diff --git a/cmd/ww/main.c b/cmd/ww/main.c
index c124c349..ad29cfb5 100644
--- a/cmd/ww/main.c
+++ b/cmd/ww/main.c
@@ -38,7 +38,7 @@ static const char *usage =
 "                    -o FILE publishes a non-main archive FILE + FILE.wwi\n"
 "                    -o DIR publishes each selected command beneath DIR\n"
 "    lib/...         every eligible package under lib, recursively\n"
-"    .               build the cwd's <basename>.ww\n";
+"    .               current directory package (default when no path is given)\n";
 
 static char *self_dir;
 static const char *self_path;
@@ -7158,6 +7158,36 @@ build_import_leaf(const char *identity, char *out, size_t outsz)
 	snprintf(out, outsz, "%s", leaf);
 }
 
+static int
+build_current_dir_spelling(const char *path)
+{
+	if (path[0] == '\0' || path[0] == '/') return 0;
+	const char *p = path;
+	int found = 0;
+	for (;;) {
+		while (*p == '/') p++;
+		if (*p == '\0') return found;
+		if (*p++ != '.' || (*p != '\0' && *p != '/')) return 0;
+		found = 1;
+	}
+}
+
+static void
+build_local_dir_leaf(const char *resolved, char *out, size_t outsz)
+{
+	char canonical[PATH_MAX];
+	const char *selected = resolved;
+	if (build_current_dir_spelling(resolved)
+	    && realpath(resolved, canonical) != NULL)
+		selected = canonical;
+	char tmp[PATH_MAX];
+	memcpy(tmp, selected, strlen(selected) + 1);
+	size_t n = strlen(tmp);
+	while (n > 1 && tmp[n - 1] == '/') tmp[--n] = '\0';
+	const char *base = strrchr(tmp, '/');
+	snprintf(out, outsz, "%s", base ? base + 1 : tmp);
+}
+
 static int
 resolve_module(const char *name, const char *incs, char *out, size_t outsz,
     int *is_dir)
@@ -7428,15 +7458,12 @@ do_build(int argc, char **argv)
 	} else if (is_dir && root_identity != NULL) {
 		build_import_leaf(root_identity, out, sizeof out);
 	} else if (is_dir) {
-		char tmp[PATH_MAX];
-		memcpy(tmp, resolved, strlen(resolved) + 1);
-		size_t n = strlen(tmp);
-		while (n > 1 && tmp[n-1] == '/') tmp[--n] = '\0';
-		const char *b = strrchr(tmp, '/');
-		snprintf(out, sizeof out, "%s", b ? b + 1 : tmp);
+		build_local_dir_leaf(resolved, out, sizeof out);
 	} else {
 		basename_no_ext(resolved, out, sizeof out);
 	}
+	if (!outflag[0] && is_dir && build_current_dir_spelling(resolved))
+		objstem = out;
 	const char *default_output_dir = !outflag[0] && build_output_dir(out)
 	    ? out : NULL;
 	if (discard_output) {
diff --git a/docs/build-system.md b/docs/build-system.md
index 74a17c8a..df0c1fe9 100644
--- a/docs/build-system.md
+++ b/docs/build-system.md
@@ -8119,6 +8119,133 @@ This is runtime/coordinator presentation, not a persisted-byte contract. Build
 workdir format remains `18`, test workdir format remains `19`, and semantic
 storage format remains `3`.
 
+### 11.40 Implemented current-directory default build names
+
+An empty `ww build` package list selects the current directory just as an
+explicit `.`, `./`, or equivalent sequence of single-dot components does.  For
+one command package and no explicit `-o`, the public executable is now named by
+the selected directory's final component.  The selector is loading syntax; it
+is not the literal output pathname.  Thus a command built while the current
+directory is `tool` publishes `tool`, not `.`, and cold private build artifacts
+use `tool.sepwork`, not `..sepwork`.
