diff --git a/Makefile b/Makefile
index dfe799b4..9705ebef 100644
--- a/Makefile
+++ b/Makefile
@@ -234,7 +234,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_w6c_ww $(BIN)/test_ww_ww $(BIN)/test_self_rebuild \
 	  $(BIN)/test_dyn_ww $(BIN)/test_selfcheck $(BIN)/test_at_test_ww \
 	  $(BIN)/test_fmt_run $(BIN)/test_log_run $(BIN)/test_fnmatch_run \
-	  $(BIN)/test_shlex_run $(BIN)/test_getenv_run \
+	  $(BIN)/test_shlex_run $(BIN)/test_getenv_run $(BIN)/test_dirs_run \
 	  $(BIN)/test_memio_run $(BIN)/test_temp_run $(BIN)/test_getopt_run \
 	  $(BIN)/test_base32_run $(BIN)/test_base64_run \
 	  $(BIN)/test_adler32_run $(BIN)/test_crc16_run \
@@ -452,6 +452,10 @@ $(BIN)/test_getenv_run: test/wcc/974_getenv_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_dirs_run: test/wcc/975_dirs_run.c $(BIN)/ww $(BIN)/w6c \
+		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_memio_run: test/wcc/980_memio_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
diff --git a/lib/dirs/dirs.ww b/lib/dirs/dirs.ww
new file mode 100644
index 00000000..47f1d43d
--- /dev/null
+++ b/lib/dirs/dirs.ww
@@ -0,0 +1,187 @@
+// dirs — XDG base directory paths. Port of Hare's lib/dirs
+// (ref/hare/dirs/xdg.ha) using the lib/temp-style static `[256]u8`
+// pathbuf in place of Hare's `path::buffer` (lib/path doesn't ship
+// a buffer type yet).
+//
+// Surface today (1:1 with Hare's xdg.ha minus runtime()):
+//
+//   dirs.config(prog: str) str   — XDG_CONFIG_HOME/<prog>, fallback $HOME/.config/<prog>
+//   dirs.cache(prog: str)  str   — XDG_CACHE_HOME/<prog>,  fallback $HOME/.cache/<prog>
+//   dirs.data(prog: str)   str   — XDG_DATA_HOME/<prog>,   fallback $HOME/.local/share/<prog>
+//   dirs.state(prog: str)  str   — XDG_STATE_HOME/<prog>,  fallback $HOME/.local/state/<prog>
+//
+// Returns are static-buffer views — borrowed for the lifetime of
+// the next dirs call (any of the four above). Callers needing the
+// bytes to outlive the next call duplicate via [[strings.dup]].
+// Same precedent as Hare's dirs:: (which doc-strings the same
+// "overwritten on subsequent calls" contract).
+//
+// Lookup algorithm (mirrors Hare's xdg.ha:lookup):
+//
+//   1. If $XDG_<NAME>_HOME is set AND its first byte is '/'
+//      (Hare's path::abs check), return "<XDG>/<prog>" after
+//      mkdir-recursive (mode 0o755).
+//   2. Otherwise return "$HOME/<default>/<prog>" after mkdir-
+//      recursive. The non-absolute and unset/empty XDG cases both
+//      fall through to this branch — matches Hare's `yield`
+//      after the `path::abs` test.
+//
+// rt_aborts in two cases (matches Hare's `as str` cast on missing
+// HOME, plus its `fs::strerror` fatal on mkdir failure):
+//
+//   - HOME is not set
+//   - mkdirs(path, 0o755) fails for a non-EEXIST reason
+//
+// Skipped from v1 (with reasons preserved for the next graduator):
+//
+//   - runtime() — needs lib/os.stat + a getuid primitive for the
+//     uid/perm/isdir verification Hare's runtime() does. A relaxed
+//     env-only version would defeat the perm contract that's the
+//     entire point of XDG_RUNTIME_DIR. Defer (drew/rob aligned).
+//
+//   - XDG_CONFIG_DIRS / XDG_DATA_DIRS — system search paths. Hare's
+//     xdg.ha doesn't ship them; lib/CLAUDE.md prohibits richer-
+//     than-Hare surfaces. Defer until upstream Hare adds them.
+//
+//   - lib/fmt's fatalf-style error reporting on mkdir failure. Hare
+//     uses `fmt::fatalf("Error creating {}: {}", path, ...)`; ww's
+//     lib/fmt is print-string-only (no {n}-placeholder parser), so
+//     we hand the bare context "dirs: mkdirs failed" to rt_abort.
