feat(stdlib): add Os.* — the OS/environment interface (#21)

An Os.* namespace, Go-flavored and game-scoped, for the environment *around*
the game: the command line, environment variables, standard streams, process
exit, the host platform, and the per-user known folders a game writes into.
Rounds the bare System.* builtins (arg/getenv/exit) into one coherent surface.

  - args / arg_count / arg     the argument vector (args() -> []string)
  - env / env_or / has_env     read env vars (null-safe via env_or)
  - set_env / unset_env        mutate this process's environment
  - exit(code)                 terminate with a status code
  - platform() / arch()        host facts (uname sysname/machine)
  - stdout_write / stderr_write  raw writes to the standard streams
  - save_dir / config_dir / cache_dir / temp_dir   per-user known folders

Pure libc over NUL-terminated strings; C-free, no new runtime. arg_count/arg/
exit stay light (no prelude) as thin aliases of the existing intrinsics; the
rest share one Os runtime prelude emitted on demand (g_uses_osrt). platform()
is portable (uname system name is field 0 on every Unix); arch() and the
known-folder layout follow the macOS/BSD conventions — the fully supported
native target today. Linux/Windows/wasm folder resolution and a target-aware
arch() are documented follow-ups.

- examples/library/os.ludic: asserts the invariants that hold regardless of
  host — env round-trip, env_or fallback, unset, args()==arg_count(), non-empty
  platform/arch and known dirs. Wired into `x test` (now 54 passed).
- docs: a new Os section + 17 per-symbol pages; inventory updated; every fence
  passes check-docs (--fmt) and the site builds via docgen.
- seed regenerated; `x bootstrap-cfree` fixpoint holds.

Closes #21

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/emit_core.ludic

@@ -29,6 +29,7 @@ var g_uses_cryptort: bool = false  # Crypto.* was emitted -> emit the SHA-256 /
 var g_uses_uuidrt: bool = false  # Uuid.* was emitted -> emit the UUID runtime (needs the crypto CSPRNG)
 var g_uses_noisert: bool = false  # Noise.* was emitted -> emit the fixed-point noise runtime
 var g_uses_logrt: bool = false  # Log.* was emitted -> emit the log level register + console sink
+var g_uses_osrt: bool = false  # Os.* (prelude-backed methods) was emitted -> emit the Os runtime
 var g_uses_datert: bool = false  # Date.*/DateTime.* was emitted -> emit the civil<->epoch conversions
 var g_uses_longstr: bool = false  # string(long) / interpolating a long was emitted -> emit fn_long_str
 

selfhost/emit_decl.ludic

@@ -108,6 +108,7 @@ function emit_program() -> void {
   if g_uses_uuidrt { emit_uuid_prelude() }       # @fn_uuid_v4 / @fn_uuid_v7 / parse / equals (over the crypto CSPRNG)
   if g_uses_noisert { emit_noise_prelude() }     # @fn_noise_value2/perlin2/simplex2/fbm2/cellular2 (Q16.16)
   if g_uses_logrt { emit_log_prelude() }         # @L_log_level + @fn_log_emit (levelled stderr sink)
+  if g_uses_osrt { emit_os_prelude() }           # @fn_os_args/platform/arch/save_dir/... (libc env + uname)
   if g_uses_datert { emit_datetime_prelude() }   # @fn_days_from_civil / @fn_civil_from_days conversions
 }
 

selfhost/emit_expr.ludic

@@ -247,6 +247,10 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
     if is_log_ns(meth) { return emit_log_ns(meth, e) }
     perr(`unknown builtin Log.{meth}`)
   }
+  if (ns == "Os") {
+    if is_os_ns(meth) { return emit_os_ns(meth, e) }
+    perr(`unknown builtin Os.{meth}`)
+  }
   if (ns == "Vector") {
     if is_vector_ns(meth) { return emit_vector_ns(meth, e) }
     perr(`unknown builtin Vector.{meth}`)

