windows: keep paths UTF-8 across the C ABI, whatever the host's code page

include/audiocpp.h

@@ -15,6 +15,8 @@
  *   - Handles are not thread-safe individually. Separate handles may be used
  *     concurrently from separate threads.
  *   - Freeing NULL is a no-op, so cleanup paths need no null checks.
+ *   - Strings passed in, file paths included, are UTF-8 whatever code page
+ *     the host process runs under on Windows. Strings returned are UTF-8.
  *
  * Lifetime note: handles keep their parents alive internally (a session holds
  * its model, a model holds its registry). Freeing out of order is therefore

include/engine/framework/io/filesystem.h

@@ -8,6 +8,20 @@
 
 namespace engine::io {
 
+/// A path from a UTF-8 string.
+///
+/// On Windows a narrow string handed to std::filesystem::path is decoded with
+/// the process code page, which is UTF-8 only when the executable asks for it.
+/// A DLL runs under its host's code page, so "Thiền Tâm Đức.wav" would name a
+/// file that is not there. Bytes that are not valid UTF-8 are decoded with the
+/// process code page instead, as before. Everywhere else this is the identity.
+std::filesystem::path path_from_utf8(std::string_view value);
+
+/// A path as UTF-8, for ggml (which opens files by UTF-8 name) and for
+/// messages. path::string() uses the process code page on Windows, so it
+/// mangles or throws on a name that page cannot hold.
+std::string path_to_utf8(const std::filesystem::path & path);
+
 bool is_existing_directory(const std::filesystem::path & path);
 bool is_existing_file(const std::filesystem::path & path);
 

src/capi/audiocpp.cpp

@@ -17,6 +17,7 @@
 
 #include "engine/framework/core/backend.h"
 #include "engine/framework/core/module.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/model.h"
 #include "engine/framework/runtime/registry.h"
 #include "engine/framework/runtime/session.h"
@@ -311,7 +312,7 @@ audiocpp_status audiocpp_registry_create(const char * config_path, audiocpp_regi
     return guard([&] {
         auto handle = std::make_unique<audiocpp_registry>();
         auto config = config_path != nullptr
-            ? std::optional<std::filesystem::path>(std::filesystem::path(config_path))
+            ? std::optional<std::filesystem::path>(engine::io::path_from_utf8(config_path))
             : std::nullopt;
         handle->registry = std::make_shared<rt::ModelRegistry>(rt::make_default_registry(config));
         handle->families = handle->registry->families();
@@ -361,7 +362,7 @@ audiocpp_status audiocpp_model_load(audiocpp_registry * registry,
     return guard([&] {
         auto handle = std::make_unique<audiocpp_model>();
         handle->registry = registry->registry;
-        handle->load_request.model_path = std::filesystem::path(model_path);
+        handle->load_request.model_path = engine::io::path_from_utf8(model_path);
         if (family_hint != nullptr) {
             handle->load_request.family_hint = std::string(family_hint);
         }
@@ -370,7 +371,7 @@ audiocpp_status audiocpp_model_load(audiocpp_registry * registry,
             if (config->weight_id != nullptr) handle->load_request.weight_id = std::string(config->weight_id);
             if (config->model_spec_override != nullptr) {
                 handle->load_request.model_spec_override =
-                    std::filesystem::path(config->model_spec_override);
+                    engine::io::path_from_utf8(config->model_spec_override);
             }
         }
         handle->load_request.options = option_map(options);

src/community_models/inflect_v2/session.cpp

@@ -1,6 +1,7 @@
 #include "engine/community_models/inflect_v2/session.h"
 
