AgentStateRestorer

Copies the mutable fields of a snapshotted AgentState back into a live one.

Why a copy instead of a swap: ReActAgent holds its AgentState in a private final field, so we cannot replace the instance from outside. The next best thing is a field-by-field overwrite of everything that has a setter or is itself mutable.

Coverage:

• summary — overwritten via setter

• replyId — overwritten via setter

• curIter — overwritten via setter

• shutdownInterrupted — overwritten via setter

• context — cleared and refilled in-place

The sub-context records (permissionContext, toolContext, tasksContext, planModeContext) are not restored — they would need additional core support to be swappable mid-run. Currently this matches the scope of session:compact (which only mutates summary + context); broader undo coverage tracks the AgentState refactor in project_java-agentstate-refactor.md.