headroom/wiki/transforms.md

Transform Reference

Headroom provides several transforms that work together to optimize LLM context.

SmartCrusher

Statistical compression for JSON tool outputs.

How It Works

SmartCrusher analyzes JSON arrays and selectively keeps important items:

1. First/Last items - Context for pagination and recency
2. Error items - 100% preservation of error states
3. Anomalies - Statistical outliers (> 2 std dev from mean)
4. Relevant items - Matches to user's query via BM25/embeddings
5. Change points - Significant transitions in data

Configuration

from headroom import SmartCrusherConfig

config = SmartCrusherConfig(
    min_tokens_to_crush=200,      # Only compress if > 200 tokens
    max_items_after_crush=50,     # Keep at most 50 items
    keep_first=3,                 # Always keep first 3 items
    keep_last=2,                  # Always keep last 2 items
    relevance_threshold=0.3,      # Keep items with relevance > 0.3
    anomaly_std_threshold=2.0,    # Keep items > 2 std dev from mean
    preserve_errors=True,         # Always keep error items
)

Example

from headroom import SmartCrusher

crusher = SmartCrusher(config)

# Before: 1000 search results (45,000 tokens)
tool_output = {"results": [...1000 items...]}

# After: ~50 important items (4,500 tokens) - 90% reduction
compressed = crusher.crush(tool_output, query="user's question")

What Gets Preserved

Category	Preserved	Why
Errors	100%	Critical for debugging
First N	100%	Context/pagination
Last N	100%	Recency
Anomalies	All	Unusual values matter
Relevant	Top K	Match user's query
Others	Sampled	Statistical representation

---

CacheAligner

Prefix stabilization for improved cache hit rates.

The Problem

LLM providers cache request prefixes. But dynamic content breaks caching:

"You are helpful. Today is January 7, 2025."  # Changes daily = no cache

The Solution

CacheAligner extracts dynamic content to stabilize the prefix:

from headroom import CacheAligner

aligner = CacheAligner()
result = aligner.align(messages)

# Static prefix (cacheable):
# "You are helpful."

# Dynamic content moved to end:
# [Current date context]

Configuration

from headroom import CacheAlignerConfig

config = CacheAlignerConfig(
    extract_dates=True,           # Move dates to dynamic section
    normalize_whitespace=True,    # Consistent spacing
    stable_prefix_min_tokens=100, # Min prefix size for alignment
)

Cache Hit Improvement

Scenario	Before	After
Daily date in prompt	0% hits	~95% hits
Dynamic user context	~10% hits	~80% hits
Consistent prompts	~90% hits	~95% hits

---

RollingWindow

Context management within token limits.

The Problem

Long conversations exceed context limits. Naive truncation breaks tool calls:

[tool_call: search]  # Kept
[tool_result: ...]   # Dropped = orphaned call!

The Solution

RollingWindow drops complete tool units, preserving pairs:

from headroom import RollingWindow

window = RollingWindow(config)
result = window.apply(messages, max_tokens=100000)

# Guarantees:
# 1. Tool calls paired with results
# 2. System prompt preserved
# 3. Recent turns kept
# 4. Oldest tool outputs dropped first

Configuration

from headroom import RollingWindowConfig

config = RollingWindowConfig(
    max_tokens=100000,            # Target token limit
    preserve_system=True,         # Always keep system prompt
    preserve_recent_turns=5,      # Keep last 5 user/assistant turns
    drop_oldest_first=True,       # Remove oldest tool outputs
)

Drop Priority

1. Oldest tool outputs - First to go
2. Old assistant messages - Summary preserved
3. Old user messages - Only if necessary
4. Never dropped: System prompt, recent turns, active tool pairs

Note: For more intelligent context management based on semantic importance rather than just position, see IntelligentContextManager below.

---

IntelligentContextManager

Semantic-aware context management with TOIN-learned importance scoring.

