diff --git a/cmd/wcc/lex.c b/cmd/wcc/lex.c
index 1a89c5a0..31c5acb5 100644
--- a/cmd/wcc/lex.c
+++ b/cmd/wcc/lex.c
@@ -34,38 +34,91 @@ lexinit(Lex *l, Arena *a, const char *file, const char *src, u64 len)
 	}
 }
 
+static void
+lskipnul(Lex *l)
+{
+	while (l->pos < l->srclen && l->src[l->pos] == '\0') {
+		Pos p = { l->file, l->line, l->col };
+		l->pos++;
+		l->col++;
+		errorf(p, "invalid NUL character");
+		l->errs++;
+		l->nulcount++;
+	}
+}
+
+/* Return the raw offset of a logical byte lookahead. Raw NUL bytes do not
+ * occupy a slot in the token stream: Go's source.nextch diagnoses them and
+ * immediately resumes decoding at the following character. */
+static u64
+lrawoff(Lex *l, u64 ahead)
+{
+	u64 p = l->pos;
+	for (;;) {
+		while (p < l->srclen && l->src[p] == '\0')
+			p++;
+		if (ahead == 0 || p >= l->srclen)
+			return p;
+		p++;
+		ahead--;
+	}
+}
+
 static int
 lpeek(Lex *l, u64 ahead)
 {
-	u64 p = l->pos + ahead;
-	if (p >= l->srclen)
-		return -1;
-	if (bomat(l->src, l->srclen, p))
-		return 0xfeff;
-	return (unsigned char)l->src[p];
+	/* Drain NUL at the current decoder position even when it is followed by
+	 * EOF; otherwise a trailing NUL could disappear without a diagnostic. */
+	for (;;) {
+		if (l->pos >= l->srclen)
+			return -1;
+		int c = (unsigned char)l->src[l->pos];
+		if (c == 0) {
+			lskipnul(l);
+			continue;
+		}
+		if (ahead == 0) {
+			if (bomat(l->src, l->srclen, l->pos))
+				return 0xfeff;
+			return c;
+		}
+		u64 p = lrawoff(l, ahead);
+		if (p >= l->srclen)
+			return -1;
+		if (bomat(l->src, l->srclen, p))
+			return 0xfeff;
+		return (unsigned char)l->src[p];
+	}
 }
 
 static int
 lget(Lex *l)
 {
-	if (l->pos >= l->srclen)
-		return -1;
-	if (bomat(l->src, l->srclen, l->pos)) {
-		Pos p = { l->file, l->line, l->col };
-		l->pos += 3;
-		l->col += 3;
-		errorf(p, "invalid BOM in the middle of the file");
-		l->errs++;
-		return 0xfeff;
+	for (;;) {
+		if (l->pos >= l->srclen)
+			return -1;
+		int c = (unsigned char)l->src[l->pos];
+		if (c == 0) {
+			lskipnul(l);
+			continue;
+		}
+		if (bomat(l->src, l->srclen, l->pos)) {
+			Pos p = { l->file, l->line, l->col };
+			l->pos += 3;
+			l->col += 3;
+			errorf(p, "invalid BOM in the middle of the file");
+			l->errs++;
+			return 0xfeff;
+		}
+		l->pos++;
+		if (c == '\n') {
+			l->line++;
+			l->col = 1;
+		} else {
+			l->col++;
+		}
+		return c;
 	}
-	int c = (unsigned char)l->src[l->pos++];
-	if (c == '\n') {
-		l->line++;
-		l->col = 1;
-	} else {
-		l->col++;
-	}
-	return c;
 }
 
 static Pos
@@ -75,6 +128,22 @@ lpos(Lex *l)
 	return p;
 }
 
+/* Copy one raw source span into token text while omitting diagnosed NUL
+ * bytes. This keeps keyword, numeric, suffix, and directive recovery on the
+ * same logical character stream as lpeek/lget. */
+static char *
+lexspan(Lex *l, u64 begin, u64 end, u64 *len)
+{
+	char *s = amalloc(l->a, end - begin + 1);
+	u64 j = 0;
+	for (u64 i = begin; i < end; i++)
+		if (l->src[i] != '\0')
+			s[j++] = l->src[i];
+	s[j] = '\0';
+	*len = j;
+	return s;
+}
+
 static int
 isidstart(int c)
 {
@@ -94,6 +163,70 @@ ishex(int c)
 	    (c >= 'A' && c <= 'F');
 }
 
