Integrate with herdr cli.

src/Pty.zig

@@ -241,7 +241,7 @@ fn buildEnv(
 
 /// Whether an inherited `NAME=value` entry names a variable the caller is
 /// about to define.
-fn shadowedBy(entry: []const u8, extra: []const []const u8) bool {
+pub fn shadowedBy(entry: []const u8, extra: []const []const u8) bool {
     const eq = std.mem.indexOfScalar(u8, entry, '=') orelse return false;
     for (extra) |candidate| {
         const candidate_eq = std.mem.indexOfScalar(u8, candidate, '=') orelse continue;
@@ -263,8 +263,14 @@ fn freeEnv(alloc: std.mem.Allocator, envp: [:null]?[*:0]const u8) void {
 /// are rather than where you began. Read straight out of procfs: there is no
 /// portable API for it, and this app is Linux-only regardless.
 pub fn cwd(self: Pty, buf: []u8) ?[]const u8 {
+    return cwdOf(self.pid, buf);
+}
+
+/// `cwd` for any process, not only one this module started — a herdr-core
+/// terminal's program, which runs on this machine but is nobody's child here.
+pub fn cwdOf(pid: pid_t, buf: []u8) ?[]const u8 {
     var link_buf: [64]u8 = undefined;
-    const link = std.mem.printSentinel(&link_buf, "/proc/{d}/cwd", .{self.pid}, 0) catch return null;
+    const link = std.mem.printSentinel(&link_buf, "/proc/{d}/cwd", .{pid}, 0) catch return null;
 
     const n = c.readlink(link.ptr, buf.ptr, buf.len);
     if (n <= 0) return null;