fix(ai): never fail decoding on Responses error frames

Co-authored-by: rekram1-node <rekram1-node@users.noreply.github.com>

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

@@ -73,11 +73,6 @@ const driver = (options: Options, body: string): WebSocketChannelDriver => {
           )
         if (event.type === "error") {
           terminal = true
-          yield* OpenResponses.decodeKnownErrorEvent(event).pipe(
-            Effect.mapError((cause) =>
-              ProviderShared.eventError(options.id, `${options.name} returned a malformed error event`, frame, cause),
-            ),
-          )
           return {
             type: "provider-failure",
             error: OpenResponses.providerFailure(event, `${options.name} stream error`, frame),

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

@@ -108,7 +108,7 @@ const incremental = (
   return input.slice(baseline.length)
 }
 
-const code = (event: OpenResponses.Event) => event.code || event.error?.code || event.response?.error?.code || undefined
+const code = (event: OpenResponses.Event) => OpenResponses.errorDetail(event).code
 
 const rejected = (
   observation: Extract<ChannelObservation, { readonly type: "provider-failure" }>,

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

@@ -1,4 +1,4 @@
-import { Effect, Option, Schema, SchemaGetter } from "effect"
+import { Effect, Option, Schema } from "effect"
 import type { Content } from "@opencode/schema/tool"
 import { HttpTransport } from "../route/transport/index.js"
 import { Protocol } from "../route/protocol.js"
@@ -333,53 +333,13 @@ export const StreamItem = Schema.StructWithRest(
 export type StreamItem = Schema.Schema.Type<typeof StreamItem>
 export type OutputItem = StreamItem & { readonly id: string }
 
-// Responses-compatible providers put streaming error details at the top level or
-// under `error`, and response failures under `response.error`. Accept all three shapes.
+// Responses-compatible providers put error details at the top level, under `error`, or under
+// `response.error`, and gateways reshape them freely: strings, numeric codes, extra fields. Those
+// fields decode as opaque values and `errorDetail` reads them defensively, so an error frame can
+// only fail on invalid JSON and otherwise always classifies with the raw body as the fallback.
 // https://www.openresponses.org/specification
-const OpenResponsesErrorObject = Schema.Struct({
-  type: optionalNull(Schema.String),
-  code: optionalNull(Schema.String),
-  message: optionalNull(Schema.String),
-  param: optionalNull(Schema.String),
-})
-const OpenResponsesErrorPayload = Schema.Union([Schema.String, OpenResponsesErrorObject]).pipe(
-  Schema.decodeTo(OpenResponsesErrorObject, {
-    decode: SchemaGetter.transform((error) => (typeof error === "string" ? { message: error } : error)),
-    encode: SchemaGetter.passthrough(),
-  }),
-)
-type OpenResponsesErrorPayload = Schema.Schema.Type<typeof OpenResponsesErrorPayload>
-
-const WebSocketErrorHeader = Schema.Union([Schema.String, Schema.Number, Schema.Boolean])
-export const WebSocketErrorEvent = Schema.StructWithRest(
-  Schema.Struct({
-    type: Schema.tag("error"),
-    status: Schema.optional(Schema.Number),
-    status_code: Schema.optional(Schema.Number),
-    code: optionalNull(Schema.String),
-    message: Schema.optional(Schema.String),
-    param: optionalNull(Schema.String),
-    error: optionalNull(OpenResponsesErrorPayload),
-    headers: Schema.optional(Schema.Record(Schema.String, WebSocketErrorHeader)),
-  }),
-  [Schema.Record(Schema.String, Schema.Unknown)],
-)
-const decodeWebSocketErrorEvent = Schema.decodeUnknownEffect(WebSocketErrorEvent)
-
-export const decodeKnownErrorEvent = (event: Event) =>
-  decodeWebSocketErrorEvent({
-    ...event,
-    status: typeof event.status === "number" ? event.status : undefined,
-    status_code: typeof event.status_code === "number" ? event.status_code : undefined,
-    headers: ProviderShared.isRecord(event.headers)
-      ? Object.fromEntries(
-          Object.entries(event.headers).filter(
-            (entry): entry is [string, string | number | boolean] =>
-              typeof entry[1] === "string" || typeof entry[1] === "number" || typeof entry[1] === "boolean",
-          ),
-        )
-      : undefined,
-  })
+const asText = (value: unknown) =>
+  typeof value === "string" && value.length > 0 ? value : typeof value === "number" ? String(value) : undefined
 