+
+A non-main current-directory package uses the same corrected cold scratch stem,
+but still has no link or public installation action.  An explicit `-o`, exact
+`-o /dev/null`, an ordinary non-current directory operand, and a contextual
+dotted package request keep their established output rules.
+
+#### Pinned Go evidence and fact classification
+
+The sole semantic authority is official Go 1.26.5 at commit
+`c19862e5f8415b4f24b189d065ed739517c548ba`:
+
+- `search.CleanPatterns` turns an empty package-pattern list into exactly `.`;
+  `ImportPathsQuiet` then treats that local pattern as a directory selection
+  ([`cmd/go/internal/search/search.go`, lines 441–480](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/search/search.go#L441-L480)).
+- `work.runBuild` loads packages and checks load errors before output planning.
+  With exactly one loaded `main` package and no `-o`, it selects
+  `DefaultExecName`
+  ([`cmd/go/internal/work/build.go`, lines 459–478](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/work/build.go#L459-L478)).
+- `load.(*Package).exeFromImportPath` takes the final loaded import-path
+  element, while `DefaultExecName` uses a source basename only for a
+  command-line-files package
+  ([`cmd/go/internal/load/pkg.go`, lines 1727–1769](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/load/pkg.go#L1727-L1769)).
+- Official command testdata distinguishes module naming from the manifest-free
+  GOPATH case and requires bare `go build` to create the directory-named `src`
+  executable
+  ([`clean_binary.txt`, lines 15–28](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/testdata/script/clean_binary.txt#L15-L28)).
+  A second manifest-free script changes to `m`, runs bare `go build`, and
+  requires executable `m`
+  ([`gccgo_m.txt`, lines 4–14](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/testdata/script/gccgo_m.txt#L4-L14));
+  `build_static.txt` likewise builds and executes the default `hello`
+  ([lines 11–14](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/testdata/script/build_static.txt#L11-L14)).
+
+Those selection, loading, default-name branches and script assertions are
+**behavior directly implemented or asserted by pinned Go**.  WW has no module
+or manifest identity for a literal root, so using the selected local directory
+leaf as its already-specified presentation fallback is **behavior derived from
+the pinned implementation**.  The directory remains loader metadata and does
+not become canonical package or import identity.
+
+#### Fresh four-axis audit and direct pre-fix measurements
+
+The bounded audit examined every permanent axis before choosing this build
+presentation difference.  Both public stages were measured at the same source
+paths:
+
+- **Go-like build:** multi-command directory selection without `-o` was already
+  aligned.  For a valid command in directory `a`, however, bare `build`,
+  `build .`, and `build ./` each exited 1 in both stages with empty stdout and
+  the same 55 stderr bytes (SHA-256
+  `2e8030a9eeb7187fbc1cb4ee9d794c352f1c31c92c884f8ae09a57e39bfe86db`):
+  `ww: build output "." already exists and is a directory`.  Explicit `-o`
+  succeeded and produced byte-identical runnable binaries, proving that only
+  default presentation was wrong.  This was the selected gap.
+- **Go-like test:** an ordinary valid zero-match directory run exited 0 in both
+  stages with identical warning, accounting, and `[no tests to run]` result
+  bytes.  The selected build branch does not enter test product naming,
+  filtering, capture, execution, result annotation, or retained test output.
+- **Go-like package:** a directory containing two selected declared package
+  names was rejected in both stages with identical diagnostics.  The selected
+  change occurs after package loading and does not alter source eligibility,
+  declaration checks, package kind, graph nodes, or actions.
+- **Go-like import:** a dotted `cyclea -> cycleb -> cyclea` graph was rejected
+  in both stages with identical cycle diagnostics.  The selected change does
+  not alter spelling, search, visibility, resolution, canonical identity, or
+  graph edges.
+
+The pre-fix statuses, streams, hashes, diagnostics, artifacts, and runtime
+results are **directly measured WW behavior**.  The cited implementation and
+testdata are **behavior directly implemented or asserted by pinned Go**.  The
+cross-axis non-effects follow from the bounded post-load output branch and are
+**behavior derived from the pinned implementation**.
