avoid infinite recursion from missing model

[amunger]

fix #302532

confirmed the fix with https://builds.code.visualstudio.com/builds/insider?commit=663b88e0e69b5172cd7b165da010f6c768f9cdd4&dev=true

[Copilot]

Pull request overview

Fixes a hang/infinite recursion scenario in the extension host language model selection flow when the main thread returns model identifiers that are missing from the extension host’s local model cache (notably in Remote-SSH scenarios, per #302532).

Changes:

• Add a resolveIfMissing parameter to getLanguageModelByIdentifier to control whether it should trigger a re-resolve via selectLanguageModels.
• Prevent re-entrant resolution loops by disabling “resolve-if-missing” when selectLanguageModels is already in progress.
• Improve logging for the “model missing from local cache” case without re-triggering model selection.

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