The session's plugin points

The session is extended through the reactor and nothing else: each of the following is a contribution point of the agent-runtimes reactor extension (agent_runtimes.plugins), delivered under datalayer.reactor.extensions beside agent-protocols. The catalogue contributes itself, the platform its stores and hooks, a third party a harness or a format from a pip package by the same route.

Point	Value	Built in
harness	A HarnessContribution: a harness spec (its capabilities table is the spec's) and the adapter that drives it, under the spec's id	The catalogue's eight harnesses; an organization's own, read from IAM, for that organization alone
session.store	A SessionStore: list, get, entries, append, copy, lineage	The record store (ai-agents) and the file store; one active
session.format	A SessionFormat: id, export, import_	datalayer-session/1
session.carry	A SessionCarry: swap(session, target) and clone(session, target) answering what carries, what is dropped and the sentence said	The default policy
session.hook	on_open, on_resume, on_swap, on_clone, on_export, on_import, on_end — each may refuse in a sentence	The audit rows in the record; an OTEL span per operation

Fail fast at the seam. A contribution whose value is not the point's shape, or whose id another plugin contributed first, is refused with the plugin's name and the reason — the host runs with the rest, and loop plugins says what was refused. A session.store configured with two active stores refuses to start. A hook that raises stops the operation, naming the hook.

A new harness as a pip package

examples/plugins/aider-harness is a package of its own. It declares

[project.entry-points."datalayer.reactor.extensions"]
aider = "aider_harness:extension"

and its extension() returns a ReactorExtension with one plugin whose provide_contributions does

from agent_runtimes.plugins.points import HARNESSES, HarnessContribution

contributions.contribute(
    HARNESSES,
    HarnessContribution(spec=spec, adapter=acp_harness_agent),
    contribution_id="aider",
)

the yaml beside it in the same schema as the catalogue's (acp.command, requires, terms, capabilities). Installed beside agent-runtimes, loop harnesses lists aider with its terms and capabilities, an agent spec says harness: aider and the runtime resolves it through the registry; a session on it swaps, clones and exports like any other. A yaml missing terms is refused at start — a harness whose terms are unknown is not served — and a second package contributing aider is refused by name. Nothing in agent-runtimes is edited.

A new export format

examples/plugins/omnigent-format contributes a SessionFormat under omnigent-jsonl/1: its importer reads another tool's session_meta + item lines into the record's entries (a message item a turn, a function_call a tool_call, the rest refused by kind, in a sentence), its exporter the inverse. loop sessions import --format omnigent-jsonl/1 file.jsonl and POST /sessions/import?format= reach it; the built-in format is contributed the same way, so the second is no special case of the first.

Run them: examples/plugins/README.md.