 #include "engine/framework/debug/profiler.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/runtime/spec_backed_model.h"
 #include "engine/framework/text/utf8.h"
@@ -39,7 +40,7 @@ std::filesystem::path session_path(
     const auto found = options.options.find(key);
     return found == options.options.end()
         ? std::filesystem::path{}
-        : std::filesystem::path(found->second);
+        : engine::io::path_from_utf8(found->second);
 }
 
 void validate_session_options(

src/community_models/kitten_tts/session.cpp

@@ -2,6 +2,7 @@
 
 #include "engine/framework/debug/profiler.h"
 #include "engine/framework/debug/trace.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/runtime/spec_backed_model.h"
 #include "engine/framework/text/chunking.h"
@@ -29,7 +30,7 @@ constexpr const char *kModelName = "Kitten TTS";
 
 std::filesystem::path session_path(const runtime::SessionOptions &options, const char *key) {
     const auto found = options.options.find(key);
-    return found == options.options.end() ? std::filesystem::path{} : std::filesystem::path(found->second);
+    return found == options.options.end() ? std::filesystem::path{} : engine::io::path_from_utf8(found->second);
 }
 
 std::string request_cache_key(const runtime::Transcript &text, const KittenFrontendSessionState &state) {

src/community_models/lfm2_audio/assets.cpp

@@ -26,7 +26,7 @@ class GgufMetadata {
         params.no_alloc = true;
         params.ctx = nullptr;
 
-        ctx_.reset(gguf_init_from_file(path.string().c_str(), params));
+        ctx_.reset(gguf_init_from_file(engine::io::path_to_utf8(path).c_str(), params));
         if (ctx_ == nullptr) {
             throw std::runtime_error("LFM2-Audio failed to read GGUF metadata: " + path.string());
         }
@@ -173,7 +173,7 @@ std::string join(const std::vector<std::string> & values) {
 
 std::filesystem::path resolve_component(
     const std::filesystem::path & root, const char * option_name, const std::string & value) {
-    const auto relative = std::filesystem::path(value).lexically_normal();
+    const auto relative = engine::io::path_from_utf8(value).lexically_normal();
     if (value.empty() || relative.is_absolute() || (!relative.empty() && *relative.begin() == "..")) {
         throw std::runtime_error(std::string(option_name) + " must be a nonempty path inside the model directory");
     }

src/community_models/moss_ttsd/session.cpp

@@ -3,6 +3,7 @@
 #include "engine/framework/audio/conversion.h"
 #include "engine/framework/audio/wav_reader.h"
 #include "engine/framework/debug/profiler.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 
 #include <algorithm>
@@ -357,7 +358,7 @@ runtime::TaskResult MossTtsdSession::run(const runtime::TaskRequest & request) {
                 speakers.emplace_back();
                 continue;
             }
-            const auto wav = engine::audio::read_wav_f32(std::filesystem::path(*path));
+            const auto wav = engine::audio::read_wav_f32(engine::io::path_from_utf8(*path));
             speakers.emplace_back(encode_reference(
                 runtime::AudioBuffer{wav.sample_rate, wav.channels, wav.samples}));
         }

src/community_models/outetts/session.cpp

@@ -1,6 +1,7 @@
 #include "engine/community_models/outetts/session.h"
 
 #include "engine/framework/audio/fft.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/runtime/spec_backed_model.h"
 #include "engine/framework/debug/trace.h"
@@ -486,7 +487,7 @@ resolve_aligner_assets(const runtime::SessionOptions &options,
        "outetts.forced_aligner_model_path"});
   if (model_path.has_value()) {
     return engine::models::qwen3_asr::load_qwen3_asr_assets(
-        std::filesystem::path(*model_path), "qwen3_forced_aligner");
+        engine::io::path_from_utf8(*model_path), "qwen3_forced_aligner");
   }
   return model_assets.embedded_aligner;
 }

src/community_models/piper_tts/session.cpp

@@ -1,6 +1,7 @@
 #include "engine/community_models/piper_tts/session.h"
 
 #include "engine/framework/debug/profiler.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/runtime/spec_backed_model.h"
 #include "engine/framework/text/chunking.h"
@@ -40,7 +41,7 @@ std::filesystem::path session_path(
     const auto found = options.options.find(key);
     return found == options.options.end()
         ? std::filesystem::path{}
-        : std::filesystem::path(found->second);
+        : engine::io::path_from_utf8(found->second);
 }
 
 void validate_session_options(

src/community_models/sanotts/session.cpp

@@ -1,6 +1,7 @@
 #include "engine/community_models/sanotts/session.h"
 
