_restore_primary_runtime restored the construction-time api_key snapshot and
never consulted the credential pool. After the pool rotated away from a
revoked/exhausted entry mid-session, every new turn restored the dead key,
re-failed instantly, burned the remaining entries, and fell through to
cross-provider fallback.
After restoring the snapshot, re-select the pool's current best entry and
swap the live credential in via _swap_credential (which already rebuilds the
OpenAI/Anthropic client, reapplies base-url headers, and carries the #33163
base_url / OAuth-detection fixes). Falls back to the snapshot key when the
pool is absent, empty, or the entry has no usable key.
Salvaged from #25206 onto current main: the original targeted the pre-refactor
monolithic method in run_agent.py; the logic now lives in
agent/agent_runtime_helpers.py and is collapsed onto _swap_credential instead
of re-inlining the client rebuild.
Fixes#25205
f0de4c6a47