> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fluffbuzz.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent loop

# Agent Loop (FluffBuzz)

An agentic loop is the full “real” run of an agent: intake → context assembly → model inference →
tool execution → streaming replies → persistence. It’s the authoritative path that turns a message
into actions and a final reply, while keeping session state consistent.

In FluffBuzz, a loop is a single, serialized run per session that emits lifecycle and stream events
as the model thinks, calls tools, and streams output. This doc explains how that authentic loop is
wired end-to-end.

## Entry points

* Gateway RPC: `agent` and `agent.wait`.
* CLI: `agent` command.

## How it works (high-level)

1. `agent` RPC validates params, resolves session (sessionKey/sessionId), persists session metadata, returns `{ runId, acceptedAt }` immediately.
2. `agentCommand` runs the agent:
   * resolves model + thinking/verbose/trace defaults
   * loads skills snapshot
   * calls `runEmbeddedPiAgent` (pi-agent-core runtime)
   * emits **lifecycle end/error** if the embedded loop does not emit one
3. `runEmbeddedPiAgent`:
   * serializes runs via per-session + global queues
   * resolves model + auth profile and builds the pi session
   * subscribes to pi events and streams assistant/tool deltas
   * enforces timeout -> aborts run if exceeded
   * returns payloads + usage metadata
4. `subscribeEmbeddedPiSession` bridges pi-agent-core events to FluffBuzz `agent` stream:
   * tool events => `stream: "tool"`
   * assistant deltas => `stream: "assistant"`
   * lifecycle events => `stream: "lifecycle"` (`phase: "start" | "end" | "error"`)
5. `agent.wait` uses `waitForAgentRun`:
   * waits for **lifecycle end/error** for `runId`
   * returns `{ status: ok|error|timeout, startedAt, endedAt, error? }`

## Queueing + concurrency

* Runs are serialized per session key (session lane) and optionally through a global lane.
* This prevents tool/session races and keeps session history consistent.
* Messaging channels can choose queue modes (collect/steer/followup) that feed this lane system.
  See [Command Queue](/concepts/queue).
* Transcript writes are also protected by a session write lock on the session file. The lock is
  process-aware and file-based, so it catches writers that bypass the in-process queue or come from
  another process.
* Session write locks are non-reentrant by default. If a helper intentionally nests acquisition of
  the same lock while preserving one logical writer, it must opt in explicitly with
  `allowReentrant: true`.

## Session + workspace preparation

* Workspace is resolved and created; sandboxed runs may redirect to a sandbox workspace root.
* Skills are loaded (or reused from a snapshot) and injected into env and prompt.
* Bootstrap/context files are resolved and injected into the system prompt report.
* A session write lock is acquired; `SessionManager` is opened and prepared before streaming. Any
  later transcript rewrite, compaction, or truncation path must take the same lock before opening or
  mutating the transcript file.

## Prompt assembly + system prompt

* System prompt is built from FluffBuzz’s base prompt, skills prompt, bootstrap context, and per-run overrides.
* Model-specific limits and compaction reserve tokens are enforced.
* See [System prompt](/concepts/system-prompt) for what the model sees.

## Hook points (where you can intercept)

FluffBuzz has two hook systems:

* **Internal hooks** (Gateway hooks): event-driven scripts for commands and lifecycle events.
* **Plugin hooks**: extension points inside the agent/tool lifecycle and gateway pipeline.

### Internal hooks (Gateway hooks)

* **`agent:bootstrap`**: runs while building bootstrap files before the system prompt is finalized.
  Use this to add/remove bootstrap context files.
* **Command hooks**: `/new`, `/reset`, `/stop`, and other command events (see Hooks doc).

See [Hooks](/automation/hooks) for setup and examples.

