fix: clear stale global context length on model switch

[hubdev4]

Summary

• Clear stale model.context_length global overrides when switching models/providers.
• Prevent custom endpoint context lengths from leaking into later provider selections.
• Keep custom endpoint context lengths scoped to custom provider model metadata.
• Add regression coverage for the deepsproxy-style custom provider flow.

Credit: this fix was implemented with Hermes Agent.

Why

model.context_length is a global runtime override. If a custom endpoint setup left context_length: 64000 in the global model: block, every provider selected afterward could inherit that 64k limit, including Codex, OpenAI, Anthropic, and other non-custom providers.

The custom provider wizard should preserve context length only as provider/model metadata, not as a global model override.

Testing

• scripts/run_tests.sh tests/cli/test_cli_provider_resolution.py tests/hermes_cli/test_custom_provider_model_switch.py tests/hermes_cli/test_model_switch_custom_providers.py tests/hermes_cli/test_user_providers_model_switch.py -q
• Result: 79 passed

Co-authored-by: Hermes Agent hermes-agent@users.noreply.github.com

[alt-glitch]

Note: PR #24724 (merged 2026-05-13) is the authoritative fix for clearing stale _config_context_length on model switch. This PR addresses a related but distinct path — global model.context_length leaking from custom endpoint setup into subsequent provider selections. Please verify this isn't already covered by #24724. Related: #24079, #11438.

[teknium1]

Thanks for isolating the persisted-config path; the underlying issue remains on current main.

Problems

• The implementation needs a conflict-aware salvage: the changed _model_flow_custom, _model_flow_named_custom, and _model_flow_api_key_provider functions were extracted from hermes_cli/main.py into hermes_cli/model_setup_flows.py by a77efada5. Current custom setup still preserves the stale value at hermes_cli/model_setup_flows.py:947-960, so the old main.py hunks do not affect the live flow.
• The new regression test stubs _save_model_choice at tests/cli/test_cli_provider_resolution.py:564, but the PR changes that helper at hermes_cli/auth.py:5148. It does not cover that central mutation.

Suggested changes

• Port the cleanup to the extracted flow and add a test using the real save path. Assert the active model.context_length is cleared while custom_providers[].models.<model>.context_length remains intact; runtime precedence is visible in agent/agent_init.py:1660-1708.

Automated hermes-sweeper review.

[teknium1]

This stubs the helper changed in hermes_cli/auth.py:5148, so the regression does not exercise that central cleanup. Keep this flow test if it validates the explicit flow cleanup, but add a separate real _save_model_choice assertion for the helper behavior.