Test selected capabilities across unavailable resume

[jif-oai]

Why

The selected-capability integration test already covers initial attachment and cold resume, but it resumes while the selected executor is still reachable.

That leaves an important World State transition untested: a thread remembers its selected capability root, resumes while that environment is unavailable, and later sees the same stable environment return.

What this tests

This extends the existing end-to-end scenario:

selected executor available
        ↓
app-server stops and the executor goes away
        ↓
thread resumes with the executor unavailable
        ↓
skills, selected MCP tools, and connector attribution are absent
        ↓
the same environment ID is attached again
        ↓
skills, MCP tools, and connector attribution return

The test also checks that the unavailable snapshot explicitly tells the model that no selected-environment skills are currently available. After reattachment, it invokes the selected skill again and verifies that a new executor-owned MCP process starts.

Scope

This is test-only. It keeps the existing assumption that an environment ID refers to stable capability contents. It does not add package-file invalidation or live transport reconnect behavior.