Two gate-found CORE/SILENT edges fixed on-branch:
- api/config.py: switching the main default to a different custom:* provider kept
the OLD provider's base_url, routing New Chat to the wrong endpoint. The
base_url-clear on provider-change now covers custom:* too (was exempted).
- static/sessions.js: newSession() skipped the configured default when S.session
was null but the picker held stale state (e.g. after deleting the last session),
inheriting the stale model. Default now wins over legacy picker regardless of
loaded-session state (explicit empty-composer override still takes priority).
- Updated 2 stale source-grep precedence assertions + widened a brittle 6000-char
newSession() slice window to 7000 (assignment block grew; intent unchanged).
- 2 new non-vacuous regression tests (custom base_url clear; precedence).
Co-authored-by: Rod Boev <rod.boev@gmail.com>