 export const Event = Schema.StructWithRest(
   Schema.Struct({
@@ -400,31 +360,18 @@ export const Event = Schema.StructWithRest(
           incomplete_details: optionalNull(Schema.Struct({ reason: Schema.optional(Schema.String) })),
           output: Schema.optional(Schema.Array(StreamItem)),
           usage: optionalNull(OpenResponsesUsage),
-          error: optionalNull(OpenResponsesErrorPayload),
+          error: Schema.optional(Schema.Unknown),
         }),
         [Schema.Record(Schema.String, Schema.Unknown)],
       ),
     ),
-    code: optionalNull(Schema.String),
-    message: Schema.optional(Schema.String),
-    param: optionalNull(Schema.String),
-    error: optionalNull(OpenResponsesErrorPayload),
+    code: Schema.optional(Schema.Unknown),
+    message: Schema.optional(Schema.Unknown),
+    error: Schema.optional(Schema.Unknown),
     status: Schema.optional(Schema.Unknown),
     status_code: Schema.optional(Schema.Unknown),
-    headers: Schema.optional(Schema.Unknown),
   }),
   [Schema.Record(Schema.String, Schema.Unknown)],
-).pipe(
-  Schema.decode({
-    decode: SchemaGetter.transform((event) => {
-      if (event.type !== "error" || event.error != null) return event
-      const { code, message, param, ...rest } = event
-      if (code === undefined && message === undefined && param === undefined) return event
-      // Flat errors (for example, Meta's) can also arrive through generic Responses endpoints.
-      return { ...rest, error: { code, message, param } }
-    }),
-    encode: SchemaGetter.passthrough(),
-  }),
 )
 export type Event = Schema.Schema.Type<typeof Event>
 export type NormalizedEvent = Event & { readonly item?: OutputItem | null }
@@ -433,16 +380,15 @@ const decodeEventValue = Schema.decodeUnknownEffect(Event)
 const decodeFrame = Schema.decodeUnknownEffect(ProviderShared.Json)
 
 /**
- * Decodes one WebSocket frame. xAI answers a rejected `response.create` with `{ "error": { "message", "type" } }` and no
- * event type; that envelope reads as an error event so the failure classifies instead of failing decoding.
+ * Decodes one WebSocket frame. Some providers and gateways answer a rejected `response.create` with a bare
+ * `{ "error": ... }` envelope and no event type; that reads as an error event so it classifies instead of
+ * failing decoding.
  */
 export const decodeChannelEvent = (frame: string) =>
   decodeFrame(frame).pipe(
     Effect.flatMap((value) =>
       decodeEventValue(
-        ProviderShared.isRecord(value) &&
-          value.type === undefined &&
-          (typeof value.error === "string" || ProviderShared.isRecord(value.error))
+        ProviderShared.isRecord(value) && value.type === undefined && value.error != null
           ? { ...value, type: "error" }
           : value,
       ),
@@ -1422,22 +1368,21 @@ const onResponseFinish = Effect.fn("OpenResponses.onResponseFinish")(function* (
   return [{ ...current, lifecycle }, events] satisfies StepResult
 })
 
-// Build the prettiest summary available from whatever the provider supplied.
-// When both code and message are present, prefix the code so consumers see
-// the failure mode (e.g. `rate_limit_exceeded: Slow down`) instead of just
-// the bare message — production rate limits and context-length failures used
-// to be indistinguishable from generic stream drops. Returns undefined when
-// the payload carries no usable summary.
-const providerErrorMessage = (event: Event, nested: OpenResponsesErrorPayload | undefined): string | undefined => {
-  const message = event.message || nested?.message || undefined
-  const code = event.code || nested?.code || undefined
-  if (message && code) return `${code}: ${message}`
-  return message || code
+/** Error code and message from wherever the frame put them; top-level fields win over nested ones. */
+export const errorDetail = (event: Event) => {
+  const raw = event.error ?? event.response?.error
+  const nested = typeof raw === "string" ? { message: raw } : ProviderShared.isRecord(raw) ? raw : undefined
+  return {
+    message: asText(event.message) ?? asText(nested?.message),
+    code: asText(event.code) ?? asText(nested?.code),
+  }
 }
 
