workspace: zero compiler warnings across all targets

254 warnings (320 counting replayed-cache re-emitters) cleaned:
unused mut/imports/variables, irrefutable if-lets and unreachable
patterns, dead code removed or annotated #[allow(dead_code)] with
the reason (C++ parity value sets, cfg(test) helpers, public API
reservations), drop(&ref) no-ops removed, fn-pointer identity via
std::ptr::fn_addr_eq, the test-stubs feature declared in
oak-node's manifest, missing docs filled. Every unused-Result site
was judged individually: meaningful errors propagate, intentional
ignores are let _ = with a note.

Two pre-existing latent bugs are documented in place, behavior
preserved: app.rs's timeline-tool observer and dialogs.rs's format
subscription both drop the returned Subscription immediately, so
they never fire.

crates/oak-node/tests/engine_units_test.rs

@@ -693,7 +693,7 @@ fn node_behavior_defaults() {
 
 	// value / process_samples / generate_frame no-ops.
 	let mut table = NodeValueTable::default();
-	let mut row = std::collections::BTreeMap::new();
+	let row = std::collections::BTreeMap::new();
 	b.value(&core, &row, Rational::new(0, 1), &mut table);
 	assert!(table.is_empty());
 	let mut samples = SampleBuffer::default();

crates/oak-node/tests/graph_test.rs

@@ -50,7 +50,7 @@ impl NodeBehavior for TestNode {
 fn build(n: usize) -> (Graph, Vec<NodeId>) {
 	let mut g = Graph::new();
 	let mut ids = Vec::new();
-	for i in 0..n {
+	for _ in 0..n {
 		let mut core = NodeCore::new();
 		core.add_input(Input::new(
 			"val_in",
@@ -159,7 +159,7 @@ fn cycle_rejection() {
 /// yields empty order; diamond graph has a valid (stable) order.
 #[test]
 fn topological_order() {
-	let mut g = Graph::new();
+	let g = Graph::new();
 	assert!(g.topological_order().is_empty());
 
 	let (mut g, ids) = build(4);

crates/oak-node/tests/phase2_units_test.rs

@@ -79,7 +79,7 @@ fn block_behaviors_and_inputs() {
 	assert!(clip.footage.is_none());
 
 	// Gap.
-	let (core, behavior) = oak_node::block::gap_create();
+	let (_core, behavior) = oak_node::block::gap_create();
 	assert_eq!(behavior.name(), "Gap");
 	assert_eq!(behavior.type_id(), "org.olivevideoeditor.Olive.gapblock");
 	let gap = GapBlockBehavior::new();
@@ -287,7 +287,7 @@ fn color_manager_state() {
 	cm.set_up_default_config().unwrap();
 	assert!(cm.is_loaded());
 
-	let mut empty = ColorManager::new();
+	let empty = ColorManager::new();
 	assert!(empty.list_colorspaces().is_empty());
 }
 

crates/oak-node/tests/serializer_test.rs

@@ -526,7 +526,7 @@ fn assert_full_roundtrip_fields(orig: &oak_node::project::Project, loaded: &oak_
 	use oak_node::folder::FolderBehavior;
 	use oak_node::footage::FootageBehavior;
 	use oak_node::sequence::SequenceBehavior;
-	use oak_node::track::{TrackBehavior, TrackListBehavior, TrackType};
+	use oak_node::track::{TrackBehavior, TrackType};
 
 	// Project shell: uuid + settings.
 	assert_eq!(loaded.uuid, orig.uuid, "uuid");

crates/oak-node/tests/traverser_test.rs

@@ -258,7 +258,7 @@ impl NodeBehavior for Echo {
 /// track read at its midpoint feeds 5.
 #[test]
 fn unconnected_input_evaluates_keyframes_at_time() {
-	use oak_node::keyframe::{Keyframe, KeyframeTrack};
+	use oak_node::keyframe::Keyframe;
 	let mut g = Graph::new();
 	let mut core = NodeCore::new();
 	core.add_input(Input::new("val_in", ValueType::Float, NodeValue::Float(0.0)));