+//     Graduates when the {n}-placeholder parser lands.
+
+use os;
+
+@symbol("rt_abort") fn rtabort(msg: str) void;
+
+// pathbuf — module-level scratch path. Sized for any
+// "<HOME>/.local/share/<prog>" composition under reasonable
+// HOME and prog lengths; dirs returns a view into pathbuf[0..pathlen].
+// NUL byte at pathbuf[pathlen] for direct handoff to [[os.mkdirs]]
+// (same precedent as lib/temp).
+let pathbuf: [256]u8;
+let pathlen: i32 = 0;
+
+// SEP — '/' byte. Same constant as lib/path's SEP.
+def SEP: u8 = 47u8;
+
+// MODE_0755 — directory creation mode passed to [[os.mkdirs]].
+// Hare uses the literal `0o755` at every call site; ww doesn't ship
+// octal literals, so we name the constant once.
+def MODE_0755: i32 = 493i32;
+
+// puts — append `s` to pathbuf at offset `off`, capping against the
+// buffer's capacity to leave room for the trailing NUL. Returns the
+// new offset. Same shape as lib/temp.puts.
+fn puts(off: i32, s: str) i32 = {
+	let i: i32 = 0;
+	for (i < s.len) {
+		if (off + i >= 255) { break; };
+		pathbuf[off + i] = s[i];
+		i += 1;
+	};
+	return off + i;
+};
+
+// build — assemble "<base>/<sub>/<prog>" into pathbuf, NUL-terminate,
+// and store the length in [[pathlen]]. If `sub` is empty, the
+// "/<sub>" segment is skipped and the result is "<base>/<prog>".
+// Embedded '/' in `sub` (e.g. ".local/share") is fine — [[os.mkdirs]]
+// handles intermediate dirs.
+fn build(base: str, sub: str, prog: str) void = {
+	let off: i32 = 0;
+	off = puts(off, base);
+	if (sub.len > 0) {
+		if (off < 255) { pathbuf[off] = SEP; off += 1; };
+		off = puts(off, sub);
+	};
+	if (off < 255) { pathbuf[off] = SEP; off += 1; };
+	off = puts(off, prog);
+	if (off > 255) { off = 255; };
+	pathbuf[off] = 0u8;
+	pathlen = off;
+};
+
+// view — return a `str` view into pathbuf[0..pathlen]. Borrowed
+// for the lifetime of the next dirs call.
+fn view() str = {
+	let r: str;
+	r.ptr = &pathbuf[0];
+	r.len = pathlen;
+	return r;
+};
+
+// ensure — wrap [[os.mkdirs]] with the rt_abort-on-non-EEXIST
+// behaviour Hare's lookup uses (`fmt::fatalf` on the HOME branch).
+// Centralised so both branches in [[lookup]] share the error path.
+fn ensure() void = {
+	match (os.mkdirs(&pathbuf[0], MODE_0755)) {
+	case void => {};
+	case let _e: os.oserror => rtabort("dirs: mkdirs failed");
+	};
+};
+
+// lookup — Hare's lookup() inlined: probe $envvar, fall through to
+// $HOME/<dflt> on unset / empty / non-absolute XDG values. Auto-
+// mkdirs the result. rt_aborts if HOME is unset (no fallback at
+// the bottom of the chain — matches Hare's `as str` cast which
+// would also fault on missing HOME).
+fn lookup(prog: str, envvar: str, dflt: str) str = {
+	match (os.getenv(envvar)) {
+	case let xdg: str => {
+		if (xdg.len > 0) {
+			if (xdg[0] == SEP) {	// Hare's path::abs(path)
+				build(xdg, "", prog);
+				ensure();
+				return view();
+			};
+		};
+	};
+	case void => {};
+	};
+	let home: str;
+	match (os.getenv("HOME")) {
+	case let h: str => { home = h; };
+	case void => rtabort("dirs: HOME is not set");
+	};
+	build(home, dflt, prog);
+	ensure();
+	return view();
+};
+
+// config — directory suitable for storing config files for `prog`.
+// $XDG_CONFIG_HOME/<prog> if set+absolute, else $HOME/.config/<prog>.
