Problem Statement

list_credentials and check_agent behaved inconsistently: check_agent loaded shell environment variables before checking credential availability, while list_credentials did not. Additionally, list_credentials failed to resolve spec-name aliases (e.g. gmail_oauth → provider google) when filtering, and silently skipped flat-file credentials saved by the GUI that lack the "/" separator used by LocalCredentialRegistry.

Proposed Solution

Align list_credentials to follow the same startup steps as check_agent:

1. Call ensure_credential_key_env() so shell-config keys are visible during availability checks.
2. Resolve spec-name aliases via CREDENTIAL_SPECS before filtering accounts by credential_id.
3. Supplement LocalCredentialRegistry results with flat-file credentials read directly from EncryptedFileStorage, deduplicated against already-listed accounts.