 #include "engine/framework/debug/profiler.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/runtime/spec_backed_model.h"
 
@@ -40,7 +41,7 @@ std::filesystem::path session_path(
     const auto found = options.options.find(key);
     return found == options.options.end()
         ? std::filesystem::path{}
-        : std::filesystem::path(found->second);
+        : engine::io::path_from_utf8(found->second);
 }
 
 void validate_session_options(

src/community_models/sense_asr/assets.cpp

@@ -1,6 +1,7 @@
 #include "engine/community_models/sense_asr/assets.h"
 
 #include "engine/framework/assets/tensor_source.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/model_spec/package.h"
 
 #include <gguf.h>
@@ -33,7 +34,7 @@ class GgufMetadataReader {
     gguf_init_params params{};
     params.no_alloc = false;
     params.ctx = nullptr;
-    gguf_context *gguf = gguf_init_from_file(path.string().c_str(), params);
+    gguf_context *gguf = gguf_init_from_file(engine::io::path_to_utf8(path).c_str(), params);
     if (gguf == nullptr) {
       throw std::runtime_error(
           "SenseVoice failed to open GGUF metadata at " + path.string());

src/community_models/vibeasr/assets.cpp

@@ -1,5 +1,6 @@
 #include "engine/community_models/vibeasr/assets.h"
 
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/model_spec/package.h"
 
 #include <gguf.h>
@@ -127,7 +128,7 @@ class GgufMetadataReader {
         gguf_init_params params{};
         params.no_alloc = true;
         params.ctx = nullptr;
-        gguf_context * gguf = gguf_init_from_file(path.string().c_str(), params);
+        gguf_context * gguf = gguf_init_from_file(engine::io::path_to_utf8(path).c_str(), params);
         if (gguf == nullptr) {
             throw std::runtime_error("Failed to read VibeASR GGUF metadata from " + path.string());
         }

src/community_models/vieneu_v3_turbo/session.cpp

@@ -4,6 +4,7 @@
 #include "engine/community_models/vieneu_v3_turbo/orchestration.h"
 
 #include "engine/framework/debug/profiler.h"
+#include "engine/framework/io/filesystem.h"
 #include "engine/framework/runtime/options.h"
 #include "engine/framework/text/chunking.h"
 
@@ -36,7 +37,7 @@ std::filesystem::path option_path(
     const std::unordered_map<std::string, std::string> & options,
     std::initializer_list<std::string_view> keys) {
     if (const auto value = runtime::find_option(options, keys)) {
-        return std::filesystem::path(*value);
+        return engine::io::path_from_utf8(*value);
     }
     return {};
 }

src/framework/assets/resource_bundle.cpp

@@ -31,7 +31,7 @@ void ResourceBundle::add_file(std::string id, const std::filesystem::path & path
         throw std::runtime_error("asset resource id must not be empty");
     }
     if (!engine::io::is_existing_file(path)) {
-        throw std::runtime_error("asset resource file does not exist: " + path.string());
+        throw std::runtime_error("asset resource file does not exist: " + engine::io::path_to_utf8(path));
     }
     auto [it, inserted] = files_.emplace(std::move(id), std::filesystem::weakly_canonical(path));
     if (!inserted) {
@@ -138,7 +138,7 @@ std::shared_ptr<const TensorSource> ResourceBundle::open_tensor_source(std::stri
     const auto path = resource == tensor_resources_.end()
         ? require_file(id)
         : resource->second.path;
-    const auto path_key = std::filesystem::weakly_canonical(path).generic_string();
+    const auto path_key = std::filesystem::weakly_canonical(path).generic_u8string();
     auto base = tensor_sources_by_path_.find(path_key);
     if (base == tensor_sources_by_path_.end()) {
         base = tensor_sources_by_path_.emplace(