545e74d0ea made _reactions_enabled consult extra.reactions before the env
var, and _apply_yaml_config seeds extra["reactions"] whenever the YAML key
is present — including the stock reactions: false every install
materializes. The documented TELEGRAM_REACTIONS=true switch therefore
became a silent no-op after the 0.21.2 update (#109032), contradicting
yaml_env_setter's "explicit env wins over YAML" contract.
Read the scoped env first and fall back to the profile's own YAML: under
multiplex a scoped miss returns the default instead of another profile's
process-env value (#72348), so only a scoped/env hit counts as explicit
and per-profile isolation is unchanged.
Fixes#109032
(cherry picked from commit 2bd5a0a5c0a5f9630fd82f133def65f225f653a3)
d92490a4e4