Adds the harness plug-in kind (interface 1). packages/plugins/harness/pi
and claude-code hold what core branched on: the adapter, thinking levels,
preflight, version probe, sandbox mounts, builtins line, typed tool names,
gate timeout, bundle files, adapter env, turn end and session-files path.
Core reaches a module only through the loader.
A session's route is the instance's harness, model and thinking vars, or
the three fallback. vars; a missing one refuses no-route, and the system
file's execution keys are never read for a session. The launcher checks
the primary route, then the fallback: harness-off, harness-refused,
thinking-unsupported, then preflight. A failed preflight falls back when
a fallback is set, and any refusal of the fallback names the primary's
failure too. Account checks run
only when the route's module counts an account. The manifest records
route, routeReason and harnessVersion, replacing piVersion and
claudeVersion. pi gets --thinking, Claude Code --effort, both from
MOSAIC_THINKING.
The business file refuses a partial fallback. routes and routes.set are
human-only bus verbs outside ORGANIZATION_KEYS; checkRoutes is shared by
routes.set, instances.set and limits.set and checks only changed routes.
The chief of staff changes an instance's model, and the assistant's whole
vars (Q169), through limits.set, so its route write runs the same checks.
A model outside launch.models refuses unknown-model, primary or fallback,
and routes.set passes that code through.
A new run binds only on a switched-on harness module name and records
its transcript path, which the usage reader uses. Settings gains a
Routing table with six selects per instance and loses the Role models
fieldset; it posts changed rows to /api/routes. webui/src/bus.mjs is
unchanged.
Until Jason's `mosaic plugins set` adds "harness": ["claude-code"], a new
launch refuses harness-off.
jason.woltje
c216f47dbb