+// Auto-created with mode 0o755. Returns a borrowed str view into
+// the module-level pathbuf; subsequent dirs calls overwrite it.
+//
+// Mirrors Hare's dirs::config (xdg.ha:47).
+export fn config(prog: str) str = {
+	return lookup(prog, "XDG_CONFIG_HOME", ".config");
+};
+
+// cache — directory suitable for cache files for `prog`.
+// $XDG_CACHE_HOME/<prog> if set+absolute, else $HOME/.cache/<prog>.
+//
+// Mirrors Hare's dirs::cache (xdg.ha:53).
+export fn cache(prog: str) str = {
+	return lookup(prog, "XDG_CACHE_HOME", ".cache");
+};
+
+// data — directory suitable for persistent data files for `prog`.
+// $XDG_DATA_HOME/<prog> if set+absolute, else $HOME/.local/share/<prog>.
+// Hare composes the default via path::set(.local, share); we emit
+// the composed string directly since lib/path doesn't ship a
+// path::buffer type yet.
+//
+// Mirrors Hare's dirs::data (xdg.ha:59).
+export fn data(prog: str) str = {
+	return lookup(prog, "XDG_DATA_HOME", ".local/share");
+};
+
+// state — directory suitable for storing program state files for
+// `prog`. $XDG_STATE_HOME/<prog> if set+absolute, else
+// $HOME/.local/state/<prog>.
+//
+// Mirrors Hare's dirs::state (xdg.ha:69).
+export fn state(prog: str) str = {
+	return lookup(prog, "XDG_STATE_HOME", ".local/state");
+};
diff --git a/lib/dirs/dirstest.ww b/lib/dirs/dirstest.ww
new file mode 100644
index 00000000..f82b360c
--- /dev/null
+++ b/lib/dirs/dirstest.ww
@@ -0,0 +1,140 @@
+// dirstest — exercises lib/dirs against an env state pre-arranged by
+// the C driver (test/wcc/975_dirs_run.c).
+//
+// Pre-arranged env (set via setenv/unsetenv before exec'ing
+// `ww run lib/dirs/dirstest.ww`; see 975_dirs_run.c):
+//
+//   HOME             = <tmpl>            (mkdtemp'd /tmp/wwdirs-XXXXXX)
+//   XDG_CONFIG_HOME  = <tmpl>/cfg        (absolute → XDG branch)
+//   XDG_CACHE_HOME   = "relative/path"   (non-abs → fallback to HOME)
+//   XDG_DATA_HOME    unset               (fallback to HOME)
+//   XDG_STATE_HOME   unset               (fallback to HOME)
+//   WW_TEST_TMPDIR   = <tmpl>            (so this fixture can compute
+//                                         the expected paths)
+//
+// Cohorts (one @test fn per row, in numeric order from main):
+//
+//   1. config("myapp")  — XDG-set+absolute  → <tmpl>/cfg/myapp
+//   2. cache("myapp")   — XDG-set+relative  → <tmpl>/.cache/myapp        (abs-check fallback)
+//   3. data("myapp")    — XDG-unset         → <tmpl>/.local/share/myapp  (HOME fallback)
+//   4. state("myapp")   — XDG-unset         → <tmpl>/.local/state/myapp  (HOME fallback)
+//
+// Static-buffer gotcha: dirs.config / dirs.cache / dirs.data /
+// dirs.state all return views into the same module-level pathbuf.
+// Each @test calls EXACTLY ONE dirs.* function, builds its expected
+// string into a separate `scratch: [256]u8` BEFORE that call, and
+// asserts immediately. Don't call two dirs.* fns and compare across
+// — the second clobbers the first's view.
+//
+// `signalled` global bumps before each test so a failing exit code
+// pinpoints the offending row (WEXITSTATUS = signalled + 10). Same
+// shape as temptest / shlextest / fnmatchtest / ostest.
+//
+// Don't `use io;` here — lib/os and lib/io collide on read/write/
+// close (task #17). We need only os.getenv + os.exit.
+
+use dirs;
+use os;
+
+let signalled: i32 = 0;
+
+fn fail() void = { os.exit(signalled + 10); };
+
+fn streq(a: str, b: str) bool = {
+	if (a.len != b.len) { return false; };
+	let i: i32 = 0;
+	for (i < a.len) {
+		if (a[i] != b[i]) { return false; };
+		i += 1;
+	};
+	return true;
+};
+
+// scratch — local buffer for expected-path construction. Independent
+// of dirs.pathbuf; both views stay valid through the streq compare
+// because they live in different buffers.
