A session row persists the provider identity a chat actually used. When that
provider is later renamed or removed (e.g. a custom_providers:/providers:
entry deleted, or a provider renamed oldone->newone), Desktop/TUI resume
restores the stale name into agent init and dies with:
agent init failed: Unknown provider '<name>'
while the CLI resumes the same session fine with the configured default.
- runtime_provider: add is_routable_provider() (full resolution chain:
built-in -> providers: -> custom_providers: -> models.dev)
- _stored_session_runtime_overrides: heal a non-routable provider via
canonical_custom_identity (base_url -> model -> configured provider),
drop to the configured default when unrecoverable, and clear the stale
base_url after healing so a dead endpoint cannot override the registry URL
- _start_agent_build: gate deferred-resume overrides on provider routability;
when the stored provider is gone, prefer the model the user picked for THIS
session, else the configured default
- tests: is_routable_provider cases, heal/fallback round-trips, gate checks
Refs #75128
99a6852019