feat: add /loop command for periodic task execution

[wenshao]

Summary

Add a /loop slash command that periodically executes a given prompt or slash command at a fixed interval, enabling hands-off monitoring and automation workflows.

Motivation

Developers frequently need to repeat the same action at regular intervals — watching a CI pipeline, polling deployment status, periodically reviewing incoming PRs. Currently this requires manually re-entering the same prompt each time.

Relation to hooks: The existing hooks system triggers actions in response to events (tool calls, session lifecycle). /loop complements this by enabling time-based periodic execution, which hooks cannot do.

Proposed Syntax

/loop [interval] <prompt or /command>
/loop status                           # show running loops
/loop stop [id]                        # stop a specific loop, or all if no id

• interval (optional): Duration such as 30s, 5m, 1h. Default: 10m.
• prompt: Any text prompt or slash command to execute each cycle.

Examples

/loop 5m check if CI pipeline has passed for current branch
/loop 10m /review-pr 2525
/loop 1h summarize new commits on main since last check
/loop 30s is the dev server healthy?
/loop status
/loop stop
/loop stop 2

Behavior Design

Core Loop

• Execute the prompt immediately on first invocation, then repeat at the specified interval
• Each iteration should be clearly delimited in output (timestamp + iteration count)
• Only one loop runs at a time (simplifies UX; multi-loop support can be a follow-up)

Stopping

• User interrupt: Ctrl+C or Escape stops the loop
• Explicit command: /loop stop
• Max iterations: Optional — e.g., /loop 5m --max 12 check CI (auto-stop after 12 cycles)

Context Management

• Each iteration starts with a fresh context to avoid context window exhaustion during long-running loops
• Sharing context across iterations can be considered as a follow-up

Error Handling

• If a single iteration fails, log the error and continue to the next cycle
• After 3 consecutive failures, warn the user and pause

User Interaction

• While a loop is running, the user should still be able to type and interact normally
• Loop output should be visually distinguished from interactive output (e.g., separator with timestamp, or collapsible sections in WebUI)

Safety

• Loop iterations respect the current approval mode — destructive actions still require confirmation unless in YOLO mode
• Show estimated token cost per iteration after the first run, so users can decide whether to continue
• Minimum interval floor (e.g., 10s) to prevent accidental API abuse

Use Cases

Scenario	Command
Monitor CI pipeline	/loop 5m check if CI passed on current branch
Watch deployment	/loop 2m is the staging deployment healthy?
Review incoming PRs	/loop 30m /review-pr
Track build output	/loop 1m check for new build errors in logs
Periodic git sync check	/loop 1h are there new commits on main I should rebase onto?

Implementation Considerations

• Register /loop and sub-commands (status, stop) in BuiltinCommandLoader
• Parse interval with s / m / h suffix support
• Run iterations as independent prompt submissions with isolated context
• Loop manager service to track active loop state (start/stop/status)
• Both CLI (Ink) and WebUI should be supported
• Use existing i18n infrastructure for status messages

[wenshao]

Update: Feature Alignment with Claude Code /loop

Based on analysis from loop-schedule comparison, the following gaps with Claude Code /loop have been identified and addressed in commit 6012fdd:

Fixed

Gap	Description	Commit
Nested slash commands	/loop 5m /review now executes /review on each iteration (submits as string through isSlashCommand() parsing)	6012fdd
Day unit	parseInterval/formatInterval now support d — e.g., /loop 1d check status	6012fdd
Natural language interval	/loop check deploy every 5m extracts interval from prompt tail	6012fdd

Previously Fixed (in 26fbe26)

Issue	Description
Race condition	Loop iterations use dedicated submission path, not shared useMessageQueue
Error detection	Checks pendingGeminiHistoryItems + backward history scan for tool errors
Slash command consistency	All iterations (including first) now go through the same callback+drain path

Remaining Gaps vs Claude Code

Gap	Priority	Notes
/tasks integration	Low	Claude Code manages loops via /tasks; Qwen Code uses standalone /loop status/stop
Ctrl+C stops loop	Low	Currently only /loop stop; could hook into signal handler
/schedule (remote cron)	Out of scope	Requires cloud infrastructure (CCR equivalent)
/loop resume	Low	resume() implemented in LoopManager but no UI entry