Agent skill

assembling-context

Use when preparing context for subagent dispatch or managing token budgets. Triggers: 'prepare context for', 'assemble context', 'token budget', 'context package', 'what context does the subagent need'. Also invoked by develop during planning and execution phases.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/axiomantic/spellbook/tree/main/skills/assembling-context

SKILL.md

Context Assembly

Invariant Principles

  1. Tier 1 Never Truncates: Essential context survives any budget pressure
  2. Budget Before Assembly: Calculate budget FIRST, then select
  3. Purpose Drives Selection: Design context differs from implementation differs from review
  4. Recency Over Completeness: Recent feedback beats historical context
  5. Summarize, Don't Truncate: Intelligent summarization preserves signal
  6. Integration Points are Tier 1: Interface contracts are essential

Inputs / Outputs

Input Required Description
purpose Yes design, implementation, review, handoff, subagent
token_budget Yes Maximum tokens available
source_context Yes Raw context to select from
Output Description
context_package Tiered context ready for injection
truncation_report What was excluded and why

Context Tiers

<CRITICAL>Over budget: remove Tier 3 first, then Tier 2. Never remove Tier 1.</CRITICAL>

Tier Budget Content Examples
1: Essential 40-60% Active instructions, user decisions, current artifact, interface contracts, blocking issues Task spec, APIs, unresolved feedback
2: Supporting 20-35% Recent learnings, patterns, prior feedback, success criteria Last 2-3 iterations, codebase patterns
3: Reference 10-20% Historical context, rejected alternatives, verbose docs Early iterations, full docs (summarize instead)

Purpose-Specific Packages

Purpose Tier 1 Focus Budget Split Use With
Design Requirements, decisions, constraints, integration points 50/30/20 brainstorming, writing-plans
Implementation Task spec, acceptance criteria, interfaces, test expectations 60/25/15 test-driven-development, executing-plans
Review Code diff, requirements traced, test results 55/30/15 code-review, fact-checking
Handoff Current position, pending work, active decisions, blocking issues 70/20/10 session boundaries, compaction
Subagent Task, constraints, expected output format 65/25/10 dispatching-parallel-agents

Token Budget

Estimation: tokens ≈ chars / 4 (conservative)

Available: context_window - system_prompt - response_reserve - tool_overhead Example: 200000 - 8000 - 4000 - 2000 = 186000

Smart Truncation: Never blind head/tail. Preserve structure: intro (30%) + conclusion (20%), mark omitted middle.

Cross-Session Context

Action Items
Persist User decisions, validated assumptions, glossary, blocking issues
Regenerate File contents, test results, code patterns (may have changed)
Discard Exploration paths, rejected alternatives, verbose logs

Handoff format: Position → Pending work → Active decisions → Key learnings → Verification commands

Reasoning Schema

Self-Check

  • Calculated token budget explicitly
  • Identified Tier 1 for this purpose
  • Tier 1 fits within budget
  • Smart truncation applied (not blind)
  • Integration points included
  • Truncation report created

<FINAL_EMPHASIS> Context assembly is invisible infrastructure. Calculate budget. Prioritize by tier. Truncate intelligently. Every token earns its place. </FINAL_EMPHASIS>

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