fix(prompt): prevent immediate BackgroundOutput polling after background task launch

Tool return values contained CTAs ("Use background_output to check") that
caused models to immediately poll instead of waiting for <system-reminder>
notifications. Unified all 5 tool return messages with explicit "Do NOT call
background_output now" guard, added pre-notification warning to BackgroundOutput
tool description, and strengthened Background Result Collection sections across
all 3 Sisyphus prompt variants (default, gpt-5-4, main) with BLOCKING
anti-pattern enforcement.

🤖 Generated with assistance of [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/tools/background-task/constants.ts

@@ -2,6 +2,8 @@ export const BACKGROUND_TASK_DESCRIPTION = `Run agent task in background. Return
 
 Use \`background_output\` to get results. Prompts MUST be in English.`
 
-export const BACKGROUND_OUTPUT_DESCRIPTION = `Get output from background task. Use full_session=true to fetch session messages with filters. System notifies on completion, so block=true rarely needed. - Timeout values are in milliseconds (ms), NOT seconds.`
+export const BACKGROUND_OUTPUT_DESCRIPTION = `Get output from background task. Use full_session=true to fetch session messages with filters. System notifies on completion, so block=true rarely needed. - Timeout values are in milliseconds (ms), NOT seconds.
+
+IMPORTANT: ONLY call this tool AFTER receiving a <system-reminder> notification for the task. Do NOT call immediately after launching a background task - wait for the notification first.`
 
 export const BACKGROUND_CANCEL_DESCRIPTION = `Cancel running background task(s). Use all=true to cancel ALL before final answer.`

src/tools/background-task/create-background-task.ts

@@ -114,10 +114,9 @@ Description: ${task.description}
 Agent: ${task.agent}
 Status: ${task.status}
 
-The system will notify you when the task completes.
-Use \`background_output\` tool with task_id="${task.id}" to check progress:
-- block=false (default): Check status immediately - returns full status info
-- block=true: Wait for completion (rarely needed since system notifies)`
+System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.
+
+Do NOT call background_output now. Wait for <system-reminder> notification first.`
       } catch (error) {
         const message = error instanceof Error ? error.message : String(error)
         return `[ERROR] Failed to launch background task: ${message}`

src/tools/call-omo-agent/background-agent-executor.ts

@@ -81,10 +81,9 @@ Description: ${task.description}
 Agent: ${task.agent} (subagent)
 Status: ${task.status}
 
-The system will notify you when the task completes.
-Use \`background_output\` tool with task_id="${task.id}" to check progress:
-- block=false (default): Check status immediately - returns full status info
-- block=true: Wait for completion (rarely needed since system notifies)`
+System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.
+
+Do NOT call background_output now. Wait for <system-reminder> notification first.`
 	} catch (error) {
 		const message = error instanceof Error ? error.message : String(error)
 		return `Failed to launch background agent task: ${message}`

src/tools/call-omo-agent/background-executor.ts

@@ -88,10 +88,9 @@ Description: ${task.description}
 Agent: ${task.agent} (subagent)
 Status: ${task.status}
 
-The system will notify you when the task completes.
-Use \`background_output\` tool with task_id="${task.id}" to check progress:
-- block=false (default): Check status immediately - returns full status info
-- block=true: Wait for completion (rarely needed since system notifies)`
+System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.
+
+Do NOT call background_output now. Wait for <system-reminder> notification first.`
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error)
     return `Failed to launch background agent task: ${message}`

src/tools/delegate-task/background-continuation.ts

@@ -51,7 +51,9 @@ Agent: ${task.agent}
 Status: ${task.status}
 
 Agent continues with full previous context preserved.
-Use \`background_output\` with task_id="${task.id}" to check progress.
+System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.
+
+Do NOT call background_output now. Wait for <system-reminder> notification first.
 
 <task_metadata>
 session_id: ${task.sessionID}

src/tools/delegate-task/background-task.ts

@@ -149,7 +149,9 @@ Description: ${task.description}
 Agent: ${task.agent}${args.category ? ` (category: ${args.category})` : ""}
 Status: ${task.status}
 
-System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.${taskMetadataBlock}`
+System notifies on completion. Use \`background_output\` with task_id="${task.id}" to check.
+
+Do NOT call background_output now. Wait for <system-reminder> notification first.${taskMetadataBlock}`
   } catch (error) {
     return formatDetailedError(error, {
       operation: "Launch background task",