+
+#### Ownership, final behavior, and preserved boundaries
+
+`cmd/ww.do_build` and `selfhost/cmd/ww.dobuild` are semantic twins and the sole
+owners of this rule.  Their current-directory predicate accepts only relative
+paths whose components are all exactly `.`.  Only in that branch do they
+canonicalize the selected directory and take its final component for output and
+cold scratch presentation.  Ordinary literal directory operands retain their
+lexical leaf, and contextual roots retain their dotted identity leaf.
+
+Direct post-fix probes through both stages show that bare, dot, and dot-slash
+builds exit 0 with empty stdout/stderr, publish mode-executable binaries named
+`a`, and produce `a.sepwork` with no `..sepwork`.  All six binaries are
+byte-identical (SHA-256
+`866c1eb875dad271d37572f43fb9d9b0eb6a2344d2e61646e655bb09f7909bf6`).
+Their unit, interface, assembly, object, archive, and init artifacts are also
+byte-identical between stages and spellings.  Current-directory library builds
+still publish nothing and link nothing; their unit, interface, assembly,
+object, and archive bytes remain stage-identical under `libcurrent.sepwork`.
+
+Loading and source selection precede this branch.  A missing dotted import
+therefore retains its byte-identical diagnostic and creates neither output nor
+scratch.  Graph and action construction, compiler/assembler/archiver/linker
+semantics, runtime behavior, and artifact content are unchanged.  A genuine
+directory occupying the derived output still rejects before tools and names
+the derived leaf in its diagnostic.
+
+Cold and warm persistent builds retain their existing keys and reuse rules.  A
+source invalidation reruns producers; an injected compiler failure preserves
+the prior executable and committed persistent generation, publishes no stage,
+and leaves no `.new`, `.install`, or `.wwtxn.*` residue.  Restoring producer
+success installs the changed executable.  Existing concurrency, interruption,
+process-group, rollback, publication, and cleanup owners gain no shared state or
+new process path.
+
+The WW-native `current_directory_build_default_output` observer proves both
+stages, all three current-directory spellings, executable mode/runtime/byte
+parity, explicit and null output controls, non-main non-publication, corrected
+cold scratch, missing-import precedence, cold/warm reuse, invalidation,
+producer-failure rollback, prior-output preservation, genuine collision, and
+residue absence.  Existing package/import graph, byte-identity, concurrent
+transaction, and interruption observers remain authoritative for mechanisms
+this presentation rule does not change.
+
+No persisted-byte contract changed.  Build workdir format remains `18`, test
+workdir format remains `19`, and semantic storage format remains `3`.
+
 ## 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 ed24db7e..85953152 100644
--- a/docs/spec.md
+++ b/docs/spec.md
@@ -340,8 +340,17 @@ ImportPath    = ident { "." ident } .
   command's synthesized default basename already names a directory, loading
   and graph validation complete and the build rejects before tools without
   changing that directory; a non-main package synthesizes no default public
-  output. Output paths and directory metadata never become package, import,
-  graph, action,
+  output. With no path operand, the current directory is selected as if `.` had
+  been supplied. For a lone literal current-directory command and no explicit
+  `-o`, `.`, `./`, and equivalent single-dot-component spellings derive the
+  default executable name from the canonical selected directory's final
+  component; cold adjacent scratch uses that same leaf plus `.sepwork`. The dot
+  spelling itself is never an output name. A current-directory non-main package
+  uses the corrected scratch presentation but still links and publishes
+  nothing. This physical leaf is fallback presentation metadata only: it never
+  displaces a requested contextual dotted identity or becomes package, import,
+  graph, action, artifact, symbol, `.wwi`, or persistence identity.
+  Output paths and directory metadata never become package, import, graph, action,
   symbol, artifact, `.wwi`, or persistence identity.
