fix(session): finalize interrupted assistant messages (#27254)

packages/opencode/src/session/prompt.ts

@@ -1755,12 +1755,25 @@ NOTE: At any point in time through this workflow you should feel free to ask the
             sessionID,
           }
           yield* sessions.updateMessage(msg)
-          const handle = yield* processor.create({
-            assistantMessage: msg,
-            sessionID,
-            model,
+
+          const finalizeInterruptedAssistant = Effect.gen(function* () {
+            if (msg.time.completed) return
+            msg.error ??= MessageV2.fromError(new DOMException("Aborted", "AbortError"), {
+              providerID: msg.providerID,
+              aborted: true,
+            })
+            msg.time.completed = Date.now()
+            yield* sessions.updateMessage(msg)
           })
 
+          const handle = yield* processor
+            .create({
+              assistantMessage: msg,
+              sessionID,
+              model,
+            })
+            .pipe(Effect.onInterrupt(() => finalizeInterruptedAssistant))
+
           const outcome: "break" | "continue" = yield* Effect.gen(function* () {
             const lastUserMsg = msgs.findLast((m) => m.info.role === "user")
             const bypassAgentCheck = lastUserMsg?.parts.some((p) => p.type === "agent") ?? false
@@ -1859,7 +1872,10 @@ NOTE: At any point in time through this workflow you should feel free to ask the
               })
             }
             return "continue" as const
-          }).pipe(Effect.ensuring(instruction.clear(handle.message.id)))
+          }).pipe(
+            Effect.ensuring(instruction.clear(handle.message.id)),
+            Effect.onInterrupt(() => finalizeInterruptedAssistant),
+          )
           if (outcome === "break") break
           continue
         }