diff --git a/cmd/wcc/lex.c b/cmd/wcc/lex.c
index ddb6fa13..d50f76c8 100644
--- a/cmd/wcc/lex.c
+++ b/cmd/wcc/lex.c
@@ -358,6 +358,78 @@ skipws(Lex *l)
 	}
 }
 
+/* Return the next initial import token without ever lexing the first ordinary
+ * declaration token. Go's named-file reader consumes header trivia while
+ * looking for another import, so NUL/comment diagnostics in that trivia remain
+ * visible; a malformed UTF-8 byte or non-leading BOM that itself begins the
+ * ordinary body is outside the header and must not be diagnosed here. */
+int
+lexheaderimport(Lex *l, Tok *out)
+{
+	for (;;) {
+		if (l->pos >= l->srclen)
+			return 0;
+		unsigned char c = (unsigned char)l->src[l->pos];
+		if (c == 0) {
+			/* The loader necessarily reaches this byte while deciding whether
+			 * another import follows. Preserve the source decoder diagnostic. */
+			lskipnul(l);
+			return 0;
+		}
+		if ((c >= 0x80 && !utf8bytevalid(l->src, l->srclen, l->pos))
+		    || bomat(l->src, l->srclen, l->pos))
+			return 0;
+		if (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+			lget(l);
+			continue;
+		}
+		if (c == '/' && l->pos + 1 < l->srclen
+		    && l->src[l->pos + 1] == '/') {
+			lget(l); lget(l);
+			linecomment(l);
+			if (l->errs != 0)
+				return 0;
+			continue;
+		}
+		if (c == '/' && l->pos + 1 < l->srclen
+		    && l->src[l->pos + 1] == '*') {
+			lget(l); lget(l);
+			int prev = -1;
+			for (;;) {
+				int x = lget(l);
+				if (x < 0) {
+					Pos p = lpos(l);
+					errorf(p, "unterminated /* comment");
+					l->errs++;
+					return 0;
+				}
+				if (prev == '*' && x == '/')
+					break;
+				prev = x;
+			}
+			if (l->errs != 0)
+				return 0;
+			continue;
+		}
+		break;
+	}
+
+	/* A compiler-owned source-boundary directive is an ordinary declaration
+	 * boundary here, just as it was when lexnext eagerly exposed the token. */
+	if (l->modreset || l->modpath != NULL)
+		return 0;
+	static const char kw[] = "import";
+	const u64 n = sizeof kw - 1;
+	if (l->srclen - l->pos < n
+	    || memcmp(l->src + l->pos, kw, n) != 0)
+		return 0;
+	if (l->srclen - l->pos > n
+	    && isidcont((unsigned char)l->src[l->pos + n]))
+		return 0;
+	*out = lexnext(l);
+	return out->kind == TK_USE;
+}
+
 static u64
 parseint(const char *s, u64 n, int base, int *ok)
 {
diff --git a/cmd/wcc/parse.c b/cmd/wcc/parse.c
index f39a5336..37029d62 100644
--- a/cmd/wcc/parse.c
+++ b/cmd/wcc/parse.c
@@ -35,6 +35,17 @@ advance(Parser *p)
 	}
 }
 
+static int
+advanceheaderimport(Parser *p)
+{
+	Tok next;
+	if (!lexheaderimport(p->l, &next))
+		return 0;
+	p->cur = next;
+	p->hasla = 0;
+	return 1;
+}
+
 static Tok
 peek(Parser *p)
 {
@@ -1359,6 +1370,140 @@ parseuse(Parser *p)
 	return n;
 }
 
+/* Parse one initial import without pulling the declaration that follows it
+ * into the header pass.  This intentionally has stricter, single-error
+ * recovery than parseuse: named test-source build loading needs only decide
+ * whether the package/import header itself is valid. */
+static Node *
+parseheaderuse(Parser *p)
+{
+	Pos pp = p->cur.pos;
+	advance(p);
+	Node *n = newnode(p->a, N_USE, pp);
+	n->usefile = p->cur.pos.file;
+	n->useline = p->cur.pos.line;
+	n->usecol = p->cur.pos.col;
+	const char *alias = NULL;
+	const char *first;
+	if (p->cur.kind == TK_UNDER) {
+		n->useblank = 1;
+		advance(p);
+	} else if (p->cur.kind != TK_IDENT) {
+		errorf(p->cur.pos, "expected identifier, got %s",
+		    tokname(p->cur.kind));
+		p->errs++;
+		return n;
+	}
+	if (p->cur.kind != TK_IDENT) {
+		errorf(p->cur.pos, "expected identifier, got %s",
+		    tokname(p->cur.kind));
+		p->errs++;
+		return n;
+	}
+	first = p->cur.text;
+	advance(p);
+	if (!n->useblank && p->cur.kind == TK_IDENT) {
+		alias = first;
+		first = p->cur.text;
+		advance(p);
+	}
+	const char *leaf = first;
+	const char *path = leaf;
+	while (p->cur.kind == TK_DOT) {
+		advance(p);
+		if (p->cur.kind != TK_IDENT) {
+			errorf(p->cur.pos, "expected identifier, got %s",
+			    tokname(p->cur.kind));
+			p->errs++;
+			return n;
+		}
+		leaf = p->cur.text;
+		path = aprintf(p->a, "%s.%s", path, leaf);
+		advance(p);
+	}
+	if (!n->useblank) {
+		n->str = alias ? alias : leaf;
+		n->strlen = strlen(n->str);
+	}
+	n->usesource = path;
+	n->usepath = path;
+	n->usealias = alias;
+	if (p->cur.kind != TK_SEMI) {
+		errorf(p->cur.pos, "expected ';' after import");
+		p->errs++;
+		return n;
+	}
+	return n;
+}
+
+/* Go's named-file loader parses a valid source only through its initial
+ * package/import section.  Keep the broader parseimports recovery pass for
+ * graph-bearing sources, but give actionless test-source omission a boundary
+ * that cannot diagnose late imports or an invalid ordinary declaration body. */
+Node *
+parsepackageheader(Parser *p)
+{
+	Pos fp = { p->l->file, 1, 1 };
+	Node *file = newnode(p->a, N_FILE, fp);
+	Node *head = NULL, *tail = NULL;
+
+	while (p->cur.kind == TK_MODPATH || p->cur.kind == TK_MODRESET) {
+		if (p->cur.kind == TK_MODPATH) {
+			p->pathmod = p->cur.text;
+			p->curmod = p->cur.text;
+			p->resetmod = NULL;
+		} else {
+			p->pathmod = NULL;
+			p->curmod = p->cur.text;
+			p->resetmod = p->cur.text;
+		}
+		p->sourceid++;
+		advance(p);
+	}
+	if (p->cur.kind != TK_MODULE) {
+		errorf(p->cur.pos, "invalid or missing package clause");
+		p->errs++;
+		return file;
+	}
+	Pos pp = p->cur.pos;
+	advance(p);
+	if (p->cur.kind != TK_IDENT) {
+		errorf(p->cur.pos, "invalid or missing package clause");
+		p->errs++;
+		return file;
+	}
+	const char *name = p->cur.text;
+	advance(p);
+	if (p->cur.kind != TK_SEMI) {
+		errorf(p->cur.pos, "expected ';' after package name");
+		p->errs++;
+		return file;
+	}
+	p->curpkg = name;
+	if (p->pathmod == NULL && p->resetmod == NULL)
+		p->curmod = name;
+	file->module = name;
+	file->pkgname = name;
+	file->sourceid = p->sourceid;
+	file->pos = pp;
+
+	while (advanceheaderimport(p)) {
+		Node *d = parseheaderuse(p);
+		d->module = p->curmod;
+		d->pkgname = p->curpkg;
+		d->sourceid = p->sourceid;
+		if (head == NULL)
+			head = d;
+		else
+			tail->next = d;
+		tail = d;
+		if (p->errs != 0)
+			break;
+	}
+	file->list = head;
+	return file;
+}
+
 Node *
 parseimports(Parser *p)
 {
diff --git a/cmd/wcc/ww.h b/cmd/wcc/ww.h
index aede6e54..db319c4d 100644
--- a/cmd/wcc/ww.h
+++ b/cmd/wcc/ww.h
@@ -218,6 +218,7 @@ struct Lex {
 
 void	lexinit(Lex*, Arena*, const char *file, const char *src, u64 len);
 Tok	lexnext(Lex*);
+int	lexheaderimport(Lex*, Tok*);
 const char *tokname(Tkind);	/* canonical spelling, e.g. "fn", "+=" */
 void	tokprint(FILE*, Tok);	/* one line, "%s:%d:%d: %s %q" */
 Tkind	kwlookup(const char *s, u64 n);	/* TK_NONE if not a keyword */
@@ -408,6 +409,8 @@ struct Parser {
 
 void	parserinit(Parser*, Arena*, Lex*);
 Node	*parsefile(Parser*);
+/* Package/import header only: stop before the first ordinary declaration. */
+Node	*parsepackageheader(Parser*);
 /* Imports-only N_FILE: module/pos identify the first package clause,
  * list holds N_USE declarations, and body holds package-clause markers. */
 Node	*parseimports(Parser*);
diff --git a/cmd/ww/main.c b/cmd/ww/main.c
index 6c46e01f..a04b70b4 100644
--- a/cmd/ww/main.c
+++ b/cmd/ww/main.c
@@ -693,6 +693,111 @@ source_package_name(const char *path, char **out)
 	return 0;
 }
 
