fix(session): type busy errors (#27410)

packages/opencode/src/session/prompt.ts

@@ -167,7 +167,7 @@ export interface Interface {
   readonly cancel: (sessionID: SessionID) => Effect.Effect<void>
   readonly prompt: (input: PromptInput) => Effect.Effect<MessageV2.WithParts>
   readonly loop: (input: LoopInput) => Effect.Effect<MessageV2.WithParts>
-  readonly shell: (input: ShellInput) => Effect.Effect<MessageV2.WithParts>
+  readonly shell: (input: ShellInput) => Effect.Effect<MessageV2.WithParts, Session.BusyError>
   readonly command: (input: CommandInput) => Effect.Effect<MessageV2.WithParts>
   readonly resolvePromptParts: (template: string) => Effect.Effect<PromptInput["parts"]>
 }
@@ -1864,12 +1864,12 @@ NOTE: At any point in time through this workflow you should feel free to ask the
       return yield* state.ensureRunning(input.sessionID, lastAssistant(input.sessionID), runLoop(input.sessionID))
     })
 
-    const shell: (input: ShellInput) => Effect.Effect<MessageV2.WithParts> = Effect.fn("SessionPrompt.shell")(
-      function* (input: ShellInput) {
-        const ready = yield* Latch.make()
-        return yield* state.startShell(input.sessionID, lastAssistant(input.sessionID), shellImpl(input, ready), ready)
-      },
-    )
+    const shell: (input: ShellInput) => Effect.Effect<MessageV2.WithParts, Session.BusyError> = Effect.fn(
+      "SessionPrompt.shell",
+    )(function* (input: ShellInput) {
+      const ready = yield* Latch.make()
+      return yield* state.startShell(input.sessionID, lastAssistant(input.sessionID), shellImpl(input, ready), ready)
+    })
 
     const command = Effect.fn("SessionPrompt.command")(function* (input: CommandInput) {
       yield* elog.info("command", { sessionID: input.sessionID, command: input.command, agent: input.agent })

packages/opencode/src/session/revert.ts

@@ -20,8 +20,8 @@ export const RevertInput = Schema.Struct({
 export type RevertInput = Schema.Schema.Type<typeof RevertInput>
 
 export interface Interface {
-  readonly revert: (input: RevertInput) => Effect.Effect<Session.Info>
-  readonly unrevert: (input: { sessionID: SessionID }) => Effect.Effect<Session.Info>
+  readonly revert: (input: RevertInput) => Effect.Effect<Session.Info, Session.BusyError>
+  readonly unrevert: (input: { sessionID: SessionID }) => Effect.Effect<Session.Info, Session.BusyError>
   readonly cleanup: (session: Session.Info) => Effect.Effect<void>
 }
 

packages/opencode/src/session/run-state.ts

@@ -7,7 +7,7 @@ import { SessionID } from "./schema"
 import { SessionStatus } from "./status"
 
 export interface Interface {
-  readonly assertNotBusy: (sessionID: SessionID) => Effect.Effect<void>
+  readonly assertNotBusy: (sessionID: SessionID) => Effect.Effect<void, Session.BusyError>
   readonly cancel: (sessionID: SessionID) => Effect.Effect<void>
   readonly ensureRunning: (
     sessionID: SessionID,
@@ -19,7 +19,7 @@ export interface Interface {
     onInterrupt: Effect.Effect<MessageV2.WithParts>,
     work: Effect.Effect<MessageV2.WithParts>,
     ready?: Latch.Latch,
-  ) => Effect.Effect<MessageV2.WithParts>
+  ) => Effect.Effect<MessageV2.WithParts, Session.BusyError>
 }
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/SessionRunState") {}
@@ -60,9 +60,6 @@ export const layer = Layer.effect(
         }),
         onBusy: status.set(sessionID, { type: "busy" }),
         onInterrupt,
-        busy: () => {
-          throw new Session.BusyError(sessionID)
-        },
       })
       data.runners.set(sessionID, next)
       return next
@@ -71,7 +68,7 @@ export const layer = Layer.effect(
     const assertNotBusy = Effect.fn("SessionRunState.assertNotBusy")(function* (sessionID: SessionID) {
       const data = yield* InstanceState.get(state)
       const existing = data.runners.get(sessionID)
-      if (existing?.busy) throw new Session.BusyError(sessionID)
+      if (existing?.busy) yield* busyError(sessionID)
     })
 
     const cancel = Effect.fn("SessionRunState.cancel")(function* (sessionID: SessionID) {
@@ -98,7 +95,9 @@ export const layer = Layer.effect(
       work: Effect.Effect<MessageV2.WithParts>,
       ready?: Latch.Latch,
     ) {
-      return yield* (yield* runner(sessionID, onInterrupt)).startShell(work, ready)
+      return yield* (yield* runner(sessionID, onInterrupt))
+        .startShell(work, ready)
+        .pipe(Effect.catchTag("RunnerBusy", () => Effect.fail(busyError(sessionID))))
     })
 
     return Service.of({ assertNotBusy, cancel, ensureRunning, startShell })
@@ -107,4 +106,8 @@ export const layer = Layer.effect(
 
 export const defaultLayer = layer.pipe(Layer.provide(SessionStatus.defaultLayer))
 
+function busyError(sessionID: SessionID) {
+  return new Session.BusyError({ sessionID })
+}
+
 export * as SessionRunState from "./run-state"

packages/opencode/src/session/session.ts

@@ -442,11 +442,9 @@ export const getUsage = (input: { model: Provider.Model; usage: LanguageModelUsa
   }
 }
 
-export class BusyError extends Error {
-  constructor(public readonly sessionID: string) {
-    super(`Session ${sessionID} is busy`)
-  }
-}
+export class BusyError extends Schema.TaggedErrorClass<BusyError>()("SessionBusyError", {
+  sessionID: SessionID,
+}) {}
 
 export type NotFound = NotFoundError