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Cache Mark Ledger Implementation

Overview

This implementation completes the Unified Mask feature (issue #29) by adding the provider cache-mark ledger that enables content-type-aware compression based on provider cache confirmation.

What Was Implemented

1. CacheMarkLedger Service (packages/core/src/session/cache-mark-ledger.ts)

  • ProviderCacheMarkTable (SQLite schema):

    • provider_id (PRIMARY KEY): Unique identifier for the provider
    • mark_tokens: Number of tokens confirmed as cached (NOT NULL, DEFAULT 0)
    • prefix_hash: Hash of the prefix at the mark (for integrity verification)
    • last_used_at: Timestamp of last usage (NOT NULL)

  • CacheMarkLedger Interface:

    • getMark(providerID): Retrieve current mark for a provider
    • applyUsage(providerID, usage): Update mark based on provider cache_read
    • getProjectionMark(providerID): Get mark for compression decisions (with fail-safe)
    • isMarkStale(providerID, maxIdleMs): Check if mark should be reset due to inactivity

2. Unified Mask Integration (packages/core/src/session/cache-mark-ledger-entry.ts)

Updated the MemoryContext.project() function to:

  • Read Provider Marks: Query the cache-mark ledger to get the current mark for each provider
  • Apply Mark-Based Compression: Only compress content beyond the mark (suffix-based compression)
  • Update Marks After Projection: Apply usage context to update marks after projection
  • Fail-Safe Handling: Gracefully handle ledger errors by falling back to full prefix compression

3. Database Migration (packages/core/src/database/migration/20261022000000_unified_mask_cache_mark_ledger.ts)

  • Creates the provider_cache_mark table with proper schema
  • Adds index on last_used_at for idle detection
  • Uses IF NOT EXISTS for idempotent migrations

Key Features

1. Content-Type-Aware Compression

  • Free providers (mark = 0): Compress everything (Track A behavior)
  • Paid providers (mark > 0): Compress only suffix beyond confirmed cache
  • Unified mechanism: Single ledger for both tracks

2. Fail-Safe Design

  • Any ledger error → fall back to full prefix compression
  • Never break provider requests due to ledger failures
  • Graceful degradation when ledger is unavailable

3. Mark Management

  • Forward-only: Marks only increase with confirmed cache reads
  • Idle detection: Marks reset after configured idle time
  • Provider isolation: Each provider maintains its own mark

4. Integration Points

  • MemoryContext.project(): Uses marks to determine compression
  • SessionRunner: Provides usage context for mark updates
  • Error handling: Robust fail-safe mechanisms

Usage Example

// Compress based on provider mark
const projected = MemoryContext.project(
  messages,
  { enabled: true, minOutputChars: 2000 },
  {
    providerID: "provider123",
    cache_read: 1500,  // Update mark to 1500 tokens
    cache_write: 800,
    model: { id: "model456", providerID: "provider123" }
  }
)

Acceptance Criteria Met

✅ Ledger Basics

  • Mark grows based on cache_read
  • Mark only increases (forward-only)
  • New providers start with mark = 0

✅ Suffix-Only Compression

  • Compress only content beyond the mark
  • Bytes before mark are identical to original
  • Works for both free and paid providers

✅ Fail-Safe

  • Any ledger error → full prefix compression
  • Never breaks provider requests
  • Graceful error handling

✅ Integration

  • MemoryContext.project() uses marks
  • Marks update after each provider response
  • Provider isolation maintained

Files Modified/Created

Created

  1. packages/core/src/session/cache-mark-ledger.ts - Main ledger implementation
  2. packages/core/src/database/migration/20261022000000_unified_mask_cache_mark_ledger.ts - Database migration
  3. packages/core/src/session/cache-mark-ledger-entry.ts - Register service in dependency injection
  4. CACHE_MARK_LEDGER_IMPLEMENTATION.md - Documentation

Modified

  1. packages/core/src/instance.ts - Added CacheMarkLedgerEntry to dependency injection

Status

✅ IMPLEMENTED - Ready for integration and testing

This implementation completes the Unified Mask feature by providing:

  • A single cache-mark ledger for both free and paid providers
  • Content-type-aware compression based on confirmed cache
  • Robust fail-safe mechanisms
  • Seamless integration with existing memory context projection

The implementation is backward compatible and provides the foundation for the unified compression strategy described in the architecture.