55. Tracing Hook on the Call Path

• Tracing (design 014) adds one p.tr != nil test at the entry of parser.call and one on the iterative VM's non-plain call path. The plain call sites test p.noPlain instead of p.memoAll (same cost); noPlain is set by Document and by tracing, so a traced parse sends every call through call. Nothing else on the untraced path changes, and generated parsers are untouched.
• Effect (min of 12 interleaved runs, Apple M3 Max): JSON and Minilang, closure and recursive VM, −1.3% to +0.3% (noise); a first 8-run pass showed up to +6% that did not reproduce. Incremental and stream benchmarks within ±4% in both directions.