GaijinEntertainment
diff --git a/‎.gitignore‎
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diff --git a/‎daslib/command_line.das‎
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diff --git a/‎daslib/logger.das‎
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@@ -140,3 +140,4 @@ build-ubsan/.ninja_log
 doc/sphinx-build-latex/environment.pickle
 opencode.json
 test-results/
+logs/
@@ -1,27 +1,33 @@
 options gen2
 options no_unused_function_arguments = false
 
+module command_line shared public
+
 //! Command-line utilities for daslang scripts and standalone executables.
 //! Provides functions for locating the daslang interpreter, which is essential
 //! when a script or standalone executable needs to spawn daslang subprocesses.
 
 require strings
 
-//! Returns the absolute path to the daslang interpreter executable.
-//! When running interpreted (`daslang.exe script.das`), `argv[0]` is already the interpreter.
-//! When running as a standalone executable (e.g. `mcp.exe`), `argv[0]` is that executable,
-//! so the filename is replaced with `daslang.exe` (or `daslang` on non-Windows).
-//! The directory is preserved, so the correct build configuration (Release, Debug, installed path) is used.
+//! Returns the path to the daslang interpreter executable, derived from
+//! ``argv[0]``. When running interpreted (``daslang.exe script.das``),
+//! ``argv[0]`` is already the interpreter. When running as a different
+//! executable (e.g. ``mcp.exe``, ``test_aot``), ``argv[0]``'s filename is
+//! replaced with ``daslang.exe`` (or ``daslang`` on non-Windows) while
+//! its directory is preserved — so the correct build configuration
+//! (Release, Debug, installed bin/) is used.
+//!
+//! Returned path follows ``argv[0]``'s shape: absolute if ``argv[0]`` is
+//! absolute, relative-to-cwd (e.g. ``./daslang``) if ``argv[0]`` is
+//! relative. ``execvp`` / ``popen_argv`` resolve relative paths against
+//! the child's cwd (inherited from parent), so a relative result still
+//! launches the right binary as long as cwd hasn't changed.
 def get_das_exe() : string {
     let args <- get_command_line_arguments()
     if (empty(args)) return ""
     var exe = args[0]
     // Normalize to forward slashes
     exe = replace(exe, "\\", "/")
-    // If relative path, make absolute using das_root
-    if (find(exe, ":") < 0 && first_character(exe) != '/') {
-        exe = "{get_das_root()}/{exe}"
-    }
     // Strip the filename, keep the directory
     let last_slash = rfind(exe, "/")
     let dir = last_slash >= 0 ? slice(exe, 0, last_slash + 1) : ""
 
@@ -0,0 +1,334 @@
+options gen2
+options indenting = 4
+options no_global_variables = false
+options no_unused_block_arguments = false
+options no_unused_function_arguments = false
+
+module logger shared public
+
+//! Structured logging for daslang tools.
+//!
+//! Writes one JSON object per line ("JSON Lines" / ``ndjson``) to
+//! ``{get_das_root()}/logs/<name>.log``. Reuses the runtime ``LOG_TRACE`` /
+//! ``LOG_DEBUG`` / ``LOG_INFO`` / ``LOG_WARNING`` / ``LOG_ERROR`` /
+//! ``LOG_CRITICAL`` levels. Each record carries an ISO 8601 UTC timestamp
+//! (millisecond precision), level name, category, message, and optional
+//! ``fields`` object.
+//!
+//! All public names carry the ``logger_`` prefix — short verbs like
+//! ``flush`` / ``close`` / ``info`` / ``debug`` would collide with user
+//! code when called unqualified. The intended call shape is
+//! ``logger_info("mcp.tool", "...")``, not ``logger::info(...)``.
+//!
+//! **Categories** are free-form strings; the convention is dotted
+//! hierarchy from tool name down to subsystem:
+//!
