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-codec/src/ffmpeg.rs

@@ -70,8 +70,13 @@ use crate::footagedescription::{FootageDescription, StreamEntry};
 use crate::frame::Frame;
 
 /// `oak_core_COLOR_RANGE_FULL`.
+///
+/// Both range constants keep the C ABI's spelling (they name the frozen
+/// `oak_core_COLOR_RANGE_*` values), hence the lint allowance.
+#[allow(non_upper_case_globals)]
 const oak_core_COLOR_RANGE_FULL: i32 = 1;
 /// `oak_core_COLOR_RANGE_LIMITED`.
+#[allow(non_upper_case_globals)]
 const oak_core_COLOR_RANGE_LIMITED: i32 = 0;
 /// `AVCOL_RANGE_JPEG` (full range; AVCOL_RANGE_MPEG = 1 is limited).
 const AVCOL_RANGE_JPEG: i32 = 2;
@@ -1899,27 +1904,6 @@ fn convert_rgba_f32_le(data: &[u8], w: u32, h: u32, stride: usize) -> Vec<u8> {
 	out
 }
 
-/// Copy a packed u16-RGBA buffer (RGBA64LE) into F32 RGBA bytes.
-fn convert_rgba64_to_f32(data: &[u8], w: u32, h: u32, stride: usize) -> Vec<u8> {
-	let mut out = vec![0u8; (w as usize) * (h as usize) * PIXEL_F32_BYTES];
-	for y in 0..h as usize {
-		let row = &data[y * stride..y * stride + (w as usize) * 8];
-		let dst =
-			&mut out[y * (w as usize) * PIXEL_F32_BYTES..(y + 1) * (w as usize) * PIXEL_F32_BYTES];
-		for (px, src_px) in dst
-			.chunks_exact_mut(PIXEL_F32_BYTES)
-			.zip(row.chunks_exact(8))
-		{
-			for c in 0..3 {
-				let v = u16::from_le_bytes([src_px[c * 2], src_px[c * 2 + 1]]);
-				px[c * 4..c * 4 + 4].copy_from_slice(&(v as f32 / 65535.0).to_le_bytes());
-			}
-			px[12..16].copy_from_slice(&1.0f32.to_le_bytes());
-		}
-	}
-	out
-}
-
 /// Copy a packed 8-bit RGBA buffer into F32 RGBA bytes (the universal
 /// swscale fallback; M12 P0 — some static FFmpeg swscale builds lack
 /// float output formats).

crates/oak-codec/src/proxymanager.rs

@@ -97,6 +97,9 @@ impl ProxyParams {
 		cstr_slice(&self.extension)
 	}
 
+	/// Only the proxy-params tests read the preset through this accessor
+	/// (the struct field itself is `pub`).
+	#[allow(dead_code)]
 	fn preset_str(&self) -> &str {
 		cstr_slice(&self.preset)
 	}

crates/oak-codec/src/task.rs

@@ -107,6 +107,10 @@ enum SubmitCb {
 	/// No callback registered.
 	None,
 	/// Extern-C callback registered via `oakcodec_set_task_submit_cb`.
+	///
+	/// Only constructed by the tests below and by the extern-C entry point
+	/// that the removed C ABI used to expose; kept for that lane.
+	#[allow(dead_code)]
 	Extern {
 		/// The C function pointer.
 		cb: OakCodecTaskSubmitFn,
@@ -151,6 +155,8 @@ pub fn set_task_submit_cb(cb: Option<&'static TaskSubmitFn>, userdata: *mut std:
 /// Register an extern-C submit callback (used by `ffi::task`).
 ///
 /// Mirrors `oakcodec_set_task_submit_cb`: a `None` pointer clears it.
+/// Only the tests below call it (the extern-C lane is exercised there).
+#[allow(dead_code)]
 pub(crate) fn set_task_submit_cb_extern(
 	cb: Option<OakCodecTaskSubmitFn>,
 	userdata: *mut std::ffi::c_void,