build(core): fix Rust library path in SConscript

diff --git a/core/SConscript.bootloader b/core/SConscript.bootloader
index 894dec8b..e9cc84b7 100644
--- a/core/SConscript.bootloader
+++ b/core/SConscript.bootloader
@@ -278,6 +278,7 @@ obj_program += env.Object(source=SOURCE_MOD_CRYPTO, CCFLAGS='$CCFLAGS -ftrivial-
 obj_program += env.Object(source=SOURCE_BOOTLOADER)
 obj_program += env.Object(source=SOURCE_NANOPB)
 obj_program += env.Object(source=SOURCE_HAL)
+obj_program += [rust]
 
 if 'boot_ucb' in FEATURES_AVAILABLE:
     obj_program += env.Object(
@@ -299,7 +300,6 @@ program_elf = env.Command(
 )
 
 env.Depends(program_elf, linkerscript_gen)
-env.Depends(program_elf, rust)
 
 SUFFIX = '_qa' if BOOTLOADER_QA else ''
 
diff --git a/core/SConscript.bootloader_emu b/core/SConscript.bootloader_emu
index f5b627f4..7a1466aa 100644
--- a/core/SConscript.bootloader_emu
+++ b/core/SConscript.bootloader_emu
@@ -266,6 +266,7 @@ obj_program += env.Object(source=SOURCE_MOD_CRYPTO, CCFLAGS='$CCFLAGS -ftrivial-
 obj_program += env.Object(source=SOURCE_BOOTLOADER)
 obj_program += env.Object(source=SOURCE_NANOPB)
 obj_program += env.Object(source=SOURCE_UNIX)
+obj_program += [rust]
 
 program_elf = env.Command(
     target='bootloader.elf',
@@ -273,7 +274,5 @@ program_elf = env.Command(
     action=
     '$CC -o $TARGET $SOURCES $_LIBDIRFLAGS $_LIBFLAGS $LINKFLAGS')
 
-env.Depends(program_elf, rust)
-
 if CMAKELISTS != 0:
     env.Depends(program_elf, cmake_gen)
diff --git a/core/SConscript.firmware b/core/SConscript.firmware
index 3f1403b6..31fdffbc 100644
--- a/core/SConscript.firmware
+++ b/core/SConscript.firmware
@@ -904,6 +904,7 @@ rust = tools.add_rust_lib(
     all_paths=ALLPATHS,
     build_dir=str(Dir('.').abspath),
 )
+obj_program += [rust]
 
 
 env.Depends(rust, protobuf_blobs)
@@ -997,7 +998,6 @@ env.Depends(program_elf, linkerscript_gen)
 
 if CMAKELISTS != 0:
     env.Depends(program_elf, cmake_gen)
-env.Depends(program_elf, rust)
 
 BINARY_NAME = f"build/firmware/firmware-{TREZOR_MODEL}"
 if not EVERYTHING:
diff --git a/core/SConscript.kernel b/core/SConscript.kernel
index 4fb7f2ac..c7fca3d0 100644
--- a/core/SConscript.kernel
+++ b/core/SConscript.kernel
@@ -444,6 +444,7 @@ rust = tools.add_rust_lib(
     all_paths=ALLPATHS,
     build_dir=str(Dir('.').abspath),
 )
+obj_program += [rust]
 
 
 if "secmon_layout" in FEATURES_AVAILABLE:
@@ -460,7 +461,6 @@ program_elf = env.Command(
 )
 
 env.Depends(program_elf, linkerscript_gen)
-env.Depends(program_elf, rust)
 
 if CMAKELISTS != 0:
     env.Depends(program_elf, cmake_gen)
diff --git a/core/SConscript.prodtest b/core/SConscript.prodtest
index 3b2c2d54..c889cd81 100644
--- a/core/SConscript.prodtest
+++ b/core/SConscript.prodtest
@@ -338,6 +338,7 @@ rust = tools.add_rust_lib(
     all_paths=ALLPATHS,
     build_dir=str(Dir('.').abspath),
 )
+obj_program += [rust]
 
 
 if (vh := ARGUMENTS.get("VENDOR_HEADER", None)):
@@ -378,7 +379,6 @@ program_elf = env.Command(
 )
 
 env.Depends(program_elf, linkerscript_gen)
-env.Depends(program_elf, rust)
 