+let scratch: [256]u8;
+
+fn putscratch(off: i32, s: str) i32 = {
+	let i: i32 = 0;
+	for (i < s.len) {
+		if (off + i >= 255) { break; };
+		scratch[off + i] = s[i];
+		i += 1;
+	};
+	return off + i;
+};
+
+// expected — build "<tmpl>/<sub>/<prog>" into scratch and return a
+// view. Mirrors dirs.build but writes into our scratch buffer so
+// the expected and got views can be compared without aliasing.
+fn expected(tmpl: str, sub: str, prog: str) str = {
+	let off: i32 = 0;
+	off = putscratch(off, tmpl);
+	if (off < 255) { scratch[off] = 47u8; off += 1; };	// '/'
+	off = putscratch(off, sub);
+	if (off < 255) { scratch[off] = 47u8; off += 1; };
+	off = putscratch(off, prog);
+	let r: str;
+	r.ptr = &scratch[0];
+	r.len = off;
+	return r;
+};
+
+fn gettmpdir() str = {
+	match (os.getenv("WW_TEST_TMPDIR")) {
+	case let s: str => return s;
+	case void => {
+		fail();
+		let empty: str;
+		return empty;
+	};
+	};
+};
+
+// ---- 1: XDG_CONFIG_HOME=<tmpl>/cfg → <tmpl>/cfg/myapp --------------
+
+@test fn test_config_xdg_set() void = {
+	let tmpl = gettmpdir();
+	let exp = expected(tmpl, "cfg", "myapp");
+	let got = dirs.config("myapp");
+	if (!streq(got, exp)) { fail(); };
+};
+
+// ---- 2: XDG_CACHE_HOME="relative/path" → fallback to $HOME/.cache --
+//
+// Exercises Hare's `if (!path::abs(path)) yield;` branch — a
+// non-absolute XDG_*_HOME silently falls through to the HOME path.
+
+@test fn test_cache_xdg_relative_fallback() void = {
+	let tmpl = gettmpdir();
+	let exp = expected(tmpl, ".cache", "myapp");
+	let got = dirs.cache("myapp");
+	if (!streq(got, exp)) { fail(); };
+};
+
+// ---- 3: XDG_DATA_HOME unset → fallback to $HOME/.local/share -------
+
+@test fn test_data_unset_fallback() void = {
+	let tmpl = gettmpdir();
+	let exp = expected(tmpl, ".local/share", "myapp");
+	let got = dirs.data("myapp");
+	if (!streq(got, exp)) { fail(); };
+};
+
+// ---- 4: XDG_STATE_HOME unset → fallback to $HOME/.local/state ------
+
+@test fn test_state_unset_fallback() void = {
+	let tmpl = gettmpdir();
+	let exp = expected(tmpl, ".local/state", "myapp");
+	let got = dirs.state("myapp");
+	if (!streq(got, exp)) { fail(); };
+};
+
+export fn main() i32 = {
+	signalled = 1; test_config_xdg_set();
+	signalled = 2; test_cache_xdg_relative_fallback();
+	signalled = 3; test_data_unset_fallback();
+	signalled = 4; test_state_unset_fallback();
+	return 0;
+};
diff --git a/lib/os/os.ww b/lib/os/os.ww
index 5836b819..49bc9253 100644
--- a/lib/os/os.ww
+++ b/lib/os/os.ww
@@ -193,6 +193,49 @@ export fn rmdir(path: *u8) i32 = {
 	return syscall1(nr.RMDIR, path: i64): i32;
 };
 
+// mkdirs — recursive mkdir. Creates `path` and any non-existent
+// parent directories with the given mode. EEXIST is silently
+// accepted (matches Hare's `errors::exists` skip in os::mkdirs);
+// any other syscall failure surfaces as `oserror`.
+//
+// `path` must be NUL-terminated AND its bytes must be writable —
+// mkdirs temporarily replaces '/' separators with NUL while
+// invoking [[mkdir]] on each prefix, then restores them. Pointing
+// `path` at a string literal will segfault. Callers hold the bytes
+// in a writable buffer (rt_alloc'd, a static `[N]u8`, etc.) — same
+// precedent as [[temp.named]]'s pathbuf.
