Compile .ds scripts under assets/ to .dsb before packing into dusk.dsk

tools/asset/pack now special-cases .ds files: each one is compiled with
duskscriptcc to a temp .dsb (no .map, nothing reads one yet) and that gets
packed under the same path with the extension swapped - the raw .ds source
never ends up in the archive. Every other asset type is unchanged, packed
byte for byte as before.

CMake passes --duskscriptcc "$<TARGET_FILE:duskscriptcc>" and adds a DEPENDS
on it, but only on the linux/knulli host target where duskscriptcc is
actually built (see its own gating in src/CMakeLists.txt) - a cross-compiled
console target has no host-built compiler to point at, so for now it can
only pack an assets/ with no .ds in it; the packer raises a clear error
rather than silently skipping or mis-packing one if it finds one anyway.

The manifest's cache-skip check also now folds in duskscriptcc's own mtime,
so a compiler rebuild invalidates every .ds's cached result even when none
of their own source files changed.

Verified by hand: a .ds under assets/scripts/ packs as the matching .dsb
(confirmed by unzipping the resulting dusk.dsk), an unrelated rebuild
correctly skips re-packing, touching duskscriptcc correctly forces a
re-pack, and a syntax error in the .ds fails the build loudly with
duskscriptcc's own error message rather than silently succeeding.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

CMakeLists.txt

@@ -142,13 +142,30 @@ endif()
 # asset edit. tools.asset.pack itself decides whether anything actually
 # changed (see its manifest check) and no-ops quickly when nothing did,
 # so this stays cheap on a build where assets are untouched.
+#
+# A .ds script under assets/ is compiled to .dsb by duskscriptcc as part of
+# packing, so dusk.dsk only ever carries bytecode. duskscriptcc is a host
+# tool, only built when target_system is the build host (linux/knulli, see
+# src/CMakeLists.txt) - a cross-compiled console target has no duskscriptcc
+# of its own to depend on or pass down, so it can only pack assets with no
+# .ds in them until something sets up a host-built duskscriptcc for it too.
+if(DUSK_TARGET_SYSTEM STREQUAL "linux" OR DUSK_TARGET_SYSTEM STREQUAL "knulli")
+  set(DUSK_ASSET_PACK_DUSKSCRIPTCC_ARGS --duskscriptcc "$<TARGET_FILE:duskscriptcc>")
+  set(DUSK_ASSET_PACK_DEPENDS duskscriptcc)
+else()
+  set(DUSK_ASSET_PACK_DUSKSCRIPTCC_ARGS "")
+  set(DUSK_ASSET_PACK_DEPENDS "")
+endif()
+
 add_custom_target(DUSK_ASSETS_BUILT ALL
   COMMAND ${CMAKE_COMMAND} -E make_directory "${DUSK_ASSETS_DIR}"
   COMMAND ${Python3_EXECUTABLE} -m tools.asset.pack
     --input "${DUSK_ASSETS_DIR}"
     --output "${DUSK_ASSETS_ZIP}"
+    ${DUSK_ASSET_PACK_DUSKSCRIPTCC_ARGS}
   WORKING_DIRECTORY "${DUSK_ROOT_DIR}"
   BYPRODUCTS "${DUSK_ASSETS_ZIP}"
+  DEPENDS ${DUSK_ASSET_PACK_DEPENDS}
   COMMENT "Packing assets into dusk.dsk"
   VERBATIM
 )