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english/.opencode/skills/context-engineering/references/context-compression.md
2026-04-12 01:06:31 +07:00

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# Context Compression
Strategies for long-running sessions exceeding context windows.
## Core Insight
Optimize **tokens-per-task** (total to completion), not tokens-per-request.
Aggressive compression causing re-fetching costs more than better retention.
## Compression Methods
| Method | Compression | Quality | Best For |
|--------|-------------|---------|----------|
| **Anchored Iterative** | 98.6% | 3.70/5 | Best balance |
| **Regenerative Full** | 98.7% | 3.44/5 | Readability |
| **Opaque** | 99.3% | 3.35/5 | Max compression |
## Anchored Iterative Summary Template
```markdown
## Session Intent
Original goal: [preserved]
## Files Modified
- file.py: Changes made
## Decisions Made
- Key decisions with rationale
## Current State
Progress summary
## Next Steps
1. Next action items
```
**On compression**: Merge new content into existing sections, don't regenerate.
## Compression Triggers
| Strategy | Trigger | Use Case |
|----------|---------|----------|
| Fixed threshold | 70-80% utilization | General purpose |
| Sliding window | Keep last N turns + summary | Conversations |
| Task-boundary | At logical completion | Multi-step workflows |
## Artifact Trail Problem
Weakest dimension (2.2-2.5/5.0). Coding agents need explicit tracking of:
- Files created/modified/read
- Function/variable names, error messages
**Solution**: Dedicated artifact section in summary.
## Probe-Based Evaluation
| Probe Type | Tests | Example |
|------------|-------|---------|
| Recall | Factual retention | "What was the error?" |
| Artifact | File tracking | "Which files modified?" |
| Continuation | Task planning | "What next?" |
| Decision | Reasoning chains | "Why chose X?" |
## Six Evaluation Dimensions
1. **Accuracy** - Technical correctness
2. **Context Awareness** - Conversation state
3. **Artifact Trail** - File tracking (universally weak)
4. **Completeness** - Coverage depth
5. **Continuity** - Work continuation
6. **Instruction Following** - Constraints
## Guidelines
1. Use anchored iterative for best quality/compression
2. Maintain explicit artifact tracking section
3. Trigger compression at 70% utilization
4. Merge into sections, don't regenerate
5. Evaluate with probes, not lexical metrics
## Related
- [Context Optimization](./context-optimization.md)
- [Evaluation](./evaluation.md)