refactor(llm): replace LLMError reasons with flat tagged union

packages/ai/AGENTS.md

@@ -184,8 +184,8 @@ The dependency arrow points down: `providers/*.ts` files import protocol routes
 - `joinText(parts)` — joins an array of `TextPart` (or anything with a `.text`) with newlines. Use this anywhere a protocol flattens text content into a single string for a provider field.
 - `parseToolInput(route, name, raw)` — Schema-decodes a tool-call argument string with the canonical "Invalid JSON input for `<route>` tool call `<name>`" error message. Treats empty input as `{}`.
 - `parseJson(route, raw, message)` — generic JSON-via-Schema decode for non-tool bodies.
-- `eventError(route, message, ...)` — typed `InvalidProviderOutput` constructor for stream-time decode failures.
-- `validateWith(decoder)` — maps Schema decode errors to `InvalidRequest`. `Route.make(...)` uses this for body validation; lower-level routes can reuse it.
+- `eventError(route, message, ...)` — typed `MalformedResponse` constructor for stream-time decode failures.
+- `validateWith(decoder)` — maps Schema decode errors to `BadRequest`. `Route.make(...)` uses this for body validation; lower-level routes can reuse it.
 - `matchToolChoice(provider, choice, branches)` — branches over `LLMRequest["toolChoice"]` for provider-specific lowering.
 
 If you find yourself copying a 3-to-5-line snippet between two protocols, lift it into `ProviderShared` next to these helpers rather than duplicating.

packages/ai/src/index.ts

@@ -2,7 +2,13 @@ export { LLMClient } from "./route/client"
 export { Auth } from "./route/auth"
 export { Provider } from "./provider"
 export { ProviderPackage } from "./provider-package"
-export { isContextOverflow, isContextOverflowFailure } from "./provider-error"
+export {
+  classifyApiFailure,
+  extractApiFailureCode,
+  isContextOverflow,
+  isContextOverflowFailure,
+  type ApiFailure,
+} from "./provider-error"
 export type {
   RouteModelInput,
   RouteRoutedModelInput,

packages/ai/src/llm.ts

@@ -3,8 +3,8 @@ import { LLMClient } from "./route/client"
 import {
   GenerationOptions,
   HttpOptions,
-  InvalidProviderOutputReason,
-  LLMError,
+  MalformedResponse,
+  type LLMError,
   LLMEvent,
   LLMRequest,
   LLMResponse,
@@ -121,22 +121,14 @@ const runGenerateObject = Effect.fn("LLM.generateObject")(function* (
     (event) => LLMEvent.is.toolCall(event) && event.name === GENERATE_OBJECT_TOOL_NAME,
   )
   if (!call || !LLMEvent.is.toolCall(call))
-    return yield* new LLMError({
-      module: "LLM",
-      method: "generateObject",
-      reason: new InvalidProviderOutputReason({
-        message: `generateObject: model did not call the forced \`${GENERATE_OBJECT_TOOL_NAME}\` tool`,
-      }),
+    return yield* new MalformedResponse({
+      message: `generateObject: model did not call the forced \`${GENERATE_OBJECT_TOOL_NAME}\` tool`,
     })
   const object = yield* tool._decode(call.input).pipe(
     Effect.mapError(
       (error) =>
-        new LLMError({
-          module: "LLM",
-          method: "generateObject",
-          reason: new InvalidProviderOutputReason({
-            message: `generateObject: tool input failed schema decode: ${error.message}`,
-          }),
+        new MalformedResponse({
+          message: `generateObject: tool input failed schema decode: ${error.message}`,
         }),
     ),
   )

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

@@ -5,7 +5,6 @@ import { Endpoint } from "../route/endpoint"
 import { Framing } from "../route/framing"
 import { Protocol } from "../route/protocol"
 import {
-  LLMError,
   LLMEvent,
   Usage,
   type CacheHint,
@@ -20,7 +19,7 @@ import {
   type ToolResultPart,
 } from "../schema"
 import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared"
-import { classifyProviderFailure } from "../provider-error"
+import { classifyApiFailure } from "../provider-error"
 import * as Cache from "./utils/cache"
 import { Lifecycle } from "./utils/lifecycle"
 import { ToolSchemaProjection } from "./utils/tool-schema"
@@ -834,11 +833,7 @@ const providerErrorMessage = (event: AnthropicEvent): string => {
 }
 
 const onError = (event: AnthropicEvent) =>
-  new LLMError({
-    module: ADAPTER,
-    method: "stream",
-    reason: classifyProviderFailure({ message: providerErrorMessage(event), code: event.error?.type }),
-  })
+  classifyApiFailure({ message: providerErrorMessage(event), code: event.error?.type })
 
 const step = (state: ParserState, event: AnthropicEvent) => {
   if (event.type === "message_start") return Effect.succeed(onMessageStart(state, event))