selfhost/emit_os.ludic

@@ -0,0 +1,188 @@
+# emit_os.ludic — the Os.* namespace: the environment *around* the game — the
+# command line, environment variables, standard streams, process exit, the host
+# platform, and the per-user known folders a game writes into. Go-flavored and
+# game-scoped: no process spawning, signals, or permission APIs — just the facts
+# a launcher, an asset pipeline, or a save system needs.
+#
+#   Os.args()              -> []string   every command-line argument (argv[0..])
+#   Os.arg_count()         -> int        how many arguments there are
+#   Os.arg(i)              -> string     the i-th argument (0 = the program path)
+#   Os.env(name)           -> string     an environment variable, or null if unset
+#   Os.env_or(name, fb)    -> string     ...or `fb` when it is unset/empty-null
+#   Os.has_env(name)       -> bool       is the variable set?
+#   Os.set_env(name, val)  -> bool       set it (true on success)
+#   Os.unset_env(name)     -> bool       remove it (true on success)
+#   Os.exit(code)                        terminate the process with a status code
+#   Os.platform()          -> string     "macos" | "linux" | ...(raw uname sysname)
+#   Os.arch()              -> string     machine arch, e.g. "arm64" | "x86_64"
+#   Os.stdout_write(s)                   write a string to standard output
+#   Os.stderr_write(s)                   write a string to standard error
+#   Os.save_dir(app)       -> string     per-user save directory for `app`
+#   Os.config_dir(app)     -> string     per-user config directory for `app`
+#   Os.cache_dir(app)      -> string     per-user cache directory for `app`
+#   Os.temp_dir()          -> string     the system temporary directory
+#
+# Determinism: args/env/platform are non-deterministic host input — read them at
+# startup to configure the game, but keep them out of the replayable simulation.
+#
+# Platform coverage: this v1 targets the native (macOS/BSD) host, the only fully
+# supported target today. platform() is portable (uname sysname is field 0 on
+# every Unix); arch() and the known-folder layout assume the macOS/BSD utsname
+# and directory conventions. Linux/Windows/wasm known-folder resolution and a
+# target-aware arch() are documented follow-ups (see issue #21).
+
+function is_os_ns(meth: pointer) -> bool {
+  if (meth == "args") or (meth == "arg_count") or (meth == "arg") { return true }
+  if (meth == "env") or (meth == "env_or") or (meth == "has_env") { return true }
+  if (meth == "set_env") or (meth == "unset_env") { return true }
+  if (meth == "exit") or (meth == "platform") or (meth == "arch") { return true }
+  if (meth == "stdout_write") or (meth == "stderr_write") { return true }
+  if (meth == "save_dir") or (meth == "config_dir") or (meth == "cache_dir") or (meth == "temp_dir") { return true }
+  return false
+}
+
+function emit_os_ns(meth: pointer, e: Node) -> Val {
+  # arg_count / arg / exit stay light — they mirror the bare intrinsics and need
+  # no Os runtime prelude, so a program using only these emits no extra IR.
+  if (meth == "arg_count") { return val(emit_bind("load i32, ptr @L_argc"), "int") }
+  if (meth == "arg") {
+    let i = emit_expr(e.kids[0])
+    let v = emit_bind("load ptr, ptr @L_argv")
+    let q = emit_bind(`getelementptr ptr, ptr {v}, i32 {i.code}`)
+    return val(emit_bind(`load ptr, ptr {q}`), "string")
+  }
+  if (meth == "exit") {
+    let n = emit_expr(e.kids[0])
+    emit(`  call void @exit(i32 {n.code})\n`)
