diff --git a/cmd/ww/main.c b/cmd/ww/main.c
index a04b70b4..16bb2a79 100644
--- a/cmd/ww/main.c
+++ b/cmd/ww/main.c
@@ -7706,6 +7706,19 @@ do_run(int argc, char **argv)
 	if (src == NULL) src = ".";
 	struct stat requested;
 	int literal = stat(src, &requested) == 0;
+	if (literal && S_ISDIR(requested.st_mode)) {
+		size_t n = strlen(src);
+		if (n >= 3 && strcmp(src + n - 3, ".ww") == 0) {
+			if (n >= 8 && strcmp(src + n - 8, "_test.ww") == 0)
+				fprintf(stderr,
+				    "ww: cannot run *_test.ww files (%s)\n", src);
+			else
+				fprintf(stderr,
+				    "%s is a directory, should be a WW file\n", src);
+			free(incs);
+			return 1;
+		}
+	}
 	char resolved[PATH_MAX];
 	int is_dir = 0;
 	if (!resolve_module(src, incs, resolved, sizeof resolved, &is_dir)) {
diff --git a/docs/build-system.md b/docs/build-system.md
index 41941c1a..ff187f7f 100644
--- a/docs/build-system.md
+++ b/docs/build-system.md
@@ -10376,6 +10376,141 @@ test/run command boundaries. No serialized representation changes: build
 workdir format remains `18`, test workdir format remains `19`, semantic storage
 format remains `3`, and no cache or result record is added.
 
+### 11.53 Implemented `.ww`-spelled directory run rejection
+
+An existing target selected by `ww run` whose exact requested spelling ends
+`.ww` is a named-source request when ordinary symlink-following `stat` reports
+a directory. Run rejects that directory before package resolution or private
+work creation. This is deliberately different from section 11.52's build/test
+directory route: the command-specific front door, not the shared resolver,
+owns the distinction.
+
+#### Pinned authority and applicability
+
+- **behavior directly implemented or asserted by pinned Go** — official Go
+  1.26.5 commit `c19862e5f8415b4f24b189d065ed739517c548ba`
+  scans leading `.go` operands at
+  `cmd/go/internal/run/run.go:73–112`, rejecting an `_test.go` spelling at
+  103–109 before passing the named set to `GoFilesPackage`.
+  `cmd/go/internal/load/pkg.go:3244–3289`, especially 3274–3281, follows
+  `Stat` and fatals when a named operand is a directory. Later checking,
+  action construction, linking, and execution at `run.go:141–173` are not
+  reached.
+- **behavior directly implemented or asserted by pinned Go** — the exact Go
+  status, header-free diagnostic, and terminating newline follow
+  `cmd/go/internal/base/base.go:137–145,175–183`,
+  `cmd/go/main.go:98–100`, and `log/log.go:200–245`. Official
+  `cmd/go/testdata/script/run_hello.txt:1–10`, `run_dirs.txt:1–20`, and
+  `run_set_executable_name.txt:4–17` anchor the named-file run front and its
+  distinction from package-form run. Indirect official directory-kind anchors
+  are `list_ambiguous_path.txt:4–15,29–36`,
+  `mod_get_go_file.txt:47–58`, and `mod_symlink_dotgo.txt:4–9`. No official
+  end-to-end `go run` test asserts this directory diagnostic; the result is
+  implemented directly by the cited source.
+- **behavior derived from the pinned implementation** — WW's `.ww`
+  named-source spelling and existing directory-package form meet at the same
+  practical boundary. The applicable adaptation uses `WW file` and
+  `*_test.ww` while preserving requested operand bytes. It requires no module,
+  manifest, registry, network lookup, generalized import grammar, cache,
+  database, CAS, or build expression.
+
+#### Ownership, selection, and diagnostics
+
+- **directly measured WW behavior** — before this change, Cstage followed a
+  direct `.ww` directory or visible `.ww`/`_test.ww` symlink into the ordinary
+  directory graph, invoked compiler, assemblers, linker, and user program, and
+  returned that program's status. WWstage instead entered raw-source loading,
+  returned status 1 with exact `ww: cannot read source\n`, and ran no producer
+  or program. Both removed the private work they had unnecessarily created.
+- **behavior derived from the pinned implementation** — the true WW owners
+  are only `cmd/ww/main.c::do_run` and
+  `selfhost/cmd/ww/main.ww::dorun`, after their existing option/target parse
+  and requested `stat`, but before `resolve_module`/`resolvemodule` and run
+  scratch creation. Changing the shared resolver would wrongly change the
+  distinct build, test, logical, and dotted-package fronts.
+- **directly measured WW behavior** — after the run-local classification,
+  both stages return status 1 with empty stdout. A requested spelling ending
+  `_test.ww` emits exactly
+  `ww: cannot run *_test.ww files (OPERAND)\n`; every other selected directory
+  ending `.ww` emits exactly
+  `OPERAND is a directory, should be a WW file\n`. The requested operand is
+  reproduced unchanged. `_test.ww` precedence applies before ordinary
+  directory rejection, including through a symlink.