+/* Named-file loading is allowed for every non-directory Stat result.  Unlike
+ * sep_slurp, this reader must not require seekability: a finite FIFO is still
+ * a named source stream, just as it is for GoFilesPackage. */
+static int
+source_header_slurp(const char *path, char **out, u64 *len)
+{
+	int fd = open(path, O_RDONLY);
+	if (fd < 0) return -1;
+	size_t cap = 4096, n = 0;
+	char *buf = malloc(cap);
+	if (buf == NULL) {
+		(void)sep_fail_nomem();
+		(void)close(fd);
+		return -1;
+	}
+	for (;;) {
+		if (n == cap) {
+			if (cap >= INT_MAX) {
+				(void)sep_fail_size();
+				free(buf);
+				(void)close(fd);
+				return -1;
+			}
+			size_t nextcap = cap > (size_t)INT_MAX / 2
+			    ? (size_t)INT_MAX : cap * 2;
+			char *next = realloc(buf, nextcap);
+			if (next == NULL) {
+				(void)sep_fail_nomem();
+				free(buf);
+				(void)close(fd);
+				return -1;
+			}
+			buf = next;
+			cap = nextcap;
+		}
+		ssize_t got = read(fd, buf + n, cap - n);
+		if (got < 0) {
+			if (errno == EINTR) continue;
+			free(buf);
+			(void)close(fd);
+			return -1;
+		}
+		if (got == 0) break;
+		n += (size_t)got;
+	}
+	if (close(fd) != 0) {
+		free(buf);
+		return -1;
+	}
+	if (n == cap) {
+		/* The loop normally grows before the read that can fill cap, but
+		 * retain an explicit terminator guard for future reader changes. */
+		if (cap >= INT_MAX) {
+			(void)sep_fail_size();
+			free(buf);
+			return -1;
+		}
+		char *next = realloc(buf, cap + 1);
+		if (next == NULL) {
+			(void)sep_fail_nomem();
+			free(buf);
+			return -1;
+		}
+		buf = next;
+	}
+	buf[n] = '\0';
+	*out = buf;
+	*len = (u64)n;
+	return 0;
+}
+
+/* Validate only the package/import header before a named test source is
+ * omitted from an ordinary build. Imports are syntax, not graph edges here. */
+static int
+source_build_header(const char *path)
+{
+	char *buf;
+	u64 len;
+	if (source_header_slurp(path, &buf, &len) < 0) {
+		fprintf(stderr, "ww: cannot read %s\n", path);
+		return -1;
+	}
+	Arena *a = newarena();
+	Lex l;
+	Parser p;
+	lexinit(&l, a, path, buf, len);
+	parserinit(&p, a, &l);
+	Node *header = parsepackageheader(&p);
+	if (l.errs || p.errs) {
+		freearena(a);
+		free(buf);
+		return -1;
+	}
+	if (header->module == NULL) {
+		Pos pp = { path, 1, 1 };
+		errorf(pp, "invalid or missing package clause");
+		freearena(a);
+		free(buf);
+		return -1;
+	}
+	freearena(a);
+	free(buf);
+	return 0;
+}
+
 static int
 source_list_add(char ***list, int *n, int *cap, const char *path)
 {
@@ -7474,11 +7579,31 @@ do_build(int argc, char **argv)
 	}
 	struct stat requested;
 	int literal = stat(src, &requested) == 0;
+	int requested_nondirectory = literal && !S_ISDIR(requested.st_mode);
 	if (source_operand_ignored(src)) {
 		source_operand_no_sources(src);
 		free(incs);
 		return 1;
 	}
+	const char *requested_base = strrchr(src, '/');
+	requested_base = requested_base ? requested_base + 1 : src;
+	size_t requested_baselen = strlen(requested_base);
+	if (requested_nondirectory && requested_baselen >= 8
+	    && strcmp(requested_base + requested_baselen - 8,
+		"_test.ww") == 0) {
+		if (source_build_header(src) < 0) {
+			free(incs);
+			return 1;
+		}
+		free(incs);
+		if (!outflag[0] || strcmp(outflag, "/dev/null") == 0)
+			return 0;
+		if (build_output_dir(outflag))
+			fputs("ww: no main packages to build\n", stderr);
+		else
+			fputs("ww: no packages to build\n", stderr);
+		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 fd1156fb..4f0501eb 100644
--- a/docs/build-system.md
+++ b/docs/build-system.md
@@ -10080,6 +10080,170 @@ No serialized format changes. Build workdir format remains `18`, test workdir
 format remains `19`, semantic storage format remains `3`, and there is no test
 result cache.
 