+// Prefix the code when both are present (`rate_limit_exceeded: Slow down`) so the failure mode is
+// visible; fall back to the raw frame rather than a generic message when neither decodes.
 export const providerFailure = (event: Event, fallback: string, body = ProviderShared.encodeJson(event)) => {
-  const nested = event.error ?? event.response?.error ?? undefined
-  const summary = providerErrorMessage(event, nested)
+  const detail = errorDetail(event)
+  const summary = detail.message && detail.code ? `${detail.code}: ${detail.message}` : (detail.message ?? detail.code)
   const message = summary ?? (body === "{}" ? fallback : body)
   const status =
     typeof event.status === "number"
@@ -1520,18 +1465,7 @@ export const step = (state: ParserState, event: NormalizedEvent) => {
   if (event.type === "response.output_item.done") return onOutputItemDone(state, event.item)
   if (event.type === "response.completed" || event.type === "response.incomplete") return onResponseFinish(state, event)
   if (event.type === "response.failed") return providerFailure(event, `${state.name} response failed`)
-  if (event.type === "error")
-    return decodeKnownErrorEvent(event).pipe(
-      Effect.mapError((cause) =>
-        ProviderShared.eventError(
-          state.id,
-          `${state.name} returned a malformed error event`,
-          ProviderShared.encodeJson(event),
-          cause,
-        ),
-      ),
-      Effect.flatMap(() => providerFailure(event, `${state.name} stream error`)),
-    )
+  if (event.type === "error") return providerFailure(event, `${state.name} stream error`)
   return Effect.succeed<StepResult>([state, NO_EVENTS])
 }
 

packages/ai/test/provider/open-responses-errors.test.ts

@@ -11,66 +11,78 @@ import { sseEvents } from "../lib/sse.js"
 
 const decodeEvent = Schema.decodeUnknownEffect(OpenResponses.protocol.stream.event)
 
-it.effect("normalizes flat errors in shared SSE and WebSocket decoding", () =>
+it.effect("decodes error frames verbatim in shared SSE and WebSocket decoding", () =>
   Effect.gen(function* () {
-    const frame = {
-      type: "error",
-      sequence_number: 4,
-      code: "server_shutting_down",
-      message: "Server is shutting down. Please retry your request.",
-      param: null,
-    }
     for (const decode of [decodeEvent, OpenResponses.decodeChannelEvent]) {
-      const event = yield* decode(JSON.stringify(frame))
-      expect(event).toEqual({
-        type: "error",
-        sequence_number: 4,
-        error: { code: frame.code, message: frame.message, param: null },
-      })
-
-      for (const unchanged of [
-        event,
+      for (const frame of [
+        { type: "error", sequence_number: 4, code: "server_shutting_down", message: "Shutting down", param: null },
         { type: "error" },
+        { type: "error", error: "Gateway failed" },
+        { type: "error", error: { code: 429, message: "slow down" } },
+        { type: "error", error: 42 },
+        { type: "error", code: 500, message: ["not", "a", "string"] },
+        { type: "response.failed", response: { id: "resp_failed", error: "Gateway failed" } },
+        { type: "response.failed", response: { id: "resp_failed", error: ["weird"] } },
         {
           type: "response.failed",
           response: { id: "resp_failed", error: { code: "server_error", message: "Internal server error" } },
         },
         { type: "response.output_text.delta", item_id: "msg_text", delta: "Hello" },
       ]) {
-        expect(yield* decode(JSON.stringify(unchanged))).toEqual(unchanged)
+        expect(yield* decode(JSON.stringify(frame))).toEqual(frame)
       }
     }
   }),
 )
 
-it.effect("continues to normalize untyped xAI WebSocket errors", () =>
+it.effect("reads bare WebSocket error envelopes as error events", () =>
   Effect.gen(function* () {
     const message = "gRPC error: Response with id=resp_missing not found"
-    for (const error of [{ type: "api_error", message }, message]) {
-      expect(yield* OpenResponses.decodeChannelEvent(JSON.stringify({ error }))).toEqual({
-        type: "error",
-        error: typeof error === "string" ? { message } : error,
-      })
+    for (const error of [{ type: "api_error", message }, message, 42]) {
+      expect(yield* OpenResponses.decodeChannelEvent(JSON.stringify({ error }))).toEqual({ type: "error", error })
+    }
+    for (const frame of [{ error: null }, { message }]) {
+      expect(yield* OpenResponses.decodeChannelEvent(JSON.stringify(frame)).pipe(Effect.flip)).toBeDefined()
     }
   }),
 )
 
