fix(session): auto-continue when model stops with reasoning-only response

Detect pattern where the model finishes with 'stop' after only
producing reasoning text, without making any tool calls. Inject a
synthetic user message to prompt the model to continue, allowing up
to 10 auto-continuations per session to prevent infinite loops.

Author: Grigory-Rylov

packages/opencode/src/session/prompt.ts

@@ -1136,6 +1136,7 @@ export const layer = Layer.effect(
         const ctx = yield* InstanceState.context
         let structured: unknown
         let step = 0
+        let autoContinueCount = 0
         const session = yield* sessions.get(sessionID).pipe(Effect.orDie)
 
         while (true) {
@@ -1178,6 +1179,48 @@ export const layer = Layer.effect(
                 callID: orphan.callID,
               })
             }
+            // AUTO-CONTINUE: Detect reasoning-only + stop without any text response or tool calls.
+            // This catches cases where the model stops mid-thought without producing output.
+            const isReasoningOnly = lastAssistantMsg && lastAssistant.finish === "stop" && lastAssistantMsg.parts.length > 0 &&
+              lastAssistantMsg.parts.every(
+                (p) => p.type === "reasoning" || p.type === "step-start" || p.type === "step-finish",
+              )
+
+            if (isReasoningOnly && autoContinueCount < 10) {
+              autoContinueCount++
+              yield* Effect.logInfo("auto-continue: reasoning-only stop, injecting continue message", {
+                "session.id": sessionID,
+                attempt: autoContinueCount,
+              })
+              const contMsgID = MessageID.ascending()
+              const contMsg = yield* sessions.updateMessage({
+                id: contMsgID,
+                role: "user",
+                sessionID,
+                time: { created: Date.now() },
+                agent: lastUser.agent,
+                model: lastUser.model,
+              })
+              yield* sessions.updatePart({
+                id: PartID.ascending(),
+                messageID: contMsg.id,
+                sessionID,
+                type: "text",
+                metadata: { auto_continue: true },
+                synthetic: true,
+                text: "[Auto-continue] Your response was cut off. Please continue from where you left off.",
+                time: {
+                  start: Date.now(),
+                  end: Date.now(),
+                },
+              })
+              continue
+            } else if (isReasoningOnly) {
+              yield* Effect.logWarning("auto-continue: max attempts (10) reached, exiting loop", {
+                "session.id": sessionID,
+              })
+            }
+
             yield* Effect.logInfo("exiting loop", { "session.id": sessionID })
             break
           }