 
   Every caller-visible build installation checks its destination after all
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index eb352b0b..cf3a4f26 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -8629,7 +8629,7 @@ fn resolvemodule(selfdir: *u8, name: *u8, incs: *u8, isdir: *i32) *u8 = {
 };
 
 fn writeusage(fd: i32) void = {
-	let s: str = "usage: ww [-V] <subcommand> [args...]\n  -V                print version and exit\n  build  [-S] [-w DIR] [-I DIR] [-o FILE|DIR] [path ...] build local package graphs\n  run    [path] ... build then exec, passing extra args to the program\n  test   [-S -o STEM] [-w DIR] [options] [path ...] build/run tests; -S emits package asm\n  version           print version and exit\n\n  path forms:\n    foo.ww          literal file\n    foo             search cwd, -I dirs, then the source library for foo.ww or foo/\n    lib/foo         directory: build its package sources\n                    -o FILE publishes a non-main archive FILE + FILE.wwi\n                    -o DIR publishes each selected command beneath DIR\n    lib/...         every eligible package under lib, recursively\n    .               build the cwd's <basename>.ww\n";
+	let s: str = "usage: ww [-V] <subcommand> [args...]\n  -V                print version and exit\n  build  [-S] [-w DIR] [-I DIR] [-o FILE|DIR] [path ...] build local package graphs\n  run    [path] ... build then exec, passing extra args to the program\n  test   [-S -o STEM] [-w DIR] [options] [path ...] build/run tests; -S emits package asm\n  version           print version and exit\n\n  path forms:\n    foo.ww          literal file\n    foo             search cwd, -I dirs, then the source library for foo.ww or foo/\n    lib/foo         directory: build its package sources\n                    -o FILE publishes a non-main archive FILE + FILE.wwi\n                    -o DIR publishes each selected command beneath DIR\n    lib/...         every eligible package under lib, recursively\n    .               current directory package (default when no path is given)\n";
 	os.write(fd, s.ptr, s.len: u64);
 };
 
@@ -8716,6 +8716,43 @@ fn defaultimportoutpath(identity: *u8) *u8 = {
 	return out.ptr;
 };
 
+fn buildcurrentdirspelling(path: *u8) bool = {
+	if (path[0u64] == 0u8 || path[0u64] == '/': u8) { return false; };
+	let i: u64 = 0u64;
+	let found: bool = false;
+	for (true) {
+		for (path[i] == '/': u8) { i += 1u64; };
+		if (path[i] == 0u8) { return found; };
+		if (path[i] != '.': u8) { return false; };
+		i += 1u64;
+		if (path[i] != 0u8 && path[i] != '/': u8) { return false; };
+		found = true;
+	};
+	return false;
+};
+
+fn buildlocaldirleaf(resolved: *u8) *u8 = {
+	let selected: *u8 = resolved;
+	if (buildcurrentdirspelling(resolved)) {
+		let canonical: *u8 = canonicaldir(pathstr(resolved));
+		if (canonical != nil) { selected = canonical; };
+	};
+	let rlen: u64 = cstrlen(selected);
+	for (rlen > 1u64) {
+		if (selected[rlen - 1u64] != '/': u8) { break; };
+		rlen -= 1u64;
+	};
+	let bo: u64 = basenameoff(selected, rlen);
+	let outbuf: []u8 = alloc([], (os.PATH_MAX: u64))!;
+	outbuf.len = os.PATH_MAX;
+	let out: *u8 = outbuf.ptr;
+	let i: u64 = bo;
+	let off: u64 = 0u64;
+	for (i < rlen) { out[off] = selected[i]; off += 1u64; i += 1u64; };
+	cstrseal(out, off);
+	return out;
+};
+
 fn dobuild(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	let src: *u8 = nil;
 	let srcindex: i32 = -1;
@@ -8897,22 +8934,14 @@ fn dobuild(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	} else { if (isdir != 0 && rootidentity != nil) {
