test: testenv.runcommandenv, the explicit-env runcommand variant

test/testenv/testenv.ww

@@ -97,10 +97,18 @@ export fn isdir(path: str) bool = {
 // failures abort; termination and exit code are the caller's verdict.
 export fn runcommand(dir: str, root: str, name: str, argv: []str,
 	lifetime: time.duration, out: *commandout) void = {
+	runcommandenv(dir, root, name, argv, os.getenvs(), lifetime, out);
+};
+
+// Explicit-env variant of [[runcommand]] for arranger observers that
+// must control the child's environment per row (exec.command.env is
+// caller-built; ww ships no setenv primitive, deliberately).
+export fn runcommandenv(dir: str, root: str, name: str, argv: []str,
+	env: []str, lifetime: time.duration, out: *commandout) void = {
 	let c: exec.command;
 	c.path = argv[0];
 	c.argv = argv;
-	c.env = os.getenvs();
+	c.env = env;
 	c.dir = dir;
 	c.stdoutpath = strings.concat(root, "/", name, ".stdout");
 	c.stderrpath = strings.concat(root, "/", name, ".stderr");