## 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:
```text
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.
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