+- **directly measured WW behavior** — the rule includes direct and symlinked
+  `.ww` directories and hidden directory spellings `.hidden.ww` and
+  `_hidden.ww`. It also precedes malformed package clauses and missing imports
+  inside the directory because no member is selected or opened. Existing run
+  option errors and target determination retain their earlier precedence.
+  A trailing separator does not end `.ww`; non-`.ww` directories and dotted
+  logical requests retain the established package route.
+
+#### Build, test, package, and import effects
+
+- **directly measured WW behavior** — package/source selection is the primary
+  axis. The rejected request creates no raw or directory package, canonical
+  identity, declared-name instance, test variant, initializer, graph node, or
+  action. Requested spelling and followed target are diagnostic observations
+  only, never canonical package, action, symbol, artifact, `.wwi`,
+  publication, or persistence identity.
+- **directly measured WW behavior** — build retains section 11.52's stat-first
+  rule for the same direct and symlink spellings. It still enumerates the
+  directory, discovers its dotted dependencies, constructs ordinary package
+  actions, and applies the established default, explicit, directory,
+  `/dev/null`, `-S`, publication, persistence, invalidation, and rollback
+  policies. Unaffected build controls retain stage-byte-identical public and
+  semantic artifacts.
+- **directly measured WW behavior** — raw `ww test`, `ww test -c`, and
+  directory `ww test -S` retain their stat-first directory selection and
+  established diagnostics/artifact bytes. Test package variants, generated
+  main, process topology, filtering, capture, result ordering, retention, and
+  result non-caching are unchanged.
+- **directly measured WW behavior** — imports are not scanned on the selected
+  run rejection and create no qualifier or edge. Dotted and non-`.ww` package
+  controls retain exact canonical import identity, dependency discovery, and
+  runtime behavior. No physical directory becomes canonical identity through
+  this rule.
+
+#### Actions, lifecycle, parity, and scope
+
+- **directly measured WW behavior** — selected rejection invokes no compiler,
+  assembler, archiver, linker, initializer, runtime, or owned child/process
+  group. A fixture-preoccupied exact `/tmp/ww_run_<pid>` plus sentinel remains
+  untouched, proving that the driver does not acquire or mutate its run-scratch
+  path; final cleanup leaves that path absent. It also creates no output,
+  `.sepwork`, unit, `.wwi`, assembly, object, archive, executable, capture,
+  result, transaction, stage, backup, or persistent record. Thus
+  producer/runtime failure, publication, reuse, invalidation, and rollback are
+  inapplicable on this preflight route; all prior caller and committed bytes
+  remain untouched.
+- **directly measured WW behavior** — classification is request-local,
+  read-only, and isolated under concurrency. An interruption in this preflight
+  owns no child or filesystem resource. The general direct-driver interruption
+  gap from section 11.52 remains open: a different request interrupted after
+  transaction staging can still leave fixed-name `.new` files and poison
+  later persistent reuse. This slice neither reaches nor fixes that machinery.
+- **directly measured WW behavior** — Cstage and WWstage match exactly on
+  status, stdout, stderr, diagnostic bytes, empty producer traces, artifact
+  absence, exact PID-path non-acquisition and final absence, concurrent
+  isolation, and cleanup for every selected row. Unaffected controls retain
+  diagnostic and public or semantic artifact-byte parity.
+- **behavior derived from the pinned implementation** — this narrow
+  file-kind slice does not implement the complete suffix-first run front.
+  Regular or missing `_test.ww`, missing or logical `.ww`, multiple named
+  sources, finite FIFOs, and hidden regular sources retain their prior routes
+  and remain separately open where different. Recursive requests, ordinary
+  directory requests, and generalized imports are not changed.
+
+The focused WW-native observer covers direct, symlinked, hidden, ordinary, and
+`_test.ww` directory spellings; malformed-package and missing-import
+precedence; exact requested diagnostics; empty tool/runtime traces; exact
+PID-path non-acquisition and final absence; concurrency and cleanup;
+trailing-separator,
+non-`.ww`, regular-source, and dotted logical run controls; and unchanged
+same-spelling build and raw/compile-only/assembly-only test boundaries. No
+serialized representation changes: build workdir format remains `18`, test
+workdir format remains `19`, semantic storage format remains `3`, and no cache
+or result record is added.
+
 ## 12. Candidate architectures and hard-gate decision
 
 Five candidates were developed as coherent systems, not as feature bins.
diff --git a/docs/spec.md b/docs/spec.md
index 64eec652..e46db098 100644
--- a/docs/spec.md
+++ b/docs/spec.md
@@ -370,10 +370,31 @@ ImportPath    = ident { "." ident } .
   no new package, dotted-import, graph, action, symbol, artifact, `.wwi`,
   publication, or persistence identity. Raw `ww test`, `ww test -c`, and
   `ww test -S` already use the same directory classification and are unchanged.