+### 11.51 Implemented explicit named test-source build omission
+
+A single existing raw `ww build` operand whose requested final basename ends
+exactly `_test.ww` is now a test-only named source.  WW syntax-observes only the
+package clause and its initial contiguous import section, preserves any read/header
+diagnostic, then omits the valid test-only root before logical resolution or
+action construction.  This is deliberately distinct from the leading-dot and
+underscore rule in 11.50: `_test.ww` reaches that earlier exclusion, whereas a
+visible `x_test.ww` reaches this test-only omission.
+
+#### Pinned authority, tests, and applicability
+
+- **behavior directly implemented or asserted by pinned Go** — official Go
+  1.26.5 commit `c19862e5f8415b4f24b189d065ed739517c548ba` recognizes an
+  existing non-directory named `.go` operand in `PackagesAndErrors`
+  ([`cmd/go/internal/load/pkg.go`, lines 2903–2918](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/load/pkg.go#L2903-L2918)),
+  builds its synthetic command-line package with `UseAllFiles`
+  ([lines 3244–3315](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/load/pkg.go#L3244-L3315)),
+  and classifies `_test.go` separately from `GoFiles`
+  ([`go/build/build.go`, lines 930–1036](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build.go#L930-L1036)).
+  `UseAllFiles` bypasses ordinary target and build-expression rejection, but
+  not that test-file classification
+  ([lines 1438–1509](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build.go#L1438-L1509)).
+- **behavior directly implemented or asserted by pinned Go** — on a
+  successfully scanned header, `readGoInfo` reads the initial package/import
+  header and one stop byte, then removes that byte before parsing; on header
+  syntax recovery it deliberately drains the remaining source
+  ([`go/build/read.go`, lines 265–315](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/read.go#L265-L315)).
+  Every raw NUL reached by its reader is a read error
+  ([lines 71–89](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/read.go#L71-L89));
+  `parser.ImportsOnly` stops before ordinary declarations
+  ([`go/parser/parser.go`, lines 2887–2923](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/parser/parser.go#L2887-L2923)).
+  Thus a package or initial-import header error precedes omission, while a
+  later declaration/body error does not become an ordinary-build error.
+- **behavior directly implemented or asserted by pinned Go** — ordinary
+  initial loading does not recursively resolve test imports
+  ([`cmd/go/internal/load/pkg.go`, lines 350–358](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/load/pkg.go#L350-L358));
+  `go/build` records their metadata at `go/build/build.go:1037–1040`.
+  Build checks loader errors first and then omits a test-only root before
+  output/action construction
+  ([`cmd/go/internal/work/build.go`, lines 459–559 and 731–745](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/work/build.go#L459-L559)).
+- **behavior directly implemented or asserted by pinned Go** — related
+  official anchors are `go/build/build_test.go:382–421` (`TestMatchFile`),
+  `go/build/build_test.go:812–831` (`TestDirectives` and `XTestDirectives`),
+  `go/build/read_test.go:17–73,120–159,165–249` (header boundary, NUL, and
+  syntax recovery),
+  `cmd/go/testdata/script/test_relative_cmdline.txt:1–49`, and
+  `cmd/go/testdata/script/build_test_only.txt:1–18`.  The pinned official
+  repository has no script that directly invokes `go build NAME_test.go`; the
+  exact named-build result below is derived from its pinned loader and action
+  ordering, not presented as an unanchored direct script assertion.
+- **behavior derived from the pinned implementation** — one valid named test
+  source produces no build action.  No effective `-o` and exact `/dev/null`
+  succeed silently; a non-directory output reports `ww: no packages to
+  build\n`; an existing or trailing-slash output directory reports
+  `ww: no main packages to build\n`.  Header loading occurs before those
+  empty-selection branches.
+- **behavior derived from the pinned implementation** — the pinned body
+  boundary is byte-sensitive: an ordinary non-`i` stop byte, a first malformed
+  UTF-8 byte, or a later BOM byte is excluded, while a reached NUL and an
+  unterminated comment remain load errors; a following byte `i` is attempted as
+  another import. WW applies the corresponding rule at its lexical `import`
+  boundary: it never lexes the first ordinary body token, but preserves NUL and
+  comment diagnostics encountered while skipping header trivia.
+
+The rule honestly applies to WW's local, manifest-free literal `.ww` model:
+`*_test.ww` already means test source for directory selection and `ww test`.
+It introduces no module, manifest, registry, lock, network resolver, cache,
+generalized import grammar, source build expression, or test-result cache.
+
+#### Source and identity ownership
+
+- **behavior directly implemented or asserted by pinned Go** — named-source
+  package construction presents `Stat`-derived file information through its
+  synthetic directory.  The operand spelling remains the file name presented
+  to selection, even though `Stat` follows a symlink.
+- **behavior derived from the pinned implementation** — the twin true owners
+  are `cmd/ww/main.c::do_build` and `selfhost/cmd/ww/main.ww::dobuild`, after
+  the existing hidden-prefix check and before `resolve_module` / `resolvemodule`.
+  A requested visible non-directory spelling ending `_test.ww` is classified
+  from that spelling; a symlink to a directory remains a directory request.
+  The finite-stream header reader is not a regular-file restriction: a supplied
+  finite FIFO is read as a source, while an unreadable entry reports its header
+  read failure.  Physical parent directories and symlink targets remain loader
+  metadata, never canonical package or import identity.
+- **behavior derived from the pinned implementation** — platform-looking
+  visible names such as `x_windows_test.ww` remain test-only named sources.
+  Multiple named sources, logical operands without `.ww`, directories,
+  recursive requests, `ww run`, and all visible non-test raw operands retain
+  their prior routes.  In particular, this does not implement Go's multiple
+  named-source package collection.
+- **behavior derived from the pinned implementation** — the header observation
+  is discarded after classification.  It creates no canonical package,
+  command-line package representative, dotted import identity, qualifier,
+  symbol namespace, `.wwi`, action, archive, publication, or persistence key.
+  Initial import syntax is checked solely for load-error precedence; omitted
+  test-source imports are not resolved and create no graph edge or action.
+
+#### Build, test, package, and import effects
+
+- **behavior directly measured WW behavior** — before this change, both stages
+  compiled, linked, published, persisted, and ran a valid visible
+  `only_test.ww`; `ww build -w WORK -o OUT only_test.ww` exited 0 with empty
+  streams, a byte-identical mode-0755 executable, populated work state, and
+  runtime status 19.  A missing test-only import likewise reached ordinary
+  import resolution.
+- **behavior derived from the pinned implementation** — post-contract build
+  behavior is an empty production selection after a valid header: no compiler,
+  assembler, archiver, linker, generated main, test harness, test child, or
+  program process starts.  `-S` follows the same no-action rule.  No runtime
+  result can occur.
+- **behavior derived from the pinned implementation** — package behavior is
+  confined to the transient header check; no production/test variant or
+  package action remains.  Import behavior is likewise confined to syntax;
+  missing test-only dotted imports, late imports, body syntax/type errors, and
+  runtime faults cannot enter the production graph.
+- **behavior derived from the pinned implementation** — test behavior is an
+  explicit non-effect.  Raw `ww test`, `ww test -c`, and `ww test -S` continue
+  to select named test files.  Directory and recursive `ww build` already
+  exclude selected test sources and remain unchanged.
+
+#### Diagnostics, artifacts, and lifecycle
+
+- **behavior derived from the pinned implementation** — CLI-shape and
+  multiple-operand delegation retain their prior precedence; 11.50 prefix
+  exclusion precedes this header reader.  Header read/package/initial-import
+  diagnostics precede output policy. A first ordinary malformed UTF-8/BOM body
+  byte is excluded, while a reached NUL or unterminated header-trivia comment
+  is a header diagnostic. Once the header is valid, no unresolved import,
+  graph, producer, linker, or runtime diagnostic may surface. Both
+  stages use the same header boundary and must produce byte-identical status,
+  stdout, and stderr.
+- **behavior derived from the pinned implementation** — cold no-action success
+  creates no default/explicit output, output directory, `.wwi`, unit, assembly,
+  object, archive, init product, `.sepwork`, workdir, stamp, transaction,
+  capture, result, or private build temporary.  Output-policy diagnostics also
+  create none of those products.
+- **behavior derived from the pinned implementation** — a warm request starts
+  no transaction, mutation, invalidation, reuse check, timestamp refresh, or
+  producer.  Existing output, sidecar, workdir and artifacts remain
+  byte-identical on success and failure; no `.new`, `.install`, `.wwtxn.*`,
+  backup, or recovery residue remains.  Restoring a visible non-test source
+  reuses prior valid warm state by the unchanged ordinary route.
+- **behavior derived from the pinned implementation** — no action means no
+  publication, rollback work, producer/runtime failure path, shared lock, or
+  child process.  Concurrent Cstage/WWstage no-action and header-diagnostic
+  requests are isolated.  Interruption during header reading leaves no owned
+  persistent state; after a valid header there is no child or publication window
+  to clean up.  Every reader closes its descriptor and releases request-local
+  storage before return.
+- **behavior derived from the pinned implementation** — focused proof covers
+  valid, malformed-header, missing-test-import, wrong-platform, symlink and
+  finite-stream operands; default/file/directory/null/assembly output modes;
+  cold/warm preservation; trace-proven tool and runtime absence; rollback,
+  interruption, concurrency, cleanup, complete per-stage work preservation, and
+  Cstage/WWstage semantic-artifact parity. The complete per-stage snapshot
+  includes `.wwtool.ww`; cross-stage comparison excludes only that intentionally
+  different producer binary snapshot. Unaffected visible production controls
+  retain byte-identical outputs.
+
+No serialized format changes accompany this omission.  Build workdir format
+remains `18`, test workdir format remains `19`, semantic storage format remains
+`3`, and the slice adds no cache or persistent record.
+
 ## 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 7cb7b7ec..7ffc3777 100644
--- a/docs/spec.md
+++ b/docs/spec.md
@@ -326,15 +326,38 @@ ImportPath    = ident { "." ident } .
   eligible. Only the requested basename participates: a hidden parent does not
   hide visible `main.ww`, a hidden symlink spelling stays hidden for any
   existing non-directory target, and a visible symlink spelling stays eligible.
-  The excluded operand creates no package, declaration, import binding/edge,
-  action, artifact, initialization, test,
-  publication, or persistent state. `ww build` reports the existing
-  `directory contains no WW package sources` condition; an explicit running
-  raw `ww test` also emits its command-owned `FAIL`, while `-c` and `-S` do not.
-  This rule does not add multiple named-source package support, does not change
-  visible `*_test.ww` handling, and does not apply to logical operands,
-  directory/recursive requests, imports, or `ww run`. The diagnostic parent is
-  presentation metadata and never canonical identity.
+  The prefix-excluded operand creates no package, declaration, import
+  binding/edge, action, artifact, initialization, test, publication, or
+  persistent state. `ww build` reports the existing `directory contains no WW
+  package sources` condition; an explicit running raw `ww test` also emits its
+  command-owned `FAIL`, while `-c` and `-S` do not.
+- A visible single raw operand passed to `ww build` whose requested final
+  basename ends exactly `_test.ww` is test-only after its package clause and
+  contiguous initial import section have been read. Prefix exclusion remains
+  first, so a bare `_test.ww` is never opened. Header read, package-clause, and
+  initial-import syntax errors retain their ordinary precedence; after a valid
+  header the sole root is omitted. Its dotted imports are not resolved, and a
+  late import, body parse/type error, or runtime behavior is not observed. The
+  first ordinary body token is not lexed, so an immediately following malformed
+  UTF-8 byte or non-leading BOM is outside the header. A raw NUL reached while
+  locating that token and an unterminated comment in header trivia remain load
+  errors. Go's byte reader probes a following `i` as a possible `import`; the
+  corresponding WW boundary is the exact lexical `import` token, so an ordinary
+  WW identifier merely beginning with `i` is body syntax. This named-source
+  rule retains all-files platform behavior: a
+  visible `x_windows_test.ww` is still test-only. It classifies the requested
+  basename of a visible symlink, not its target name; a symlink whose target is
+  a directory remains a directory request.
+- Omission creates no canonical package, command-line package node, import
+  binding or edge, graph/action, symbol, initializer, executable, archive,
+  interface, publication, transaction, default `.sepwork`, or work-state
+  mutation. It does not alter `ww test`, `ww test -c`, `ww test -S`, logical
+  operands, directory/recursive selection, multiple named-source support,
+  imports, or `ww run`. Physical directory and symlink-target data remain
+  observation metadata, never package, import, graph, action, artifact,
+  symbol, `.wwi`, publication, or persistence identity. 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
@@ -467,6 +490,15 @@ ImportPath    = ident { "." ident } .
   Output paths and directory metadata never become package, import, graph, action,
   symbol, artifact, `.wwi`, or persistence identity.
 
+  A valid omitted single raw `*_test.ww` build has an empty selection. With no
+  effective `-o`, including an assembly-only request, and with exact
+  `-o /dev/null`, it succeeds silently. A non-directory effective output fails
+  with `ww: no packages to build`; an output-directory effective output fails
+  with `ww: no main packages to build`. These empty-selection outcomes occur
+  only after the raw test source's header has loaded successfully, create no
+  output path or parent, and preserve every pre-existing output and work-state
+  byte unchanged.
+
   Every caller-visible build installation checks its destination after all
   applicable compile, assemble, archive, and link producers finish. Ordinary
   `stat` follows symlinks. An existing directory rejects as
diff --git a/docs/test-system-v2.md b/docs/test-system-v2.md
index 17b59a11..35c51e84 100644
--- a/docs/test-system-v2.md
+++ b/docs/test-system-v2.md
@@ -239,6 +239,32 @@ platform classification, symlink spelling, output rollback, residue, and
 diagnostic/artifact parity. Directory package coordination and test process,
 filter, timeout, signal, and descendant topology are unchanged.
 
+The corresponding focused dual-stage named-test-source build observer proves
+the distinct `ww build` rule for one visible raw operand ending exactly
+`_test.ww`. It requires each stage to read the package clause and contiguous
+initial imports before omitting the sole root: unreadable/header-syntax inputs
+retain their diagnostics, while a valid header prevents import resolution,
+graph/action creation, producers, runtime, publication, persistence, and all
+ordinary body-derived diagnostics. It separately proves that a first malformed
+UTF-8 or non-leading BOM body byte is outside the header, while a reached NUL
+and an unterminated header-trivia comment retain loader diagnostics. It also
+proves WW's grammar-level adaptation of Go's following-`i` byte probe: only the
+exact lexical `import` token continues the header, while an identifier such as
+`imported` begins the ordinary body. It covers
+normal, `-S`, and `/dev/null` successful
+empty selections; the exact `no packages to build` and `no main packages to
+build` output branches; requested-basename prefix, symlink, symlink-directory,
+and wrong-platform spelling controls; cold absence and warm preservation of
+outputs/work state; tool/process absence, interruption, concurrency, and
+residue cleanup. Cstage and WWstage agree on status, stdout, stderr,
+diagnostics, semantic artifact/work snapshots, and unaffected-control artifact
+bytes. Complete per-stage warm snapshots additionally cover the intentionally
+stage-specific `.wwtool.ww` producer-provenance file.
+Raw `ww test`, `-c`, and `-S` test routes retain explicit test-file selection;
+directory/recursive selection, package/import identities, graph/action
+identities, persistence formats (build 18, test 19, semantic 3), and test
+process topology are explicit non-effects.
+
 List mode uses that same product process and initialization boundary but starts
 no per-test child. The shared language harness emits only selected qualified
 test names, one per line in descriptor order. A valid filter selecting no tests
diff --git a/lib/ww/syntax/lex.ww b/lib/ww/syntax/lex.ww
index 5d645df2..0e4d8849 100644
--- a/lib/ww/syntax/lex.ww
+++ b/lib/ww/syntax/lex.ww
@@ -410,6 +410,75 @@ fn skipws(l: *lex) bool = {
 	return false;
 };
 
