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528 Compaction Ontology 3fa52597
ASecurity``` ┌─────────────────────┐ │ User Request │ └──────────┬──────────┘ │ ▼ ┌──────────────────────────────────────────────────────────────────────────────┐ │ RequestOrchestrator │ │ (core/agents/main.py)
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[](https://www.skillsdirectory.com/skills/tools-only-528-compaction-ontology-3fa52597)---
title: Compaction System Ontology
link: compaction-ontology
type: doc
path: docs/codebase-map/architecture/compaction-ontology.md
depth: 2
seams: [A, M, D]
ontological_relations:
- relates_to: [[core-compaction]]
- relates_to: [[core-state]]
- relates_to: [[core-agents]]
- affects: [[session-messages]]
- affects: [[context-window]]
tags:
- compaction
- context-management
- architecture
- ontology
created_at: 2026-01-20T16:25:00Z
updated_at: 2026-01-20T16:25:00Z
---
# Compaction System Ontology
## Entity Relationships
```
┌─────────────────────┐
│ User Request │
└──────────┬──────────┘
│
▼
┌──────────────────────────────────────────────────────────────────────────────┐
│ RequestOrchestrator │
│ (core/agents/main.py) │
│ │
│ ┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐ │
│ │ state_manager │───▶│ session.conversation.messages│───▶│ prune_old_tool │ │
│ │ │ │ │ │ _outputs() │ │
│ └─────────────────┘ └─────────────────┘ └────────┬────────┘ │
│ │ │
└──────────────────────────────────────────────────────────┼──────────────────┘
│
┌────────────────────────────────┼────────────────────┐
│ ▼ │
│ ┌─────────────────────────────────┐ │
│ │ compaction.py │ │
│ │ │ │
│ │ ┌───────────────────────────┐ │ │
│ │ │ get_prune_thresholds() │──┼───┼──┐
│ │ └───────────────────────────┘ │ │ │
│ │ │ │ │
│ │ ┌───────────────────────────┐ │ │ │
│ │ │ is_tool_return_part() │ │ │ │
│ │ └───────────────────────────┘ │ │ │
│ │ │ │ │
│ │ ┌───────────────────────────┐ │ │ │
│ │ │ estimate_part_tokens() │──┼───┼──┼──┐
│ │ └───────────────────────────┘ │ │ │ │
│ │ │ │ │ │
│ │ ┌───────────────────────────┐ │ │ │ │
│ │ │ prune_part_content() │ │ │ │ │
│ │ └───────────────────────────┘ │ │ │ │
│ └─────────────────────────────────┘ │ │ │
│ │ │ │
└────────────────────────────────────────────────────┘ │ │
│ │
┌─────────────────────────────────────────────────────────────┘ │
│ │
▼ │
┌─────────────────────┐ │
│ limits.py │ │
│ │ │
│ _load_settings() │ │
└─────────────────────┘ │
│
┌───────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────┐
│ token_counter.py │
│ │
│ estimate_tokens() │
│ CHARS_PER_TOKEN=4 │
└─────────────────────┘
```
## Ontological Classes
### Primary Entities
| Entity | Type | Location | Description |
|--------|------|----------|-------------|
| `Compaction` | Process | `core/compaction.py` | Context pruning system |
| `Message` | Data | `session.conversation.messages` | Conversation history item |
| `Part` | Data | `message.parts` | Sub-component of message |
| `ToolReturn` | Data | `part_kind="tool-return"` | Tool execution result |
| `Token` | Unit | Estimated | Context window unit |
### Secondary Entities
| Entity | Type | Location | Description |
|--------|------|----------|-------------|
| `Threshold` | Config | `compaction.py` | Pruning boundaries |
| `Placeholder` | Constant | `compaction.py` | Replacement text |
| `Session` | State | `state.py` | Conversation container |
## Relationships
### Compositional (HAS-A)
```
Session
└── messages: list[Message]
└── parts: list[Part]
└── content: str | Any
└── part_kind: str
```
### Functional (OPERATES-ON)
| Subject | Verb | Object |