-  `ww run` retains its separate named-operand front door. Multiple operands,
-  recursive and logical requests, regular and non-regular source targets, and
-  dangling symlinks are not changed. Build workdir format remains 18, test
-  workdir format remains 19, and semantic storage format remains 3.
+  `ww run` retains its separate named-operand front door, with its
+  `.ww`-spelled directory rule specified next. Multiple operands, recursive
+  and logical requests, regular and non-regular source targets, and dangling
+  symlinks are not changed. Build workdir format remains 18, test workdir
+  format remains 19, and semantic storage format remains 3.
+- For `ww run`, an existing selected target whose exact requested spelling
+  ends `.ww` is a named-source request when symlink-following `stat` reports a
+  directory. The command rejects it before shared resolution, directory
+  enumeration, source/import loading, graph/action construction, private run
+  scratch, producers, or runtime. A requested suffix `_test.ww` has the earlier
+  exact diagnostic
+  `ww: cannot run *_test.ww files (OPERAND)\n`; every other such directory has
+  exact diagnostic `OPERAND is a directory, should be a WW file\n`. Both forms
+  return status 1 with empty stdout and reproduce the requested operand bytes
+  unchanged. The rule follows a terminal symlink, includes `.hidden.ww` and
+  `_hidden.ww` directory spellings, and precedes any malformed package or
+  missing import inside the directory. A trailing separator does not end
+  `.ww`; ordinary non-`.ww` directories, dotted logical requests, regular and
+  missing operands, multiple named operands, and non-directory non-regular
+  targets retain their established routes. The rejected spelling and followed
+  target are diagnostic metadata only and create no package/import identity,
+  graph/action, symbol, artifact, `.wwi`, publication, transaction,
+  persistence, process, or filesystem owner. Build and all test forms retain
+  their distinct stat-first directory behavior. Build workdir format remains
+  18, test workdir format remains 19, and semantic storage format remains 3.
 - `import acme.codec;` loads the canonical package `acme.codec`. If that
   package declares `package wire;`, the importing file sees its exported names
   as `wire.Name`; `codec.Name` is not an additional binding. An explicit alias
diff --git a/docs/test-system-v2.md b/docs/test-system-v2.md
index c2d4c8d9..84b2ebd0 100644
--- a/docs/test-system-v2.md
+++ b/docs/test-system-v2.md
@@ -278,12 +278,29 @@ parity, direct and symlinked `.ww` directories, a dotted dependency, output
 modes, cold/warm transaction behavior, compiler and signaled-linker failure
 preservation, selected-route concurrency, cleanup, and the exact test-command
 behavior. Direct driver interruption remains owned by the unchanged directory
-machinery and is not claimed fixed here. The shared resolver and `ww run` are
-deliberately unchanged—and the observer
-retains their pre-existing stage difference—because pinned Go's run command
-has a distinct named-file front door.
-No test product, result, package/import identity, or serialized format changes;
-build remains 18, test remains 19, and semantic storage remains 3.
+machinery and is not claimed fixed here.
+
+Pinned Go's run command has a distinct suffix-first named-file front door.
+Accordingly, an existing `ww run` target whose exact requested spelling ends
+`.ww` and whose symlink-following `stat` result is a directory is rejected in
+the twin run fronts before the shared resolver and private run scratch. An
+`_test.ww` spelling emits exactly
+`ww: cannot run *_test.ww files (OPERAND)\n`; every other selected `.ww`
+directory emits exactly `OPERAND is a directory, should be a WW file\n`.
+Both stages return status 1 with empty stdout, open no directory member, scan
+no import, construct no package/graph/action, invoke no producer or runtime,
+and create no run scratch or artifact. This includes direct and symlinked
+directories and hidden directory spellings; directory contents cannot displace
+the classifier diagnostic. A trailing separator and non-`.ww` or dotted
+package requests retain the directory package route. The same-spelling build,
+raw test, `test -c`, and directory `test -S` routes remain stat-first and keep
+their existing diagnostics and artifact bytes. Thus this run change creates no
+test product, result, package/import identity, test-process/filter change, or
+serialized-format change; build remains 18, test remains 19, and semantic
+storage remains 3. Regular or missing `_test.ww`, missing/logical `.ww`,
+multiple named sources, finite FIFOs, and hidden regular sources are not
+claimed by this existing-directory slice. The general direct-driver `.new`
+interruption residue also remains open.