+// Return the next initial import without lexing the first ordinary body token.
+// Header trivia is still decoded, so reached NUL and comment diagnostics keep
+// loader precedence; a malformed UTF-8 byte or middle BOM that begins the body
+// is deliberately outside this pass.
+export fn lexheaderimport(l: *lex, out: *tok) bool = {
+	for (true) {
+		if (l.lpos >= l.srclen) { return false; };
+		let c: i32 = srcb(l, l.lpos);
+		if (c == 0) {
+			lskipnul(l);
+			return false;
+		};
+		if ((c >= 128 && !utf8bytevalid(l.src, l.srclen, l.lpos))
+			|| bomat(l.src, l.srclen, l.lpos)) {
+			return false;
+		};
+		if (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+			lget(l);
+			continue;
+		};
+		if (c == '/' && l.lpos + 1u64 < l.srclen
+			&& srcb(l, l.lpos + 1u64) == '/') {
+			lget(l); lget(l);
+			linecomment(l);
+			if (l.errs != 0) { return false; };
+			continue;
+		};
+		if (c == '/' && l.lpos + 1u64 < l.srclen
+			&& srcb(l, l.lpos + 1u64) == '*') {
+			lget(l); lget(l);
+			let prev: i32 = -1;
+			for (true) {
+				let x: i32 = lget(l);
+				if (x < 0) {
+					let cp: pos;
+					curpos(l, &cp);
+					errat(l, &cp, "unterminated /* comment");
+					return false;
+				};
+				if (prev == '*' && x == '/') { break; };
+				prev = x;
+			};
+			if (l.errs != 0) { return false; };
+			continue;
+		};
+		break;
+	};
+	if (l.modreset != 0 || l.modpathset != 0) { return false; };
+	let kw: str = tokname(tkind.TK_USE);
+	if (l.srclen - l.lpos < kw.len: u64) { return false; };
+	let i: i32 = 0;
+	for (i < kw.len) {
+		if (srcb(l, l.lpos + (i: u64)) != kw[i]: i32) {
+			return false;
+		};
+		i += 1;
+	};
+	if (l.srclen - l.lpos > kw.len: u64) {
+		let next: i32 = srcb(l, l.lpos + (kw.len: u64));
+		if ((next >= 'a' && next <= 'z')
+			|| (next >= 'A' && next <= 'Z')
+			|| (next >= '0' && next <= '9') || next == '_') {
+			return false;
+		};
+	};
+	lexnext(l, out);
+	return out.kind == tkind.TK_USE;
+};
+
 fn parseint(p: *u8, n: u64, base: i32, ok: *bool) u64 = {
 	let v: u64 = 0u64;
 	let b: u64 = base: u64;
diff --git a/lib/ww/syntax/parse.ww b/lib/ww/syntax/parse.ww
index cde23a2a..6764aa73 100644
--- a/lib/ww/syntax/parse.ww
+++ b/lib/ww/syntax/parse.ww
@@ -57,9 +57,7 @@ export type parser = struct {
 	commandpackage: bool,
 };
 
-fn refill(p: *parser) void = {
-	let t: tok;
-	lexnext(p.l, &t);
+fn installtok(p: *parser, t: *tok) void = {
 	p.curkind = t.kind;
 	p.curfile = t.file;
 	p.curline = t.line;
@@ -70,6 +68,19 @@ fn refill(p: *parser) void = {
 	p.curtsuffix = t.tsuffix;
 };
 
+fn refill(p: *parser) void = {
+	let t: tok;
+	lexnext(p.l, &t);
+	installtok(p, &t);
+};
+
+fn advanceheaderimport(p: *parser) bool = {
+	let t: tok;
+	if (!lexheaderimport(p.l, &t)) { return false; };
+	installtok(p, &t);
+	return true;
+};
+
 export fn parserinit(p: *parser, l: *lex) void = {
 	p.l = l;
 	p.errs = 0;
@@ -490,6 +501,121 @@ fn skipimportattrs(p: *parser) void = {
 	};
 };
 
+// Parse one initial import for the named-source header pass. Unlike the full
+// recovery scanner, this stops on the first malformed header token and never
+// consumes an ordinary declaration body.
+fn parseheaderuse(p: *parser) *node = {
+	let pf: str = p.curfile;
+	let pl: i32 = p.curline;
+	let pc: i32 = p.curcol;
+	advance(p);
+	let n: *node = newnode(nkind.N_USE, pf, pl, pc);
+	n.usefile = p.curfile;
+	n.useline = p.curline;
+	n.usecol = p.curcol;
+	let alias: str;
+	let first: str;
+	if (p.curkind == tkind.TK_UNDER) {
+		n.useblank = 1;
+		advance(p);
+	};
+	if (p.curkind != tkind.TK_IDENT) {
+		errmsg(p, strings.concat("expected identifier, got ",
+			tokname(p.curkind)));
+		return n;
+	};
+	first = p.curtext;
+	advance(p);
+	if (n.useblank == 0 && p.curkind == tkind.TK_IDENT) {
+		alias = first;
+		first = p.curtext;
+		advance(p);
+	};
+	let leaf: str = first;
+	let path: str = leaf;
+	for (p.curkind == tkind.TK_DOT) {
+		advance(p);
+		if (p.curkind != tkind.TK_IDENT) {
+			errmsg(p, strings.concat("expected identifier, got ",
+				tokname(p.curkind)));
+			return n;
+		};
+		leaf = p.curtext;
+		path = strings.concat(path, ".", leaf);
+		advance(p);
+	};
+	if (n.useblank != 0) { n.str = ""; }
+	else { if (alias.len > 0) { n.str = alias; } else { n.str = leaf; }; };
+	n.usesource = path;
+	n.usepath = path;
+	n.usealias = alias;
+	if (p.curkind != tkind.TK_SEMI) {
+		errmsg(p, "expected ';' after import");
+		return n;
+	};
+	return n;
+};
+
+// A valid named source is loader-visible only through its initial package and
+// contiguous import section. Keep parseimports for graph-bearing source
+// recovery; this boundary deliberately ignores every ordinary declaration.
+export fn parsepackageheader(p: *parser) *node = {
+	let f: *node = newnode(nkind.N_FILE, p.curfile, 1, 1);
+	let head: *node = nil;
+	let tail: *node = nil;
+	for (p.curkind == tkind.TK_MODPATH
+		|| p.curkind == tkind.TK_MODRESET) {
+		if (p.curkind == tkind.TK_MODPATH) {
+			p.pathmod = p.curtext;
+			p.curmod = p.curtext;
+			p.resetmod = "";
+		} else {
+			p.pathmod = "";
+			p.curmod = p.curtext;
+			p.resetmod = p.curtext;
+		};
+		p.sourceid += 1;
+		advance(p);
+	};
+	if (p.curkind != tkind.TK_MODULE) {
+		errmsg(p, "invalid or missing package clause");
+		return f;
+	};
+	let pf: str = p.curfile;
+	let pl: i32 = p.curline;
+	let pc: i32 = p.curcol;
+	advance(p);
+	if (p.curkind != tkind.TK_IDENT) {
+		errmsg(p, "invalid or missing package clause");
+		return f;
+	};
+	let name: str = p.curtext;
+	advance(p);
+	if (p.curkind != tkind.TK_SEMI) {
+		errmsg(p, "expected ';' after package name");
+		return f;
+	};
+	p.curpkg = name;
+	if (p.pathmod.len == 0 && p.resetmod.len == 0) { p.curmod = name; };
+	f.nmod = name;
+	f.pkgname = name;
+	f.sourceid = p.sourceid;
+	f.file = pf;
+	f.line = pl;
+	f.col = pc;
+	for (advanceheaderimport(p)) {
+		let d: *node = parseheaderuse(p);
+		d.nmod = p.curmod;
+		d.pkgname = p.curpkg;
+		d.sourceid = p.sourceid;
+		if (head == nil) { head = d; } else { tail.next = d; };
+		tail = d;
+		if (p.errs != 0) { break; };
+	};
+	f.list = head;
+	return f;
+};
+
 export fn parseimports(p: *parser) *node = {
 	let f = newnode(nkind.N_FILE, p.curfile, 1, 1);
 	let head: *node = nil;
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index 08e31d2b..fe644b91 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -991,6 +991,102 @@ fn slurp(pathcs: *u8) (*u8, u64) = {
 	return buf.ptr, nu;
 };
 