-it.effect("normalizes string errors in shared SSE and WebSocket decoding", () =>
+it.effect("extracts error details from every shape and falls back to the raw frame", () =>
   Effect.gen(function* () {
-    for (const decode of [decodeEvent, OpenResponses.decodeChannelEvent]) {
-      expect(yield* decode(JSON.stringify({ type: "error", error: "Gateway failed" }))).toEqual({
-        type: "error",
-        error: { message: "Gateway failed" },
-      })
-      expect(
-        yield* decode(
-          JSON.stringify({ type: "response.failed", response: { id: "resp_failed", error: "Gateway failed" } }),
-        ),
-      ).toEqual({
-        type: "response.failed",
-        response: { id: "resp_failed", error: { message: "Gateway failed" } },
-      })
+    const cases: Array<[frame: Record<string, unknown>, message: string, tag: string]> = [
+      [
+        { type: "error", code: "server_shutting_down", message: "Shutting down" },
+        "server_shutting_down: Shutting down",
+        "UnknownProvider",
+      ],
+      [{ type: "error", error: "Gateway failed" }, "Gateway failed", "UnknownProvider"],
+      [{ type: "error", error: { code: 429, message: "slow down" } }, "429: slow down", "UnknownProvider"],
+      [{ type: "error", error: { message: "slow down" }, status: 429 }, "slow down", "RateLimit"],
+      [{ type: "error", code: 500, message: ["not", "a", "string"] }, "500", "UnknownProvider"],
+      [
+        { type: "response.failed", response: { id: "resp_failed", error: "Gateway failed" } },
+        "Gateway failed",
+        "UnknownProvider",
+      ],
+    ]
+    for (const [frame, message, tag] of cases) {
+      const event = yield* OpenResponses.decodeChannelEvent(JSON.stringify(frame))
+      const error = OpenResponses.providerFailure(event, "fallback", JSON.stringify(frame))
+      expect(error.message).toBe(message)
+      expect(error.reason._tag).toBe(tag)
+      expect(error.reason.body).toBe(JSON.stringify(frame))
     }
+    for (const frame of [
+      { type: "error", error: 42 },
+      { type: "response.failed", response: { id: "resp_failed", error: ["weird"] } },
+    ]) {
+      const event = yield* OpenResponses.decodeChannelEvent(JSON.stringify(frame))
+      const error = OpenResponses.providerFailure(event, "fallback", JSON.stringify(frame))
+      expect(error.message).toBe(JSON.stringify(frame))
+      expect(error.reason._tag).toBe("UnknownProvider")
+    }
+    expect(OpenResponses.providerFailure({ type: "error" }, "fallback", "{}").message).toBe("fallback")
+    expect(OpenResponses.providerFailure({ type: "error" }, "fallback", "{}").reason._tag).toBe("ProviderInternal")
   }),
 )
 

packages/core/src/plugin/warming.ts

@@ -57,6 +57,9 @@ export const Plugin = define({
 
     const hook = (event: SessionHooks["context"]) =>
       Effect.gen(function* () {
+        const session = yield* ctx.session.get({ sessionID: event.sessionID }).pipe(Effect.orDie)
+        if (session.parentID) return
+
         const active = sessions.get(event.sessionID)
         const settings = yield* loadSettings()
         if (!settings) {

packages/core/src/session/model-request.ts

@@ -320,15 +320,24 @@ export const layer = Layer.effect(
       // which transport actually carries the request, so both hook families are always offered.
       const webSocket =
         input.webSocket === "session" && model.transport === "websocket"
-          ? transport.bind(session.id, (connect) =>
-              hooks
-                .trigger("session", "experimental.ws.handshake", {
-                  ...scope,
-                  url: connect.url,
-                  headers: connect.headers,
-                })
-                .pipe(Effect.map((event) => ({ url: event.url, headers: event.headers }))),
-            )
+          ? transport.bind(session.id, {
+              handshake: (connect) =>
+                hooks
+                  .trigger("session", "experimental.ws.handshake", {
+                    ...scope,
+                    url: connect.url,
+                    headers: connect.headers,
+                  })
+                  .pipe(Effect.map((event) => ({ url: event.url, headers: event.headers }))),
+              send: (frame) =>
+                hooks
+                  .trigger("session", "experimental.ws.send", { ...scope, frame })
+                  .pipe(Effect.map((event) => event.frame)),
+              receive: (frame) =>
+                hooks
+                  .trigger("session", "experimental.ws.receive", { ...scope, frame })
+                  .pipe(Effect.map((event) => event.frame)),
+            })
           : undefined
 
       return {

packages/core/src/session/model-transport.ts

@@ -59,11 +59,18 @@ export interface Handshake {
   readonly headers: Record<string, string>
 }
 