 
 List mode uses that same product process and initialization boundary but starts
 no per-test child. The shared language harness emits only selected qualified
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index 3fc3a9b7..3db700b8 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -9321,6 +9321,16 @@ fn dorun(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	case void => requestedliteral = true;
 	case let e: os.oserror => void;
 	};
+	if (requestedliteral
+		&& ((requestedstat.mode: u32) & 61440u32) == os.mode.DIR: u32
+		&& cstrendswithlit(src, ".ww")) {
+		if (cstrendswithlit(src, "_test.ww")) {
+			cerrpath("ww: cannot run *_test.ww files (", src, ")\n");
+		} else {
+			cerrpath("", src, " is a directory, should be a WW file\n");
+		};
+		return 1;
+	};
 	let isdir: i32 = 0;
 	let resolved: *u8 = resolvemodule(selfdir, src, incs.ptr, &isdir);
 	if (resolved == nil) {
diff --git a/test/package/package_test.ww b/test/package/package_test.ww
index 0f1bd096..5ff62011 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -1466,8 +1466,8 @@ fn cwdwritedata(dir: str, label: str) void = {
 };
 
 // A visible raw test-source build observes only its initial package/import
-// header and then omits it. A .ww-spelled directory, including a symlink with
-// a _test.ww spelling, instead enters the ordinary directory-package route.
+// header and then omits it. Build and test retain their directory-package
+// front door, while run's named-source front rejects a .ww-spelled directory.
 // Neither classification may redefine package or dotted-import identity.
 @test fn named_test_sources_are_header_loaded_then_omitted() void = {
 	let root: str = fresh();
@@ -1593,6 +1593,8 @@ fn cwdwritedata(dir: str, label: str) void = {
 	let linkersignaldiag: str = "";
 	let directorytestrunout: str = "";
 	let directorytestrunerr: str = "";
+	let directoryrunout: str = "";
+	let directoryrunerr: str = "";
 	let directorytestrunartifacts: str = "";
 	let directorytestbin: str = "";
 	let directorytestcompileartifacts: str = "";
@@ -2202,21 +2204,25 @@ fn cwdwritedata(dir: str, label: str) void = {
 		if (si == 0) { directorytestasm = strings.dup(out.stderr); }
 		else { assert(same(directorytestasm, out.stderr)); };
 
-		// Run was not changed by the build-only dispatcher fix. Cstage follows
-		// the selected directory and executes it; WWstage retains its exact
-		// pre-existing raw-source failure for the same requested symlink.
+		// Run's named-source front rejects the requested _test.ww spelling
+		// before directory loading, tool production, or runtime execution.
 		let directoryrunav: []str = [driver(stages[si]), "run", "-I", include,
 			dirlink];
 		runcommandenv(root, strings.concat("testonly-directory-run-", tags[si]),
 			directoryrunav, env,
 			(60i64 * (time.second: i64)): time.duration, &out);
+		let directoryrundiag: str = strings.concat(
+			"ww: cannot run *_test.ww files (", dirlink, ")\n");
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0 && same(out.stderr, directoryrundiag)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
 		if (si == 0) {
-			expectexit(&out, 5);
-			assert(out.stdout.len == 0 && out.stderr.len == 0);
+			directoryrunout = strings.dup(out.stdout);
+			directoryrunerr = strings.dup(out.stderr);
 		} else {
-			expectexit(&out, 1);
-			assert(out.stdout.len == 0
-				&& same(out.stderr, "ww: cannot read source\n"));
+			assert(same(directoryrunout, out.stdout)
+				&& same(directoryrunerr, out.stderr));
 		};
 		rewritefile(dirtargettest, dirtargettestexcluded);
 
@@ -2420,6 +2426,396 @@ fn cwdwritedata(dir: str, label: str) void = {
 	clean(root);
 };
 
+fn expectrundirectoryrejection(root: str, name: str, av: []str, env: []str,
+	pidrecord: str, ctrace: str, atrace: str, ltrace: str, want: str) void = {
+	rewritefile(pidrecord, "");
+	rewritefile(ctrace, "");
+	rewritefile(atrace, "");
+	rewritefile(ltrace, "");
+	let out: commandout;
+	runcommandenv(root, name, av, env,
+		(60i64 * (time.second: i64)): time.duration, &out);
+	let ownedrun: str = readfile(pidrecord);
+	let ownedmarker: str = strings.concat(ownedrun, "/observer-marker");
+	let ownedvalid: bool = ownedrun.len > 12
+		&& strings.hasprefix(ownedrun, "/tmp/ww_run_");
+	let observed: bool = out.termination == exec.termination.EXIT
+		&& out.code == 1 && out.stdout.len == 0 && same(out.stderr, want)
+		&& ownedvalid && os.exists(ownedrun)
+		&& same(readfile(ownedmarker), "observer-owned\n")
+		&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+		&& readfile(ltrace).len == 0;
+	let markerclean: i32 = -1;
+	let dirclean: i32 = -1;
+	if (ownedvalid) {
+		markerclean = os.remove(ownedmarker);
+		dirclean = os.rmdir(ownedrun);
+	};
+	assert(observed && markerclean == 0 && dirclean == 0
+		&& !os.exists(ownedrun));
+};
+
+// Run's named-source spelling owns the directory rejection. The physical
+// directory remains only loader metadata for the distinct build and test
+// fronts, and rejected source contents cannot create package or import state.
