## Why
This stack crosses World State, executor skills, selected plugin
metadata, MCP processes, connectors, dynamic environments, and resume.
This PR adds two end-to-end scenarios that validate those pieces
together.
Both tests enable `deferred_executor`, so they exercise the real
delayed-environment path.
## Scenario 1: availability across turns and resume
```text
1. Start a thread with one selected plugin root bound to E1.
2. E1 is unavailable.
- executor skill is absent
- selected MCP is absent
- connector has no selected-plugin attribution
3. Start E1 and register the same stable environment ID.
4. Start a new turn.
- the executor skill appears through World State
- its body beats a colliding host skill
- the selected MCP tool is advertised and executes inside E1
- the connector is attributed to the selected plugin
5. Start another turn without changing E1.
- the MCP PID stays the same, proving runtime reuse
6. Restart app-server and resume the thread.
- durable selected-root intent is restored
- skills, MCP, and connector attribution are restored
- a new MCP PID proves ephemeral process state was rebuilt
```
## Scenario 2: availability changes inside one turn
```text
1. Start a turn while E1 is unavailable.
2. The first model sample sees no executor skill, MCP, or selected connector.
3. The turn pauses on request_user_input.
4. Start E1 and register it while that same turn is still active.
5. Continue the turn.
6. The very next model sample sees:
- the executor skill catalog
- the selected MCP tool
- selected-plugin connector attribution
7. The model calls the MCP, and its output proves execution happened inside E1.
```
This second scenario specifically protects the aeon-style behavior:
capability state is captured again for every sampling step, not only at
the next user turn.
## Scope
These are integration tests only. They do not add a combinatorial matrix
for unsupported plugin-file mutation, environment generations, transport
disconnects, or delayed `required = true` executor MCPs.
jif