRecovery
       yield* TestLLM.push(
-        [LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" })],
-        [LLMEvent.providerError({ message: "summary unavailable" })],
+        [LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" })],
+        [LLMEvent.providerError({ message: "summary unavailable", data: {} })],
       )
       yield* admit(session, "Continue")
       expect((yield* session.resume(sessionID).pipe(Effect.flip)).message).toBe("prompt too long")
@@ -2502,7 +2502,7 @@ describe("SessionRunnerLLM", () => {
     Effect.gen(function* () {
       const session = yield* setupOverflowRecovery
       yield* TestLLM.push(
-        [LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" })],
+        [LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" })],
         TestLLM.text("## Objective\n- Interrupted", "text-summary"),
       )
       const first = yield* TestLLM.gate
@@ -4078,9 +4078,10 @@ describe("SessionRunnerLLM", () => {
   it.effect("projects provider errors as terminal assistant step failures", () =>
     Effect.gen(function* () {
       const session = yield* setup
+      const data = { type: "error", error: { type: "server_error" } }
       yield* TestLLM.push([
         LLMEvent.stepStart({ index: 0 }),
-        LLMEvent.providerError({ message: "Provider unavailable" }),
+        LLMEvent.providerError({ message: "Provider unavailable", data }),
       ])
 
       expect((yield* runPrompt(session, "Fail durably").pipe(Effect.flip)).message).toBe("Provider unavailable")
@@ -4088,7 +4089,11 @@ describe("SessionRunnerLLM", () => {
       expect(requests).toHaveLength(1)
       expect(yield* session.context(sessionID)).toMatchObject([
         { type: "user", text: "Fail durably" },
-        { type: "assistant", finish: "error", error: { type: "provider.unknown", message: "Provider unavailable" } },
+        {
+          type: "assistant",
+          finish: "error",
+          error: { type: "provider.unknown", message: "Provider unavailable", data },
+        },
       ])
     }),
   )
@@ -4096,7 +4101,7 @@ describe("SessionRunnerLLM", () => {
   it.effect("projects provider errors emitted before assistant step start", () =>
     Effect.gen(function* () {
       const session = yield* setup
-      yield* TestLLM.push([LLMEvent.providerError({ message: "Provider unavailable" })])
+      yield* TestLLM.push([LLMEvent.providerError({ message: "Provider unavailable", data: {} })])
 
       expect((yield* runPrompt(session, "Fail before step").pipe(Effect.flip)).message).toBe("Provider unavailable")
 
@@ -4183,7 +4188,7 @@ describe("SessionRunnerLLM", () => {
         LLMEvent.textStart({ id: "text-partial" }),
         LLMEvent.textDelta({ id: "text-partial", text: "Partial" }),
         LLMEvent.textEnd({ id: "text-partial" }),
-        LLMEvent.providerError({ message: "prompt too long", classification: "context-overflow" }),
+        LLMEvent.providerError({ message: "prompt too long", data: {}, classification: "context-overflow" }),
       ])
       expect((yield* runPrompt(session, "Fail after output").pipe(Effect.flip)).message).toBe("prompt too long")
 
@@ -4958,7 +4963,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push([
         LLMEvent.stepStart({ index: 0 }),
         LLMEvent.toolCall({ id: "call-before-provider-error", name: "echo", input: { text: "settled" } }),
-        LLMEvent.providerError({ message: "Provider unavailable" }),
+        LLMEvent.providerError({ message: "Provider unavailable", data: {} }),
       ])
 
       const run = yield* session.resume(sessionID).pipe(Effect.forkChild)
@@ -4985,7 +4990,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push([
         LLMEvent.stepStart({ index: 0 }),
         hostedCall("call-hosted-provider-error", "effect"),
-        LLMEvent.providerError({ message: "Provider unavailable" }),
+        LLMEvent.providerError({ message: "Provider unavailable", data: {} }),
       ])
 
       expect((yield* runPrompt(session, "Fail hosted tool durably").pipe(Effect.flip)).message).toBe(
@@ -5017,7 +5022,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push([
         LLMEvent.stepStart({ index: 0 }),
         LLMEvent.toolCall({ id: "call-defect-provider-error", name: "defect", input: {} }),
-        LLMEvent.providerError({ message: "Provider unavailable" }),
+        LLMEvent.providerError({ message: "Provider unavailable", data: {} }),
       ])
 
       expect((yield* runPrompt(session, "Defect while provider fails").pipe(Effect.flip)).message).toBe(
@@ -5044,7 +5049,7 @@ describe("SessionRunnerLLM", () => {
       yield* TestLLM.push([
         LLMEvent.stepStart({ index: 0 }),
         LLMEvent.toolCall({ id: "call-store-provider-error", name: "storefail", input: {} }),
-        LLMEvent.providerError({ message: "Provider unavailable" }),
+        LLMEvent.providerError({ message: "Provider unavailable", data: {} }),
       ])
 
       expect(yield* session.resume(sessionID).pipe(Effect.exit)).toMatchObject({

packages/core/test/session-title.test.ts

@@ -310,7 +310,7 @@ it.effect("retries after a failed title request", () =>
     yield* insertSession(sessionID)
     yield* prompt(sessionID, "Retry this title")
     const title = yield* SessionTitle.Service
-    titleStream = () => Stream.make(LLMEvent.providerError({ message: "Provider unavailable" }))
+    titleStream = () => Stream.make(LLMEvent.providerError({ message: "Provider unavailable", data: {} }))
 
     yield* title.generateForFirstPrompt(sessionID)
     titleStream = successfulTitle

packages/schema/src/session-error.ts

@@ -8,4 +8,5 @@ export const Error = Schema.Struct({
   type: Schema.String,
   message: Schema.String,
   status: Schema.Int.check(Schema.isBetween({ minimum: 100, maximum: 599 })).pipe(optional),
+  data: Schema.Json.pipe(optional),
 }).annotate({ identifier: "Session.StructuredError" })

packages/schema/test/session-error.test.ts

@@ -12,6 +12,11 @@ describe("SessionError", () => {
     const values: SessionError.Error[] = [
       { type: "provider.rate-limit", message: "Slow down" },
       { type: "provider.auth", message: "Authentication failed" },
+      {
+        type: "provider.unknown",
+        message: "Stream error",
+        data: { type: "error", error: { type: "server_error" } },
+      },
       { type: "provider.future-condition", message: "A future provider failure" },
       { type: "unknown", message: "Unexpected" },
     ]