+// Named source recognition accepts every existing non-directory Stat result.
+// Read to EOF without seeking so a finite FIFO follows the same package-header
+// loading path as a regular file.
+fn sourceheaderslurp(pathcs: *u8) (*u8, u64, u64) = {
+	let fd: i32 = os.open(pathstr(pathcs), os.flag.RDONLY, 0i32);
+	if (fd < 0) { return nil, 0u64, 0u64; };
+	let cap: i32 = 4096;
+	let allocation: ([]u8 | nomem) = sepallocbytes(cap);
+	let buf: []u8;
+	match (allocation) {
+	case let value: []u8 => buf = value;
+	case nomem => {
+		sepfailnomem();
+		os.close(fd);
+		return nil, 0u64, 0u64;
+	};
+	};
+	let used: u64 = 0u64;
+	for (true) {
+		if (used == cap: u64) {
+			if (cap == SEP_COUNT_MAX) {
+				sepfailsize();
+				os.close(fd);
+				os.free(buf.ptr: *void, cap: u64);
+				return nil, 0u64, 0u64;
+			};
+			let nextcap: i32 = cap;
+			if (cap > SEP_COUNT_MAX / 2) { nextcap = SEP_COUNT_MAX; }
+			else { nextcap = cap * 2; };
+			let nextallocation: ([]u8 | nomem) = sepallocbytes(nextcap);
+			let next: []u8;
+			match (nextallocation) {
+			case let value: []u8 => next = value;
+			case nomem => {
+				sepfailnomem();
+				os.close(fd);
+				os.free(buf.ptr: *void, cap: u64);
+				return nil, 0u64, 0u64;
+			};
+			};
+			bytecpy(next.ptr, buf.ptr, used);
+			os.free(buf.ptr: *void, cap: u64);
+			buf = next;
+			cap = nextcap;
+		};
+		let got: i64 = os.read(fd, buf.ptr + used,
+			(cap: u64) - used);
+		if (got == -(os.EINTR: i32): i64) { continue; };
+		if (got < 0i64) {
+			os.close(fd);
+			os.free(buf.ptr: *void, cap: u64);
+			return nil, 0u64, 0u64;
+		};
+		if (got == 0i64) { break; };
+		used += got: u64;
+	};
+	if (os.close(fd) != 0) {
+		os.free(buf.ptr: *void, cap: u64);
+		return nil, 0u64, 0u64;
+	};
+	buf[used] = 0u8;
+	return buf.ptr, used, cap: u64;
+};
+
+// Validate only the package/import header. The returned syntax is deliberately
+// discarded: an ordinary build creates no package or import graph for this
+// test-only named source.
+fn sourcebuildheader(path: *u8) bool = {
+	let view: str = pathstr(path);
+	let bufp: *u8;
+	let blen: u64;
+	let bcap: u64;
+	bufp, blen, bcap = sourceheaderslurp(path);
+	if (bufp == nil) {
+		cerrpath("ww: cannot read ", path, "\n");
+		return false;
+	};
+	let l: syntax.lex;
+	syntax.lexinit(&l, view, bufp, blen);
+	let ps: syntax.parser;
+	syntax.parserinit(&ps, &l);
+	let header: *syntax.node = syntax.parsepackageheader(&ps);
+	if (l.errs > 0 || ps.errs > 0) {
+		os.free(bufp: *void, bcap);
+		return false;
+	};
+	if (header.nmod.len == 0) {
+		cerrpos(view, 1, 1);
+		cerr(": error: invalid or missing package clause\n");
+		os.free(bufp: *void, bcap);
+		return false;
+	};
+	os.free(bufp: *void, bcap);
+	return true;
+};
+
 fn makestem(stem: *u8, src: *u8) void = {
 	let n: u64 = cstrlen(src);
 	let stop: u64 = n;
@@ -8943,15 +9039,35 @@ fn dobuild(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 			nil, nil, false, true);
 	};
 	let requestedliteral: bool = false;
+	let requestednondirectory: bool = false;
 	let requestedstat: os.filestat;
 	match (os.stat(&requestedstat, pathstr(src))) {
-	case void => requestedliteral = true;
+	case void => {
+		requestedliteral = true;
+		let typ: u32 = (requestedstat.mode: u32) & 61440u32;
+		requestednondirectory = typ != os.mode.DIR: u32;
+	};
 	case let e: os.oserror => void;
 	};
 	if (sourceoperandignored(src)) {
 		sourceoperandnosources(src);
 		return 1;
 	};
+	let requestedlen: u64 = cstrlen(src);
+	let requestedbase: u64 = basenameoff(src, requestedlen);
+	if (requestednondirectory && requestedlen - requestedbase >= 8u64
+		&& cstrendswithlit(src, "_test.ww")) {
+		if (!sourcebuildheader(src)) { return 1; };
+		if (outflag == nil || cstreqlit(outflag, "/dev/null")) {
+			return 0;
+		};
+		if (buildoutputdir(outflag)) {
+			cerr("ww: no main packages to build\n");
+		} else {
+			cerr("ww: no packages to build\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 0cee0c38..1c5e5c54 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -705,6 +705,136 @@ fn directoryisempty(path: str) bool = {
 	return true;
 };
 
+fn snapshotu64(out: *[]u8, value: u64) void = {
+	let v: u64 = value;
+	let i: i32 = 0;
+	for (i < 8) {
+		append(*out, (v & 255u64): u8);
+		v >>= 8u64;
+		i += 1;
+	};
+};
+
+fn snapshotbytes(out: *[]u8, value: str) void = {
+	snapshotu64(out, value.len: u64);
+	let i: i32 = 0;
+	for (i < value.len) { append(*out, value[i]); i += 1; };
+};
+
+fn treepaths(root: str, relative: str, paths: *[]str) void = {
+	let current: str = root;
+	if (relative.len != 0) { current = strings.concat(root, "/", relative); };
+	let fd: i32 = os.open(current, os.flag.RDONLY, 0i32);
+	assert(fd >= 0);
+	let buf: []u8 = alloc([], 16384u64)!;
+	buf.len = 16384;
+	let n: i64 = os.getdents64(fd, buf.ptr, buf.len: u64);
+	for (n > 0i64) {
+		let off: i32 = 0;
+		for (off < n: i32) {
+			let reclen: i32 = (buf[off + 16]: i32)
+				+ ((buf[off + 17]: i32) * 256);
+			assert(reclen >= 20 && off + reclen <= n: i32);
+			let len: i32 = 0;
+			for (buf[off + 19 + len] != 0u8) { len += 1; };
+			let dot: bool = len == 1 && buf[off + 19] == '.';
+			let dotdot: bool = len == 2 && buf[off + 19] == '.'
+				&& buf[off + 20] == '.';
+			if (!dot && !dotdot) {
+				let name: str;
+				name.ptr = buf.ptr + (off + 19): u64;
+				name.len = len;
+				let child: str = strings.dup(name);
+				if (relative.len != 0) {
+					child = strings.concat(relative, "/", child);
+				};
+				append(*paths, child);
+				let full: str = strings.concat(root, "/", child);
+				let fi: os.filestat;
+				match (os.lstat(&fi, full)) {
+				case void => void;
+				case let e: os.oserror => abort("tree lstat failed");
+				};
+				let kind: u32 = (fi.mode: u32) & 61440u32;
+				if (kind == os.mode.DIR: u32) {
+					treepaths(root, child, paths);
+				};
+			};
+			off += reclen;
+		};
+		n = os.getdents64(fd, buf.ptr, buf.len: u64);
+	};
+	assert(n == 0i64);
+	assert(os.close(fd) == 0);
+};
+
+// Canonical complete-tree state: relative names, types, modes, and regular or
+// symlink bytes. Timestamps and inode numbers are observation metadata, not
+// semantic build state, and are deliberately excluded.
+fn treesnapshotfiltered(root: str, skipdriver: bool) str = {
+	let paths: []str = alloc([], 16u64)!;
+	append(paths, "");
+	treepaths(root, "", &paths);
+	let i: i32 = 1;
+	for (i < paths.len) {
+		let j: i32 = i;
+		for (j > 0 && strings.compare(paths[j - 1], paths[j]) > 0) {
+			let swap: str = paths[j - 1];
+			paths[j - 1] = paths[j];
+			paths[j] = swap;
+			j -= 1;
+		};
+		i += 1;
+	};
+	let out: []u8 = alloc([], 4096u64)!;
+	i = 0;
+	for (i < paths.len) {
+		if (skipdriver && same(paths[i], ".wwtool.ww")) {
+			i += 1;
+			continue;
+		};
+		let full: str = root;
+		if (paths[i].len != 0) {
+			full = strings.concat(root, "/", paths[i]);
+		};
+		let fi: os.filestat;
+		match (os.lstat(&fi, full)) {
+		case void => void;
+		case let e: os.oserror => abort("snapshot lstat failed");
+		};
+		snapshotbytes(&out, paths[i]);
+		snapshotu64(&out, fi.mode: u32: u64);
+		let kind: u32 = (fi.mode: u32) & 61440u32;
+		if (kind == os.mode.REG: u32) {
+			snapshotbytes(&out, readfile(full));
+		} else { if (kind == os.mode.LINK: u32) {
+			let target: [4096]u8;
+			let got: i64 = os.readlink(full, &target[0], 4096u64);
+			assert(got >= 0i64 && got <= 4096i64);
+			let value: str;
+			value.ptr = &target[0];
+			value.len = got: i32;
+			snapshotbytes(&out, value);
+		} else {
+			snapshotu64(&out, 0u64);
+		}; };
+		i += 1;
+	};
+	return strings.frombytes(out);
+};
+
+fn treesnapshot(root: str) str = {
+	return treesnapshotfiltered(root, false);
+};
+
+// The two bootstrap stages intentionally snapshot different driver binaries
+// in `.wwtool.ww`. Exclude only that producer-provenance file when comparing
+// semantic artifacts across stages; per-stage preservation uses the complete
+// snapshot above and therefore still covers it.
+fn artifacttreesnapshot(root: str) str = {
+	return treesnapshotfiltered(root, true);
+};
+
 fn discardedlinkcleaned(marker: str) void = {
 	let output: str = readfile(marker);
 	assert(output.len != 0);
@@ -1335,6 +1465,493 @@ fn cwdwritedata(dir: str, label: str) void = {
 	clean(root);
 };
 