 BINARY_NAME = f"build/prodtest/prodtest-{TREZOR_MODEL}"
 BINARY_NAME += "-" + tools.get_version('embed/projects/prodtest/version.h')
diff --git a/core/SConscript.prodtest_emu b/core/SConscript.prodtest_emu
index d2f033ea..dca61f1b 100644
--- a/core/SConscript.prodtest_emu
+++ b/core/SConscript.prodtest_emu
@@ -302,6 +302,7 @@ obj_program += env.Object(source=SOURCE_MOD_CRYPTO, CCFLAGS='$CCFLAGS -ftrivial-
 obj_program += env.Object(source=SOURCE_PRODTEST)
 obj_program += env.Object(source=SOURCE_HAL)
 obj_program += env.Object(source=SOURCE_MLDSA)
+obj_program += [rust]
 
 program_elf = env.Command(
     target='prodtest.elf',
@@ -309,7 +310,5 @@ program_elf = env.Command(
     action=
     '$CC -o $TARGET $SOURCES $_LIBDIRFLAGS $_LIBFLAGS $LINKFLAGS')
 
-env.Depends(program_elf, rust)
-
 if CMAKELISTS != 0:
     env.Depends(program_elf, cmake_gen)
diff --git a/core/SConscript.unix b/core/SConscript.unix
index 0925df59..b31d8da5 100644
--- a/core/SConscript.unix
+++ b/core/SConscript.unix
@@ -925,7 +925,7 @@ rust = tools.add_rust_lib(
     all_paths=ALLPATHS,
     build_dir=str(Dir('.').abspath),
 )
-
+obj_program += [rust]
 
 env.Depends(rust, protobuf_blobs)
 env.Depends(rust, TRANSLATION_DATA)
@@ -938,4 +938,3 @@ program = env.Command(
 
 if CMAKELISTS != 0:
     env.Depends(program, cmake_gen)
-env.Depends(program, rust)
diff --git a/core/site_scons/tools.py b/core/site_scons/tools.py
index 1bf8be08..96aa4f16 100644
--- a/core/site_scons/tools.py
+++ b/core/site_scons/tools.py
@@ -151,21 +151,18 @@ def add_rust_lib(*, env, build, profile, features, all_paths, build_dir):
     RUST_TARGET = env.get("ENV")["RUST_TARGET"]
 
     # Determine the profile build flags.
-    if profile == "release":
-        profile = "--release"
-        is_debug = False
-        RUST_LIBDIR = f"build/{build}/rust/{RUST_TARGET}/release"
-    else:
-        profile = ""
-        is_debug = True
-        RUST_LIBDIR = f"build/{build}/rust/{RUST_TARGET}/debug"
+    is_debug = {"dev": True, "release": False}[profile]
+
+    # Don't prefix with `build_dir` - the paths below should be relative to it.
+    RUST_LIBDIR = f"rust/{RUST_TARGET}/{'debug' if is_debug else 'release'}"
     RUST_LIBPATH = f"{RUST_LIBDIR}/lib{RUST_LIB}.a"
 
     def cargo_build():
         lib_features = []
         lib_features.extend(features)
 
-        cargo_opts = [
+        cargo_opts = [] if is_debug else ["--release"]
+        cargo_opts += [
             f"--target={RUST_TARGET}",
             f"--target-dir=../../build/{build}/rust",
             "--no-default-features",
@@ -178,7 +175,7 @@ def add_rust_lib(*, env, build, profile, features, all_paths, build_dir):
                 "-Z build-std-features=panic_immediate_abort",
             ]
 
-        build_cmd = f"cargo build {profile} " + " ".join(cargo_opts)
+        build_cmd = "cargo build " + " ".join(cargo_opts)
 
         unstable_rustc_flags = [
             # see https://nnethercote.github.io/perf-book/type-sizes.html#measuring-type-sizes for more details
@@ -200,13 +197,13 @@ def add_rust_lib(*, env, build, profile, features, all_paths, build_dir):
             f"cd embed/rust; {build_cmd} > {build_dir}/rust-type-sizes.log"
         )
 
+    # Target path should be relative to `build_dir`.
     rust = env.Command(
         target=RUST_LIBPATH,
         source="",
         action=cargo_build(),
     )
-
-    env.Append(LINKFLAGS=[f"-L{RUST_LIBDIR}"])
-    env.Append(LINKFLAGS=[f"-l{RUST_LIB}"])
+    # TODO: run `cargo` only if needed
+    env.AlwaysBuild(rust)
 
     return rust