Extends the picker fix to the read that actually uses the key: switch_model's
user-provider credential resolution (the ${VAR} api_key expansion and the
key_env fallback at the resolve-credentials step) still read os.environ raw
and passed the result to resolve_runtime_provider as explicit_api_key — so
under multiplex_profiles the actual switch, not just the picker listing,
could adopt another profile's key. Same _scoped_key_env helper, same
fail-closed semantics; identical behavior when multiplexing is off.
Adds end-to-end switch_model tests pinning that an installed scope wins over
the process environment for both read shapes.
854007d1c routed the remaining main-agent fallback key reads through
agent.secret_scope so the multiplexed gateway's per-profile scope applies.
list_authenticated_providers - which gateway/slash_commands.py calls
directly for /model - still resolved custom-endpoint and fallback-entry
credentials with raw os.environ.get(key_env), so under multiplex_profiles
one profile's picker reads whatever key the process environment happens to
hold, i.e. another profile's.
no multiplexing : profileA-key (unchanged)
scope installed : profileB-key (was profileA-key)
Route both reads through a _scoped_key_env() helper over
secret_scope.get_secret(). get_secret is identical to os.getenv when
multiplexing is off, so single-profile deployments are byte-for-byte
unchanged; a fail-closed UnscopedSecretError is treated as "no credential
visible for this profile", which is how the picker already handles a
missing key.
Scope: only the two key_env credential reads. The other environment reads
in that function are provider-presence probes (AWS creds, LM_BASE_URL),
a separate concern.