Restores the env-source seeding loop in _seed_from_env that was dropped
by upstream refactors. Without this, any env-source entry whose env var
name isn't in the provider registry's hardcoded api_key_env_vars tuple
stays empty forever, gets filtered out of rotation by _available_entries,
and round-robin silently degrades to single-key behavior.
Forward-port of ba71e00db07c6263ee8d44b27dfbce2a92e6b39c onto current main
f1ccf436a2. Narrow insertion after final
env_vars list in _seed_from_env: scan only existing entries whose source
begins with env:, extract/dedupe the named variable, and let the existing
seeding path hydrate it via get_env_prefer_dotenv (preserving _Seeder,
secret-scope/profile isolation, borrowed-secret sanitization, and
suppression behavior).
Tests: 10 new tests in test_credential_pool_seed_existing_env_sources.py
covering three-key hydration, round_robin cycling, dotenv/secret-scope
resolution without os.environ bypass, duplicate dedupe, manual rows
untouched, unset remains unavailable, and sanitized persistence.
McClean-Newton
23afade67b