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feat(opencode): add LLM provider fallback chain #26292

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3 changes: 3 additions & 0 deletions packages/core/src/session-message.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,9 @@ export class AssistantTool extends Schema.Class<AssistantTool>("Session.Message.
export class AssistantText extends Schema.Class<AssistantText>("Session.Message.Assistant.Text")({
type: Schema.Literal("text"),
text: Schema.String,
ignored: Schema.optional(Schema.Boolean),
synthetic: Schema.optional(Schema.Boolean),
fallbackNotice: Schema.optional(Schema.Union([Schema.Literal("using"), Schema.Literal("switch"), Schema.Literal("resume")])),
}) {}

export class AssistantReasoning extends Schema.Class<AssistantReasoning>("Session.Message.Assistant.Reasoning")({
Expand Down
101 changes: 9 additions & 92 deletions packages/llm/src/protocols/anthropic-messages.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -10,11 +10,9 @@ import {
type CacheHint,
type FinishReason,
type LLMRequest,
type MediaPart,
type ProviderMetadata,
type ToolCallPart,
type ToolDefinition,
type ToolResultContentPart,
type ToolResultPart,
} from "../schema"
import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared"
Expand All @@ -41,17 +39,6 @@ const AnthropicTextBlock = Schema.Struct({
})
type AnthropicTextBlock = Schema.Schema.Type<typeof AnthropicTextBlock>

const AnthropicImageBlock = Schema.Struct({
type: Schema.tag("image"),
source: Schema.Struct({
type: Schema.tag("base64"),
media_type: Schema.String,
data: Schema.String,
}),
cache_control: Schema.optional(AnthropicCacheControl),
})
type AnthropicImageBlock = Schema.Schema.Type<typeof AnthropicImageBlock>

const AnthropicThinkingBlock = Schema.Struct({
type: Schema.tag("thinking"),
thinking: Schema.String,
Expand Down Expand Up @@ -97,24 +84,15 @@ const AnthropicServerToolResultBlock = Schema.Struct({
})
type AnthropicServerToolResultBlock = Schema.Schema.Type<typeof AnthropicServerToolResultBlock>

// Anthropic accepts either a plain string or an ordered array of text/image
// blocks inside `tool_result.content`. The array form is required when a tool
// returns image bytes (screenshot, image search, etc.) so they can be passed
// to the model as proper image inputs instead of being JSON-stringified into
// the prompt — which silently inflates context by megabytes and can push the
// conversation over the model's token limit.
const AnthropicToolResultContent = Schema.Union([AnthropicTextBlock, AnthropicImageBlock])

const AnthropicToolResultBlock = Schema.Struct({
type: Schema.tag("tool_result"),
tool_use_id: Schema.String,
content: Schema.Union([Schema.String, Schema.Array(AnthropicToolResultContent)]),
content: Schema.String,
is_error: Schema.optional(Schema.Boolean),
cache_control: Schema.optional(AnthropicCacheControl),
})

const AnthropicUserBlock = Schema.Union([AnthropicTextBlock, AnthropicImageBlock, AnthropicToolResultBlock])
type AnthropicUserBlock = Schema.Schema.Type<typeof AnthropicUserBlock>
const AnthropicUserBlock = Schema.Union([AnthropicTextBlock, AnthropicToolResultBlock])
const AnthropicAssistantBlock = Schema.Union([
AnthropicTextBlock,
AnthropicThinkingBlock,
Expand Down Expand Up @@ -206,13 +184,7 @@ const AnthropicEvent = Schema.Struct({
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) }),
),
error: Schema.optional(Schema.Struct({ type: Schema.String, message: Schema.String })),
})
type AnthropicEvent = Schema.Schema.Type<typeof AnthropicEvent>

