Add Pi runtime context and fast model settings

[YJJosh]

Summary

• Add Pi context-window controls based on model limits and the active profile’s /context command support.
• Synchronize model, reasoning, context-window, and Codex Fast settings before sending prompts.
• Enable Fast service for supported GPT-5.6 Codex models and validate context values against command injection.
• Expand server and composer tests and document the Pi runtime settings behavior.

Testing

• Not run (PR content generated from the provided commit and diff).

Note

Add Pi runtime context window selection and fast model settings

• Adds /context command support to the Pi adapter, allowing context-window size to be synchronized before each prompt via syncContextWindow in PiAdapter.ts.
• Model discovery in piModelDiscovery.ts now exposes a 'Context Window' selector with an 'Auto' default and preset numeric options when the Pi profile advertises the context command.
• Expands Fast-supported model slugs to include gpt-5.6-* variants and adds parsePiContextWindow to validate/normalize context values before sending them to Pi.
• Reasoning defaults to high when supported, both in Pi model capabilities and in Codex model capabilities when defaultReasoningEffort is unavailable.
• Behavioral Change: unsupported /context and /fast selections now emit runtime warnings and are silently ignored instead of throwing errors.

^{Macroscope summarized 86fac02.}

[chatgpt-codex-connector]

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[YJJosh]

@macroscope-app review

[macroscopeapp]

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[macroscopeapp]

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR adds new runtime context window and fast model settings that change Pi provider behavior. An unresolved review comment identifies a profile-mismatch issue where advertised options may cause errors with certain profile selections.

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