fix(models): preserve GPT-5.6 variant capabilities

[steipete]

Summary

• recognize GPT-5.6 Sol, Terra, and Luna behind terminal OpenRouter routing variants
• retain 372K context and 128K output capabilities without rewriting routed model IDs
• cover all three GPT-5.6 variants across :online, :nitro, :floor, and :exacto

Testing

• swift test --filter 'ModelParsingTests|OpenAICompatibleHelperTests' (51 tests)
• TACHIKOMA_DISABLE_API_TESTS=true TACHIKOMA_TEST_MODE=mock swift test --no-parallel (797 tests)
• mint run nicklockwood/SwiftFormat@0.61.1 swiftformat --lint .
• swiftlint lint --reporter xcode --strict --quiet
• autoreview: clean, no accepted/actionable findings

[clawsweeper]

ClawSweeper status: review started.

I am starting a fresh review of this pull request: fix(models): preserve GPT-5.6 variant capabilities This is item 1/1 in the current shard. Shard 0/1.

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[chatgpt-codex-connector]

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Reviewed commit: a9e0d31827

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[chatgpt-codex-connector]

Restrict route-suffix stripping to OpenRouter variants

This strips any non-empty colon suffix before capability detection, but gpt56Model(for:) is also used by OpenAICompatibleProvider and TogetherProvider, where a colon can be part of an arbitrary model tag rather than OpenRouter routing metadata. In those contexts an ID such as gpt-5.6-sol:4k is now classified as the full GPT-5.6 Sol model and gets 372K context / 128K output capabilities instead of the safe defaults, which can make clients send requests the backend cannot handle. Please limit this stripping to known OpenRouter route suffixes or OpenRouter-specific code paths.

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[steipete]

Exact-head proof for a9e0d31827f7dc681cb21294f2d5f6954fd732a0:

• regression matrix: GPT-5.6 Sol/Terra/Luna × :online, :nitro, :floor, and :exacto; exact routed IDs retained
• focused production-path tests: 51 passed
• full mock-safe suite: 797 tests in 104 suites passed
• SwiftFormat 0.61.1: 0/188 files require formatting
• SwiftLint 0.65.0 strict: clean
• autoreview: no accepted/actionable findings (0.96 confidence)
• GitHub Actions: all applicable exact-head macOS, Ubuntu, Swift 6, package, examples, format, and lint checks passed