78 lines
4.2 KiB
Markdown
78 lines
4.2 KiB
Markdown
---
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summary: "Command queue design that serializes inbound auto-reply runs"
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read_when:
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- Changing auto-reply execution or concurrency
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---
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# Command Queue (2026-01-16)
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We serialize inbound auto-reply runs (all channels) through a tiny in-process queue to prevent multiple agent runs from colliding, while still allowing safe parallelism across sessions.
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## Why
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- Auto-reply runs can be expensive (LLM calls) and can collide when multiple inbound messages arrive close together.
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- Serializing avoids competing for shared resources (session files, logs, CLI stdin) and reduces the chance of upstream rate limits.
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## How it works
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- A lane-aware FIFO queue drains each lane with a configurable concurrency cap (default 1 for unconfigured lanes; main defaults to 4, subagent to 8).
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- `runEmbeddedPiAgent` enqueues by **session key** (lane `session:<key>`) to guarantee only one active run per session.
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- Each session run is then queued into a **global lane** (`main` by default) so overall parallelism is capped by `agents.defaults.maxConcurrent`.
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- When verbose logging is enabled, queued runs emit a short notice if they waited more than ~2s before starting.
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- Typing indicators still fire immediately on enqueue (when supported by the channel) so user experience is unchanged while we wait our turn.
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## Queue modes (per channel)
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Inbound messages can steer the current run, wait for a followup turn, or do both:
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- `steer`: inject immediately into the current run (cancels pending tool calls after the next tool boundary). If not streaming, falls back to followup.
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- `followup`: enqueue for the next agent turn after the current run ends.
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- `collect`: coalesce all queued messages into a **single** followup turn (default). If messages target different channels/threads, they drain individually to preserve routing.
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- `steer-backlog` (aka `steer+backlog`): steer now **and** preserve the message for a followup turn.
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- `interrupt` (legacy): abort the active run for that session, then run the newest message.
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- `queue` (legacy alias): same as `steer`.
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Steer-backlog means you can get a followup response after the steered run, so
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streaming surfaces can look like duplicates. Prefer `collect`/`steer` if you want
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one response per inbound message.
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Send `/queue collect` as a standalone command (per-session) or set `messages.queue.byChannel.discord: "collect"`.
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Defaults (when unset in config):
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- All surfaces → `collect`
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Configure globally or per channel via `messages.queue`:
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```json5
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{
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messages: {
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queue: {
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mode: "collect",
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debounceMs: 1000,
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cap: 20,
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drop: "summarize",
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byChannel: { discord: "collect" }
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}
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}
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}
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```
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## Queue options
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Options apply to `followup`, `collect`, and `steer-backlog` (and to `steer` when it falls back to followup):
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- `debounceMs`: wait for quiet before starting a followup turn (prevents “continue, continue”).
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- `cap`: max queued messages per session.
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- `drop`: overflow policy (`old`, `new`, `summarize`).
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Summarize keeps a short bullet list of dropped messages and injects it as a synthetic followup prompt.
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Defaults: `debounceMs: 1000`, `cap: 20`, `drop: summarize`.
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## Per-session overrides
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- Send `/queue <mode>` as a standalone command to store the mode for the current session.
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- Options can be combined: `/queue collect debounce:2s cap:25 drop:summarize`
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- `/queue default` or `/queue reset` clears the session override.
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## Scope and guarantees
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- Applies to auto-reply agent runs across all inbound channels that use the gateway reply pipeline (WhatsApp web, Telegram, Slack, Discord, Signal, iMessage, webchat, etc.).
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- Default lane (`main`) is process-wide for inbound + main heartbeats; set `agents.defaults.maxConcurrent` to allow multiple sessions in parallel.
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- Additional lanes may exist (e.g. `cron`, `subagent`) so background jobs can run in parallel without blocking inbound replies.
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- Per-session lanes guarantee that only one agent run touches a given session at a time.
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- No external dependencies or background worker threads; pure TypeScript + promises.
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## Troubleshooting
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- If commands seem stuck, enable verbose logs and look for “queued for …ms” lines to confirm the queue is draining.
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- If you need queue depth, enable verbose logs and watch for queue timing lines.
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