Model access denial caching reworked with a 'reprobe' system

What

When Claude Code decides a model isn't accessible and caches that denial, it now tracks this in a new per-session state object called sessionModelDenyReprobe. This replaces the older fields that used to track this (lastGoodAntOverrideConfig and antCapabilitiesByModelId).

The new state tracks:

• Which models have been confirmed accessible (honoredModels)
• Denials that are contested and being rechecked (contestedDenies)
• Models that were genuinely refused (refusedModels)
• A generation counter and a restricted flag

The logic that checks model access was rewritten to use this state: it can mark a cached denial as contested and kick off an asynchronous recheck ('reprobe') that can overturn a previously cached denial if the model turns out to be accessible after all.

Why

Previously, once a model was cached as denied, Claude Code might keep treating it as unavailable even if that access actually became valid again. The reprobe system lets a stale denial get corrected automatically instead of requiring a restart or manual retry.