The Problem

RollingWindow drops messages by position (oldest first), but position doesn't equal importance:

• An error message from turn 3 might be critical
• A verbose success response from turn 10 might be expendable
• Messages referenced by later turns should be preserved

The Solution

IntelligentContextManager uses multi-factor importance scoring:

from headroom.transforms import IntelligentContextManager, IntelligentContextConfig

manager = IntelligentContextManager(config)
result = manager.apply(messages, tokenizer, model_limit=128000)

# Guarantees:
# 1. System messages never dropped (configurable)
# 2. Last N turns always protected
# 3. Tool calls/responses dropped atomically
# 4. Drops by importance score, not just position

How Scoring Works

Messages are scored on multiple factors (all learned, no hardcodes):

Factor	Weight	Description
Recency	20%	Exponential decay from conversation end
Semantic Similarity	20%	Embedding similarity to recent context
TOIN Importance	25%	Learned from retrieval patterns
Error Indicators	15%	TOIN-learned error field detection
Forward References	15%	Messages referenced by later messages
Token Density	5%	Information density (unique/total tokens)

Key principle: No hardcoded patterns. Error detection uses TOIN's field_semantics.inferred_type == "error_indicator", not keyword matching.

Configuration

from headroom.transforms import IntelligentContextManager
from headroom.config import IntelligentContextConfig, ScoringWeights

# Custom scoring weights
weights = ScoringWeights(
    recency=0.20,
    semantic_similarity=0.20,
    toin_importance=0.25,
    error_indicator=0.15,
    forward_reference=0.15,
    token_density=0.05,
)

config = IntelligentContextConfig(
    enabled=True,
    keep_system=True,              # Never drop system messages
    keep_last_turns=2,             # Protect last N user turns
    output_buffer_tokens=4000,     # Reserve for model output
    use_importance_scoring=True,   # Enable semantic scoring
    scoring_weights=weights,       # Custom weights
    toin_integration=True,         # Use TOIN patterns
    recency_decay_rate=0.1,        # Exponential decay lambda
    compress_threshold=0.1,        # Try compression first if <10% over
)

manager = IntelligentContextManager(config)

Strategy Selection

Based on how much over budget you are:

Overage	Strategy	Action
Under budget	NONE	No action needed
< 10% over	COMPRESS_FIRST	Try deeper compression
>= 10% over	DROP_BY_SCORE	Drop lowest-scored messages

TOIN + CCR Integration

IntelligentContextManager is a message-level compressor. Just like SmartCrusher compresses items in a JSON array, IntelligentContext "compresses" messages in a conversation by dropping low-value ones.

Bidirectional TOIN integration:

1. Scoring uses TOIN patterns: Learned retrieval rates and field semantics inform importance scores
2. Drops are recorded to TOIN: When messages are dropped, TOIN learns the pattern
3. CCR stores originals: Dropped messages are stored in CCR for potential retrieval
4. Retrievals feed back to TOIN: If users retrieve dropped messages, TOIN learns to score those patterns higher

from headroom.telemetry import get_toin

toin = get_toin()
manager = IntelligentContextManager(config, toin=toin)

# TOIN provides (for scoring):
# - retrieval_rate: How often this message pattern is retrieved (high = important)
# - field_semantics: Learned field types (error_indicator, identifier, etc.)
# - commonly_retrieved_fields: Fields that users frequently need

# TOIN receives (from drops):
# - Message pattern signatures (role counts, has_tools, has_errors)
# - Token counts (original vs marker size)
# - Retrieval feedback when users access CCR

What this means:

• When you drop a message pattern and users frequently retrieve it, TOIN learns to score it higher next time
• When you drop a pattern and no one retrieves it, that confirms it was safe to drop
• The feedback loop improves drop decisions across all users, not just in one session

Example: Before vs After

RollingWindow (position-based):

Messages: [sys, user1, asst1, user2, asst2_error, user3, asst3, user4, asst4]
Over budget by 3 messages.
Drops: user1, asst1, user2 (oldest first)
Result: Loses context, keeps verbose asst3

IntelligentContextManager (score-based):

