Bug Description

When using a custom provider with a per-model context_length, the global model.context_length (e.g. 200K) always wins — the custom provider's setting is silently ignored. The displayed context length jumps to the global default regardless of what's configured.

Root Cause

Two bugs stacked:

1. model_metadata.py — resolution order bug: Step 0 of get_model_context_length() returns the global config_context_length before Step 0b ever checks custom_providers[].models[].context_length. The per-model override is unreachable.

2. cli.py — missing custom_providers in display: Both CLI /model display paths call resolve_display_context_length() without passing custom_providers, so even if the resolution were correct internally, the displayed value would still show 200K.

(The gateway display paths in run.py already pass custom_providers correctly — this was a CLI-only omission.)

Fix

agent/model_metadata.py — In Step 0, before returning the global config_context_length, check for a matching custom provider entry. If the current provider is a custom provider with a models.<model>.context_length override, return that value instead.

cli.py — Both display paths now load custom_providers from config and pass them to resolve_display_context_length().

How to Verify

1. Add a custom provider with a per-model context_length:

   custom_providers:
     - name: my-inference
       base_url: http://192.168.1.116:8080/v1
       model: my-model.gguf
       models:
         my-model.gguf:
           context_length: 131072

2. Switch to this provider (/model custom:my-inference)
3. CLI now displays 131,072 instead of 200,000

Risk Assessment

Low. Both changes are additive — they only enable a path that was previously blocked (custom_providers lookup inside existing guard clauses). For non-custom-provider users, behavior is identical: no custom_providers means no override, falls through to the global default as before.

Test Plan

• Manual: /model display now shows correct context for custom providers
• Python unit test: resolve_display_context_length() returns 131072 with custom_providers, 200000 without
• Existing tests pass (no behavioral change for non-custom providers)