avav25/context-engineering

Context Engineering

Context engineering is the discipline of systematically selecting, structuring, and delivering the smallest possible set of high-signal tokens that make a task plausibly solvable for an LLM — reliably, safely, and cost-effectively.

This skill provides actionable patterns, checklists, and templates for the full context pipeline — from first principles through production readiness.

When to Use

• Designing context pipelines for AI agents (what enters the LLM context window, in what order)
• Reviewing context quality and token efficiency of existing systems
• Building RAG systems (retrieval pipeline, chunking, packing, grounding)
• Implementing memory (session, working, long-term, organizational, tool-output)
• Designing agent harness (init/continuation prompts, state management, token budgets, caching)
• Multi-agent orchestration (context boundaries, payload schemas, fan-out merge)
• Production readiness assessment for AI systems (8-checklist gate)
• Privacy and compliance for AI features (multi-tenant isolation, consent, data residency)

When NOT to Use

• Prompt technique selection and template patterns → use prompt-engineering skill
• Security audit of individual prompts → use prompt-engineering skill → security-checklist.md
• Non-AI software engineering tasks → use Agent(software-engineer) + stack-specific role
• Infrastructure and deployment → use Agent(devops-engineer)

Context Engineering vs Prompt Engineering

These are complementary disciplines:

• Prompt engineering = designing the instruction text (technique selection, template patterns, formatting, few-shot)
• Context engineering = designing the full context PIPELINE (what enters the window, in what order, how it's managed across turns, how it degrades gracefully)

Context engineering is the system; prompt engineering is one layer within it.

Key Concepts

First Principles

1. Attention is finite — curate, don't stuff. "More context" is not monotonically better
2. Position effects — critical info at beginning and end ("lost-in-the-middle"). Models use tokens near the start and end more effectively than those buried in the middle
3. High-signal tokens > high-volume tokens — compact, discriminative context beats verbose dumps
4. Separation of concerns — policy, knowledge, examples, output contract in distinct layers. Enables independent swap, A/B testing, failure analysis
5. Context is a pipeline — produced by a system (retrieval, ranking, summarization, memory, policy filters, schema enforcement), not concatenated strings

The Context Stack (8-Layer Architecture)

Ordered layers, top = highest priority. Higher layers override lower on conflict.

| Layer | What Goes Here | Design Notes | |---|---|---| | 1. System policy & safety | Non-negotiable constraints, content policies, refusal rules | First in window — highest attention. Cacheable | | 2. Developer instructions | Role definitions, hard rules, reasoning protocols, conventions | Maps to: Claude Code rules ((auto-loaded), (agent)) | | 3. Tool contracts | Schemas, descriptions, permissions, failure modes, retry policies | Tool descriptions ARE prompts — optimize them | | 4. Runtime state | Current project context, CLAUDE.md, active file, task state, structured state blob | Maps to: Claude Code CLAUDE.md files | | 5. Knowledge context (RAG) | Retrieved documents, search results, file contents | Must be wrapped as untrusted data with grounding envelopes | | 6. Memory | Session, working, long-term, organizational, tool-output | Must be scoped, filtered, and conflict-resolved | | 7. Examples (few-shot) | Minimal, high-leverage exemplars aligned to output contract | Dynamic selection preferred; skip if schema suffices | | 8. Output contract | JSON Schema, format instructions, constraints, error handling | End of context — recency bias helps compliance |

Rule: keep policy/instructions (Layers 1-2) separate from knowledge (Layer 5). Mixing them is a root cause of prompt injection and "obedience confusion."

→ Full reference: context-stack-model.md

Cacheable Prefix Design

Layers 1-3 rarely change → group all static content at the beginning of the prompt to enable KV cache reuse. Append dynamic content (Layer 4-8) at the end. Never interleave static and dynamic blocks.

Track cache_prefix_ratio = cached_tokens / total_input_tokens (target > 0.3).

Token Budget Allocation

Treat context window as a finite resource with explicit budget per layer:

| Allocation | Suggested % | Notes | |---|---|---| | System + rules + tools (L1-3) | 15-25% | Stable, cacheable prefix | | Runtime state (L4) | 5-10% | Structured state blob | | Knowledge / RAG (L5) | 30-40% | Dynamic, highest signal variance | | Memory (L6) | 10-15% | Filtered, relevance-ranked | | Examples (L7) | 0-10% | Only when needed | | Output contract (L8) | 5-10% | Schema + error handling |

Overflow strategy: truncate lowest-priority layers first (L7 → L6 → L5).

Resource Files

| File | Contents | Guide §§ | |---|---|---| | context-stack-model.md | 8-layer architecture, layer design patterns, position effects, mapping to Claude Code assets | §3 | | memory-engineering.md | Memory taxonomy, CRUD lifecycle, conflict handling, compression strategies | §6 | | agent-harness-patterns.md | Init/continuation, state blobs, token budgets, caching, failure modes, streaming | §7 | | rag-engineering.md | Pipeline blueprint (7 stages), chunking, packing, degradation signals | §5 | | multi-agent-patterns.md | Context boundaries, payload schemas, return contracts, fan-out, contamination | §7.6, §14 | | production-checklists.md | All 8 production readiness checklists | §11 | | reference-templates.md | Grounding envelope, untrusted wrapper, structured output, tool error envelope | §12 | | privacy-compliance-ai.md | Multi-tenant isolation, data controls, consent, regional compliance | §9 |

Integration

• Follows rules: Agent(prompt-engineer) (prompt-level techniques, security, eval-first quality)
• Used by workflows: /ai-assets (context engineering validation), /feature-dev (AI features), /feature-plan (AI work packages), /code-review (context quality review)
• Companion skill: prompt-engineering skill (technique selection, template patterns, eval, security checklist)
• Collaborates with roles: Agent(solution-architect) (AI system design), Agent(product-manager) (agent contracts), Agent(sre-engineer) (context observability), Agent(software-engineer) (implementation)
• Primary source: guides/context_engineering_guide.md