+/* Consume one // body, then classify the driver's internal module directive
+ * from its logical (NUL-filtered) text. Keeping a single moving lexer cursor
+ * makes even long generated module paths linear rather than repeatedly
+ * rescanning from the start of the comment. The trailing newline remains for
+ * the ordinary whitespace loop. */
+static void
+linecomment(Lex *l)
+{
+	u64 begin = l->pos;
+	u64 nulbegin = l->nulcount;
+	int c;
+	while ((c = lpeek(l, 0)) >= 0 && c != '\n')
+		lget(l);
+	u64 end = l->pos;
+	u64 n;
+	const char *body;
+	if (l->nulcount == nulbegin) {
+		n = end - begin;
+		body = l->src + begin;
+	} else {
+		body = lexspan(l, begin, end, &n);
+	}
+
+	static const char pre[] = "ww:module";
+	const u64 plen = sizeof pre - 1;
+	if (n < plen || memcmp(body, pre, plen) != 0 || n == plen)
+		return;
+	u64 i = plen;
+	if (body[i] == '-') {
+		static const char rest[] = "-reset";
+		const u64 rlen = sizeof rest - 1;
+		if (n - i < rlen || memcmp(body + i, rest, rlen) != 0)
+			return;
+		i += rlen;
+		if (i == n) {
+			l->modreset = 1;
+			l->modpath = NULL;	/* #9: reset supersedes a pending path */
+			return;
+		}
+		if (body[i] != ' ' && body[i] != '\t')
+			return;
+		while (i < n && (body[i] == ' ' || body[i] == '\t'))
+			i++;
+		u64 s = i;
+		while (i < n && body[i] != '\r' && body[i] != ' '
+		    && body[i] != '\t')
+			i++;
+		l->modreset = 1;
+		l->modpath = NULL;	/* #9: see above */
+		if (i > s)
+			l->modresetpath = astrndup(l->a, body + s, i - s);
+		return;
+	}
+	if (body[i] != ' ' && body[i] != '\t')
+		return;
+	while (i < n && (body[i] == ' ' || body[i] == '\t'))
+		i++;
+	u64 s = i;
+	while (i < n && body[i] != '\r' && body[i] != ' ' && body[i] != '\t')
+		i++;
+	if (i > s)
+		l->modpath = astrndup(l->a, body + s, i - s);
+}
+
 static int
 skipws(Lex *l)
 {
@@ -107,78 +240,9 @@ skipws(Lex *l)
 		}
 		if (c == '/' && lpeek(l, 1) == '/') {
 			lget(l); lget(l);
-			/* #16 option-B: the driver emits `//ww:module-reset`
-			 * before a package-less file's bytes; recognize the
-			 * whole-line directive (without consuming differently)
-			 * and flag it so lexnext emits TK_MODRESET. The body is
-			 * then skipped like any comment. Mirrors the removed
-			 * `// MODULE:` lexer directive. */
-			{
-				static const char pre[] = "ww:module";
-				size_t i = 0;
-				while (pre[i] && lpeek(l, i) == pre[i])
-					i++;
-				if (pre[i] == '\0') {
-					int nx = lpeek(l, i);
-					if (nx == '-') {
-						static const char rest[] = "-reset";
-						size_t j = 0;
-						while (rest[j] && lpeek(l, i + j) == rest[j])
-							j++;
-						if (rest[j] == '\0') {
-							int af = lpeek(l, i + j);
-							if (af == '\n' || af < 0) {
-								l->modreset = 1;
-								l->modpath = NULL;	/* #9: a reset supersedes a path opened
-											 * earlier in this skipws run (empty/
-											 * export-less inlined module body) */
-							} else if (af == ' '
-							    || af == '\t') {
-								/* `//ww:module-reset <path>`
-								 * — sep primary body tagged by
-								 * its full dotted import path so
-								 * definer == importer (#57). */
-								size_t k = i + j;
-								while (lpeek(l, k) == ' '
-								    || lpeek(l, k) == '\t')
-									k++;
-								size_t s = k;
-								int dch;
-								while ((dch = lpeek(l, k)) >= 0
-								    && dch != '\n'
-								    && dch != '\r'
-								    && dch != ' '
-								    && dch != '\t')
-									k++;
-								l->modreset = 1;
-								l->modpath = NULL;	/* #9: see above — clear pending path */
-								if (k > s)
-									l->modresetpath =
-									    astrndup(l->a,
-									    l->src + l->pos + s,
-									    k - s);
-							}
-						}
-					} else if (nx == ' ' || nx == '\t') {
-						/* `//ww:module <path>` — M1 import boundary. */
-						size_t k = i;
-						while (lpeek(l, k) == ' '
-						    || lpeek(l, k) == '\t')
-							k++;
-						size_t s = k;
-						int ch;
-						while ((ch = lpeek(l, k)) >= 0
-						    && ch != '\n' && ch != '\r'
-						    && ch != ' ' && ch != '\t')
-							k++;
-						if (k > s)
-							l->modpath = astrndup(l->a,
-							    l->src + l->pos + s, k - s);
-					}
-				}
-			}
-			while ((c = lpeek(l, 0)) >= 0 && c != '\n')
-				lget(l);
+			/* #16 option-B: classify the driver's whole-line internal
+			 * module boundary after consuming it once. */
+			linecomment(l);
 			continue;
 		}
 		if (c == '/' && lpeek(l, 1) == '*') {
@@ -318,11 +382,38 @@ escape(Lex *l, int *out)
 	return -1;
 }
 