+//! - ``"mcp"`` — top-level events for the MCP server
+//! - ``"mcp.req"`` / ``"mcp.res"`` — JSON-RPC request / response framing
+//! - ``"mcp.tool"`` — tool dispatch (start / complete / error)
+//! - ``"mcp.live"``, ``"mcp.live.launch"`` — live-reload subsystem
+//! - ``"mcp.heap"`` — heap-collection ticks
+//!
+//! Filters apply at the most-specific dotted prefix:
+//! :func:`logger_set_category_level` ``("mcp.live", LOG_DEBUG)`` enables
+//! debug for ``"mcp.live"``, ``"mcp.live.launch"``, etc. — anything else
+//! stays at the global :func:`logger_set_min_level`.
+//!
+//! :func:`logger_install_hook` plugs a GLOBAL debug agent into the runtime
+//! so accidental ``print()`` / ``to_log()`` calls are diverted into the
+//! log file instead of stdout/stderr — important for stdio-transport
+//! processes (MCP server, language servers) where any stdout write
+//! corrupts the wire format. One install covers every Context including
+//! future ``new_thread`` workers.
+
+require daslib/json public
+require daslib/fio public
+require strings
+require daslib/jsonrpc
+require daslib/debugger
+require daslib/rtti
+
+// ── State (per-Context) ──────────────────────────────────────────────
+
+var private log_file : FILE const? = null
+var private log_path : string
+var private log_name : string
+var private log_open_attempted = false
+var private log_open_failed = false
+var private log_min_level = LOG_INFO
+var private log_category_overrides : table<string; int>
+var private log_fallback_to_stderr = true
+
+// ── Internal helpers ─────────────────────────────────────────────────
+
+def private level_name(level : int) : string {
+    return "critical" if (level >= LOG_CRITICAL)
+    return "error" if (level >= LOG_ERROR)
+    return "warning" if (level >= LOG_WARNING)
+    return "info" if (level >= LOG_INFO)
+    return "debug" if (level >= LOG_DEBUG)
+    return "trace"
+}
+
+// Resolve filter level for a category. Most-specific dotted prefix wins —
+// "mcp.live.foo" first looks up the full path, then "mcp.live", then "mcp",
+// before falling back to the global min level.
+def private resolve_level(category : string) : int {
+    var probe = category
+    while (true) {
+        if (key_exists(log_category_overrides, probe)) return log_category_overrides[probe]
+        let dot = probe |> rfind(".")
+        break if (dot < 0)
+        probe = probe |> slice(0, dot)
+    }
+    return log_min_level
+}
+
+def private should_log(level : int; category : string) : bool {
+    return level >= resolve_level(category)
+}
+
+def private ensure_dir(path : string) {
+    let dir = dir_name(path)
+    return if (empty(dir))
+    let st = stat(dir)
+    return if (st.is_valid && st.is_dir)
+    mkdir(dir)
+}
+
+def private ensure_open() {
+    return if (log_file != null || log_open_failed || empty(log_path))
+    log_open_attempted = true
+    ensure_dir(log_path)
+    log_file = fopen(log_path, "ab")
+    if (log_file == null) {
+        log_open_failed = true
+    }
+}
+
+// JSON-encode the four fixed fields directly into the writer, then append
+// the optional `fields` object via daslib/json's public `write_json` (no
+// json_boost reflection — fast path).
+def private write_record(var w : StringBuilderWriter; ts, lvl, cat, msg : string; fields : JsonValue?) {
+    w |> write("\{\"ts\":\"")
+    write_escape_string(w, ts)
+    w |> write("\",\"level\":\"")
+    write_escape_string(w, lvl)
+    w |> write("\",\"cat\":\"")
+    write_escape_string(w, cat)
+    w |> write("\",\"msg\":\"")
+    write_escape_string(w, msg)
+    if (fields != null) {
+        w |> write("\",\"fields\":")
+        // write_json always pretty-prints (depth=0 still inserts \n/\t between
+        // elements). One JSON object per line is load-bearing for JSON Lines,
+        // so flatten via the jsonrpc framing helper (preserves whitespace
+        // inside string literals).
