Context Management

The context manager (context/manager.go) is the single owner of the conversation context window. No other package directly mutates the message list.

Ownership Model

The manager holds a []types.Message slice protected by a mutex. Other packages interact through:

• AddMessage() — append a message
• Messages() — get a copy of the current window
• PreTurnCheck() — run proactive compaction if needed
• ReactiveCompact() — compact in response to model rejection
• ApplyBackfill() — prepend checkpoint summaries

Compaction

When the context window exceeds 90% of the active model’s limit, compaction triggers:

1. Split messages into “to summarize” and “preserved” (last 3 turns)
2. Send the turns-to-summarize to the model as a separate API call with the dialect’s compaction prompt
3. Replace old turns with the model’s summary
4. Create a checkpoint capturing the pre-compaction state

This is a separate API call — not the full context window. This prevents the compaction request itself from exceeding the model’s limit.

Reactive Compaction

If the proactive check underestimates and the model rejects with context_length_exceeded, reactive compaction fires. The request is retried exactly once after compacting.

Callback Wiring

The context manager can’t import dialect/ or stream/ (would create import cycles). Instead, cmd/ghyll provides callbacks at init:

ManagerDeps{
    TokenCount:       dialect.MinimaxTokenCount,
    CompactionCall:   session.compactionCall,  // wires stream.Send
    CreateCheckpoint: session.createCheckpoint, // wires memory.Store
}

This keeps the package graph acyclic while allowing cross-cutting flows.