Authoring Trigger Plugins

Audience: developers extending Animus with a custom event source — Slack sockets, file watchers, cron timers, third-party webhook adapters, or anything that pushes work into the daemon from outside.

This guide is the trigger-flavored companion to Plugin Author Guide. Read that first; this document zooms in on the trigger_backend plugin kind specifically.

1. When to reach for a trigger plugin

Animus ships four trigger types in workflow YAML:

`type:`	What it is	When to use it
`file_watcher`	Built-in glob watcher driven by the daemon's tick loop	Watching files inside the project root with a simple debounce
`webhook`	Built-in HTTP webhook listener	Receiving inbound HTTP POSTs (Stripe, generic SaaS) into the daemon's HTTP transport
`github_webhook`	Built-in GitHub webhook listener with event-shape validation	Reacting to GitHub pushes, PRs, issues
`plugin`	External `trigger_backend` plugin	Anything else: Slack sockets, JetBrains IDE hooks, custom polling adapters, queue subscriptions, cron, IMAP listeners — anything that needs first-party process state outside the daemon

A plugin trigger delegates event production to a standalone executable the daemon discovers, spawns, and supervises. The plugin emits trigger/event notifications over stdio; the daemon routes each event into the same pending_events queue the built-in trigger types use, then drains them on the tick loop and dispatches the configured workflow.

Pick plugin when:

The source needs a long-lived subprocess (websocket, IMAP IDLE, an inotify watcher outside the project tree, a tail of a remote log).
The event shape needs domain-specific decoding the daemon should not carry (Slack thread metadata, JIRA webhook signatures, a corporate intranet listener).
You want to package and version the integration independently of the daemon release cycle.

Pick a built-in type when:

Globs under the project root suffice (file_watcher).
The daemon's HTTP transport can be a public endpoint (webhook, github_webhook).

2. The trigger protocol surface

Triggers are the third plugin kind alongside subject_backend and provider. Wire shapes live in crates/animus-plugin-protocol/src/lib.rs and are mirrored upstream in launchapp-dev/animus-protocol at tag v0.5.5. Generated projects depend on the upstream crate; the in-tree copy in this repo is the source of truth the daemon supervises against.

Method-name constants

Constant	Wire method	Direction	Purpose
`TRIGGER_METHOD_WATCH`	`trigger/watch`	host → plugin	Open the event stream. Plugin acks then keeps pushing notifications.
`TRIGGER_METHOD_EVENT`	`trigger/event`	plugin → host	Notification carrying a `TriggerEvent`.
`TRIGGER_METHOD_ACK`	`trigger/ack`	host → plugin	Confirms a delivered event id. Plugins use this to trim a server-side queue or advance a cursor.

Lifecycle methods (initialize, initialized, $/ping, health/check, shutdown, exit) are inherited from the generic plugin contract documented in the Plugin Author Guide.

Event payload

A TriggerEvent carries:

pub struct TriggerEvent {
    pub event_id: String,
    pub trigger_id: Option<String>,
    pub subject_id: Option<String>,
    pub subject_kind: Option<String>,
    pub action_hint: Option<TriggerActionHint>,
    pub payload: serde_json::Value,
}

event_id — plugin-assigned, stable across restarts when possible. The daemon uses it to send trigger/ack.
trigger_id — matches a triggers[].id in your workflow YAML. Required for the daemon to route the event to the right workflow_ref. Best practice: read the expected trigger_id out of the opaque config block in trigger/watch so workflow authors can rename it without touching plugin code.
subject_id / subject_kind — optional. If set, the host resolves the subject through the configured subject backend and may kick that subject's assigned workflow instead of the trigger's workflow_ref.
action_hint — advisory. RunWorkflow and CreateTask are the defined variants; the host falls back to the trigger's workflow_ref when omitted.
payload - opaque JSON forwarded to the spawned workflow as input. Workflow YAML templates can reference it as {{trigger.payload.<key>}}.

Acknowledgements

TriggerAckParams carries the event_id and an optional TriggerAckStatus (Dispatched, Queued, Unmatched, Skipped, Failed, Shutdown). Backends that don't track delivery state can return a no-op response; backends with durable state should advance a cursor when status == Dispatched.