+/**
+ * Per-exchange taps. `handshake` runs before the connection is selected; `send` sees each outbound
+ * frame after the driver builds it; `receive` sees each inbound frame before the driver observes it.
+ */
+export interface Interceptor {
+  readonly handshake?: (connect: Handshake) => Effect.Effect<Handshake>
+  readonly send?: (frame: string) => Effect.Effect<string>
+  readonly receive?: (frame: string) => Effect.Effect<string>
+}
+
 export interface Interface {
-  readonly bind: (
-    sessionID: SessionSchema.ID,
-    handshake?: (connect: Handshake) => Effect.Effect<Handshake>,
-  ) => WebSocketChannelExecutor
+  readonly bind: (sessionID: SessionSchema.ID, interceptor?: Interceptor) => WebSocketChannelExecutor
   readonly close: (sessionID: SessionSchema.ID) => Effect.Effect<void>
   readonly closeAll: Effect.Effect<void>
 }
@@ -278,7 +285,7 @@ export const makeLayer = (connector: WebSocketConnector) =>
       const start = Effect.fn("SessionModelTransport.start")(function* (
         owner: State,
         input: WebSocketChannelExchange,
-        handshake?: (connect: Handshake) => Effect.Effect<Handshake>,
+        interceptor?: Interceptor,
       ) {
         if (owner.closed)
           return yield* transportError("Session WebSocket owner is closed", {
@@ -288,8 +295,8 @@ export const makeLayer = (connector: WebSocketConnector) =>
             delivery: "not-sent",
           })
         if (owner.httpFallback) return fallback(input)
-        const selected = handshake
-          ? yield* handshake({ url: input.connect.url, headers: { ...input.connect.headers } })
+        const selected = interceptor?.handshake
+          ? yield* interceptor.handshake({ url: input.connect.url, headers: { ...input.connect.headers } })
           : undefined
         const exchange: WebSocketChannelExchange = selected
           ? { ...input, connect: { ...input.connect, url: selected.url, headers: Headers.fromInput(selected.headers) } }
@@ -354,6 +361,9 @@ export const makeLayer = (connector: WebSocketConnector) =>
           Effect.onInterrupt(() => closeChannel(owner, channel)),
         )
         if (create.mode === "full") channel.checkpoint = undefined
+        const message = interceptor?.send
+          ? yield* interceptor.send(create.message).pipe(Effect.onInterrupt(() => closeChannel(owner, channel)))
+          : create.message
         yield* Effect.logDebug("session websocket sending", {
           sessionTransport: "websocket",
           phase: "send",
@@ -364,7 +374,7 @@ export const makeLayer = (connector: WebSocketConnector) =>
           delivery: "send-attempted",
         }
         channel.active = active
-        const sent = yield* channel.connection.sendText(create.message).pipe(
+        const sent = yield* channel.connection.sendText(message).pipe(
           Effect.withSpan("SessionModelTransport.send"),
           Effect.onInterrupt(() => closeChannel(owner, channel)),
           Effect.result,
@@ -405,6 +415,7 @@ export const makeLayer = (connector: WebSocketConnector) =>
                 }),
               ),
           }),
+          Stream.mapEffect((frame) => (interceptor?.receive ? interceptor.receive(frame) : Effect.succeed(frame))),
           Stream.mapEffect((frame) => exchange.driver.observe(create, frame)),
           Stream.tap((observation) =>
             Effect.sync(() => {
@@ -482,10 +493,7 @@ export const makeLayer = (connector: WebSocketConnector) =>
         return { frames, complete, http: channel.connection.http }
       })
 
