docs: add proactive compression docs

[opieter-aws]

Description

Related Issues

Type of Change

• New content
• Content update/revision
• Structure/organization improvement
• Typo/formatting fix
• Bug fix
• Other (please describe):

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using npm run dev
• Links in the documentation are valid and working

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[github-actions]

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Updated at: 2026-05-07T21:14:44.278Z

[github-actions]

Assessment: Comment

The documentation is well-written and clearly explains a complex feature (proactive context compression). The code snippets follow existing patterns, the section structure is logical, and cross-references between token counting and proactive compression are solid.

Review Notes

• Correctness: The token counting snippet in index.ts references an undefined agent variable — see inline comment for details.
• Design doc alignment: The design doc (0008) uses threshold as the parameter name while these docs use compressionThreshold. If the implementation landed with compressionThreshold, this is fine (design doc is aspirational), but worth confirming.

Nice work documenting both the high-level concept and the internals (token estimation strategy, provider support table).

[github-actions]

Assessment: Approve

This PR adds clear, well-organized documentation for proactive context compression. The code snippets follow established patterns (function scoping, snippet markers), cross-references between pages are consistent, and the external link to the SDK source code is valid. The prior review comment about the undefined agent variable in the token counting snippet has been resolved. No new issues identified.