The profile_home stamp exists to let serves_routed_profile() see a foreign-home scope without the
HERMES_HOME override. Stamping the LAUNCH home from the own-home binders (launch_profile_runtime_scope,
_worker_profile_scope's launch arm, model_switch's launch arm) added nothing for production but, under
a test conftest where server._hermes_home differs from HERMES_HOME, flipped the launch profile to
'routed' and charged every turn a routed tool/plugin discovery. Own-home binders now leave the stamp
None; the foreign-home arms keep it.
is_profile_gate_env resolved the platform prefix set (Platform enum + bundled plugin scan + registry)
once per env key; strip_profile_gate_env walks the whole child env, so a spawn paid the scan
hundreds of times. The static half is lru_cached, the dynamic registry union is taken once per strip.
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