+@test fn run_dot_ww_directories_are_named_sources() void = {
+	let root: str = fresh();
+	let source: str = strings.concat(root, "/source");
+	let include: str = strings.concat(root, "/include");
+	let dependency: str = strings.concat(include, "/domain/value");
+	let logical: str = strings.concat(include, "/domain/logical");
+	let ordinary: str = strings.concat(source, "/ordinary.ww");
+	let ordinarylink: str = strings.concat(source, "/requested.ww");
+	let testdirectory: str = strings.concat(source, "/direct_test.ww");
+	let testlink: str = strings.concat(source, "/requested_test.ww");
+	let hidden: str = strings.concat(source, "/.hidden.ww");
+	let private: str = strings.concat(source, "/_hidden.ww");
+	let malformed: str = strings.concat(source, "/malformed.ww");
+	let missingimport: str = strings.concat(source, "/missing-import.ww");
+	let nonsuffix: str = strings.concat(source, "/directory-control");
+	let nonsuffixlink: str = strings.concat(source, "/directory-link");
+	let regular: str = strings.concat(source, "/regular.ww");
+	let rawtest: str = strings.concat(source, "/raw_control_test.ww");
+	let prior: str = strings.concat(root, "/prior-public-output");
+	mkdirall(dependency); mkdirall(logical); mkdirall(ordinary);
+	mkdirall(testdirectory); mkdirall(hidden); mkdirall(private);
+	mkdirall(malformed); mkdirall(missingimport); mkdirall(nonsuffix);
+	writefile(strings.concat(dependency, "/value.ww"), strings.concat(
+		"package value;\n",
+		"export fn number() i32 = { return 37; };\n"));
+	writefile(strings.concat(ordinary, "/main.ww"), strings.concat(
+		"package main;\nimport domain.value;\n",
+		"fn main() i32 = { return value.number(); };\n"));
+	writefile(strings.concat(testdirectory, "/main.ww"),
+		"package main;\nfn main() i32 = { return 47; };\n");
+	writefile(strings.concat(hidden, "/main.ww"),
+		"package main;\nfn main() i32 = { return 48; };\n");
+	writefile(strings.concat(private, "/main.ww"),
+		"package main;\nfn main() i32 = { return 49; };\n");
+	writefile(strings.concat(malformed, "/main.ww"),
+		"this directory has no package clause\n");
+	writefile(strings.concat(missingimport, "/main.ww"), strings.concat(
+		"package main;\nimport absent.before.run.classification;\n",
+		"fn main() i32 = { return 50; };\n"));
+	writefile(strings.concat(nonsuffix, "/main.ww"),
+		"package main;\nfn main() i32 = { return 43; };\n");
+	writefile(regular,
+		"package main;\nfn main() i32 = { return 39; };\n");
+	writefile(strings.concat(logical, "/main.ww"),
+		"package main;\nfn main() i32 = { return 41; };\n");
+	writefile(rawtest, strings.concat(
+		"package runroute;\n",
+		"@test fn raw_control() void = { assert(true); };\n"));
+	writefile(prior, "prior-public-bytes\n");
+	assert(os.symlink(ordinary, ordinarylink) == 0);
+	assert(os.symlink(testdirectory, testlink) == 0);
+	assert(os.symlink(nonsuffix, nonsuffixlink) == 0);
+
+	let driverwrapper: str = strings.concat(root, "/driver-wrapper.sh");
+	let compilerwrapper: str = strings.concat(root, "/compiler-wrapper.sh");
+	let assemblerwrapper: str = strings.concat(root, "/assembler-wrapper.sh");
+	let linkerwrapper: str = strings.concat(root, "/linker-wrapper.sh");
+	writeexecutable(driverwrapper, strings.concat(
+		"#!/bin/sh\nowned=/tmp/ww_run_$$\n",
+		"printf '%s' \"$owned\" > \"$WW_RUN_PID_RECORD\"\n",
+		"if test \"$WW_RUN_PREOCCUPY\" = 1; then\n",
+		" mkdir \"$owned\" || exit 124\n",
+		" printf 'observer-owned\\n' > \"$owned/observer-marker\"\n",
+		"fi\n",
+		"exec \"$WW_RUN_REAL_DRIVER\" \"$@\"\n"));
+	writeexecutable(compilerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'compile\\n' >> \"$WW_RUN_CTRACE\"\n",
+		"exec \"$WW_RUN_REAL_C\" \"$@\"\n"));
+	writeexecutable(assemblerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'assemble\\n' >> \"$WW_RUN_ATRACE\"\n",
+		"exec \"$WW_RUN_REAL_A\" \"$@\"\n"));
+	writeexecutable(linkerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'link\\n' >> \"$WW_RUN_LTRACE\"\n",
+		"exec \"$WW_RUN_REAL_L\" \"$@\"\n"));
+
+	let stages: []str = ["ww", "ww_ww"];