+// A visible raw test-source build observes only its initial package/import
+// header.  It must not turn that observation into a package, import, action,
+// artifact, or work-state identity.
+@test fn named_test_sources_are_header_loaded_then_omitted() void = {
+	let root: str = fresh();
+	let source: str = strings.concat(root, "/source");
+	let dirsource: str = strings.concat(source, "/directory");
+	let dirtarget: str = strings.concat(source, "/directory-target");
+	mkdirall(source); mkdirall(dirsource); mkdirall(dirtarget);
+
+	let ignored: str = strings.concat(source, "/raw_windows_test.ww");
+	let platform: str = strings.concat(source, "/platform_windows_test.ww");
+	let badpackage: str = strings.concat(source, "/bad_package_test.ww");
+	let badimport: str = strings.concat(source, "/bad_import_test.ww");
+	let bodyutf8: str = strings.concat(source, "/body_utf8_test.ww");
+	let bodybom: str = strings.concat(source, "/body_bom_test.ww");
+	let bodynul: str = strings.concat(source, "/body_nul_test.ww");
+	let badcomment: str = strings.concat(source, "/bad_comment_test.ww");
+	let linktarget: str = strings.concat(source, "/target.ww");
+	let link: str = strings.concat(source, "/requested_test.ww");
+	let dirlink: str = strings.concat(source, "/directory_test.ww");
+	let rawmain: str = strings.concat(source, "/raw.ww");
+	let runsource: str = strings.concat(source, "/run_test.ww");
+	let testroute: str = strings.concat(source, "/route_test.ww");
+	let warmpath: str = strings.concat(source, "/warm.ww");
+	let warmtest: str = strings.concat(source, "/warm_test.ww");
+	let header: str = strings.concat(
+		"package raw_test;\nimport absent.pkg;\n",
+		"this body is deliberately malformed and never reaches a producer {\n",
+		"import late.missing;\n");
+	writefile(ignored, header);
+	writefile(platform, header);
+	writefile(linktarget, header);
+	writefile(badpackage, "this source has no package clause\n");
+	writefile(badimport, "package malformed;\nimport ;\n");
+	putinvalidutf8file(bodyutf8, "package body;\n",
+		"fn deliberately_unparsed(\n", false);
+	writemidbomfile(bodybom, "package body;\n",
+		"fn deliberately_unparsed(\n");
+	writenulfile(bodynul, "package body;\n", "fn body() void = {};\n");
+	writefile(badcomment, "package body;\n/* unterminated");
+	writefile(rawmain, "package main;\nfn main() i32 = { return 4; };\n");
+	writefile(runsource,
+		"package main;\nfn main() i32 = { return 9; };\n");
+	writefile(testroute, strings.concat(
+		"package route;\n",
+		"@test fn still_selected() void = { assert(true); };\n"));
+	writefile(warmpath, "package main;\nfn main() i32 = { return 6; };\n");
+	writefile(strings.concat(dirsource, "/main.ww"),
+		"package main;\nfn main() i32 = { return 3; };\n");
+	writefile(strings.concat(dirtarget, "/main.ww"),
+		"package main;\nfn main() i32 = { return 5; };\n");
+	assert(os.symlink(linktarget, link) == 0);
+	assert(os.symlink(dirtarget, dirlink) == 0);
+
+	let compilerwrapper: str = strings.concat(root, "/testonly-w6c.sh");
+	let assemblerwrapper: str = strings.concat(root, "/testonly-w6a.sh");
+	let linkerwrapper: str = strings.concat(root, "/testonly-w6l.sh");
+	writeexecutable(compilerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'compile\\n' >> \"$WW_TESTONLY_CTRACE\"\n",
+		"exec \"$WW_TESTONLY_REAL_C\" \"$@\"\n"));
+	writeexecutable(assemblerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'assemble\\n' >> \"$WW_TESTONLY_ATRACE\"\n",
+		"exec \"$WW_TESTONLY_REAL_A\" \"$@\"\n"));
+	writeexecutable(linkerwrapper, strings.concat(
+		"#!/bin/sh\nprintf 'link\\n' >> \"$WW_TESTONLY_LTRACE\"\n",
+		"exec \"$WW_TESTONLY_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 packagebad: []str = ["", ""];
+	let importbad: []str = ["", ""];
+	let nulbad: []str = ["", ""];
+	let commentbad: []str = ["", ""];
+	let multibad: []str = ["", ""];
+	let environments: [][]str = alloc([], stages.len: u64)!;
+	let tracecs: []str = alloc([], stages.len: u64)!;
+	let traceas: []str = alloc([], stages.len: u64)!;
+	let tracels: []str = alloc([], stages.len: u64)!;
+	let cwarmbin: str = "";
+	let cwarmartifacts: str = "";
+	let ccompiled: str = "";
+	let ctestasm: str = "";
+	let crawbin: str = "";
+	let baseenv: []str = os.getenvs();
+	let si: i32 = 0;
+	for (si < stages.len) {
+		let ctrace: str = strings.concat(root, "/testonly-c-", tags[si]);
+		let atrace: str = strings.concat(root, "/testonly-a-", tags[si]);
+		let ltrace: str = strings.concat(root, "/testonly-l-", tags[si]);
+		writefile(ctrace, ""); writefile(atrace, ""); writefile(ltrace, "");
+		append(tracecs, ctrace); append(traceas, atrace); append(tracels, ltrace);
+		let env: []str = alloc([], (baseenv.len + 10): u64)!;
+		let ei: i32 = 0;
+		for (ei < baseenv.len) {
+			if (!strings.hasprefix(baseenv[ei], "WW_W6C=")
+				&& !strings.hasprefix(baseenv[ei], "WW_W6A=")
+				&& !strings.hasprefix(baseenv[ei], "WW_W6L=")
+				&& !strings.hasprefix(baseenv[ei], "WW_TESTONLY_")) {
+				append(env, baseenv[ei]);
+			};
+			ei += 1;
+		};
+		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_TESTONLY_CTRACE=", ctrace));
+		append(env, strings.concat("WW_TESTONLY_ATRACE=", atrace));
+		append(env, strings.concat("WW_TESTONLY_LTRACE=", ltrace));
+		append(env, strings.concat("WW_TESTONLY_REAL_C=", driver(compilers[si])));
+		append(env, strings.concat("WW_TESTONLY_REAL_A=", driver(assemblers[si])));
+		append(env, strings.concat("WW_TESTONLY_REAL_L=", driver(linkers[si])));
+		append(environments, env);
+
+		let out: commandout;
+		let unused: str = strings.concat(root, "/unused-", tags[si]);
+		let defaultav: []str = [driver(stages[si]), "build", "-w", unused,
+			ignored];
+		runcommandenv(root, strings.concat("testonly-default-", tags[si]),
+			defaultav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		let defaultoutput: str = strings.concat(source, "/raw_windows_test");
+		let defaultsepwork: str = strings.concat(defaultoutput, ".sepwork");
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !os.exists(unused) && !os.exists(defaultoutput)
+			&& !os.exists(defaultsepwork)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+
+		let asmwork: str = strings.concat(root, "/asm-unused-", tags[si]);
+		let asmav: []str = [driver(stages[si]), "build", "-S", "-w", asmwork,
+			ignored];
+		runcommandenv(root, strings.concat("testonly-assembly-", tags[si]),
+			asmav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && !os.exists(asmwork)
+			&& !os.exists(defaultoutput) && !os.exists(defaultsepwork)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+
+		let nullwork: str = strings.concat(root, "/null-unused-", tags[si]);
+		let nullav: []str = [driver(stages[si]), "build", "-w", nullwork,
+			"-o", "/dev/null", ignored];
+		runcommandenv(root, strings.concat("testonly-null-", tags[si]),
+			nullav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && !os.exists(nullwork)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+
+		let filework: str = strings.concat(root, "/file-unused-", tags[si]);
+		let fileout: str = strings.concat(root, "/file-output-", tags[si]);
+		let fileav: []str = [driver(stages[si]), "build", "-w", filework,
+			"-o", fileout, ignored];
+		runcommandenv(root, strings.concat("testonly-file-", tags[si]),
+			fileav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0 && same(out.stderr, "ww: no packages to build\n")
+			&& !os.exists(filework) && !os.exists(fileout)
+			&& !os.exists(strings.concat(fileout, ".new"))
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+		let fileasmav: []str = [driver(stages[si]), "build", "-S", "-w",
+			filework, "-o", fileout, ignored];
+		runcommandenv(root, strings.concat("testonly-file-assembly-", tags[si]),
+			fileasmav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0 && same(out.stderr, "ww: no packages to build\n")
+			&& !os.exists(filework) && !os.exists(fileout));
+
+		let outputdir: str = strings.concat(root, "/output-dir-", tags[si]);
+		let marker: str = strings.concat(outputdir, "/marker");
+		mkdirall(outputdir); writefile(marker, "caller-owned\n");
+		let dirwork: str = strings.concat(root, "/dir-unused-", tags[si]);
+		let dirav: []str = [driver(stages[si]), "build", "-w", dirwork,
+			"-o", outputdir, ignored];
+		runcommandenv(root, strings.concat("testonly-directory-", tags[si]),
+			dirav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& same(out.stderr, "ww: no main packages to build\n")
+			&& same(readfile(marker), "caller-owned\n") && !os.exists(dirwork));
+		let trailingav: []str = [driver(stages[si]), "build", "-w", dirwork,
+			"-o", strings.concat(outputdir, "/"), ignored];
+		runcommandenv(root, strings.concat("testonly-directory-trailing-", tags[si]),
+			trailingav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& same(out.stderr, "ww: no main packages to build\n")
+			&& same(readfile(marker), "caller-owned\n") && !os.exists(dirwork)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+
+		let badwork: str = strings.concat(root, "/bad-unused-", tags[si]);
+		let badout: str = strings.concat(root, "/bad-output-", tags[si]);
+		let badpackageav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, badpackage];
+		runcommandenv(root, strings.concat("testonly-bad-package-", tags[si]),
+			badpackageav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& has(out.stderr, "invalid or missing package clause\n")
+			&& !has(out.stderr, "no packages to build") && !os.exists(badwork)
+			&& !os.exists(badout) && readfile(ctrace).len == 0
+			&& readfile(atrace).len == 0 && readfile(ltrace).len == 0);
+		packagebad[si] = strings.dup(out.stderr);
+		let badimportav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, badimport];
+		runcommandenv(root, strings.concat("testonly-bad-import-", tags[si]),
+			badimportav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		let importwant: str = strings.concat(badimport,
+			":2:8: error: expected identifier, got ;\n");
+		assert(out.stdout.len == 0 && same(out.stderr, importwant)
+			&& !has(out.stderr, "no packages to build") && !os.exists(badwork)
+			&& !os.exists(badout) && readfile(ctrace).len == 0
+			&& readfile(atrace).len == 0 && readfile(ltrace).len == 0);
+		importbad[si] = strings.dup(out.stderr);
+
+		// Pinned readGoInfo discards the first ordinary body stop byte, even
+		// when it starts malformed UTF-8 or a non-leading BOM. Reached NUL and
+		// unterminated header-trivia comments remain loader errors.
+		let utf8av: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, bodyutf8];
+		runcommandenv(root, strings.concat("testonly-body-utf8-", tags[si]),
+			utf8av, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& same(out.stderr, "ww: no packages to build\n")
+			&& !os.exists(badwork) && !os.exists(badout));
+		let bomav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, bodybom];
+		runcommandenv(root, strings.concat("testonly-body-bom-", tags[si]),
+			bomav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& same(out.stderr, "ww: no packages to build\n")
+			&& !os.exists(badwork) && !os.exists(badout));
+		let nulav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, bodynul];
+		runcommandenv(root, strings.concat("testonly-body-nul-", tags[si]),
+			nulav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		let nulwant: str = strings.concat(bodynul,
+			":2:1: error: invalid NUL character\n");
+		assert(out.stdout.len == 0 && same(out.stderr, nulwant)
+			&& !os.exists(badwork) && !os.exists(badout));
+		nulbad[si] = strings.dup(out.stderr);
+		let commentav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-o", badout, badcomment];
+		runcommandenv(root, strings.concat("testonly-bad-comment-", tags[si]),
+			commentav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		let commentwant: str = strings.concat(badcomment,
+			":2:16: error: unterminated /* comment\n");
+		assert(out.stdout.len == 0 && same(out.stderr, commentwant)
+			&& !os.exists(badwork) && !os.exists(badout)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+		commentbad[si] = strings.dup(out.stderr);
+
+		let spellingwork: str = strings.concat(root, "/spelling-unused-", tags[si]);
+		let platformav: []str = [driver(stages[si]), "build", "-w",
+			spellingwork, platform];
+		runcommandenv(root, strings.concat("testonly-platform-", tags[si]),
