lib/path: #138 c3-posix dirname/basename — faithful posix.ha port, table-driven @test (cstage)

dirname/basename ported verbatim from ref/hare/path/posix.ha:17,37,
re-routing Hare's byte scanning to bytes.rtrim/rindex. Additive to the
c2-stack buffer core; no harness/Makefile/module-const changes.

Work-var renamed path->p to avoid Hare's param-shadowing
`let path = toutf8(path)`: ww's cgen N_LET prepends the new local into the
name-keyed localfind chain BEFORE the init is emitted, so the shadow-init
reads the fresh uninit slot — a silent miscompile, both-wrong-identical,
filed #152 and fixed independently next. drew ruled path->p a permanent
acceptable spelling (internal work-var, not API surface; avoids a
param-shadow footgun; not a rule-7 workaround). WHY-comment + #152 pointer
at both sites.

Tests: 10-row dirname/basename table (posix.ha:51-71 verbatim) — root,
no-sep, empty, trailing-sep, multi-sep all covered, expecteds traced.

C-first: cstage @test green; the str-view-vs-literal rows are #146-deferred
(wwstage byte-id, rides #125). Gate: all 324 passed, byte-id 990-997 green,
w6c/w6c_ww unchanged (lib-only additive).

lib/path/path.ww

@@ -1,8 +1,9 @@
 // path — filesystem path manipulation. UTF-8 paths, '/' separator.
 // Mirrors Hare's path:: surface (ref/hare/path/). This is the
 // path::buffer stack-buffer port (c2-stack subset: error/posix defs +
-// buffer + isroot + appendlit + appendnorm + push + string + set).
-// init/abs/dirname/basename and the rest land in later folds.
+// buffer + isroot + appendlit + appendnorm + push + string + set) plus
+// the c3-posix subset (dirname + basename, ref/hare/path/posix.ha).
+// init/abs and the rest land in later folds.
 
 package path;
 
@@ -137,3 +138,51 @@ export fn set(buf: *buffer, items: str...) (str | error) = {
 	buf.end = 0;
 	return push(buf, items...);
 };
+
+// ---- POSIX jail (ref/hare/path/posix.ha) ------------------------------
+// POSIX-compliant dirname/basename. They do NOT normalize the input and
+// operate on plain str (no buffer), so they sit apart from the stack
+// paradigm above — same POSIX-complaint as posix.ha:7-11.
+
+// ref/hare/path/posix.ha:17. Does *not* normalize; the return is either a
+// literal ("."/sepstr) or a borrowed view of the input. Div: toutf8 stays
+// strings.toutf8; len(path)→path.len; fromutf8_unsafe→strings.frombytes
+// (rule-9 carve-out); rindex z:size→i32; reslice `[..z]`→`[0:z]` (div #4).
+// Div: Hare shadows the param (`let path = strings::toutf8(path)`); ww's
+// new `let` binding is in scope for its OWN initializer, so the shadow
+// reads the uninitialized local — work var renamed `p` (cstage self-init
+// scope bug, #152).
+export fn dirname(path: str) str = {
+	let p: []u8 = strings.toutf8(path);
+	if (p.len == 0) { return "."; };
+
+	p = bytes.rtrim(p, SEP);
+	if (p.len == 0) { return sepstr; };
+
+	match (bytes.rindex(p, SEP)) {
+	case void => { return "."; };
+	case let z: i32 => { p = p[0:z]; };
+	};
+	p = bytes.rtrim(p, SEP);
+
+	if (p.len == 0) { return sepstr; };
+	return strings.frombytes(p);
+};
+
+// ref/hare/path/posix.ha:37. Does *not* normalize; the return is a
+// borrowed view of the input. Div: as dirname (incl. param-shadow rename
+// to `p`, #152); reslice `[z+1..]`→`[z+1:]` (div #4); empty-match no-op
+// arm spelled `case void => void;` (bytes.ww:130 precedent).
+export fn basename(path: str) str = {
+	let p: []u8 = strings.toutf8(path);
+	if (p.len == 0) { return "."; };
+
+	p = bytes.rtrim(p, SEP);
+	if (p.len == 0) { return sepstr; };
+
+	match (bytes.rindex(p, SEP)) {
+	case void => void;
+	case let z: i32 => { p = p[z+1:]; };
+	};
+	return strings.frombytes(p);
+};