diff --git a/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts b/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
index b12be2cfc2..df2b40de56 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
@@ -52,6 +52,14 @@ export const sessionHandlers = HttpApiBuilder.group(InstanceHttpApi, "session",
     const bus = yield* Bus.Service
     const scope = yield* Scope.Scope
 
+    const mapBusy = <A, E, R>(effect: Effect.Effect<A, E, R>): Effect.Effect<A, E | HttpApiError.BadRequest, R> =>
+      effect.pipe(
+        Effect.catchCause((cause): Effect.Effect<never, E | HttpApiError.BadRequest> => {
+          if (Cause.squash(cause) instanceof Session.BusyError) return Effect.fail(new HttpApiError.BadRequest({}))
+          return Effect.failCause(cause)
+        }),
+      )
+
     const list = Effect.fn("SessionHttpApi.list")(function* (ctx: { query: typeof ListQuery.Type }) {
       return yield* session.list({
         directory: ctx.query.scope === "project" ? undefined : ctx.query.directory,
@@ -329,7 +337,7 @@ export const sessionHandlers = HttpApiBuilder.group(InstanceHttpApi, "session",
       payload: typeof ShellPayload.Type
     }) {
       yield* requireSession(ctx.params.sessionID)
-      return yield* promptSvc.shell({ ...ctx.payload, sessionID: ctx.params.sessionID })
+      return yield* mapBusy(promptSvc.shell({ ...ctx.payload, sessionID: ctx.params.sessionID }))
     })
 
     const revert = Effect.fn("SessionHttpApi.revert")(function* (ctx: {
@@ -337,12 +345,12 @@ export const sessionHandlers = HttpApiBuilder.group(InstanceHttpApi, "session",
       payload: typeof RevertPayload.Type
     }) {
       yield* requireSession(ctx.params.sessionID)
-      return yield* revertSvc.revert({ sessionID: ctx.params.sessionID, ...ctx.payload })
+      return yield* mapBusy(revertSvc.revert({ sessionID: ctx.params.sessionID, ...ctx.payload }))
     })
 
     const unrevert = Effect.fn("SessionHttpApi.unrevert")(function* (ctx: { params: { sessionID: SessionID } }) {
       yield* requireSession(ctx.params.sessionID)
-      return yield* revertSvc.unrevert({ sessionID: ctx.params.sessionID })
+      return yield* mapBusy(revertSvc.unrevert({ sessionID: ctx.params.sessionID }))
     })
 
     const permissionRespond = Effect.fn("SessionHttpApi.permissionRespond")(function* (ctx: {
@@ -358,7 +366,7 @@ export const sessionHandlers = HttpApiBuilder.group(InstanceHttpApi, "session",
       params: { sessionID: SessionID; messageID: MessageID }
     }) {
       yield* requireSession(ctx.params.sessionID)
-      yield* runState.assertNotBusy(ctx.params.sessionID)
+      yield* mapBusy(runState.assertNotBusy(ctx.params.sessionID))
       yield* session.removeMessage(ctx.params)
       return true
     })
diff --git a/packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts b/packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts
index bb75f6602c..5896410370 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts
@@ -1,5 +1,4 @@
 import { Provider } from "@/provider/provider"
-import { Session } from "@/session/session"
 import { iife } from "@/util/iife"
 import { NamedError } from "@opencode-ai/core/util/error"
 import * as Log from "@opencode-ai/core/util/log"
@@ -33,14 +32,6 @@ export const errorLayer = HttpRouter.middleware<{ handles: unknown }>()((effect)
           }),
         )
       }
-      if (error instanceof Session.BusyError) {
-        return Effect.succeed(
-          HttpServerResponse.jsonUnsafe(new NamedError.Unknown({ message: error.message }).toObject(), {
-            status: 400,
-          }),
-        )
-      }
-
       return Effect.succeed(
         HttpServerResponse.jsonUnsafe(
           new NamedError.Unknown({