context-optimization

# Context Optimization Techniques

Context optimization extends the effective capacity of limited context windows through strategic compression, masking, caching, and partitioning. Effective optimization increases useful capacity without requiring larger models or longer windows — but only when applied with measurement discipline. The techniques below are ordered by impact and risk.

## When to Activate

Activate this skill when:
- Context budgets or token costs constrain task complexity
- Observation masking can replace verbose tool outputs with retrievable references
- Prefix or KV-cache hit rate needs improvement
- Retrieval scoping can reduce irrelevant loaded context
- Context partitioning can extend effective capacity across agents
- Budget triggers are needed for masking, compaction, or partitioning

Do not activate this skill for adjacent work owned by other skills:
- Explaining why attention or context windows behave this way: `context-fundamentals`.
- Diagnosing active lost-in-middle, poisoning, distraction, confusion, or clash: `context-degradation`.
- Designing a structured handoff summary for a long conversation: `context-compression`.
- Storing large outputs, plans, or logs as files: `filesystem-context`.

## Core Concepts

Apply four primary strategies in this priority order:

1. **KV-cache optimization** — Reorder and stabilize prompt structure so the inference engine reuses cached Key/Value tensors. This is the cheapest optimization when the runtime supports prefix caching: low quality risk, immediate cost and latency savings. Apply it first when stable prefixes exist.

2. **Observation masking** — Replace verbose tool outputs with compact references once their purpose has been served. Tool outputs can dominate agent trajectories (claim-context-optimization-tool-output-dominance), so masking often yields the largest capacity gains. The original content remains retrievable if needed downstream.

3. **Compaction** — Summarize accumulated context when utilization exceeds 70%, then reinitialize with the summary. This distills the window's contents while preserving task-critical state. Compaction is lossy — apply it after masking has already removed the low-value bulk.

4. **Context partitioning** — Split work across sub-agents with isolated contexts when a single window cannot hold the full problem. Each sub-agent operates in a clean context focused on its subtask. Reserve this for tasks where estimated context exceeds 60% of the window limit, because coordination overhead is real.

The governing principle: context quality matters more than quantity. Every optimization preserves signal while reducing noise. Measure before optimizing, then measure the optimization's effect.

## Detailed Topics

### Compaction Strategies

Trigger compaction when context utilization exceeds 70%: summarize the current context, then reinitialize with the summary. This distills the window's contents in a high-fidelity manner, enabling continuation with minimal performance degradation. Prioritize compressing tool outputs first (they consume 80%+ of tokens), then old conversation turns, then retrieved documents. Never compress the system prompt — it anchors model behavior and its removal causes unpredictable degradation.

Preserve different elements by message type:

- **Tool outputs**: Extract key findings, metrics, error codes, and conclusions. Strip verbose raw output, stack traces (unless debugging is ongoing), and boilerplate headers.
- **Conversational turns**: Retain decisions, commitments, user preferences, and context shifts. Remove filler, pleasantries, and exploratory back-and-forth that led to a conclusion already captured.
- **Retrieved documents**: Keep claims, facts, and data points relevant to the active task. Remove supporting evidence and elaboration that served a one-time reasoning purpose.

Target 50-70% token reduction with less than 5% quality degradation. If compaction exceeds 70% reduction, audit the summary for critical information loss — over-aggressive compaction is the most common failure mode.

### Observation Masking

Mask observations selectively based on recency and ongoing relevance — not uniformly. Apply these rules:

- **Never mask**: Observations critical to the current task, observations from the most recent turn, observations used in active reasoning chains, and error outputs when debugging is in progress.
- **Mask after 3+ turns**: Verbose outputs whose key points have already been extracted into the conversation flow. Replace with a compact reference: `[Obs:{ref_id} elided. Key: {summary}. Full content retrievable.]`
- **Always mask immediately**: Repeated/duplicate outputs, boilerplate headers and footers, outputs already summarized earlier in the conversation.

Masking should achieve 60-80% reduction in masked observations with less than 2% quality impact. The key is maintaining retrievability — store the full content externally and keep the reference ID in context so the agent can request the original if needed.

### KV-Cache Optimization

Maximize prefix cache hits by structuring prompts so that stable content occupies the prefix and dynamic content appears at the end. KV-cache stores Key and Value tensors computed during inference; when consecutive requests share an identical prefix, the cached tensors are reused, saving both cost and latency.

Apply this ordering in every prompt:
1. System prompt (most stable — never changes within a session)
2. Tool definitions (stable across requests)
3. Frequently reused templates and few-shot examples
4. Conversation history (grows but shares prefix with prior turns)
5. Current query and dynamic content (least stable — always last)

Design prompts for cache stability: remove timestamps, session counters, and request IDs from the system prompt. Move dynamic metadata into a separate user message or tool result where it does not break the prefix. Even a single whitespace change in the prefix invalidates the entire cach