3. The daemon lifecycle

The TriggerSupervisor (in crates/orchestrator-daemon-runtime/src/schedule/trigger_supervisor.rs) owns the runtime relationship with every installed trigger plugin:

Discover. On daemon start the supervisor calls orchestrator_plugin_host::discover_plugins(project_root) and keeps the subset whose manifest declares plugin_kind = "trigger_backend".
Spawn. Each plugin is launched as a stdio child via PluginHost::spawn_with_options, with stderr forwarded into the daemon log.
Handshake. The supervisor drives the initialize / initialized exchange. Plugins that fail the handshake within the lifecycle timeout are abandoned with a StartFailed lifecycle event.
Watch. The supervisor sends trigger/watch with the merged config from any matching workflow YAML triggers and starts draining the notification stream.
Route. Every trigger/event notification is appended to TriggerRunState::pending_events. The tick loop's TriggerDispatch::process_due_triggers drains those events each tick and enqueues the configured workflow.
Ack. After the host accepts an event for dispatch it sends trigger/ack with the event id and a TriggerAckStatus.
Supervise. If the plugin's stdio closes or an error bubbles up, the supervisor restarts it with exponential backoff (1s, 2s, 4s, 8s, 16s, capped at 60s). After MAX_RESTART_ATTEMPTS consecutive failures it emits a final Crashed event and gives up; plugins that run cleanly for at least HEALTHY_WINDOW reset their attempt counter.
Shutdown. On daemon stop the supervisor sends shutdown to each plugin, waits up to 2 seconds for the child to exit, then closes stdio.

The ANIMUS_DAEMON_DISABLE_TRIGGERS=1 env var skips trigger supervision entirely. Useful when debugging whether observed behavior is plugin-sourced or comes from the built-in webhook/file-watcher path.

4. Manifest format

A trigger plugin needs:

A --manifest JSON output on the binary itself (the daemon's primary discovery path).
A plugin.toml mirror of the manifest for static tooling (animus plugin info against an uninstalled tree, CI lint, the public registry).

Minimal plugin.toml for a trigger:

name        = "animus-trigger-fswatch"
version     = "0.1.0"
plugin_kind = "trigger_backend"
description = "Reference filesystem-watch trigger backend"
binary      = "animus-trigger-fswatch"
protocol    = "stdio"

env_required = []

The runtime manifest emitted by --manifest is built by the animus-plugin-runtime Plugin::new(...).description(...).methods(...) chain — keep plugin.toml in sync with that chain when you change declared methods or env requirements.

The host clears the daemon's environment before spawn and forwards only a minimal shell allowlist (PATH, HOME, TMPDIR, LANG, LC_ALL, RUST_LOG, RUST_BACKTRACE, TZ) plus anything listed in env_required. Secrets the plugin needs at spawn time (Slack token, GitHub PAT, ...) must be declared here.

5. Scaffold a new trigger plugin

animus plugin scaffold trigger <name> writes a minimal, self-contained Cargo project from built-in templates. Unlike animus plugin new (which clones launchapp-dev/animus-plugin-template), the scaffold subcommand works offline and pins a known-good protocol tag:

animus plugin scaffold trigger fswatch \
    --owner acme-co \
    --license MIT

Output (default):

animus-trigger-fswatch/
├── Cargo.toml          # depends on animus-plugin-protocol + animus-plugin-runtime @ v0.5.5
├── plugin.toml         # static manifest mirror
├── src/main.rs         # initialize + trigger/watch + trigger/ack + health/check
├── README.md           # build, install, wire, debug
└── .gitignore

Flags:

Flag	Default	Purpose
`<NAME>`	required	Plugin short name in kebab-case
`--owner <OWNER>`	`$USER` then `launchapp-dev`	GitHub user/org for the generated `repository` field
`--out-dir <PATH>`	`./animus-trigger-<name>`	Output directory
`--license <ID>`	`MIT`	SPDX license identifier for `Cargo.toml`
`--description <TEXT>`	auto	Short description for Cargo.toml + README
`--protocol-tag <TAG>`	`v0.5.5`	`launchapp-dev/animus-protocol` git tag to pin
`--force`	off	Overwrite existing output directory
`--json`	off	Emit result envelope as JSON

The generated src/main.rs is a working skeleton: it implements every method the supervisor expects and emits a periodic heartbeat event so you can wire the plugin end-to-end before plumbing real upstream state. Replace the loop in spawn_event_loop with your real upstream listener.

6. Walkthrough: `examples/triggers/fswatch`

examples/triggers/fswatch/ is a complete working trigger plugin you can use as the next reference past the scaffold output. It watches a glob list and emits a trigger/event notification when a matching file is modified.

Build + install

cd examples/triggers/fswatch
cargo build --release
animus plugin install --path target/release/animus-trigger-fswatch
animus plugin info animus-trigger-fswatch

Workflow YAML wiring

workflows:
  - id: review-source-change
    phases:
      - name: review
        tool: claude

triggers:
  - id: fswatch-default
    type: plugin
    workflow_ref: review-source-change
    config:
      trigger_id: fswatch-default
      globs:
        - src/**/*.rs
        - docs/**/*.md
      debounce_ms: 250

The daemon forwards every enabled type: plugin entry from workflow YAML in TriggerWatchParams.config:

{
  "triggers": [
    {
      "id": "fswatch-default",
      "workflow_ref": "review-source-change",
      "config": {
        "trigger_id": "fswatch-default",
        "globs": ["src/**/*.rs", "docs/**/*.md"],
        "debounce_ms": 250
      }
    }
  ]
}

