---
name: context-engineering
description: Context window monitoring and budget management. Keeps orchestrator at 15-30% context usage while subagents get full 200k tokens. Provides warnings at thresholds, context-aware summarization triggers, and wave-level budget planning.
allowed-tools: Read Bash(*)
metadata:
  author: babysitter-sdk
  version: "1.0.0"
  category: gsd-core
  backlog-id: SK-GSD-003
graph:
  domains: [domain:software-engineering]
  skillAreas: [skill-area:agentic-loops, skill-area:orchestration-loop]
  workflows: [workflow:feature-development]
  topics: [topic:developer-experience]
  roles: [role:tech-lead, role:backend-engineer]
---

- **Subagents**: Get full 200k tokens of fresh context per spawn.
- **Context budget**: Plan how much context each wave of execution will consume.

This skill provides:
- Context window usage estimation for the current session
- Warning injection at configurable thresholds (70%, 85%, 95%)
- Orchestrator budget enforcement
- Subagent context allocation recommendations
- Context-aware summarization triggers
- Stale context detection and pruning suggestions
- Wave-level context budget planning

## Capabilities

### 1. Context Usage Estimation

Estimate current context window usage based on conversation history size:

```
Tokens used:     ~45,000 / 200,000
Usage:           22.5%
Status:          HEALTHY
Next threshold:  70% (warning) at ~140,000 tokens
```

Estimation methods:
- Character count / 4 (rough approximation)
- Tool output tracking (each tool call adds to context)
- File read accumulation tracking

### 2. Threshold Warnings

Inject warnings at configurable thresholds:

```
[CONTEXT 70%] Warning: Context window at 70%. Consider summarizing completed work.
[CONTEXT 85%] Critical: Context window at 85%. Spawn new subagent for remaining work.
[CONTEXT 95%] Emergency: Context window at 95%. Wrap up immediately. Write state and exit.
```

Actions per threshold:
- **70%**: Suggest summarizing completed work, pruning stale context
- **85%**: Strongly recommend spawning new subagent with fresh context
- **95%**: Emergency wrap-up: write STATE.md, commit, create continue-here.md

### 3. Orchestrator Budget Enforcement

Monitor orchestrator-specific budget:

```
Target orchestrator usage: 15-30%
Current orchestrator usage: 18%
Remaining budget: 12% (~24,000 tokens)

Budget allocation:
- Phase context loading: 5% (PROJECT, ROADMAP, STATE)
- Agent spawn overhead: 3% per agent
- Result processing: 2% per agent result
- State updates: 1%
```

### 4. Subagent Context Allocation

Recommend context allocation for subagent spawns:

```
Agent: gsd-executor
Available context: 200,000 tokens (fresh)
Recommended loading:
- Plan file: ~2,000 tokens
- Relevant source files: ~15,000 tokens
- Project context: ~3,000 tokens
- Remaining for execution: ~180,000 tokens
```

### 5. Context-Aware Summarization

Trigger summarization when context is filling:

```
Summarization triggers:
- Tool output > 10,000 characters: summarize before continuing
- File read > 5,000 lines: extract relevant sections only
- Agent result > 20,000 characters: summarize key outcomes
```

Summarization strategies:
- **Completed work**: Replace detailed execution logs with summary
- **File contents**: Replace full file reads with relevant excerpts
- **Agent results**: Extract key outcomes, discard detailed reasoning

### 6. Stale Context Detection

Identify context that is no longer relevant:

```
Stale context candidates:
- File contents read 10+ interactions ago
- Agent results from completed (not current) phases
- Tool outputs that were informational only
- Research documents already synthesized into plans
```

### 7. Wave-Level Budget Planning

Plan context budget across execution waves:

```
Wave 1 (3 parallel agents):
  Spawn cost: 3 * 3% = 9%
  Result processing: 3 * 2% = 6%
  Wave total: 15%

Wave 2 (2 parallel agents):
  Spawn cost: 2 * 3% = 6%
  Result processing: 2 * 2% = 4%
  Wave total: 10%

Total orchestrator budget needed: 25%
Target: 30% -> Sufficient with 5% margin
```

## Tool Use Instructions

### Checking Context Usage
1. Use `Bash` to estimate current session token count if available
2. Track cumulative tool output sizes during the session
3. Calculate percentage against 200,000 token window
4. Return usage report with threshold proximity

### Injecting Warnings
1. Compare current usage against configured thresholds
2. If threshold exceeded, format appropriate warning message
3. Include recommended action based on threshold level
4. For 95%: include emergency state-save instructions

### Planning Wave Budgets
1. Use `Read` to load plan files for the phase
2. Count agents needed per wave
3. Estimate per-agent spawn and result cost
4. Sum wave costs and compare to orchestrator budget target
5. Recommend wave splitting if budget exceeded

## Process Integration

- `execute-phase.js` - Monitor context during multi-wave execution, trigger summarization between waves
- `iterative-convergence.js` - Track context across convergence iterations, spawn fresh agents when context fills
- `new-project.js` - Budget context for parallel research agents (4 spawns + synthesis)

## Output Format

```json
{
  "operation": "check|warn|plan|summarize",
  "status": "healthy|warning|critical|emergency",
  "usage": {
    "estimatedTokens": 45000,
    "maxTokens": 200000,
    "percentage": 22.5,
    "nextThreshold": 70
  },
  "recommendation": "Continue normally|Summarize completed work|Spawn new agent|Emergency wrap-up",
  "waveBudget": {
    "totalWaves": 2,
    "estimatedOrchestratorUsage": 25,
    "withinBudget": true
  }
}
```

## Configuration

| Setting | Default | Description |
|---------|---------|-------------|
| `contextWarningThreshold` | `70` | Warning threshold percentage |
| `contextCriticalThreshold` | `85` | Critical threshold percentage |
| `contextEmergencyThreshold` | `95` | Emergency threshold percentage |
| `orchestratorBudgetTarget` | `30` | Target max orchestrator context % |
| `agentSpawnCost` | `3` | Estimated % per agent spawn overhead |
| `agentResultCost` | `2` | Estimated % per agent result processing |
| `autoSummarize` | `true` | Auto-trigger summarization at thresholds |

## Error Handling

| Error | Cause | Resolution |
|-------|-------|------------|
| `Token estimation inaccurate` | Approximation drift | Use conservative estimates (overestimate usage) |
| `Budget exceeded mid-wave` | Underestimated agent costs | Defer remaining agents to next session with continue-here.md |
| `Emergency threshold hit` | Orchestrator doing too much work inline | Immediately write state, commit, create handoff document |
| `Stale context false positive` | Context still needed | Maintain a "pinned context" list that is never pruned |

## Constraints

- Token estimates are approximations (character/4 heuristic); always err on the side of caution
- Never discard context that has not been persisted to disk (STATE.md, summaries, etc.)
- Orchestrator should never exceed 30% context usage
- Emergency wrap-up at 95% is non-negotiable; quality degrades severely above this
- Wave budget planning must account for worst-case agent result sizes
- Context monitoring is advisory; it cannot forcibly stop execution