+static const char *
+lextypesuffix(Lex *l, u64 *len)
+{
+	char got[4];
+	u64 n = 0;
+	while (n < sizeof got && isidcont(lpeek(l, n))) {
+		got[n] = (char)lpeek(l, n);
+		n++;
+	}
+	if (n == 0 || n > 3 || isidcont(lpeek(l, n)))
+		return NULL;
+	static const char *const names[] = {
+		"i8", "i16", "i32", "i64",
+		"u8", "u16", "u32", "u64",
+		"f32", "f64", NULL
+	};
+	for (int i = 0; names[i]; i++) {
+		u64 nl = strlen(names[i]);
+		if (nl == n && memcmp(names[i], got, n) == 0) {
+			*len = n;
+			return names[i];
+		}
+	}
+	return NULL;
+}
+
 static Tok
 lexnum(Lex *l, Pos start)
 {
 	Tok t = (Tok){ TK_INT, start, NULL, 0, {0}, TK_NONE };
 	u64 begin = l->pos;
+	u64 nulbegin = l->nulcount;
 	int base = 10;
 	int isfloat = 0;
 	int c = lpeek(l, 0);
@@ -361,8 +452,14 @@ lexnum(Lex *l, Pos start)
 		}
 	}
 
-	u64 n = l->pos - begin;
-	t.text = astrndup(l->a, l->src + begin, n);
+	u64 rawend = l->pos;
+	u64 n;
+	if (l->nulcount == nulbegin) {
+		n = rawend - begin;
+		t.text = astrndup(l->a, l->src + begin, n);
+	} else {
+		t.text = lexspan(l, begin, rawend, &n);
+	}
 	t.tlen = n;
 
 	if (isfloat) {
@@ -371,8 +468,8 @@ lexnum(Lex *l, Pos start)
 		char *clean = amalloc(l->a, n + 1);
 		u64 j = 0;
 		for (u64 i = 0; i < n; i++)
-			if (l->src[begin + i] != '_')
-				clean[j++] = l->src[begin + i];
+			if (t.text[i] != '_')
+				clean[j++] = t.text[i];
 		clean[j] = '\0';
 		errno = 0;
 		t.v.fval = strtod(clean, NULL);
@@ -381,7 +478,7 @@ lexnum(Lex *l, Pos start)
 			l->errs++;
 		}
 	} else {
-		const char *digs = l->src + begin;
+		const char *digs = t.text;
 		u64 dn = n;
 		if (base != 10) {
 			digs += 2;
@@ -398,28 +495,12 @@ lexnum(Lex *l, Pos start)
 
 	/* A typed suffix must be glued (no whitespace) to the digits. */
 	if (isidstart(lpeek(l, 0))) {
-		u64 sb = l->pos;
-		i32 sc = l->col;
-		while (isidcont(lpeek(l, 0))) lget(l);
-		u64 sl = l->pos - sb;
-		const char *names[] = {
-			"i8", "i16", "i32", "i64",
-			"u8", "u16", "u32", "u64",
-			"f32", "f64", NULL
-		};
-		const char *match = NULL;
-		for (int i = 0; names[i]; i++) {
-			u64 nl = strlen(names[i]);
-			if (nl == sl && memcmp(names[i], l->src + sb, nl) == 0) {
-				match = names[i];
-				break;
-			}
-		}
+		u64 sl;
+		const char *match = lextypesuffix(l, &sl);
 		if (match) {
-			t.tsuffix = astrndup(l->a, l->src + sb, sl);
-		} else {
-			l->pos = sb;
-			l->col = sc;
+			for (u64 i = 0; i < sl; i++)
+				lget(l);
+			t.tsuffix = astrndup(l->a, match, sl);
 		}
 	}
 	return t;
@@ -429,18 +510,27 @@ static Tok
 lexident(Lex *l, Pos start)
 {
 	u64 begin = l->pos;
+	u64 nulbegin = l->nulcount;
 	while (isidcont(lpeek(l, 0)))
 		lget(l);
-	u64 n = l->pos - begin;
-	const char *p = l->src + begin;
+	u64 n;
+	const char *p;
+	int filtered = l->nulcount != nulbegin;
+	if (!filtered) {
+		n = l->pos - begin;
+		p = l->src + begin;
+	} else {
+		p = lexspan(l, begin, l->pos, &n);
+	}
+	char *text = filtered ? (char *)p : astrndup(l->a, p, n);
 	/* bare '_' is the discard marker. `_x`, `_1` are normal idents. */
 	if (n == 1 && p[0] == '_') {
-		Tok t = (Tok){ TK_UNDER, start, astrndup(l->a, p, n), n, {0}, TK_NONE };
+		Tok t = (Tok){ TK_UNDER, start, text, n, {0}, TK_NONE };
 		return t;
 	}
 	Tkind k = kwlookup(p, n);
 	Tok t = (Tok){ k != TK_NONE ? k : TK_IDENT, start,
-	    astrndup(l->a, p, n), n, {0}, TK_NONE };
+	    text, n, {0}, TK_NONE };
 	return t;
 }
 