Plugins read this list, pick the entries they understand, and emit events whose trigger_id matches the corresponding id. The daemon is intentionally agnostic about per-plugin filtering — it ships every plugin-typed trigger to every trigger plugin, and each plugin is expected to ignore unknown entries silently. This keeps the workflow YAML schema minimal (no plugin_name on each trigger) at the cost of making plugins responsible for filtering.

fswatch deserializes its entry's config block into:

struct FswatchConfig {
    trigger_id: Option<String>,
    globs: Vec<String>,
    debounce_ms: Option<u64>,
}

The plugin attaches a notify::RecommendedWatcher to each glob's parent directory, debounces bursty modify events into one delivery per debounce window, and emits:

{
  "event_id": "fswatch:src/lib.rs:1717003812000",
  "trigger_id": "fswatch-default",
  "action_hint": "run_workflow",
  "payload": {
    "path": "src/lib.rs",
    "kind": "modified",
    "occurred_at": "2026-05-30T18:30:12Z"
  }
}

The daemon resolves trigger_id against the workflow YAML, runs review-source-change, and acknowledges receipt via trigger/ack. The fswatch plugin removes the acked id from its in-memory delivered set; backends with durable state would persist the cursor at this point.

Architectural notes worth lifting

Cancellation. The watch handler calls ctx.keep_cancellation() so the cancellation token survives the ack-and-return of the handler. The background loop selects on cancellation.cancelled() and exits cleanly when the daemon issues shutdown.
Health. The plugin reports Degraded until the watcher is attached, Healthy while it is running, and Unhealthy if the background loop crashed. Use this pattern so the daemon's animus daemon health surface reflects reality.
Debounce. A flapping editor that touches a file four times in one save is one event. Match the debounce window to your workload.

7. Debugging

Symptom	First check
Plugin doesn't show up in `animus plugin list`	`--manifest` JSON shape — run the binary with `--manifest` and confirm `plugin_kind == "trigger_backend"`
Plugin shows up but never fires events	Daemon process log at `~/.animus/<repo-scope>/daemon/daemon.log` and structured runtime events at `~/.animus/<repo-scope>/logs/events.jsonl` — supervisor emits `StartFailed`, `Started`, `Restart`, `Crashed`, and `Event` lifecycle JSON lines
Events fire but no workflow runs	Workflow YAML `triggers[].id` does not match the plugin's `trigger_id`; check `animus workflow validate`
Plugin keeps restarting	Check the daemon log for the `Crashed` event and the stderr forwarded from the plugin
Want to isolate the plugin	`ANIMUS_DAEMON_DISABLE_TRIGGERS=1 animus daemon start` — supervisor is skipped, so any remaining trigger fires came from the built-in `file_watcher` / `webhook` path
Want to drive the plugin manually	Pipe JSON-RPC on stdin (see the fswatch README for a worked example)

Plugin stderr is forwarded into the daemon process log unchanged. Set RUST_LOG=<plugin_crate>=debug in the daemon's environment to surface the plugin's tracing output.

8. Publishing

Once your plugin is stable:

Tag a release on a public GitHub repo (launchapp-dev/animus-trigger-foo or your own org).
Use cosign sign-blob --keyless to sign the release asset.
Submit a PR to launchapp-dev/animus-plugin-registry adding your plugin to plugins.json. Once merged, users can install with animus plugin install <owner>/<repo> and discover via animus plugin search --kind trigger.

See Plugin Author Guide §6 for the publishing details that apply to every plugin kind.

9. See also

docs/guides/plugin-author-guide.md — the kind-agnostic plugin authoring story.
docs/reference/workflow-yaml.md — the workflow YAML reference, including the triggers: section.
docs/reference/cli/index.md — animus plugin scaffold and animus plugin install reference.
examples/triggers/fswatch/README.md — worked reference implementation.
crates/animus-plugin-protocol/src/lib.rs — the wire-shape source of truth.
crates/orchestrator-daemon-runtime/src/schedule/trigger_supervisor.rs — daemon-side supervisor.

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Authoring Trigger Plugins

1. When to reach for a trigger plugin

2. The trigger protocol surface

Method-name constants

Event payload

Acknowledgements

3. The daemon lifecycle

4. Manifest format

5. Scaffold a new trigger plugin

6. Walkthrough: `examples/triggers/fswatch`

Build + install

Workflow YAML wiring

Architectural notes worth lifting

7. Debugging

8. Publishing

9. See also

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Authoring Trigger Plugins

1. When to reach for a trigger plugin

2. The trigger protocol surface

Method-name constants

Event payload

Acknowledgements

3. The daemon lifecycle

4. Manifest format

5. Scaffold a new trigger plugin

6. Walkthrough: examples/triggers/fswatch

Build + install

Workflow YAML wiring

Architectural notes worth lifting

7. Debugging

8. Publishing

9. See also

6. Walkthrough: `examples/triggers/fswatch`