Expand Down Expand Up @@ -300,46 +272,6 @@ const lowerServerToolResult = Effect.fn("AnthropicMessages.lowerServerToolResult
return { type: wireType, tool_use_id: part.id, content: part.result.value } satisfies AnthropicServerToolResultBlock
})

const lowerImage = Effect.fn("AnthropicMessages.lowerImage")(function* (part: MediaPart) {
if (!part.mediaType.startsWith("image/"))
return yield* invalid(`Anthropic Messages user media content only supports images`)
return {
type: "image" as const,
source: {
type: "base64" as const,
media_type: part.mediaType,
data: ProviderShared.mediaBase64(part),
},
} satisfies AnthropicImageBlock
})

// Tool results may carry structured text/images. Keep media as provider-native
// content instead of JSON-stringifying base64 into a prompt string.
const lowerToolResultContentItem = Effect.fn("AnthropicMessages.lowerToolResultContentItem")(function* (
item: ToolResultContentPart,
) {
if (item.type === "text") return { type: "text" as const, text: item.text } satisfies AnthropicTextBlock
if (item.mediaType.startsWith("image/"))
return {
type: "image" as const,
source: {
type: "base64" as const,
media_type: item.mediaType,
data: ProviderShared.mediaBase64(item),
},
} satisfies AnthropicImageBlock
return yield* invalid(`Anthropic Messages tool-result media content only supports images, got ${item.mediaType}`)
})

const lowerToolResultContent = Effect.fn("AnthropicMessages.lowerToolResultContent")(function* (part: ToolResultPart) {
// Text / json / error results stay as a string for backward compatibility
// with existing cassettes and provider expectations.
if (part.result.type !== "content") return ProviderShared.toolResultText(part)
// Preserve the narrowed array element type when compiled through a consumer package.
const content: ReadonlyArray<ToolResultContentPart> = part.result.value
return yield* Effect.forEach(content, lowerToolResultContentItem)
})

const lowerMessages = Effect.fn("AnthropicMessages.lowerMessages")(function* (
request: LLMRequest,
breakpoints: Cache.Breakpoints,
Expand All @@ -348,17 +280,11 @@ const lowerMessages = Effect.fn("AnthropicMessages.lowerMessages")(function* (

for (const message of request.messages) {
if (message.role === "user") {
const content: AnthropicUserBlock[] = []
const content: AnthropicTextBlock[] = []
for (const part of message.content) {
if (part.type === "text") {
content.push({ type: "text", text: part.text, cache_control: cacheControl(breakpoints, part.cache) })
continue
}
if (part.type === "media") {
content.push(yield* lowerImage(part))
continue
}
return yield* ProviderShared.unsupportedContent("Anthropic Messages", "user", ["text", "media"])
if (!ProviderShared.supportsContent(part, ["text"]))
return yield* ProviderShared.unsupportedContent("Anthropic Messages", "user", ["text"])
content.push({ type: "text", text: part.text, cache_control: cacheControl(breakpoints, part.cache) })
}
messages.push({ role: "user", content })
continue
Expand Down Expand Up @@ -402,7 +328,7 @@ const lowerMessages = Effect.fn("AnthropicMessages.lowerMessages")(function* (
content.push({
type: "tool_result",
tool_use_id: part.id,
content: yield* lowerToolResultContent(part),
content: ProviderShared.toolResultText(part),
is_error: part.result.type === "error" ? true : undefined,
cache_control: cacheControl(breakpoints, part.cache),
})
Expand Down Expand Up @@ -709,18 +635,9 @@ const onMessageDelta = (state: ParserState, event: AnthropicEvent): StepResult =
return [{ ...state, lifecycle, usage }, events]
}

// Prefix `error.type` so overloads, rate limits, and quota errors are visible
// even when the provider message is generic or empty.
const providerErrorMessage = (event: AnthropicEvent): string => {
const type = event.error?.type
const message = event.error?.message
if (type && message) return `${type}: ${message}`
return message || type || "Anthropic Messages stream error"
}

const onError = (state: ParserState, event: AnthropicEvent): StepResult => [
state,
[LLMEvent.providerError({ message: providerErrorMessage(event) })],
[LLMEvent.providerError({ message: event.error?.message ?? "Anthropic Messages stream error" })],
]

const step = (state: ParserState, event: AnthropicEvent) => {
Expand Down
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