 		out = defaultimportoutpath(rootidentity);
 	} else { if (isdir != 0) {
-		let rlen: u64 = cstrlen(resolved);
-		for (rlen > 1u64) {
-			if (resolved[rlen - 1u64] != 47u8) { break; };
-			rlen -= 1u64;
-		};
-		let bo: u64 = basenameoff(resolved, rlen);
-		let outbuf: []u8 = alloc([], (os.PATH_MAX: u64))!;
-		outbuf.len = os.PATH_MAX;
-		out = outbuf.ptr;
-		let i: u64 = bo;
-		let off: u64 = 0u64;
-		for (i < rlen) { out[off] = resolved[i]; off += 1u64; i += 1u64; };
-		cstrseal(out, off);
+		out = buildlocaldirleaf(resolved);
 	} else {
 		out = defaultoutpath(resolved);
 	}; }; };
+	if ((outflag == nil || outflag[0u64] == 0u8) && isdir != 0
+		&& buildcurrentdirspelling(resolved)) {
+		objstem = out;
+	};
 	let defaultoutputdir: *u8 = nil;
 	if ((outflag == nil || outflag[0u64] == 0u8) && buildoutputdir(out)) {
 		defaultoutputdir = out;
diff --git a/test/package/package_test.ww b/test/package/package_test.ww
index e9f1bc67..66b1ef5f 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -14074,6 +14074,227 @@ fn runtimepath(relative: str) str = {
 	clean(root);
 };
 
+// Empty build patterns select the current directory.  A literal dot is
+// loading syntax, not the caller-visible output name: command publication and
+// cold scratch use the selected directory leaf without making that physical
+// leaf package or import identity.
+@test fn current_directory_build_default_output() void = {
+	let root: str = fresh();
+	let command: str = strings.concat(root, "/current-command");
+	let library: str = strings.concat(root, "/current-library");
+	let bad: str = strings.concat(root, "/bad-current");
+	mkdirall(command); mkdirall(library); mkdirall(bad);
+	let commandfile: str = strings.concat(command, "/main.ww");
+	let original: str = "package main;\nfn main() i32 = { return 23; };\n";
+	let changed: str = "package main;\nfn main() i32 = { return 24; };\n";
+	writefile(commandfile, original);
+	writefile(strings.concat(library, "/library.ww"), strings.concat(
+		"package declared_library;\n",
+		"export fn value() i32 = { return 7; };\n"));
+	writefile(strings.concat(bad, "/main.ww"), strings.concat(
+		"package main;\nimport missing.current;\n",
+		"fn main() i32 = { return missing.current.value(); };\n"));
+
+	let compilerwrapper: str = strings.concat(root, "/current-w6c.sh");
+	writeexecutable(compilerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'compile\\n' >> \"$WW_CURRENT_TRACE\"\n",
+		"if test \"$WW_CURRENT_FAIL\" = 1; then\n",
+		" printf 'injected current-directory compiler failure\\n' >&2\n",
+		" exit 97\nfi\nexec \"$WW_CURRENT_REAL_C\" \"$@\"\n"));
+
+	let stages: []str = ["ww", "ww_ww"];
+	let compilers: []str = ["w6c", "w6c_ww"];
+	let tags: []str = ["c", "ww"];
+	let spellings: []str = ["", ".", "./"];
+	let spellingtags: []str = ["bare", "dot", "slash"];
+	let baseenv: []str = os.getenvs();
+	let commandref: str = "";
+	let changedref: str = "";
+	let missingref: str = "";
+	let failref: str = "";
+	let collisionref: str = "";
+	let out: commandout;
+	let si: i32 = 0;
+	for (si < stages.len) {
+		rewritefile(commandfile, original);
+		let defaultbin: str = strings.concat(command, "/current-command");
+		let defaultscratch: str = strings.concat(defaultbin, ".sepwork");
+		let legacyscratch: str = strings.concat(command, "/..sepwork");
+
+		// Bare, dot, and dot-slash spellings select the same package and
+		// produce the same directory-named executable and cold artifacts.
