feat(modes): add native compact and extreme surfaces

[lennney]

Summary

• Introduce the public Native, Compact, and Extreme product modes for the
  0.2.0-alpha.1 line.
• Preserve complete authorized tool schemas for Compact and Extreme discovery,
  validate arguments against the original schema before contacting upstream,
  and keep exact result recovery through read_result.
• Replace legacy compressor and model-selection evaluation paths with the
  public mode evaluation runner, schemas, deterministic evidence, and agent
  engineering contract.

Why

The new surface keeps a small, predictable tool interface where it helps Host
compatibility while preserving parameter completeness and recoverable delivery.
Native remains available for Hosts that need the normal authorized catalog.

Validation

• npm run ci
• 43 test files passed, 499 tests passed, 1 skipped
• Coverage: 83.46% statements, 78.12% branches, 93.29% functions
• Package boundary: 73 files, 403284 unpacked bytes, zero source maps
• Public-boundary review removed private worktree naming from contribution docs

Safety and scope

• Configuration is version 2; version 1 is rejected without automatic
  migration.
• No private workbench plans, hidden tasks, thresholds, credentials, or Host
  model calls are included.
• This PR does not publish a release or make registry changes.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

State Extreme's 50% threshold in the correct direction

For an Extreme response whose projected delivery is more than half the exact response, the implementation passes it through (minimumSavingsRatio: 0.5 and the check in src/result-capsule-store.ts); projection occurs only when the delivered response is at most half the original size. This text says the opposite, which can mislead users evaluating when Extreme will activate. The Chinese README already describes the intended “at least half smaller” behavior.

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