Summary

This PR fixes a set of context length inconsistencies that still affect custom-provider runtimes across different execution paths.

What it fixes

• Normalize persistent context-length cache keys so /v1 and /v1/ resolve to the same provider endpoint
• Preserve configured context-length overrides when switching models
• Preserve configured context-length overrides when activating fallback models
• Avoid incorrectly reusing a per-model custom_providers context override for a different target model
• Add regression tests for cache normalization, switch-model handling, fallback handling, and configured override persistence

Root cause

There were two separate issues:

1. Persistent context-length cache lookups treated .../v1 and .../v1/ as different keys, which caused cache misses for the same custom provider endpoint in different runtime paths.
2. Runtime context refresh paths (switch_model() / fallback activation) did not consistently resolve the configured context-length override for the active target model and endpoint.

As a result, custom providers that were correctly configured in config.yaml could still fall back to an incorrect detected context length in some paths.

Implementation details

• Added base URL normalization for persistent context-length cache writes
• Made cache reads backward-compatible with legacy slash variants
• Added runtime-target-aware context-length resolution in AIAgent
• Reused that runtime-target-aware resolution when refreshing model metadata during model switch and fallback activation

Tests

Verified with:

• tests/agent/test_model_metadata.py
• tests/run_agent/test_switch_model_context.py
• tests/run_agent/test_fallback_model.py
• tests/run_agent/test_provider_fallback.py
• tests/run_agent/test_invalid_context_length_warning.py
• tests/run_agent/test_compression_feasibility.py

Local result:

• 147 passed

Notes

This PR is intentionally scoped to the runtime-path inconsistency and cache-key normalization issue. It does not introduce broader changes to provider metadata discovery beyond what is needed to make configured context lengths behave consistently.