+		let pi: i32 = 0;
+		for (pi < spellings.len) {
+			let av: []str = [driver(stages[si]), "build"];
+			if (spellings[pi].len != 0) { append(av, spellings[pi]); };
+			runcommanddir(root, strings.concat("current-", tags[si], "-",
+				spellingtags[pi]), command, av,
+				(60i64 * (time.second: i64)): time.duration, &out);
+			expectexit(&out, 0);
+			assert(out.stdout.len == 0 && out.stderr.len == 0);
+			assert(os.exists(defaultbin) && os.exists(defaultscratch));
+			assert(!os.exists(legacyscratch));
+			assert((permissionmode(defaultbin) & 73u32) == 73u32);
+			let built: str = readfile(defaultbin);
+			if (commandref.len == 0) { commandref = strings.dup(built); }
+			else { assert(same(commandref, built)); };
+			let runav: []str = [defaultbin];
+			runcommand(root, strings.concat("current-run-", tags[si], "-",
+				spellingtags[pi]), runav, time.second, &out);
+			expectexit(&out, 23);
+			assert(!directoryhasnew(command)
+				&& !directoryhasfragment(command, ".install")
+				&& !directoryhasfragment(command, ".wwtxn."));
+			assert(os.remove(defaultbin) == 0);
+			clean(defaultscratch);
+			pi += 1;
+		};
+
+		// Explicit output and exact null output keep their established
+		// disposition and never create the default current-directory name.
+		let explicitout: str = strings.concat(root, "/explicit-", tags[si]);
+		let explicitav: []str = [driver(stages[si]), "build", "-o",
+			explicitout];
+		runcommanddir(root, strings.concat("current-explicit-", tags[si]),
+			command, explicitav,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0);
+		assert(same(commandref, readfile(explicitout))
+			&& !os.exists(defaultbin) && !os.exists(defaultscratch));
+		assert(os.remove(explicitout) == 0);
+		clean(strings.concat(explicitout, ".sepwork"));
+		let nullav: []str = [driver(stages[si]), "build", "-o", "/dev/null"];
+		runcommanddir(root, strings.concat("current-null-", tags[si]), command,
+			nullav, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0);
+		assert(!os.exists(defaultbin) && !os.exists(defaultscratch)
+			&& !os.exists(legacyscratch));
+
+		// A non-main current-directory build compiles and archives privately,
+		// but neither links nor publishes a directory-named file.
+		let librarybin: str = strings.concat(library, "/current-library");
+		let libraryscratch: str = strings.concat(librarybin, ".sepwork");
+		let librarylegacy: str = strings.concat(library, "/..sepwork");
+		let libraryav: []str = [driver(stages[si]), "build"];
+		runcommanddir(root, strings.concat("current-library-", tags[si]),
+			library, libraryav,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0);
+		assert(!os.exists(librarybin) && os.exists(libraryscratch)
+			&& !os.exists(librarylegacy));
+		assert(!directoryhasnew(library)
+			&& !directoryhasfragment(library, ".wwtxn."));
+		clean(libraryscratch);
+
+		// Import loading retains precedence over output planning.  Failure
+		// creates neither the corrected output nor either scratch spelling.
+		let badbin: str = strings.concat(bad, "/bad-current");
+		let badav: []str = [driver(stages[si]), "build"];
+		runcommanddir(root, strings.concat("current-missing-", tags[si]), bad,
+			badav, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& has(out.stderr, "cannot find package missing.current\n"));
+		assert(!os.exists(badbin)
+			&& !os.exists(strings.concat(badbin, ".sepwork"))
+			&& !os.exists(strings.concat(bad, "/..sepwork")));
+		if (si == 0) { missingref = strings.dup(out.stderr); }
+		else { assert(same(missingref, out.stderr)); };
+
+		// Persistent cold/warm reuse keeps the same output.  An invalidated
+		// producer failure preserves both that prior output and clean public
+		// state; a later successful invalidation publishes the changed binary.
