Function declare_scene_tree_phases 

pub fn declare_scene_tree_phases(
    writer: &CheckpointWriter,
    tree: &SceneTree,
    phases: &HashMap<String, WorkloadPhase>,
)

Declare every phase node in a freshly-pre-mapped scene tree to the writer. Called once at session bootstrap, immediately after [crate::executor::pre_map_tree] returns. Each phase gets a Pending entry with no hash; the runtime updates the hash via CheckpointWriter::update_phase_hash when the phase compiles.

The phases map carries each phase’s checkpoint: declaration (parsed by nmbrs-workload); entries with checkpoint: idempotent set skip_eligible = true, all others set false.