|---------|------|--------|
| `prune_old_tool_outputs` | scans | `messages` |
| `prune_old_tool_outputs` | identifies | `tool-return` parts |
| `prune_old_tool_outputs` | mutates | `part.content` |
| `estimate_part_tokens` | delegates-to | `estimate_tokens()` |
### Dependency (DEPENDS-ON)
```
compaction.py
│
└──▶ token_counter.py::estimate_tokens()
main.py
│
├──▶ compaction.py::prune_old_tool_outputs()
│
└──▶ state.py::session.conversation.messages
```
### Trigger (INVOKED-BY)
```
User Request
│
└──▶ RequestOrchestrator._run_impl()
│
└──▶ prune_old_tool_outputs() [line 342]
```
## Data Flow
### Input/Output
```
INPUT:
messages: list[ModelMessage] # Full conversation history
model: str # Model name (for token estimation)
OUTPUT:
messages: list[ModelMessage] # Same list, mutated in-place
tokens_reclaimed: int # Net tokens freed
```
### State Transitions
```
┌─────────────────────────────────────────────┐
│ │
▼ │
┌──────────────┐ ┌──────┴───────┐
│ PRISTINE │──────[accumulate > protect]──▶│ CANDIDATE │
│ (protected) │ │ (to prune) │
└──────────────┘ └──────┬───────┘
│
[total > minimum_threshold]
│
▼
┌──────────────┐
│ PRUNED │
│ (placeholder)│
└──────────────┘
```
## Threshold Ontology
```
┌─────────────────────────────────────────────────────────────────────┐
│ 200,000 token context window │
│ │
│ ┌──────────────────────────────────────────┬───────────────────┐ │
│ │ PRUNABLE ZONE │ PROTECTED ZONE │ │
│ │ (oldest) │ (40,000 tokens) │ │
│ │ │ │ │
│ │ Only pruned if total > 20,000 tokens │ Never pruned │ │
│ └──────────────────────────────────────────┴───────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────────────┘
```
## Invariants
### Pre-conditions
| Invariant | Check Location | Failure Behavior |
|-----------|----------------|------------------|
| `messages` is mutable list | Caller responsibility | Silent no-op |
| `len(messages) > 0` | line 179 | Early return |
| `user_turns >= 2` | line 183-185 | Early return |
### Post-conditions
| Invariant | Guarantee |
|-----------|-----------|
| Message list identity preserved | Same list object returned |
| Protected content unchanged | Recent tokens untouched |
| Pruned parts contain placeholder | Exactly `PRUNE_PLACEHOLDER` |
| Idempotent | Re-running produces no change |
### Class Invariants
| Class | Invariant |
|-------|-----------|
| `Part` | `part_kind` is immutable |
| `Message` | `parts` list is mutable |
| `Session` | `messages` persists across requests |
## Seams
### Architecture Seams (A)
- **Trigger Location**: Can move compaction to different lifecycle points
- **Proactive vs Reactive**: Currently proactive; could add reactive overflow handling
### Module Seams (M)
- **Threshold Configuration**: Currently hardcoded; could externalize to config
- **Token Estimation**: Uses heuristic; could swap in actual tokenizer
- **Placeholder Format**: Static string; could make dynamic/contextual
### Data Seams (D)
- **Pruning Granularity**: Currently part-level; could do message-level
- **Preservation Rules**: Currently all tool-returns; could add selective rules
- **Content Summarization**: Currently placeholder; could add LLM summarization
## Cross-References
| Document | Relationship |
|----------|--------------|
| [[core-compaction]] | Implementation details |
| [[core-state]] | Session/message storage |
| [[core-agents]] | Integration point |
| [[conversation-turns]] | Message structure |
| [[architecture]] | System overview |
Files in this skill
- README.md
- skill.md
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