+		let work: str = strings.concat(root, "/current-work-", tags[si]);
+		let trace: str = strings.concat(root, "/current-trace-", tags[si]);
+		mkdirall(work); writefile(trace, "");
+		let env: []str = alloc([], (baseenv.len + 4): u64)!;
+		let ei: i32 = 0;
+		for (ei < baseenv.len) {
+			if (!strings.hasprefix(baseenv[ei], "WW_W6C=")
+				&& !strings.hasprefix(baseenv[ei], "WW_CURRENT_")) {
+				append(env, baseenv[ei]);
+			};
+			ei += 1;
+		};
+		append(env, strings.concat("WW_W6C=", compilerwrapper));
+		append(env, strings.concat("WW_CURRENT_REAL_C=",
+			driver(compilers[si])));
+		append(env, strings.concat("WW_CURRENT_TRACE=", trace));
+		let failindex: i32 = env.len;
+		append(env, "WW_CURRENT_FAIL=");
+		let persistav: []str = [driver(stages[si]), "build", "-w", work];
+		runcommandenvdir(root, strings.concat("current-cold-", tags[si]),
+			persistav, env, command,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& readfile(trace).len != 0);
+		let prior: str = readfile(defaultbin);
+		assert(same(commandref, prior));
+		rewritefile(trace, "");
+		runcommandenvdir(root, strings.concat("current-warm-", tags[si]),
+			persistav, env, command,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& readfile(trace).len == 0 && same(prior, readfile(defaultbin)));
+		rewritefile(commandfile, changed); rewritefile(trace, "");
+		env[failindex] = "WW_CURRENT_FAIL=1";
+		runcommandenvdir(root, strings.concat("current-fail-", tags[si]),
+			persistav, env, command,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(readfile(trace).len != 0
+			&& has(out.stderr, "injected current-directory compiler failure\n")
+			&& has(out.stderr, "ww: w6c failed for ")
+			&& same(prior, readfile(defaultbin)));
+		assert(!directoryhasnew(command) && !directoryhasnew(work)
+			&& !directoryhasfragment(command, ".install")
+			&& !directoryhasfragment(command, ".wwtxn.")
+			&& !directoryhasfragment(work, ".wwtxn."));
+		if (si == 0) { failref = strings.dup(out.stderr); }
+		else { assert(same(failref, out.stderr)); };
+		env[failindex] = "WW_CURRENT_FAIL="; rewritefile(trace, "");
+		runcommandenvdir(root, strings.concat("current-changed-", tags[si]),
+			persistav, env, command,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& readfile(trace).len != 0);
+		let changedbytes: str = readfile(defaultbin);
+		assert(!same(prior, changedbytes));
+		if (changedref.len == 0) { changedref = strings.dup(changedbytes); }
+		else { assert(same(changedref, changedbytes)); };
+		let changedrun: []str = [defaultbin];
+		runcommand(root, strings.concat("current-changed-run-", tags[si]),
+			changedrun, time.second, &out);
+		expectexit(&out, 24);
+		assert(os.remove(defaultbin) == 0);
+		clean(work);
+		rewritefile(commandfile, original);
+
+		// A genuine destination-directory collision still rejects at output
+		// preflight, now naming the derived leaf rather than the dot selector.
+		mkdirall(defaultbin);
+		runcommanddir(root, strings.concat("current-collision-", tags[si]),
+			command, libraryav,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0 && same(out.stderr, strings.concat(
+			"ww: build output \"current-command\" already exists and is a directory\n")));
+		assert(!os.exists(defaultscratch) && !os.exists(legacyscratch));
+		if (si == 0) { collisionref = strings.dup(out.stderr); }
+		else { assert(same(collisionref, out.stderr)); };
+		clean(defaultbin);
+		si += 1;
+	};
+	assert(!directoryhasnew(root) && !directoryhasfragment(root, ".wwtxn."));
+	clean(root);
+};
+
 // A single directory root used to bypass the package coordinator and treat
 // every non-null -o spelling as one file.  Exercise the Go output-directory
 // branch at that dispatch boundary while the established graph transaction