+        w |> write(compact_json_whitespace(write_json(fields)))
+        w |> write("}\n")
+    } else {
+        w |> write("\"}\n")
+    }
+}
+
+def private emit(level : int; category, message : string; fields : JsonValue?) {
+    return if (!should_log(level, category))
+    ensure_open()
+    let line = build_string() $(var w) {
+        write_record(w, iso8601_now(), level_name(level), category, message, fields)
+    }
+    if (log_file != null) {
+        fwrite(log_file, line)
+        fflush(log_file)
+        return
+    }
+    // Open failed (or path never set). stderr is always safe — it isn't the
+    // JSON-RPC channel for stdio-transport servers, so a tail fallback can't
+    // corrupt protocol framing.
+    if (log_fallback_to_stderr) {
+        fwrite(fstderr(), line)
+    }
+}
+
+// ── Public configuration ─────────────────────────────────────────────
+//
+// All public names carry the ``logger_`` prefix on purpose. Short verbs
+// like ``flush`` / ``close`` / ``info`` / ``debug`` collide with user
+// code when callers ``require daslib/logger`` and reach for the
+// unqualified form. The prefix keeps the call sites readable
+// (``logger_info("foo", "bar")``) without forcing ``logger::`` everywhere.
+
+def logger_set_name(name : string) {
+    //! Configure the log file as ``{get_das_root()}/logs/<name>.log``.
+    //! Re-opens if the path changes; closes the previous handle. Each
+    //! Context tracks its own state — call once per context.
+    let new_path = path_join(get_das_root(), "logs/{name}.log")
+    logger_set_path(new_path)
+    log_name = name
+}
+
+def logger_set_path(path : string) {
+    //! Override the log file path explicitly. Pass an absolute path or a
+    //! path relative to the current working directory.
+    if (path == log_path) return
+    if (log_file != null) {
+        fclose(log_file)
+        log_file = null
+    }
+    log_path = path
+    // Clear logical name so logger_get_name() matches the doc claim:
+    // "empty if the path was set directly". logger_set_name() restores
+    // log_name immediately after it calls us, so that path still works.
+    log_name = ""
+    log_open_attempted = false
+    log_open_failed = false
+}
+
+def logger_get_path() : string {
+    //! Returns the currently configured log file path (empty if unset).
+    return log_path
+}
+
+def logger_get_name() : string {
+    //! Returns the logical name passed to :func:`logger_set_name`
+    //! (empty if the path was set directly via :func:`logger_set_path`).
+    return log_name
+}
+
+def logger_set_min_level(level : int) {
+    //! Global minimum level. Records below this are dropped before
+    //! formatting. Default ``LOG_INFO``.
+    log_min_level = level
+}
+
+def logger_get_min_level() : int {
+    //! Returns the currently configured global minimum level.
+    return log_min_level
+}
+
+def logger_set_category_level(category : string; level : int) {
+    //! Override the level filter for one category. Dotted prefix
+    //! matching: an override on ``"mcp.live"`` applies to ``"mcp.live"``,
+    //! ``"mcp.live.foo"``, ``"mcp.live.bar"`` (unless they have their own
+    //! more specific override).
+    log_category_overrides[category] = level
+}
+
+def logger_clear_category_levels() {
+    //! Remove all per-category overrides.
+    log_category_overrides |> clear
+}
+
+def logger_set_stderr_fallback(enabled : bool) {
+    //! Enable / disable writing to stderr when the log file can't be
+    //! opened. Defaults to true; set to false for strict stdio-transport
+    //! servers that must NEVER write to either stream on file failure.
+    log_fallback_to_stderr = enabled
+}
+
+// ── Log calls ────────────────────────────────────────────────────────
+
+def logger_log(level : int; category, message : string; fields : JsonValue? = null) {
+    //! Generic log entry. Prefer the named-level helpers below.
+    emit(level, category, message, fields)
+}
+
+def logger_trace(category, message : string; fields : JsonValue? = null) {
+    //! Verbose trace-level record. ``LOG_TRACE``.