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

@@ -3,7 +3,6 @@ import { Route } from "../route/client"
 import { Endpoint } from "../route/endpoint"
 import { Protocol } from "../route/protocol"
 import {
-  LLMError,
   LLMEvent,
   Usage,
   type CacheHint,
@@ -18,7 +17,7 @@ import {
   type ToolResultPart,
 } from "../schema"
 import { BedrockEventStream } from "./bedrock-event-stream"
-import { classifyProviderFailure } from "../provider-error"
+import { classifyApiFailure } from "../provider-error"
 import { JsonObject, optionalArray, ProviderShared } from "./shared"
 import { BedrockAuth } from "./utils/bedrock-auth"
 import { BedrockCache } from "./utils/bedrock-cache"
@@ -597,13 +596,9 @@ const step = (state: ParserState, event: BedrockEvent) =>
       ] as const
     ).find((entry) => entry[1] !== undefined)
     if (exception) {
-      return yield* new LLMError({
-        module: ADAPTER,
-        method: "stream",
-        reason: classifyProviderFailure({
-          message: exception[1]?.message ?? "Bedrock Converse stream error",
-          code: exception[0],
-        }),
+      return yield* classifyApiFailure({
+        message: exception[1]?.message ?? "Bedrock Converse stream error",
+        code: exception[0],
       })
     }
 

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

@@ -5,7 +5,6 @@ import { Endpoint } from "../route/endpoint"
 import { HttpTransport, WebSocketTransport } from "../route/transport"
 import { Protocol } from "../route/protocol"
 import {
-  LLMError,
   LLMEvent,
   Usage,
   type FinishReason,
@@ -20,7 +19,7 @@ import {
   type ToolResultPart,
 } from "../schema"
 import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared"
-import { classifyProviderFailure } from "../provider-error"
+import { classifyApiFailure } from "../provider-error"
 import { OpenAIOptions } from "./utils/openai-options"
 import { Lifecycle } from "./utils/lifecycle"
 import { ToolSchemaProjection } from "./utils/tool-schema"
@@ -910,11 +909,7 @@ const providerErrorMessage = (event: OpenAIResponsesEvent, fallback: string): st
 const providerError = (event: OpenAIResponsesEvent, fallback: string) => {
   const code = event.code || event.error?.code || event.response?.error?.code || undefined
   const message = providerErrorMessage(event, fallback)
-  return new LLMError({
-    module: ADAPTER,
-    method: "stream",
-    reason: classifyProviderFailure({ message, code }),
-  })
+  return classifyApiFailure({ message, code })
 }
 
 const step = (state: ParserState, event: OpenAIResponsesEvent) => {

packages/ai/src/protocols/shared.ts

@@ -3,9 +3,9 @@ import { Effect, Schema, Stream } from "effect"
 import * as Sse from "effect/unstable/encoding/Sse"
 import { Headers, HttpClientRequest } from "effect/unstable/http"
 import {
-  InvalidProviderOutputReason,
-  InvalidRequestReason,
-  LLMError,
+  BadRequest,
+  MalformedResponse,
+  type LLMError,
   type ContentPart,
   type LLMRequest,
   type MediaPart,
@@ -88,11 +88,7 @@ export const sumTokens = (...values: ReadonlyArray<number | undefined>): number
 }
 
 export const eventError = (route: string, message: string, raw?: string) =>
-  new LLMError({
-    module: "ProviderShared",
-    method: "stream",
-    reason: new InvalidProviderOutputReason({ route, message, raw }),
-  })
+  new MalformedResponse({ route, message, raw })
 
 export const parseJson = (route: string, input: string, message: string) =>
   Effect.try({
@@ -252,15 +248,9 @@ export const sseFraming = (bytes: Stream.Stream<Uint8Array, LLMError>): Stream.S
  * Canonical invalid-request constructor. Lift one-line `const invalid =
  * (message) => invalidRequest(message)` aliases out of every
  * route so the error constructor lives in one place. If we ever extend
- * `InvalidRequestReason` with route context or trace metadata, the change
- * lands here.
+ * `BadRequest` with route context or trace metadata, the change lands here.
  */
-export const invalidRequest = (message: string) =>
-  new LLMError({
-    module: "ProviderShared",
-    method: "request",
-    reason: new InvalidRequestReason({ message }),
-  })
+export const invalidRequest = (message: string) => new BadRequest({ message })
 
 export const matchToolChoice = <Auto, None, Required, Tool>(
   route: string,

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

@@ -1,5 +1,5 @@
 import { Effect } from "effect"
-import { LLMError, LLMEvent, type ProviderMetadata, type ToolCall } from "../../schema"
+import { isLLMError, LLMEvent, type LLMError, type ProviderMetadata, type ToolCall } from "../../schema"
 import { eventError, parseToolInput, type ToolAccumulator } from "../shared"
 
 type StreamKey = string | number
@@ -95,7 +95,7 @@ const appendTool = <K extends StreamKey>(
 }
 
 export const isError = <K extends StreamKey>(result: AppendOutcome<K> | LLMError): result is LLMError =>
-  result instanceof LLMError
+  isLLMError(result)
 
 /**
  * Register a tool call whose start event arrived before any argument deltas.