CODEX GAINS THREAD HIERARCHY QUERIES, EXEC-SERVER GOES REMOTE-NATIVE

The thread filtering work [1] solves a real coordination problem: clients managing spawned subagents need an authoritative snapshot of immediate children when reconnecting or recovering from missed events. Previously, thread/list had no parent query capability, forcing clients to either scan unrelated threads or reconstruct relationships from transient events and rollout history. The parent relationship already lives in persisted thread_spawn_edges state, so this is a clean surface addition that Review and Guardian threads don't participate in. In parallel, exec-server is gaining Windows-native execution support [2]. The shift moves TurnEnvironmentSelection.cwd from AbsolutePathBuf to PathUri, letting remote environments preserve their native working directory and shell. This unblocks the remote_env_windows test to run actual Windows processes instead of just recording early path mismatches. Together, these changes push the execution and coordination layer closer to multiplatform maturity.