+//
+// Mirrors Hare's os::mkdirs (recursive variant of os::mkdir).
+export fn mkdirs(path: *u8, mode: i32) (void | oserror) = {
+	// Find the path length (excluding trailing NUL).
+	let n: i32 = 0;
+	for (path[n] != 0u8) { n += 1; };
+	if (n == 0) { return; };
+
+	// Walk forward; at each '/' boundary, NUL-terminate the prefix,
+	// mkdir it, restore the slash, continue. Skip index 0 so a
+	// leading '/' on absolute paths doesn't trigger an empty mkdir.
+	let i: i32 = 1;
+	for (i < n) {
+		if (path[i] == 47u8) {	// '/'
+			path[i] = 0u8;
+			let r: i32 = mkdir(path, mode);
+			path[i] = 47u8;
+			if (r < 0) {
+				if (r != -17) { return r: i64: oserror; };
+			};
+		};
+		i += 1;
+	};
+
+	// mkdir the full path.
+	let r: i32 = mkdir(path, mode);
+	if (r < 0) {
+		if (r != -17) { return r: i64: oserror; };
+	};
+	return;
+};
+
 // getpid(2). Used by the driver to mint unique scratch paths.
 export fn getpid() i32 = {
 	return syscall0(nr.GETPID): i32;
diff --git a/test/wcc/975_dirs_run.c b/test/wcc/975_dirs_run.c
new file mode 100644
index 00000000..9bc85192
--- /dev/null
+++ b/test/wcc/975_dirs_run.c
@@ -0,0 +1,84 @@
+/*
+ * 975_dirs_run — execute the lib/dirs @test fixture under the C-side
+ * `ww run` driver and assert exit 0.
+ *
+ * Workflow:
+ *   1. mkdtemp /tmp/wwdirs-XXXXXX  — fresh per run, no cross-run
+ *      stale state, no parallel-test conflicts.
+ *   2. setenv the four cohort env states (see lib/dirs/dirstest.ww
+ *      file header for the contract).
+ *   3. exec `ww run lib/dirs/dirstest.ww`. The fixture reads
+ *      WW_TEST_TMPDIR + the XDG_/HOME envs and asserts.
+ *   4. system("rm -rf <tmpl>") to reclaim the tmpdir + the
+ *      auto-created child dirs (dirs.* mkdir-recursive on the way
+ *      down, so the directory tree is non-empty by test exit).
+ *
+ * Same wrapper shape as 970-974; cleanup-on-failure is rm-rf'd so a
+ * test failure never leaves residue in /tmp.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return 1;
+}
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char absbin[1024];
+	if (bin[0] != '/') {
+		char cwd[1024];
+		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+	char cwd[1024];
+	if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+
+	/* mkdtemp the per-run scratch root. */
+	char tmpl[64];
+	strcpy(tmpl, "/tmp/wwdirs-XXXXXX");
+	if (mkdtemp(tmpl) == NULL) {
+		perror("mkdtemp");
+		return 1;
+	}
+
+	/* Pre-arrange env. The child `ww run` inherits these. */
+	char cfg[128];
+	snprintf(cfg, sizeof cfg, "%s/cfg", tmpl);
+	setenv("HOME", tmpl, 1);
+	setenv("XDG_CONFIG_HOME", cfg, 1);
+	setenv("XDG_CACHE_HOME", "relative/path", 1);	/* non-abs → fallback */
+	unsetenv("XDG_DATA_HOME");
+	unsetenv("XDG_STATE_HOME");
+	setenv("WW_TEST_TMPDIR", tmpl, 1);
+
+	const char *src = "lib/dirs/dirstest.ww";
+	char path[1024], cmd[2048];
+	snprintf(path, sizeof path, "%s/%s", cwd, src);
+	snprintf(cmd, sizeof cmd, "%s/ww run %s", bin, path);
+	int rc = runwait(cmd);
+
+	/* Cleanup regardless of pass/fail — no residue under /tmp. */
+	char rmcmd[256];
+	snprintf(rmcmd, sizeof rmcmd, "rm -rf %s", tmpl);
+	(void)system(rmcmd);
+
+	if (rc != 0) {
+		fprintf(stderr, "dirs_run FAIL: %s exited %d\n", src, rc);
+		return 1;
+	}
+	printf("dirs_run: %s ok\n", src);
+	return 0;
+}