### Plugin hooks (agent + gateway lifecycle)

These run inside the agent loop or gateway pipeline:

* **`before_model_resolve`**: runs pre-session (no `messages`) to deterministically override provider/model before model resolution.
* **`before_prompt_build`**: runs after session load (with `messages`) to inject `prependContext`, `systemPrompt`, `prependSystemContext`, or `appendSystemContext` before prompt submission. Use `prependContext` for per-turn dynamic text and system-context fields for stable guidance that should sit in system prompt space.
* **`before_agent_start`**: legacy compatibility hook that may run in either phase; prefer the explicit hooks above.
* **`before_agent_reply`**: runs after inline actions and before the LLM call, letting a plugin claim the turn and return a synthetic reply or silence the turn entirely.
* **`agent_end`**: inspect the final message list and run metadata after completion.
* **`before_compaction` / `after_compaction`**: observe or annotate compaction cycles.
* **`before_tool_call` / `after_tool_call`**: intercept tool params/results.
* **`before_install`**: inspect built-in scan findings and optionally block skill or plugin installs.
* **`tool_result_persist`**: synchronously transform tool results before they are written to the session transcript.
* **`message_received` / `message_sending` / `message_sent`**: inbound + outbound message hooks.
* **`session_start` / `session_end`**: session lifecycle boundaries.
* **`gateway_start` / `gateway_stop`**: gateway lifecycle events.

Hook decision rules for outbound/tool guards:

* `before_tool_call`: `{ block: true }` is terminal and stops lower-priority handlers.
* `before_tool_call`: `{ block: false }` is a no-op and does not clear a prior block.
* `before_install`: `{ block: true }` is terminal and stops lower-priority handlers.
* `before_install`: `{ block: false }` is a no-op and does not clear a prior block.
* `message_sending`: `{ cancel: true }` is terminal and stops lower-priority handlers.
* `message_sending`: `{ cancel: false }` is a no-op and does not clear a prior cancel.

See [Plugin hooks](/plugins/architecture#provider-runtime-hooks) for the hook API and registration details.

## Streaming + partial replies

* Assistant deltas are streamed from pi-agent-core and emitted as `assistant` events.
* Block streaming can emit partial replies either on `text_end` or `message_end`.
* Reasoning streaming can be emitted as a separate stream or as block replies.
* See [Streaming](/concepts/streaming) for chunking and block reply behavior.

## Tool execution + messaging tools

* Tool start/update/end events are emitted on the `tool` stream.
* Tool results are sanitized for size and image payloads before logging/emitting.
* Messaging tool sends are tracked to suppress duplicate assistant confirmations.

## Reply shaping + suppression

* Final payloads are assembled from:
  * assistant text (and optional reasoning)
  * inline tool summaries (when verbose + allowed)
  * assistant error text when the model errors
* The exact silent token `NO_REPLY` / `no_reply` is filtered from outgoing
  payloads.
* Messaging tool duplicates are removed from the final payload list.
* If no renderable payloads remain and a tool errored, a fallback tool error reply is emitted
  (unless a messaging tool already sent a user-visible reply).

## Compaction + retries

* Auto-compaction emits `compaction` stream events and can trigger a retry.
* On retry, in-memory buffers and tool summaries are reset to avoid duplicate output.
* See [Compaction](/concepts/compaction) for the compaction pipeline.

## Event streams (today)

* `lifecycle`: emitted by `subscribeEmbeddedPiSession` (and as a fallback by `agentCommand`)
* `assistant`: streamed deltas from pi-agent-core
* `tool`: streamed tool events from pi-agent-core

## Chat channel handling

* Assistant deltas are buffered into chat `delta` messages.
* A chat `final` is emitted on **lifecycle end/error**.

## Timeouts

* `agent.wait` default: 30s (just the wait). `timeoutMs` param overrides.
* Agent runtime: `agents.defaults.timeoutSeconds` default 172800s (48 hours); enforced in `runEmbeddedPiAgent` abort timer.
* LLM idle timeout: `agents.defaults.llm.idleTimeoutSeconds` aborts a model request when no response chunks arrive before the idle window. Set it explicitly for slow local models or reasoning/tool-call providers; set it to 0 to disable. If it is not set, FluffBuzz uses `agents.defaults.timeoutSeconds` when configured, otherwise 120s. Cron-triggered runs with no explicit LLM or agent timeout disable the idle watchdog and rely on the cron outer timeout.

## Where things can end early

* Agent timeout (abort)
* AbortSignal (cancel)
* Gateway disconnect or RPC timeout
* `agent.wait` timeout (wait-only, does not stop agent)

## Related

* [Tools](/tools) — available agent tools
* [Hooks](/automation/hooks) — event-driven scripts triggered by agent lifecycle events
* [Compaction](/concepts/compaction) — how long conversations are summarized
* [Exec Approvals](/tools/exec-approvals) — approval gates for shell commands
* [Thinking](/tools/thinking) — thinking/reasoning level configuration