+			platformav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && !os.exists(spellingwork));
+		let linkav: []str = [driver(stages[si]), "build", "-w", spellingwork,
+			link];
+		runcommandenv(root, strings.concat("testonly-requested-link-", tags[si]),
+			linkav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && !os.exists(spellingwork)
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0);
+
+		// A directory target remains a directory request despite a test-looking
+		// requested spelling; this is deliberately the one producer-positive row.
+		let linkdirwork: str = strings.concat(root, "/link-dir-work-", tags[si]);
+		let linkdirout: str = strings.concat(root, "/link-dir-output-", tags[si]);
+		mkdirall(linkdirwork);
+		let linkdirav: []str = [driver(stages[si]), "build", "-w", linkdirwork,
+			"-o", linkdirout, dirlink];
+		runcommandenv(root, strings.concat("testonly-directory-link-", tags[si]),
+			linkdirav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		if (si == 0) {
+			expectexit(&out, 0);
+			assert(out.stdout.len == 0 && out.stderr.len == 0
+				&& os.exists(linkdirout) && readfile(ctrace).len != 0
+				&& readfile(atrace).len != 0 && readfile(ltrace).len != 0);
+		} else {
+			// The selected non-directory classifier must not absorb this
+			// pre-existing WWstage resolution difference into the slice.
+			expectexit(&out, 1);
+			assert(out.stdout.len == 0
+				&& same(out.stderr, "ww: cannot read source\n")
+				&& !os.exists(linkdirout) && readfile(ctrace).len == 0
+				&& readfile(atrace).len == 0 && readfile(ltrace).len == 0);
+		};
+		rewritefile(ctrace, ""); rewritefile(atrace, ""); rewritefile(ltrace, "");
+
+		// A valid retained raw source seeds state. Renaming only its requested
+		// basename to test-only must leave all public and private bytes untouched.
+		let warmwork: str = strings.concat(root, "/warm-work-", tags[si]);
+		let warmout: str = strings.concat(root, "/warm-output-", tags[si]);
+		mkdirall(warmwork);
+		let warmav: []str = [driver(stages[si]), "build", "-w", warmwork,
+			"-o", warmout, warmpath];
+		runcommandenv(root, strings.concat("testonly-warm-seed-", tags[si]),
+			warmav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && os.exists(warmout));
+		let warmbin: str = strings.dup(readfile(warmout));
+		let warmtree: str = strings.dup(treesnapshot(warmwork));
+		if (si == 0) {
+			cwarmbin = strings.dup(warmbin);
+			cwarmartifacts = strings.dup(artifacttreesnapshot(warmwork));
+		} else {
+			assert(same(cwarmbin, warmbin)
+				&& same(cwarmartifacts, artifacttreesnapshot(warmwork)));
+		};
+		assert(os.rename(warmpath, warmtest) == 0);
+		rewritefile(ctrace, ""); rewritefile(atrace, ""); rewritefile(ltrace, "");
+		let warmtestav: []str = [driver(stages[si]), "build", "-w", warmwork,
+			"-o", warmout, warmtest];
+		runcommandenv(root, strings.concat("testonly-warm-omit-", tags[si]),
+			warmtestav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0 && same(out.stderr, "ww: no packages to build\n")
+			&& same(warmbin, readfile(warmout)) && !os.exists(strings.concat(warmout, ".new"))
+			&& readfile(ctrace).len == 0 && readfile(atrace).len == 0
+			&& readfile(ltrace).len == 0 && !directoryhasnew(warmwork)
+			&& !directoryhasfragment(warmwork, ".wwtxn.")
+			&& same(warmtree, treesnapshot(warmwork)));
+		if (si == 1) {
+			assert(same(cwarmbin, readfile(warmout))
+				&& same(cwarmartifacts, artifacttreesnapshot(warmwork)));
+		};
+		assert(os.rename(warmtest, warmpath) == 0);
+		runcommandenv(root, strings.concat("testonly-warm-restored-", tags[si]),
+			warmav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& same(warmbin, readfile(warmout)) && !directoryhasnew(warmwork)
+			&& same(warmtree, treesnapshot(warmwork)));
+		if (si == 1) {
+			assert(same(cwarmbin, readfile(warmout))
+				&& same(cwarmartifacts, artifacttreesnapshot(warmwork)));
+		};
+
+		// Test and run keep their existing raw-source semantics, while a visible
+		// non-test raw build and a multi-operand error do not enter this slice.
+		rewritefile(ctrace, ""); rewritefile(atrace, ""); rewritefile(ltrace, "");
+		let testwork: str = strings.concat(root, "/route-work-", tags[si]);
+		mkdirall(testwork);
+		let testav: []str = [driver(stages[si]), "test", "-w", testwork,
+			testroute];
+		runcommandenv(root, strings.concat("testonly-raw-test-", tags[si]),
+			testav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stderr.len == 0 && has(out.stdout, "still_selected ... ok\n")
+			&& readfile(ctrace).len != 0);
+		let compiled: str = strings.concat(root, "/route-compiled-", tags[si]);
+		let compileav: []str = [driver(stages[si]), "test", "-c", "-o", compiled,
+			testroute];
+		runcommandenv(root, strings.concat("testonly-raw-test-compile-", tags[si]),
+			compileav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && os.exists(compiled));
+		let compiledbytes: str = strings.dup(readfile(compiled));
+		if (si == 0) { ccompiled = strings.dup(compiledbytes); }
+		else { assert(same(ccompiled, compiledbytes)); };
+		let testasm: str = strings.concat(root, "/route-assembly-", tags[si]);
+		let testasmav: []str = [driver(stages[si]), "test", "-S", "-o", testasm,
+			testroute];
+		runcommandenv(root, strings.concat("testonly-raw-test-assembly-", tags[si]),
+			testasmav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		let testasmtree: str = strings.concat(testasm, ".sepwork");
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& os.exists(testasmtree));
+		let testasmstate: str = strings.dup(artifacttreesnapshot(testasmtree));
+		if (si == 0) { ctestasm = strings.dup(testasmstate); }
+		else { assert(same(ctestasm, testasmstate)); };
+		let runav: []str = [driver(stages[si]), "run", runsource];
+		runcommandenv(root, strings.concat("testonly-run-", tags[si]), runav,
+			env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 9);
+		let rawout: str = strings.concat(root, "/raw-output-", tags[si]);
+		let rawav: []str = [driver(stages[si]), "build", "-o", rawout, rawmain];
+		runcommandenv(root, strings.concat("testonly-raw-build-", tags[si]),
+			rawav, env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0 && os.exists(rawout));
+		let rawbytes: str = strings.dup(readfile(rawout));
+		if (si == 0) { crawbin = strings.dup(rawbytes); }
+		else { assert(same(crawbin, rawbytes)); };
+		let multiout: str = strings.concat(root, "/multi-output-", tags[si]);
+		rewritefile(ctrace, ""); rewritefile(atrace, ""); rewritefile(ltrace, "");
+		let multiav: []str = [driver(stages[si]), "build", "-o", multiout,
+			rawmain, ignored];
+		runcommandenv(root, strings.concat("testonly-multiple-", tags[si]),
+			multiav, env, (30i64 * (time.second: i64)): time.duration, &out);
+		let multiwant: str = strings.concat(
+			"wwtest package: ", rawmain,
+			": cannot canonicalize package directory\n",
+			"wwtest package: ", ignored,
+			": cannot canonicalize package directory\n");
+		assert(out.termination == exec.termination.EXIT && out.code != 0
+			&& out.stdout.len == 0 && same(out.stderr, multiwant)
+			&& !os.exists(multiout) && readfile(ctrace).len == 0
+			&& readfile(atrace).len == 0 && readfile(ltrace).len == 0);
+		multibad[si] = strings.dup(out.stderr);
+
+		si += 1;
+	};
+	assert(same(packagebad[0], packagebad[1]));
+	assert(same(importbad[0], importbad[1]));
+	assert(same(nulbad[0], nulbad[1]));
+	assert(same(commentbad[0], commentbad[1]));
+	assert(same(multibad[0], multibad[1]));
+
+	// Two simultaneous omitted requests have no work/output collision and no
+	// producer invocation in either stage.
+	let ti: i32 = 0;
+	for (ti < stages.len) {
+		rewritefile(tracecs[ti], "");
+		rewritefile(traceas[ti], "");
+		rewritefile(tracels[ti], "");
+		ti += 1;
+	};
+	let pcwork: str = strings.concat(root, "/parallel-c-unused");
+	let pwwork: str = strings.concat(root, "/parallel-ww-unused");
+	let pcav: []str = [driver("ww"), "build", "-w", pcwork, ignored];
+	let pwav: []str = [driver("ww_ww"), "build", "-w", pwwork, ignored];
+	let pc: exec.command;
+	pc.path = pcav[0]; pc.argv = pcav; pc.env = environments[0]; pc.dir = repo();
+	pc.stdoutpath = strings.concat(root, "/parallel-c.stdout");
+	pc.stderrpath = strings.concat(root, "/parallel-c.stderr");
+	pc.deadline = time.add(time.now(time.clock.monotonic),
+		(30i64 * (time.second: i64)): time.duration);
+	pc.grace = (100i64 * (time.millisecond: i64)): time.duration;
+	let pw: exec.command;
+	pw.path = pwav[0]; pw.argv = pwav; pw.env = environments[1]; pw.dir = repo();
+	pw.stdoutpath = strings.concat(root, "/parallel-ww.stdout");
+	pw.stderrpath = strings.concat(root, "/parallel-ww.stderr");
+	pw.deadline = time.add(time.now(time.clock.monotonic),
+		(30i64 * (time.second: i64)): time.duration);
+	pw.grace = (100i64 * (time.millisecond: i64)): time.duration;
+	let pcp: exec.process;
+	let pwp: exec.process;
+	exec.start(&pcp, &pc); exec.start(&pwp, &pw);
+	let pcdone: bool = false;
+	let pwdone: bool = false;
+	for (!pcdone || !pwdone) {
+		if (!pcdone) { pcdone = exec.poll(&pcp); };
+		if (!pwdone) { pwdone = exec.poll(&pwp); };
+		if (!pcdone || !pwdone) {
+			time.sleep(time.millisecond, time.clock.monotonic);
+		};
+	};
+	assert(pcp.result.errno == 0 && pcp.result.cleanuperrno == 0
+		&& pcp.result.termination == exec.termination.EXIT && pcp.result.code == 0
+		&& pwp.result.errno == 0 && pwp.result.cleanuperrno == 0
+		&& pwp.result.termination == exec.termination.EXIT && pwp.result.code == 0);
+	assert(readfile(pc.stdoutpath).len == 0 && readfile(pc.stderrpath).len == 0
+		&& readfile(pw.stdoutpath).len == 0 && readfile(pw.stderrpath).len == 0
+		&& !os.exists(pcwork) && !os.exists(pwwork));
+	ti = 0;
+	for (ti < stages.len) {
+		assert(readfile(tracecs[ti]).len == 0
+			&& readfile(traceas[ti]).len == 0
+			&& readfile(tracels[ti]).len == 0);
+		ti += 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.
diff --git a/test/tool/wwdump_test.ww b/test/tool/wwdump_test.ww
index 1ef89689..2057a74e 100644
--- a/test/tool/wwdump_test.ww
+++ b/test/tool/wwdump_test.ww
@@ -18,10 +18,11 @@ package wwdump_test;
 // wwdump_ww's exit code is deliberately NOT gated: the diagnostics
 // land on stderr regardless, and the armed bail flips the exit code —
 // the line count is the one signal stable across the fold sequence.
-// #90 sep-feed: `ww build -S` resolves import-bearing fixtures to an
-// owner unit and direct exports; this raw wwdump-only gate explicitly
-// composes those artifacts because wwdump has no package-input CLI. The
-// import-free test/wcc/901_*.ww companions stay raw-fed.
+// #90 sep-feed: `ww build -S` resolves production fixtures and `ww test
+// -S` resolves test fixtures to an owner unit and direct exports; this raw
+// wwdump-only gate explicitly composes those artifacts because wwdump has no
+// package-input CLI. The import-free test/wcc/901_*.ww companions stay
+// raw-fed.
 //
 // wwdumpgate (#52, F15 c4) — the -c and -r arms gate on parse-stage
 // errors instead of silently emitting over a broken AST: parse-errored
@@ -87,18 +88,20 @@ fn countdiag(stderr: str) i32 = {
 		if (seps[i]) {
 			let stem: str = strings.concat(td, "/unit");
 			let bo: testenv.commandout;
-			let bav: []str = [testenv.driver("ww"), "build", "-S", "-o",
+			let action: str = "build";
+			if (strings.hassuffix(rels[i], "_test.ww")) { action = "test"; };
+			let bav: []str = [testenv.driver("ww"), action, "-S", "-o",
 				stem, src];
 			testenv.runcommand(td, td, "resolve", bav, tmo(), &bo);
 			if (bo.termination != exec.termination.EXIT || bo.code != 0) {
 				fail(classes[i], strings.concat(rels[i],
-					": no resolved sep unit (ww build -S failed)"));
+					": no resolved sep unit (ww build/test -S failed)"));
 			};
 			let work: str = strings.concat(stem, ".sepwork/");
 			let owner: str = strings.concat(work, "__root.unit.ww");
 			if (!testenv.exists(owner)) {
 				fail(classes[i], strings.concat(rels[i],
-					": __root.unit.ww missing after ww build -S"));
+					": __root.unit.ww missing after ww build/test -S"));
 			};
 			let deps: []str = [];
 			if (i == 0) { append(deps, "math.checked"); append(deps, "types"); };
diff --git a/test/wcc/200_parse.c b/test/wcc/200_parse.c
index bfdb0dfd..9cbdad2a 100644
--- a/test/wcc/200_parse.c
+++ b/test/wcc/200_parse.c
@@ -100,6 +100,40 @@ imports_to_str(const char *src, int *errs, const char **pkg)
 	return buf;
 }
 