Messages scored:
  - asst2_error: 0.85 (TOIN learned error indicator)
  - asst1: 0.45 (old, low density)
  - asst3: 0.40 (verbose, low unique tokens)

Drops: asst1, asst3, user1 (lowest scores)
Result: Preserves critical error message

Backwards Compatibility

Convert from RollingWindowConfig:

from headroom.config import IntelligentContextConfig, RollingWindowConfig

rolling_config = RollingWindowConfig(
    max_tokens=100000,
    preserve_system=True,
    preserve_recent_turns=3,
)

# Convert to intelligent context config
intelligent_config = IntelligentContextConfig(
    keep_system=rolling_config.preserve_system,
    keep_last_turns=rolling_config.preserve_recent_turns,
)

---

LLMLinguaCompressor — RETIRED

The earlier LLMLingua-2 integration (LLMLinguaCompressor, LLMLinguaConfig, is_llmlingua_model_loaded, unload_llmlingua_model, the headroom-ai[llmlingua] extra, and the --llmlingua proxy flag) was retired in 0.9.x and replaced by Kompress (ModernBERT). pip install 'headroom-ai[llmlingua]' no longer resolves; use the [ml] extra instead. The Kompress transform shipped with the proxy runs as Transform 4 in the live-zone pipeline (see ARCHITECTURE.md).

---

CodeAwareCompressor (Optional)

AST-based compression for source code using tree-sitter.

When to Use

Transform	Best For	Speed	Compression
SmartCrusher	JSON arrays	~1ms	70-90%
CodeAwareCompressor	Source code	~10-50ms	40-70%
Kompress (ML)	Any text	50-200ms	80-95%

Key Benefits

• Syntax validity guaranteed — Output always parses correctly
• Preserves critical structure — Imports, signatures, types, error handlers
• Multi-language support — Python, JavaScript, TypeScript, Go, Rust, Java, C, C++
• Lightweight — ~50MB vs ~1GB for the ML compressor

Installation

pip install "headroom-ai[code]"  # Adds tree-sitter-language-pack

Configuration

from headroom.transforms import CodeAwareCompressor, CodeCompressorConfig, DocstringMode

config = CodeCompressorConfig(
    preserve_imports=True,              # Always keep imports
    preserve_signatures=True,           # Always keep function signatures
    preserve_type_annotations=True,     # Keep type hints
    preserve_error_handlers=True,       # Keep try/except blocks
    preserve_decorators=True,           # Keep decorators
    docstring_mode=DocstringMode.FIRST_LINE,  # FULL, FIRST_LINE, REMOVE
    target_compression_rate=0.2,        # Keep 20% of tokens
    max_body_lines=5,                   # Lines to keep per function body
    min_tokens_for_compression=100,     # Skip small content
    language_hint=None,                 # Auto-detect if None
)

compressor = CodeAwareCompressor(config)

Example

from headroom.transforms import CodeAwareCompressor

compressor = CodeAwareCompressor()

code = '''
import os
from typing import List

def process_items(items: List[str]) -> List[str]:
    """Process a list of items."""
    results = []
    for item in items:
        if not item:
            continue
        processed = item.strip().lower()
        results.append(processed)
    return results
'''

result = compressor.compress(code, language="python")
print(result.compressed)
# import os
# from typing import List
#
# def process_items(items: List[str]) -> List[str]:
#     """Process a list of items."""
#     results = []
#     for item in items:
#     # ... (5 lines compressed)
#     pass

print(f"Compression: {result.compression_ratio:.0%}")  # ~55%
print(f"Syntax valid: {result.syntax_valid}")  # True

Supported Languages

Tier	Languages	Support Level
1	Python, JavaScript, TypeScript	Full AST analysis
2	Go, Rust, Java, C, C++	Function body compression

Memory Management

from headroom.transforms import is_tree_sitter_available, unload_tree_sitter

# Check if tree-sitter is installed
print(is_tree_sitter_available())  # True/False

# Free memory when done (parsers are lazy-loaded)
unload_tree_sitter()

---

ContentRouter

Intelligent compression orchestrator that routes content to the optimal compressor.