+	let compilers: []str = ["w6c", "w6c_ww"];
+	let assemblers: []str = ["w6a", "w6a_ww"];
+	let linkers: []str = ["w6l", "w6l_ww"];
+	let tags: []str = ["c", "ww"];
+	let environments: [][]str = alloc([], 2u64)!;
+	let rejectenvironments: [][]str = alloc([], 2u64)!;
+	let pidrecords: []str = alloc([], 2u64)!;
+	let ctraces: []str = alloc([], 2u64)!;
+	let atraces: []str = alloc([], 2u64)!;
+	let ltraces: []str = alloc([], 2u64)!;
+	let inherited: []str = os.getenvs();
+	let si: i32 = 0;
+	for (si < stages.len) {
+		let pidrecord: str = strings.concat(root, "/driver-pid-", tags[si]);
+		let ctrace: str = strings.concat(root, "/compiler-trace-", tags[si]);
+		let atrace: str = strings.concat(root, "/assembler-trace-", tags[si]);
+		let ltrace: str = strings.concat(root, "/linker-trace-", tags[si]);
+		writefile(pidrecord, ""); writefile(ctrace, "");
+		writefile(atrace, ""); writefile(ltrace, "");
+		append(pidrecords, pidrecord); append(ctraces, ctrace);
+		append(atraces, atrace); append(ltraces, ltrace);
+		let env: []str = alloc([], (inherited.len + 11): u64)!;
+		let ei: i32 = 0;
+		for (ei < inherited.len) {
+			if (!strings.hasprefix(inherited[ei], "WW_W6C=")
+				&& !strings.hasprefix(inherited[ei], "WW_W6A=")
+				&& !strings.hasprefix(inherited[ei], "WW_W6L=")
+				&& !strings.hasprefix(inherited[ei], "WW_RUN_")) {
+				append(env, inherited[ei]);
+			};
+			ei += 1;
+		};
+		append(env, strings.concat("WW_RUN_REAL_DRIVER=", driver(stages[si])));
+		append(env, strings.concat("WW_RUN_PID_RECORD=", pidrecord));
+		append(env, strings.concat("WW_W6C=", compilerwrapper));
+		append(env, strings.concat("WW_W6A=", assemblerwrapper));
+		append(env, strings.concat("WW_W6L=", linkerwrapper));
+		append(env, strings.concat("WW_RUN_CTRACE=", ctrace));
+		append(env, strings.concat("WW_RUN_ATRACE=", atrace));
+		append(env, strings.concat("WW_RUN_LTRACE=", ltrace));
+		append(env, strings.concat("WW_RUN_REAL_C=", driver(compilers[si])));
+		append(env, strings.concat("WW_RUN_REAL_A=", driver(assemblers[si])));
+		append(env, strings.concat("WW_RUN_REAL_L=", driver(linkers[si])));
+		append(environments, env);
+		let rejectenv: []str = alloc([], (env.len + 1): u64)!;
+		let ri: i32 = 0;
+		for (ri < env.len) { append(rejectenv, env[ri]); ri += 1; };
+		append(rejectenv, "WW_RUN_PREOCCUPY=1");
+		append(rejectenvironments, rejectenv);
+		si += 1;
+	};
+
+	let selected: []str = [ordinary, ordinarylink, testdirectory, testlink,
+		hidden, private, malformed, missingimport];
+	let selectedlabels: []str = ["direct", "symlink", "direct-test",
+		"symlink-test", "dot-hidden", "underscore-hidden", "malformed",
+		"missing-import"];
+	let selectedtest: []bool = [false, false, true, true, false, false,
+		false, false];
+	let sourcebefore: str = strings.dup(treesnapshot(source));
+	si = 0;
+	for (si < stages.len) {
+		let ri: i32 = 0;
+		for (ri < selected.len) {
+			let want: str;
+			if (selectedtest[ri]) {
+				want = strings.concat("ww: cannot run *_test.ww files (",
+					selected[ri], ")\n");
+			} else {
+				want = strings.concat(selected[ri],
+					" is a directory, should be a WW file\n");
+			};
+			let av: []str = [driverwrapper, "run", "-I", include,
+				selected[ri]];
+			expectrundirectoryrejection(root, strings.concat("run-reject-",
+				tags[si], "-", selectedlabels[ri]), av, rejectenvironments[si],
+				pidrecords[si], ctraces[si], atraces[si], ltraces[si], want);
+			ri += 1;
+		};
+		let boundaryav: []str = [driverwrapper, "run", "-I", include,
+			ordinarylink, "-I", "program-argument"];
+		let boundarywant: str = strings.concat(ordinarylink,
+			" is a directory, should be a WW file\n");
+		expectrundirectoryrejection(root, strings.concat("run-boundary-",
+			tags[si]), boundaryav, rejectenvironments[si], pidrecords[si],
+			ctraces[si], atraces[si], ltraces[si], boundarywant);
+		si += 1;
+	};
+	assert(same(sourcebefore, treesnapshot(source))
+		&& same(readfile(prior), "prior-public-bytes\n")
+		&& !directoryhasfragment(root, ".sepwork")
+		&& !directoryhasfragment(root, ".wwtxn.")
