Profile isolation is a ContextVar; plain threading.Thread targets start
with an empty context, so the plugin's nine daemon threads (session
init, prewarm, first-turn base/prefetch, prefetch, sync, memwrite,
async writer, context prefetch) resolved ambient state — config path,
active host, hermes home, oauth token paths — against the DEFAULT
profile whenever they ran under a routed profile's turn.
Adds spawn_context_thread(), which copies the caller's context at spawn
time so the thread sees the profile scope it was created under, and
routes every plugin thread spawn through it. Defense-in-depth under the
bound-config work: even ambient resolution on these threads now lands
on the right profile.
The copy_context approach follows the gateway's own
_run_in_executor_with_context pattern; #81401 applied it to the init
thread, this extends it to all nine spawns.
Co-authored-by: angel12 <angel12@users.noreply.github.com>
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