-      const bind = (
-        sessionID: SessionSchema.ID,
-        handshake?: (connect: Handshake) => Effect.Effect<Handshake>,
-      ): WebSocketChannelExecutor => ({
+      const bind = (sessionID: SessionSchema.ID, interceptor?: Interceptor): WebSocketChannelExecutor => ({
         execute: (exchange) => {
           const owner = state(sessionID)
           let execution: WebSocketChannelExecution | undefined
@@ -495,7 +503,7 @@ export const makeLayer = (connector: WebSocketConnector) =>
             },
             frames: Stream.unwrap(
               Effect.acquireRelease(owner.lock.take(1), () => owner.lock.release(1), { interruptible: true }).pipe(
-                Effect.andThen(start(owner, exchange, handshake)),
+                Effect.andThen(start(owner, exchange, interceptor)),
                 Effect.tap((started) =>
                   Effect.sync(() => {
                     execution = started

packages/core/test/session-model-request-hooks.test.ts

@@ -80,7 +80,7 @@ describe("SessionModelRequest HTTP hooks", () => {
     }).pipe(Effect.provideService(SessionModelTransport.Service, transport)),
   )
 
-  it.effect("offers the WebSocket executor alongside HTTP hooks and routes the handshake hook", () =>
+  it.effect("offers the WebSocket executor alongside HTTP hooks and routes the WebSocket hooks", () =>
     Effect.gen(function* () {
       const hooks = yield* PluginHooks.Service
       const seen: string[] = []
@@ -92,13 +92,31 @@ describe("SessionModelRequest HTTP hooks", () => {
           delete event.headers["api-key"]
         }),
       )
+      yield* hooks.register("session", "experimental.ws.send", (event) =>
+        Effect.sync(() => {
+          seen.push(`send:${event.kind}:${event.frame}`)
+          event.frame = `${event.frame}+plugin`
+        }),
+      )
+      yield* hooks.register("session", "experimental.ws.receive", (event) =>
+        Effect.sync(() => {
+          seen.push(`receive:${event.kind}:${event.frame}`)
+          event.frame = event.frame.toUpperCase()
+        }),
+      )
       const bound: Array<{ url: string; headers: Record<string, string> }> = []
+      const frames: string[] = []
       const websocketTransport = SessionModelTransport.Service.of({
-        bind: (_sessionID, handshake) => ({
+        bind: (_sessionID, interceptor) => ({
           execute: () =>
             Effect.gen(function* () {
-              if (!handshake) throw new Error("Expected a handshake interceptor")
-              bound.push(yield* handshake({ url: "wss://example.test/v1/responses", headers: { "api-key": "k" } }))
+              if (!interceptor?.handshake || !interceptor.send || !interceptor.receive)
+                throw new Error("Expected a full WebSocket interceptor")
+              bound.push(
+                yield* interceptor.handshake({ url: "wss://example.test/v1/responses", headers: { "api-key": "k" } }),
+              )
+              frames.push(yield* interceptor.send("create"))
+              frames.push(yield* interceptor.receive("created"))
               return { frames: Stream.empty, complete: Effect.void }
             }),
         }),
@@ -127,7 +145,12 @@ describe("SessionModelRequest HTTP hooks", () => {
       expect(prepared.options.webSocket).toBeDefined()
       yield* prepared.options.webSocket!.execute({} as never)
       expect(bound).toEqual([{ url: "wss://example.test/v1/responses", headers: { authorization: "Bearer minted" } }])
-      expect(seen).toEqual(["handshake:primary:wss://example.test/v1/responses"])
+      expect(frames).toEqual(["create+plugin", "CREATED"])
+      expect(seen).toEqual([
+        "handshake:primary:wss://example.test/v1/responses",
+        "send:primary:create",
+        "receive:primary:created",
+      ])
     }),
   )
 })

packages/core/test/session-model-transport.test.ts

@@ -178,12 +178,13 @@ describe("SessionModelTransport", () => {
       fixture.connector,
       Effect.gen(function* () {
         const transport = yield* SessionModelTransport.Service
-        const executor = transport.bind(session, (connect) =>
-          Effect.succeed({
-            url: connect.url,
-            headers: { ...connect.headers, authorization: `Bearer ${tokens.shift()}` },
-          }),
-        )
+        const executor = transport.bind(session, {
+          handshake: (connect) =>
+            Effect.succeed({
+              url: connect.url,
+              headers: { ...connect.headers, authorization: `Bearer ${tokens.shift()}` },
+            }),
+        })
         yield* collect(executor, exchange("first", { headers: { "api-key": "k" } }))
         yield* collect(executor, exchange("second", { headers: { "api-key": "k" } }))
         yield* collect(executor, exchange("third", { headers: { "api-key": "k" } }))
@@ -196,6 +197,36 @@ describe("SessionModelTransport", () => {
     )
   })
 
