Close the remaining gap on src/core/wire-mesh-transport.ts's mutation score (78.70% -> 80%)

[Mearman]

PR #101 raised wire-mesh-transport.ts from 69.91% to 78.70% (97 killed, 73 timeout, 46 survived, out of 216 covered mutants), just short of the repo's configured thresholds.high: 80. The remaining 46 survivors are real, traceable gaps, not equivalent mutants -- deliberately left for a dedicated follow-up pass rather than forcing them through under heavy shared-machine load. The unusually high error count (158) alongside 216 covered mutants is also worth investigating directly, not just working around.

Sub-issue of #64.