When cached or freshly-discovered provider models carry UNK_CONTEXT_WINDOW
(222222) / UNK_MAX_TOKENS (8888) sentinels, #mergeResolvedModels was
replacing the bundled model wholesale — wiping out the correct values.
Switch to a field-level merge that preserves the bundled model's
contextWindow and maxTokens when the replacement only has sentinel
fallbacks. Custom models (via #mergeCustomModels) already had this
protection via ?? fallback; provider discoveries didn't.
Fixes the TUI showing 222222/8888 instead of the real context/token
limits for discovered models.
Burke T
fcaafda0fa