+    emit(LOG_TRACE, category, message, fields)
+}
+
+def logger_debug(category, message : string; fields : JsonValue? = null) {
+    //! Debug-level record. ``LOG_DEBUG``.
+    emit(LOG_DEBUG, category, message, fields)
+}
+
+def logger_info(category, message : string; fields : JsonValue? = null) {
+    //! Informational record. ``LOG_INFO`` — the default level.
+    emit(LOG_INFO, category, message, fields)
+}
+
+def logger_warning(category, message : string; fields : JsonValue? = null) {
+    //! Warning record. ``LOG_WARNING``.
+    emit(LOG_WARNING, category, message, fields)
+}
+
+def logger_error(category, message : string; fields : JsonValue? = null) {
+    //! Error record. ``LOG_ERROR``.
+    emit(LOG_ERROR, category, message, fields)
+}
+
+def logger_critical(category, message : string; fields : JsonValue? = null) {
+    //! Critical / fatal record. ``LOG_CRITICAL``.
+    emit(LOG_CRITICAL, category, message, fields)
+}
+
+// ── Lifecycle ────────────────────────────────────────────────────────
+
+def logger_flush() {
+    //! Explicit flush. Each write already flushes; only useful if you
+    //! disable auto-flush in a fork.
+    if (log_file != null) {
+        fflush(log_file)
+    }
+}
+
+def logger_close() {
+    //! Close the log file. Subsequent writes will lazy-reopen.
+    if (log_file != null) {
+        fclose(log_file)
+        log_file = null
+    }
+    log_open_attempted = false
+    log_open_failed = false
+}
+
+// ── Debug-agent hook ─────────────────────────────────────────────────
+//
+// Intercepts ``Context::to_out`` (the underlying mechanism behind ``print``
+// and ``to_log``) and routes every message into the configured log file
+// instead of stdout/stderr. Critical for stdio-transport processes — MCP
+// servers, language servers, anything where stdout is the wire format.
+//
+// Registered as a GLOBAL debug agent (not thread-local) under the
+// ``"daslib_logger"`` category. One install covers every Context that
+// later spawns; ``new_thread`` workers don't need to re-install. The
+// agent's ``onLog`` is dispatched into its installing Context, which
+// owns the log file handle — cross-context invocations route writes
+// through that single handle.
+
+let private LOGGER_AGENT_CATEGORY = "daslib_logger"
+
+class private LogHookAgent : DapiDebugAgent {
+    def override onLog(context : Context?; at : LineInfo const?; level : int; text : string#) : bool {
+        // Fail-open when logging isn't configured — let the default
+        // stdout/stderr path through instead of swallowing silently.
+        // Makes accidental "hook before logger_set_name" calls harmless
+        // rather than blackholing every print().
+        if (empty(log_path) && !log_fallback_to_stderr) return false
+        var fields : JsonValue? = null
+        if (at != null && at.fileInfo != null) {
+            fields = JV({"at" => JV("{at.fileInfo.name}:{at.line}")})
+        }
+        emit(level, "runtime", string(text), fields)
+        return true
+    }
+}
+
+def logger_install_hook() {
+    //! Install a global debug agent that diverts ``print`` and
+    //! ``to_log`` (from any Context, current or future) into the
+    //! configured log file. Idempotent — safe to call from every
+    //! module's [init], from MCP main, etc. Worker threads spawned via
+    //! ``new_thread`` inherit the hook automatically; no per-context
+    //! re-install needed.
+    return if (has_debug_agent_context(LOGGER_AGENT_CATEGORY))
+    install_new_debug_agent(new LogHookAgent(), LOGGER_AGENT_CATEGORY)
+}
+
+def logger_init(name : string) {
+    //! Convenience: ``logger_set_name(name)`` + ``logger_install_hook()``.
+    //! The common-case one-liner for tools that want both behaviors.
+    logger_set_name(name)
+    logger_install_hook()
+}