What does this PR do?

When context_length == MINIMUM_CONTEXT_LENGTH (64000), the threshold calculation max(int(context_length * 0.50), MINIMUM_CONTEXT_LENGTH) produces max(32000, 64000) = 64000, setting the compression threshold to 100% of the context window. The API errors before tokens ever reach that value, so auto-compression never triggers for models at the minimum context length.

The fix clamps threshold_tokens to at most 95% of context_length after the existing floor, preserving the MINIMUM_CONTEXT_LENGTH floor for large-context models (where the clamp is a no-op) while ensuring compression can always trigger before the API limit.

Related Issue

Fixes #14690

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• agent/context_compressor.py: After the existing max() floor, clamp threshold_tokens to at most 95% of context_length. Applied in both __init__ and update_model(). Additionally, update_model() now recomputes all derived budgets (tail_token_budget, max_summary_tokens) — previously it only updated threshold_tokens, leaving stale budget values after model switches.

How to Test

1. Run:

   python -m pytest tests/agent/test_context_compressor.py -v

2. 4 new tests in TestThresholdClampAtMinimumContext:
   • Threshold is below context_length at MINIMUM_CONTEXT_LENGTH
   • should_compress() triggers correctly at threshold boundary
   • update_model() produces a working threshold
   • Large-context models are unaffected by the clamp

Tested on macOS (Python 3.11).

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS 15 (Darwin 24.6.0)

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

python -m pytest tests/agent/test_context_compressor.py -v
# 4 new tests in TestThresholdClampAtMinimumContext pass