How It Works

ContentRouter analyzes content and selects the best compression strategy:

1. Detect content type — JSON, code, logs, search results, plain text
2. Consider source hints — File paths, tool names for high-confidence routing
3. Route to compressor — SmartCrusher, CodeAwareCompressor, SearchCompressor, etc.
4. Log decisions — Transparent routing for debugging

Configuration

from headroom.transforms import ContentRouter, ContentRouterConfig, CompressionStrategy

config = ContentRouterConfig(
    min_section_tokens=100,             # Minimum tokens to compress
    enable_code_aware=True,             # Use CodeAwareCompressor for code
    enable_search_compression=True,     # Use SearchCompressor for grep output
    enable_log_compression=True,        # Use LogCompressor for logs
    default_strategy=CompressionStrategy.TEXT,  # Fallback strategy
)

router = ContentRouter(config)

Example

from headroom.transforms import ContentRouter

router = ContentRouter()

# Router auto-detects content type and routes to optimal compressor
result = router.compress(content)

print(result.strategy_used)  # CompressionStrategy.CODE_AWARE, SMART_CRUSHER, etc.
print(result.routing_log)  # List of routing decisions

Compression Strategies

Strategy	Used For	Compressor
CODE_AWARE	Source code	CodeAwareCompressor
SMART_CRUSHER	JSON arrays	SmartCrusher
SEARCH	Grep/find output	SearchCompressor
LOG	Log files	LogCompressor
TEXT	Plain text	TextCompressor
PASSTHROUGH	Small content	None

(The earlier LLMLINGUA strategy was retired with the LLMLingua integration; ML compression is now provided by Kompress.)

Content Detection

The router automatically detects content types by analyzing the content itself:

• Source code: Detected by syntax patterns, indentation, keywords
• JSON arrays: Detected by JSON structure with array elements
• Search results: Detected by file:line: patterns
• Log output: Detected by timestamp and log level patterns
• Plain text: Fallback for prose content

No manual hints required - the router inspects content directly.

TOIN Integration

ContentRouter records all compressions to TOIN (Tool Output Intelligence Network) for cross-user learning:

• All strategies tracked: Code, search, logs, text, and ML compressions are recorded
• Retrieval feedback: When users retrieve original content via CCR, TOIN learns which compressions need expansion
• Pattern learning: TOIN builds signatures for each content type to improve future compressions

This enables the feedback loop where compression decisions improve based on actual user behavior across all content types, not just JSON arrays.

---

TransformPipeline

Combine transforms for optimal results.

from headroom import TransformPipeline, SmartCrusher, CacheAligner, RollingWindow

pipeline = TransformPipeline([
    SmartCrusher(),      # First: compress tool outputs
    CacheAligner(),      # Then: stabilize prefix
    RollingWindow(),     # Finally: fit in context
])

result = pipeline.transform(messages)
print(f"Saved {result.tokens_saved} tokens")

With ML compression (Optional, Kompress)

The earlier hand-assembled TransformPipeline([..., LLMLinguaCompressor(), ...]) recipe is no longer supported. ML compression now ships as part of the live-zone pipeline when the [ml] extra is installed; see ARCHITECTURE.md for the current placement.

Recommended Order

Order	Transform	Purpose
1	CacheAligner	Stabilize prefix for caching
2	SmartCrusher	Compress JSON tool outputs
3	Kompress (ML)	ML compression on remaining text (optional, [ml] extra)
4	RollingWindow	Enforce token limits (always last)

Why this order?

• CacheAligner first to maximize prefix stability
• SmartCrusher handles JSON arrays efficiently
• Kompress compresses remaining long text
• RollingWindow truncates only if still over limit

---

Safety Guarantees

All transforms follow strict safety rules:

1. Never remove human content - User/assistant text is sacred
2. Never break tool ordering - Calls and results stay paired
3. Parse failures are no-ops - Malformed content passes through
4. Preserves recency - Last N turns always kept
5. 100% error preservation - Error items never dropped