+  test("sends the frame the send tap returns and observes the frame the receive tap returns", async () => {
+    const fixture = automatic()
+    const seen: Array<{ tap: "send" | "receive"; frame: string }> = []
+    await run(
+      fixture.connector,
+      Effect.gen(function* () {
+        const transport = yield* SessionModelTransport.Service
+        const executor = transport.bind(session, {
+          send: (frame) => {
+            seen.push({ tap: "send", frame })
+            return Effect.succeed(`${frame}:rewritten`)
+          },
+          receive: (frame) => {
+            seen.push({ tap: "receive", frame })
+            return Effect.succeed(`${frame}:observed`)
+          },
+        })
+        const frames = yield* collect(executor, exchange("first"))
+
+        // The wire carries the rewritten outbound frame; the driver sees the rewritten inbound frame.
+        expect(fixture.connections.map((item) => item.sent)).toEqual([["first:rewritten"]])
+        expect(frames).toEqual(["completed:first:rewritten:observed"])
+        expect(seen).toEqual([
+          { tap: "send", frame: "first" },
+          { tap: "receive", frame: "completed:first:rewritten" },
+        ])
+      }),
+    )
+  })
+
   test("does not carry a checkpoint across physical connection rotation", async () => {
     const fixture = automatic()
     const checkpoints: Array<unknown> = []

packages/plugin/src/effect/session.ts

@@ -99,6 +99,31 @@ export interface SessionWebSocketHandshake {
   headers: Record<string, string>
 }
 
+/**
+ * Outbound frame about to be written to the Session's socket, after the provider driver has built
+ * it. Replacing `frame` sends the replacement verbatim; the driver still tracks state from the
+ * provider's replies, so a rewrite that changes protocol meaning is on the plugin. Experimental.
+ */
+export interface SessionWebSocketSend {
+  readonly sessionID: Session.ID
+  readonly agent: Agent.ID
+  readonly model: Model.Ref
+  readonly kind: SessionRequestKind
+  frame: string
+}
+
+/**
+ * Inbound frame read from the Session's socket, before the provider driver observes it. Replacing
+ * `frame` hands the replacement to the driver verbatim. Experimental.
+ */
+export interface SessionWebSocketReceive {
+  readonly sessionID: Session.ID
+  readonly agent: Agent.ID
+  readonly model: Model.Ref
+  readonly kind: SessionRequestKind
+  frame: string
+}
+
 export type SessionRetryDecision = { retry: false } | { retry: true; delay: number }
 
 export interface SessionRetry {
@@ -120,6 +145,8 @@ export interface SessionHooks {
   readonly "http.request": SessionHttpRequest
   readonly "http.response": SessionHttpResponse
   readonly "experimental.ws.handshake": SessionWebSocketHandshake
+  readonly "experimental.ws.send": SessionWebSocketSend
+  readonly "experimental.ws.receive": SessionWebSocketReceive
   readonly retry: SessionRetry
 }
 

packages/plugin/src/promise/session.ts

@@ -99,6 +99,31 @@ export interface SessionWebSocketHandshake {
   headers: Record<string, string>
 }
 
+/**
+ * Outbound frame about to be written to the Session's socket, after the provider driver has built
+ * it. Replacing `frame` sends the replacement verbatim; the driver still tracks state from the
+ * provider's replies, so a rewrite that changes protocol meaning is on the plugin. Experimental.
+ */
+export interface SessionWebSocketSend {
+  readonly sessionID: Session.ID
+  readonly agent: Agent.ID
+  readonly model: Model.Ref
+  readonly kind: SessionRequestKind
+  frame: string
+}
+
+/**
+ * Inbound frame read from the Session's socket, before the provider driver observes it. Replacing
+ * `frame` hands the replacement to the driver verbatim. Experimental.
+ */
+export interface SessionWebSocketReceive {
+  readonly sessionID: Session.ID
+  readonly agent: Agent.ID
+  readonly model: Model.Ref
+  readonly kind: SessionRequestKind
+  frame: string
+}
+
 export type SessionRetryDecision = { retry: false } | { retry: true; delay: number }
 