+		&& !directoryhasfragment(root, ".capture")
+		&& !directoryhasfragment(root, ".result")
+		&& !directoryhasfragment(root, ".request"));
+
+	// Concurrent preflight rejections leave independently preoccupied exact
+	// run paths and diagnostics untouched.
+	let pi: i32 = 0;
+	for (pi < stages.len) {
+		rewritefile(pidrecords[pi], ""); rewritefile(ctraces[pi], "");
+		rewritefile(atraces[pi], ""); rewritefile(ltraces[pi], "");
+		pi += 1;
+	};
+	let cav: []str = [driverwrapper, "run", ordinary];
+	let wav: []str = [driverwrapper, "run", ordinarylink];
+	let cc: exec.command;
+	cc.path = cav[0]; cc.argv = cav;
+	cc.env = rejectenvironments[0]; cc.dir = repo();
+	cc.stdoutpath = strings.concat(root, "/parallel-c.stdout");
+	cc.stderrpath = strings.concat(root, "/parallel-c.stderr");
+	cc.deadline = time.add(time.now(time.clock.monotonic),
+		(60i64 * (time.second: i64)): time.duration);
+	cc.grace = (100i64 * (time.millisecond: i64)): time.duration;
+	let wc: exec.command;
+	wc.path = wav[0]; wc.argv = wav;
+	wc.env = rejectenvironments[1]; wc.dir = repo();
+	wc.stdoutpath = strings.concat(root, "/parallel-ww.stdout");
+	wc.stderrpath = strings.concat(root, "/parallel-ww.stderr");
+	wc.deadline = time.add(time.now(time.clock.monotonic),
+		(60i64 * (time.second: i64)): time.duration);
+	wc.grace = (100i64 * (time.millisecond: i64)): time.duration;
+	let cp: exec.process;
+	let wp: exec.process;
+	exec.start(&cp, &cc); exec.start(&wp, &wc);
+	let cdone: bool = false;
+	let wdone: bool = false;
+	for (!cdone || !wdone) {
+		if (!cdone) { cdone = exec.poll(&cp); };
+		if (!wdone) { wdone = exec.poll(&wp); };
+		if (!cdone || !wdone) {
+			time.sleep(time.millisecond, time.clock.monotonic);
+		};
+	};
+	let cownedrun: str = readfile(pidrecords[0]);
+	let wownedrun: str = readfile(pidrecords[1]);
+	let cownedmarker: str = strings.concat(cownedrun, "/observer-marker");
+	let wownedmarker: str = strings.concat(wownedrun, "/observer-marker");
+	let cownedvalid: bool = cownedrun.len > 12
+		&& strings.hasprefix(cownedrun, "/tmp/ww_run_");
+	let wownedvalid: bool = wownedrun.len > 12
+		&& strings.hasprefix(wownedrun, "/tmp/ww_run_");
+	let parallelobserved: bool = cp.result.errno == 0
+		&& cp.result.cleanuperrno == 0
+		&& cp.result.termination == exec.termination.EXIT && cp.result.code == 1
+		&& wp.result.errno == 0 && wp.result.cleanuperrno == 0
+		&& wp.result.termination == exec.termination.EXIT && wp.result.code == 1
+		&& readfile(cc.stdoutpath).len == 0 && readfile(wc.stdoutpath).len == 0
+		&& same(readfile(cc.stderrpath), strings.concat(ordinary,
+			" is a directory, should be a WW file\n"))
+		&& same(readfile(wc.stderrpath), strings.concat(ordinarylink,
+			" is a directory, should be a WW file\n"))
+		&& cownedvalid && wownedvalid
+		&& os.exists(cownedrun) && os.exists(wownedrun)
+		&& same(readfile(cownedmarker), "observer-owned\n")
+		&& same(readfile(wownedmarker), "observer-owned\n")
+		&& readfile(ctraces[0]).len == 0 && readfile(atraces[0]).len == 0
+		&& readfile(ltraces[0]).len == 0 && readfile(ctraces[1]).len == 0
+		&& readfile(atraces[1]).len == 0 && readfile(ltraces[1]).len == 0
+		&& same(sourcebefore, treesnapshot(source))
+		&& same(readfile(prior), "prior-public-bytes\n");
+	let cmarkerclean: i32 = -1;
+	let cdirclean: i32 = -1;
+	let wmarkerclean: i32 = -1;
+	let wdirclean: i32 = -1;
+	if (cownedvalid) {
+		cmarkerclean = os.remove(cownedmarker);
+		cdirclean = os.rmdir(cownedrun);
+	};
+	if (wownedvalid) {
+		wmarkerclean = os.remove(wownedmarker);
+		wdirclean = os.rmdir(wownedrun);
+	};
+	assert(parallelobserved && cmarkerclean == 0 && cdirclean == 0
+		&& wmarkerclean == 0 && wdirclean == 0
+		&& !os.exists(cownedrun) && !os.exists(wownedrun));
+
+	let cbuildbytes: str = "";
+	let cbuildartifacts: str = "";
+	let cteststdout: str = "";
+	let ctestbinary: str = "";
+	si = 0;
+	for (si < stages.len) {
+		let out: commandout;
+		let trailing: str = strings.concat(ordinary, "/");
+		let trailingav: []str = [driverwrapper, "run", "-I", include, trailing];
+		runcommandenv(root, strings.concat("run-trailing-", tags[si]), trailingav,
+			environments[si], (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 37);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !os.exists(readfile(pidrecords[si])));
