Overview

Cache Trace.num_turns incrementally so turn-limit and interception reads scale with newly appended graph nodes rather than the full rollout history.

Design

The message graph is owned by Trace.nodes, and normal graph commits append nodes. The trace now keeps a private (counted_nodes, sampled_turns) cache:

• unchanged node length returns the cached count immediately
• growth counts only the unseen suffix
• observed shrinkage resets and rebuilds the count from the remaining nodes

The cache is a Pydantic private attribute, so wire and disk serialization remain unchanged and deserialized traces begin with a cold cache. Turn semantics are also unchanged: only nodes marked sampled count, independent of branch topology. This does not restructure the graph or alter interception control flow.

For a progressive rollout with a count read after every append, the prior expression visits N(N + 1) / 2 nodes. The incremental path visits each appended node once, reducing that work from quadratic to linear.

Performance

Measured on 20,000 progressive sampled turns with separate old/new processes and three uninstrumented timing repetitions:

Resource measurements stayed effectively flat:

The incremental implementation performs no suffix-list copy; it walks newly appended nodes directly by index.