+    emit("  unreachable\n")
+    g_term = true
+    return val("0", "void")
+  }
+  if (meth == "env") {                              # raw getenv: null when unset
+    let nm = emit_expr(e.kids[0])
+    return val(emit_bind(`call ptr @getenv(ptr {nm.code})`), "string")
+  }
+  if (meth == "has_env") {
+    let nm = emit_expr(e.kids[0])
+    let r = emit_bind(`call ptr @getenv(ptr {nm.code})`)
+    let ne = emit_bind(`icmp ne ptr {r}, null`)
+    return val(emit_bind(`zext i1 {ne} to i32`), "bool")
+  }
+  if (meth == "stdout_write") or (meth == "stderr_write") {
+    var strm = "@__stdoutp"
+    if (meth == "stderr_write") { strm = "@__stderrp" }
+    let s = emit_expr(e.kids[0])
+    let f = emit_bind(`load ptr, ptr {strm}`)
+    let n = emit_bind(`call i64 @strlen(ptr {s.code})`)
+    emit(`  call i64 @fwrite(ptr {s.code}, i64 1, i64 {n}, ptr {f})\n`)
+    return val("0", "void")
+  }
+  # everything below is served by the Os runtime prelude
+  g_uses_osrt = true
+  if (meth == "args") { return val(emit_bind("call ptr @fn_os_args()"), "[]string") }
+  if (meth == "env_or") {
+    let nm = emit_expr(e.kids[0]);  let fb = emit_expr(e.kids[1])
+    return val(emit_bind(`call ptr @fn_os_getenv_or(ptr {nm.code}, ptr {fb.code})`), "string")
+  }
+  if (meth == "set_env") {
+    let nm = emit_expr(e.kids[0]);  let v = emit_expr(e.kids[1])
+    let r = emit_bind(`call i32 @setenv(ptr {nm.code}, ptr {v.code}, i32 1)`)
+    let ok = emit_bind(`icmp eq i32 {r}, 0`)
+    return val(emit_bind(`zext i1 {ok} to i32`), "bool")
+  }
+  if (meth == "unset_env") {
+    let nm = emit_expr(e.kids[0])
+    let r = emit_bind(`call i32 @unsetenv(ptr {nm.code})`)
+    let ok = emit_bind(`icmp eq i32 {r}, 0`)
+    return val(emit_bind(`zext i1 {ok} to i32`), "bool")
+  }
+  if (meth == "platform") { return val(emit_bind("call ptr @fn_os_platform()"), "string") }
+  if (meth == "arch")     { return val(emit_bind("call ptr @fn_os_arch()"), "string") }
+  if (meth == "save_dir") {
+    let a = emit_expr(e.kids[0])
+    return val(emit_bind(`call ptr @fn_os_save_dir(ptr {a.code})`), "string")
+  }
+  if (meth == "config_dir") {
+    let a = emit_expr(e.kids[0])
+    return val(emit_bind(`call ptr @fn_os_config_dir(ptr {a.code})`), "string")
+  }
+  if (meth == "cache_dir") {
+    let a = emit_expr(e.kids[0])
+    return val(emit_bind(`call ptr @fn_os_cache_dir(ptr {a.code})`), "string")
+  }
+  # temp_dir
+  return val(emit_bind("call ptr @fn_os_temp_dir()"), "string")
+}
+
+# emit_os_prelude — the Os runtime, emitted once per program that uses the
+# prelude-backed Os.* methods (g_uses_osrt). Pure libc over NUL-terminated
+# strings; declares the few POSIX symbols the header does not already carry.
+function emit_os_prelude() -> void {
+  emith("declare i32 @setenv(ptr, ptr, i32)\n")
+  emith("declare i32 @unsetenv(ptr)\n")
+  emith("declare i32 @uname(ptr)\n")
+
+  # string constants (escaped + length-counted by emit_str_const)
+  let k_home  = emit_str_const("HOME")
+  let k_dot   = emit_str_const(".")
+  let k_appsp = emit_str_const("/Library/Application Support/")
+  let k_cache = emit_str_const("/Library/Caches/")
+  let k_tmpk  = emit_str_const("TMPDIR")
+  let k_tmp   = emit_str_const("/tmp")
+  let k_darw  = emit_str_const("Darwin")
+  let k_macos = emit_str_const("macos")
+  let k_linux_k = emit_str_const("Linux")
+  let k_linux   = emit_str_const("linux")
+
+  # getenv(name) or a fallback when it is unset
+  emith("define ptr @fn_os_getenv_or(ptr %name, ptr %fb) {\n")