 export interface SessionRetry {
@@ -120,6 +145,8 @@ export interface SessionHooks {
   readonly "http.request": SessionHttpRequest
   readonly "http.response": SessionHttpResponse
   readonly "experimental.ws.handshake": SessionWebSocketHandshake
+  readonly "experimental.ws.send": SessionWebSocketSend
+  readonly "experimental.ws.receive": SessionWebSocketReceive
   readonly retry: SessionRetry
 }
 

services/www/src/docs/content/build/plugins/effect.mdx

@@ -1277,6 +1277,26 @@ effect: (ctx) =>
   }),
 ```
 
+`experimental.ws.send` and `experimental.ws.receive` expose the frames themselves: `send` runs after the provider
+driver builds an outbound frame, `receive` runs on each inbound frame before the driver observes it. Whatever `frame` holds when the hook returns is what crosses the wire or reaches the driver;
+OpenCode does not validate it.
+
+```ts
+effect: (ctx) =>
+  Effect.gen(function* () {
+    yield* ctx.session.hook(
+      "experimental.ws.send",
+      (event) =>
+        Effect.sync(() => {
+          const body = JSON.parse(event.frame)
+          if (body.type === "response.create") body.metadata = { ...body.metadata, session: event.sessionID }
+          event.frame = JSON.stringify(body)
+        }),
+      { providerID: "openai" },
+    )
+  }),
+```
+
 Override the retry decision for a provider failure or replace its delay in milliseconds. The hook runs after OpenCode
 classifies the failure and proposes its policy, but before any retry is scheduled. It does not expose how OpenCode
 internally performs the next attempt.
@@ -1317,6 +1337,9 @@ interface SessionHooks {
   readonly "model.request": SessionModelRequest
   readonly "http.request": SessionHttpRequest
   readonly "http.response": SessionHttpResponse
+  readonly "experimental.ws.handshake": SessionWebSocketHandshake
+  readonly "experimental.ws.send": SessionWebSocketSend
+  readonly "experimental.ws.receive": SessionWebSocketReceive
   readonly retry: SessionRetry
 }
 

services/www/src/docs/content/build/plugins/index.mdx

@@ -1410,7 +1410,31 @@ await ctx.session.hook(
 )
 ```
 
-This hook is experimental and its name or shape may change.
+`experimental.ws.send` and `experimental.ws.receive` expose the frames themselves, the WebSocket counterpart of
+editing an HTTP request or response body. `send` runs after the provider driver builds an outbound frame and before it
+is written; `receive` runs on each inbound frame before the driver observes it. Both carry the frame as a string and
+send whatever `frame` holds when the hook returns.
+
+OpenCode does not validate rewritten frames. The driver tracks state from the provider's replies, so a rewrite that
+changes protocol meaning is the plugin's responsibility, just as a rewritten HTTP body is.
+
+```ts
+await ctx.session.hook(
+  "experimental.ws.send",
+  (event) => {
+    const body = JSON.parse(event.frame)
+    if (body.type === "response.create") body.metadata = { ...body.metadata, session: event.sessionID }
+    event.frame = JSON.stringify(body)
+  },
+  { providerID: "openai" },
+)
+
+await ctx.session.hook("experimental.ws.receive", (event) => {
+  if (event.frame.includes('"type":"error"')) console.error(event.frame)
+})
+```
+
+These hooks are experimental and their names or shapes may change.
 
 #### Retry policy
 
@@ -1458,6 +1482,8 @@ interface SessionHooks {
   "http.request": SessionHttpRequestHook
   "http.response": SessionHttpResponseHook
   "experimental.ws.handshake": SessionWebSocketHandshakeHook
+  "experimental.ws.send": SessionWebSocketSendHook
+  "experimental.ws.receive": SessionWebSocketReceiveHook
   retry: SessionRetryHook
 }
 
@@ -1470,6 +1496,22 @@ interface SessionWebSocketHandshakeHook {
   headers: Record<string, string>
 }
 
+interface SessionWebSocketSendHook {
+  readonly sessionID: string
+  readonly agent: string
+  readonly model: { providerID: string; id: string; variant?: string }
+  readonly kind: "primary" | "compaction" | "title" | "generate"
+  frame: string
+}
+
+interface SessionWebSocketReceiveHook {
+  readonly sessionID: string
+  readonly agent: string
+  readonly model: { providerID: string; id: string; variant?: string }
+  readonly kind: "primary" | "compaction" | "title" | "generate"
+  frame: string
+}
+
 type RetryDecision = { retry: false } | { retry: true; delay: number }
 
 interface SessionRetryHook {