@rodboev. providers.<name>.models.<model>.context_length overrides (standard provider,
no base_url) were invisible to the session context resolver → wrong window shown/persisted,
could trip auto-compression at the wrong threshold. New _context_length_lookup_inputs_for_model
helper resolves provider config / base_url / custom_providers across route-load, session-save,
and SSE-usage paths; provider-scoped overrides match by provider name and forward as
config_context_length (returned before any base-url-gated probe).
Maintainer pre-merge items both already satisfied in PR head: no-base_url regression test
(test_route_resolver_uses_provider_model_context_length_without_base_url) present; session-save
_cfg_base_url assigned before the helper call (safe-bound, no NameError on TypeError fallback).
Verified api code byte-identical to PR head; 14 context-length tests pass. + CHANGELOG v0.51.300.
Co-authored-by: nesquena-hermes <[email protected]>