+  emith("entry:\n  %r = call ptr @getenv(ptr %name)\n  %z = icmp eq ptr %r, null\n  br i1 %z, label %use, label %got\n")
+  emith("use:\n  ret ptr %fb\n")
+  emith("got:\n  ret ptr %r\n}\n")
+
+  # concatenate two NUL-terminated strings into a fresh malloc'd buffer
+  emith("define ptr @fn_os_join2(ptr %a, ptr %b) {\n")
+  emith("entry:\n  %la = call i64 @strlen(ptr %a)\n  %lb = call i64 @strlen(ptr %b)\n")
+  emith("  %sum = add i64 %la, %lb\n  %tot = add i64 %sum, 1\n  %m = call ptr @malloc(i64 %tot)\n")
+  emith("  call ptr @memcpy(ptr %m, ptr %a, i64 %la)\n")
+  emith("  %m2 = getelementptr i8, ptr %m, i64 %la\n  call ptr @memcpy(ptr %m2, ptr %b, i64 %lb)\n")
+  emith("  %end = getelementptr i8, ptr %m, i64 %sum\n  store i8 0, ptr %end\n  ret ptr %m\n}\n")
+
+  emith("define ptr @fn_os_join3(ptr %a, ptr %b, ptr %c) {\n")
+  emith("entry:\n  %ab = call ptr @fn_os_join2(ptr %a, ptr %b)\n  %r = call ptr @fn_os_join2(ptr %ab, ptr %c)\n  ret ptr %r\n}\n")
+
+  # the user's home directory, or "." when HOME is unset
+  emith(`define ptr @fn_os_home() {{\n  %r = call ptr @fn_os_getenv_or(ptr {k_home}, ptr {k_dot})\n  ret ptr %r\n}}\n`)
+
+  # per-user known folders (macOS/BSD layout)
+  emith(`define ptr @fn_os_save_dir(ptr %app) {{\n  %h = call ptr @fn_os_home()\n  %r = call ptr @fn_os_join3(ptr %h, ptr {k_appsp}, ptr %app)\n  ret ptr %r\n}}\n`)
+  emith(`define ptr @fn_os_config_dir(ptr %app) {{\n  %h = call ptr @fn_os_home()\n  %r = call ptr @fn_os_join3(ptr %h, ptr {k_appsp}, ptr %app)\n  ret ptr %r\n}}\n`)
+  emith(`define ptr @fn_os_cache_dir(ptr %app) {{\n  %h = call ptr @fn_os_home()\n  %r = call ptr @fn_os_join3(ptr %h, ptr {k_cache}, ptr %app)\n  ret ptr %r\n}}\n`)
+  emith(`define ptr @fn_os_temp_dir() {{\n  %r = call ptr @fn_os_getenv_or(ptr {k_tmpk}, ptr {k_tmp})\n  ret ptr %r\n}}\n`)
+
+  # Os.args() -> a %LSlice of the argv strings (data = argv, len = cap = argc), a
+  # snapshot the caller may iterate or index like any other []string.
+  emith("define ptr @fn_os_args() {\n")
+  emith("entry:\n  %c = load i32, ptr @L_argc\n  %v = load ptr, ptr @L_argv\n")
+  emith("  %h = call ptr @malloc(i64 16)\n")
+  emith("  %d0 = getelementptr inbounds %LSlice, ptr %h, i32 0, i32 0\n  store ptr %v, ptr %d0\n")
+  emith("  %d1 = getelementptr inbounds %LSlice, ptr %h, i32 0, i32 1\n  store i32 %c, ptr %d1\n")
+  emith("  %d2 = getelementptr inbounds %LSlice, ptr %h, i32 0, i32 2\n  store i32 %c, ptr %d2\n")
+  emith("  ret ptr %h\n}\n")
+
+  # platform(): uname sysname (field 0, portable) mapped to a short id
+  emith("define ptr @fn_os_platform() {\n")
+  emith("entry:\n  %buf = call ptr @malloc(i64 8192)\n  call i32 @uname(ptr %buf)\n")
+  emith(`  %cd = call i32 @strncmp(ptr %buf, ptr {k_darw}, i64 6)\n  %isd = icmp eq i32 %cd, 0\n  br i1 %isd, label %mac, label %chkl\n`)
+  emith(`mac:\n  ret ptr {k_macos}\n`)
+  emith(`chkl:\n  %cl = call i32 @strncmp(ptr %buf, ptr {k_linux_k}, i64 5)\n  %isl = icmp eq i32 %cl, 0\n  br i1 %isl, label %lin, label %other\n`)
+  emith(`lin:\n  ret ptr {k_linux}\n`)
+  emith("other:\n  ret ptr %buf\n}\n")
+
+  # arch(): the uname `machine` field. On macOS/BSD utsname each field is 256
+  # bytes, so `machine` (index 4) sits at offset 1024. Documented BSD-layout
+  # assumption (see the header note); other layouts are a follow-up.
+  emith("define ptr @fn_os_arch() {\n")
+  emith("entry:\n  %buf = call ptr @malloc(i64 8192)\n  call i32 @uname(ptr %buf)\n")
+  emith("  %m = getelementptr i8, ptr %buf, i64 1024\n  ret ptr %m\n}\n")
+}