Overview

Reduce synchronous token-limit overhead by avoiding repeated reconstruction of the same derived branch paths. The trace node graph remains the source of truth, limit precedence and soft-cap behavior are unchanged, and the commit only changes the production interception server.

What changed

• Return immediately when no token cap is configured.
• Count directly from Trace.nodes when canonical append order proves the graph is a single root-to-leaf path.
• Materialize Trace.branches once for compacted, subagent, or otherwise non-linear graphs, then reuse that view across enabled input, output, and total token checks.
• Preserve the existing max_turns → input → output → total precedence and >= boundaries.

Why

Trace.nodes stores each message once, while Trace.branches is an uncached derived view built by finding leaves and walking each parent chain. The previous input, output, and total properties each requested that view independently. When several token caps were enabled and still below their thresholds, the same graph paths were reconstructed up to three times.

The canonical linear case can safely use the existing node order without allocating a branch view. Other graph shapes continue through the established branch abstraction, but share one snapshot rather than rebuilding it for every count. This keeps arbitrary node ordering and branching semantics on the existing path.

Performance

Measurements use median time.perf_counter() wall time with GC before each repetition; peak Python allocation is measured separately with tracemalloc so tracing overhead does not affect timings.

The branched peak remains unchanged because both paths hold at most one full branch snapshot at a time; the saving is reduced allocation churn and graph-walk CPU from eliminating additional snapshots. Since limit checks run synchronously from the interception session, the wall-time reduction also shortens the corresponding event-loop stall.

At higher token density, mask summation becomes a larger share of the work: the 2k-node / 10-branch case at 128 tokens per node measured 8.711 ms → 6.964 ms, saving 1.747 ms (20.1%). This is expected because the change targets graph reconstruction rather than token-mask arithmetic.

Scope

The commit contains only verifiers/v1/interception/server.py. Benchmark scripts, focused test scaffolding, project metadata, and lockfiles are intentionally excluded.