+static char *
+header_to_str(const char *src, size_t len, int *errs, const char **pkg)
+{
+	Arena *a = newarena();
+	Lex l;
+	Parser p;
+	lexinit(&l, a, "header.ww", src, len);
+	parserinit(&p, a, &l);
+	Node *n = parsepackageheader(&p);
+	*errs = p.errs + l.errs;
+	*pkg = n->module ? strdup(n->module) : NULL;
+
+	char *buf = NULL;
+	size_t outlen = 0;
+	FILE *f = open_memstream(&buf, &outlen);
+	if (f != NULL) {
+		astprint(f, n);
+		fclose(f);
+	}
+	freearena(a);
+	return buf;
+}
+
+static int
+header_errors(const char *src)
+{
+	int errs;
+	const char *pkg;
+	char *got = header_to_str(src, strlen(src), &errs, &pkg);
+	free((void *)pkg);
+	free(got);
+	return errs;
+}
+
 static int
 must_import_shape(const char *src, int imports_only, const char *binding,
     const char *path, const char *alias)
@@ -300,6 +334,119 @@ main(void)
 		free((void *)pkg);
 		free(got);
 	}
+	{
+		const char *src =
+		    "package main;\n"
+		    "import zed;\n"
+		    "import stable alpha.beta;\n"
+		    "fn body() void = {};\n";
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(src, strlen(src), &errs, &pkg);
+		if (errs != 0 || pkg == NULL || strcmp(pkg, "main") != 0
+		    || got == NULL || strstr(got, "(use \"zed\"") == NULL
+		    || strstr(got, "(use \"stable\"") == NULL
+		    || strstr(got, "body") != NULL) {
+			fputs("package-header parse mismatch\n", stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	{
+		const char *src =
+		    "package main;\n"
+		    "\xff";
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(src, strlen(src), &errs, &pkg);
+		if (errs != 0 || pkg == NULL || strcmp(pkg, "main") != 0
+		    || got == NULL) {
+			fputs("package-header observed the first malformed UTF-8 body byte\n",
+			    stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	{
+		const char src[] =
+		    "package main;\n"
+		    "import alpha;\n"
+		    "\xef\xbb\xbf";
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(src, sizeof src - 1, &errs, &pkg);
+		if (errs != 0 || pkg == NULL || strcmp(pkg, "main") != 0
+		    || got == NULL || strstr(got, "(use \"alpha\"") == NULL) {
+			fputs("package-header observed the first body BOM\n", stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	{
+		const char src[] = "package main;\n\0fn body() void = {};\n";
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(src, sizeof src - 1, &errs, &pkg);
+		if (errs == 0) {
+			fputs("package-header ignored a reached NUL boundary byte\n",
+			    stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	if (header_errors("package main;\n/* unterminated") == 0) {
+		fputs("package-header accepted unterminated header trivia\n", stderr);
+		fail++;
+	}
+	{
+		const char *src =
+		    "package main;\n"
+		    "/* between */ import alpha; // after\n"
+		    "import beta;\n"
+		    "\xff";
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(src, strlen(src), &errs, &pkg);
+		if (errs != 0 || got == NULL
+		    || strstr(got, "(use \"alpha\"") == NULL
+		    || strstr(got, "(use \"beta\"") == NULL) {
+			fputs("package-header comment/import boundary mismatch\n", stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	{
+		int errs;
+		const char *pkg;
+		char *got = header_to_str(
+		    "package main;\nimported body;\nimport late;\n",
+		    strlen("package main;\nimported body;\nimport late;\n"),
+		    &errs, &pkg);
+		if (errs != 0 || got == NULL || strstr(got, "late") != NULL) {
+			fputs("package-header mistook an ordinary identifier for import\n",
+			    stderr);
+			fail++;
+		}
+		free((void *)pkg);
+		free(got);
+	}
+	if (header_errors("package ;\n") == 0) {
+		fputs("package-header accepted a malformed package clause\n", stderr);
+		fail++;
+	}
+	if (header_errors("package main;\nimport ;\n") == 0) {
+		fputs("package-header accepted a malformed import\n", stderr);
+		fail++;
+	}
+	if (header_errors("package main\nfn body() void = {};\n") == 0) {
+		fputs("package-header accepted a missing package semicolon\n", stderr);
+		fail++;
+	}
 	{
 		int errs;
 		const char *pkg;
@@ -333,6 +480,6 @@ main(void)
 		fprintf(stderr, "%d parse tests failed\n", fail);
 		return 1;
 	}
-	printf("parse: %d/%d ok + 14 shape ok\n", n, n);
+	printf("parse: %d/%d ok + 14 shape + 10 header ok\n", n, n);
 	return 0;
 }