Resumed subagents keep the effort level of the model they started with

A subagent is a helper that Claude Code starts to handle part of a task, and it can be resumed later. Effort is how much thinking the model is asked to do.

Resumed subagents now save and restore the model their effort level was picked for, and work out their effort against that model. Before, effort was worked out from whichever model the subagent ended up using. The rule for when a resume is treated as a reply also gained an extra condition.

This sits behind a check that the CLAUDE_CODE_HARMONIC_RIDDLE environment variable can also control.