Give plugins a first-class, namespaced pub/sub event bus so plugin↔plugin
interaction is a declared, testable contract instead of ad-hoc imports.
Closes#64164 (sub-issue 03/14 of the plugin-interface expansion epic #64182).
Additive-only: when no plugin calls emit/subscribe, behavior is unchanged.
Interface (on PluginContext):
- `ctx.emit(event, payload=None) -> int` publishes to subscribers and returns
the count invoked. The namespace is FORCED to the plugin's own registry key
(`manifest.key or manifest.name`): pass only the bare event name, delivered
as `<key>:<event>`. Fail-closed — any name containing `:` (a `hermes:`
reserved-core prefix, a foreign `other:` namespace, or an own-colon'd name)
is rejected with a ValueError + logged warning naming the plugin.
- `ctx.subscribe(full_event, callback)` registers an ordered listener for a
fully-qualified `<plugin>:<event>`. Subscribing is unrestricted (any plugin
may listen to any published event); only emitting is namespace-gated.
Delivery mirrors invoke_hook: registration-order iteration, per-callback
try/except isolation (one raising subscriber never breaks delivery to the
rest), payload passed as `cb(**payload)`. A per-thread depth counter caps
re-entrant emits at 8 — mutually-emitting plugins terminate cleanly with one
logged warning, never an infinite loop or RecursionError.
Discoverability: optional advisory `emits:`/`listens:` manifest fields (no
manifest-v2 dependency; not enforced) are parsed and surfaced by a new
`hermes plugins show <name>` (alias `info`) command. `get_plugin_subscriptions()`
module accessor mirrors `get_plugin_auxiliary_tasks()`.
Tests (tests/hermes_cli/test_plugin_event_bus.py, 22): two-plugin delivery +
listener count; forced namespace (delivered as `b:ping`); spoof rejection
(parametrized `hermes:x` / foreign / own-colon'd / `:x` / `x:` / empty) with
no delivery; name-fallback when key empty; per-callback isolation; recursion
cap termination + warning; manifest emits/listens parsed (present/absent/from
yaml); module accessor; `plugins show` output. `pytest test_plugin_event_bus.py
test_plugin_auxiliary_tasks.py` → 37 passed. I independently re-verified the
namespace rejection and recursion-cap termination outside the test suite.
Note: the reserved-name gate rejects any `:`-containing input rather than a
bare-name denylist — a bare `core_event` is allowed and delivered under the
plugin's own namespace. Say the word if a reserved bare-name list is wanted.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013b1XyXitAxV7phGmKWigJX
Hans