+		let nonwwav: []str = [driverwrapper, "run", nonsuffixlink];
+		runcommandenv(root, strings.concat("run-non-ww-", tags[si]), nonwwav,
+			environments[si], (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 43);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !os.exists(readfile(pidrecords[si])));
+		let regularav: []str = [driverwrapper, "run", regular];
+		runcommandenv(root, strings.concat("run-regular-", tags[si]), regularav,
+			environments[si], (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 39);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !os.exists(readfile(pidrecords[si])));
+		let logicalav: []str = [driverwrapper, "run", "-I", include,
+			"domain.logical"];
+		runcommandenv(root, strings.concat("run-logical-", tags[si]), logicalav,
+			environments[si], (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 41);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !os.exists(readfile(pidrecords[si])));
+
+		let buildwork: str = strings.concat(root, "/build-work-", tags[si]);
+		let buildout: str = strings.concat(root, "/build-output-", tags[si]);
+		mkdirall(buildwork);
+		let buildav: []str = [driverwrapper, "build", "-w", buildwork,
+			"-I", include, "-o", buildout, ordinarylink];
+		runcommandenv(root, strings.concat("build-same-spelling-", tags[si]),
+			buildav, environments[si],
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && os.exists(buildout));
+		let buildbytes: str = strings.dup(readfile(buildout));
+		let buildartifacts: str = strings.dup(artifacttreesnapshot(buildwork));
+		if (si == 0) {
+			cbuildbytes = strings.dup(buildbytes);
+			cbuildartifacts = strings.dup(buildartifacts);
+		} else {
+			assert(same(cbuildbytes, buildbytes)
+				&& same(cbuildartifacts, buildartifacts));
+		};
+		let builtav: []str = [buildout];
+		runcommand(root, strings.concat("built-control-", tags[si]), builtav,
+			time.second, &out);
+		expectexit(&out, 37);
+
+		let testwork: str = strings.concat(root, "/test-work-", tags[si]);
+		mkdirall(testwork);
+		let testav: []str = [driverwrapper, "test", "-w", testwork, rawtest];
+		runcommandenv(root, strings.concat("raw-test-control-", tags[si]), testav,
+			environments[si], (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stderr.len == 0 && has(out.stdout, "raw_control ... ok\n"));
+		if (si == 0) { cteststdout = strings.dup(out.stdout); }
+		else { assert(same(cteststdout, out.stdout)); };
+		let testbinary: str = strings.concat(root, "/test-binary-", tags[si]);
+		let compileav: []str = [driverwrapper, "test", "-c", "-o",
+			testbinary, rawtest];
+		runcommandenv(root, strings.concat("raw-test-compile-", tags[si]),
+			compileav, environments[si],
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && os.exists(testbinary));
+		if (si == 0) { ctestbinary = strings.dup(readfile(testbinary)); }
+		else { assert(same(ctestbinary, readfile(testbinary))); };
+
+		let assemblywork: str = strings.concat(root, "/assembly-work-", tags[si]);
+		let assemblyout: str = strings.concat(root, "/assembly-output-", tags[si]);
+		mkdirall(assemblywork);
+		rewritefile(ctraces[si], ""); rewritefile(atraces[si], "");
+		rewritefile(ltraces[si], "");
+		let assemblyav: []str = [driverwrapper, "test", "-S", "-w",
+			assemblywork, "-o", assemblyout, ordinarylink];
+		runcommandenv(root, strings.concat("directory-test-assembly-", tags[si]),
+			assemblyav, environments[si],
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 2);
+		assert(out.stdout.len == 0
+			&& same(out.stderr, "ww test: -S needs a single test file\n")
+			&& !os.exists(assemblyout) && directoryisempty(assemblywork)
+			&& readfile(ctraces[si]).len == 0
+			&& readfile(atraces[si]).len == 0
+			&& readfile(ltraces[si]).len == 0);
+		si += 1;
+	};
+	assert(!directoryhasnew(root) && !directoryhasfragment(root, ".wwtxn.")
+		&& !directoryhasfragment(root, ".install")
+		&& !directoryhasfragment(root, ".capture")
+		&& !directoryhasfragment(root, ".result")
+		&& !directoryhasfragment(root, ".request"));
+	clean(root);
+};
+
 // A source file has one contiguous import section immediately after its
 // package clause.  The parser may continue after a late import for recovery,
 // but the imports-only loader and the full compiler parser both reject it.