diff --git a/cmd/wcc/ww.h b/cmd/wcc/ww.h
index 0fd38ec3..af63ea68 100644
--- a/cmd/wcc/ww.h
+++ b/cmd/wcc/ww.h
@@ -202,6 +202,7 @@ struct Lex {
 	i32	col;
 	Arena	*a;		/* token-text arena */
 	int	errs;
+	u64	nulcount;	/* raw NUL bytes diagnosed by the source decoder */
 	int	modreset;	/* a `//ww:module-reset` directive was seen in
 				 * the last skipped run; lexnext emits TK_MODRESET
 				 * before the next real token. */
diff --git a/docs/build-system.md b/docs/build-system.md
index dbd43d02..a7012d31 100644
--- a/docs/build-system.md
+++ b/docs/build-system.md
@@ -8545,6 +8545,119 @@ and diagnostic text is not a persisted-byte contract.  Build workdir format
 remains `18`, test workdir format remains `19`, and semantic storage format
 remains `3`.
 
+### 11.43 Implemented selected-source U+0000 rejection
+
+Every selected physical `.ww` source rejects a raw byte `00` (U+0000) at its
+physical line and byte column with exactly `invalid NUL character`. The rule is
+source-wide: comments, interpreted-string text, rune text, and between-token
+positions cannot turn a raw NUL into payload. An escape spelling such as
+`\x00` remains a legal literal value because it is not byte `00` in
+the source file. This section is only the raw-U+0000 rule: malformed UTF-8
+and the independently implemented per-source BOM boundary in §11.42 are not
+changed or broadened here.
+
+#### Pinned evidence, applicability, and measured prior behavior
+
+The sole authority is official Go 1.26.5 at
+`c19862e5f8415b4f24b189d065ed739517c548ba`. Its compiler owner,
+`(*source).nextch` in
+[`cmd/compile/internal/syntax/source.go`, lines 113–165](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/compile/internal/syntax/source.go#L113-L165),
+detects ASCII zero at lines 121–129, reports `invalid NUL character`, and
+continues decoding. `TestScanErrors` pins the positioned diagnostic at
+[`cmd/compile/internal/syntax/scanner_test.go`, lines 587–600](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/compile/internal/syntax/scanner_test.go#L587-L600),
+and compiler testdata [`test/nul1.go`, lines 7–52](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/test/nul1.go#L7-L52)
+requires NUL errors in strings, raw strings, line/block comments, and ordinary
+source. Go's independent public scanner has the same rule in
+[`go/scanner/scanner.go`, lines 63–108](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/scanner/scanner.go#L63-L108)
+and its tests at lines 790–819. These are **behavior directly implemented or
+asserted by pinned Go**.
+
+Before this change, directly measured Cstage and WWstage package builds both
+accepted a NUL in a line comment, wrote it into the committed synthetic unit,
+published byte-identical archive/interface products, and allowed a dotted local
+importer to link and run. The retained audit commands used `out/bin/ww` and
+`out/bin/ww_ww` with `WW_SRCLIB=/home/kimchi/src/ww/lib` over
+`/tmp/ww-pkgaudit.qtjcpO/src/nulcomment`; both exited zero with empty streams.
+The same acceptance applied to raw NUL in strings and runes. Those observations
+are **directly measured WW behavior**. Applying pinned Go's physical-source
+rule independently to WW's selected files is **behavior derived from the
+pinned implementation** and is applicable without importing Go's module,
+manifest, registry, lock, cache, database, CAS, network, generalized-import,
+or source-level build-expression model.
+
+#### Ownership, timing, and four axes
+
+The direct-frontend semantic owners are the logical source-decoder helpers in
+`cmd/wcc/lex.c` and their exact twins in `lib/ww/syntax/lex.ww`: each raw zero
+is consumed, reports the same positioned error, and is omitted before token
+recovery. Filtered token spans preserve that decoder rule through identifiers,
+numbers and suffixes, directives, escapes, operators, comments, and EOF. The
+line-comment decoder consumes each body once before classifying an internal
+module directive, so NUL filtering does not make generated path handling
+superlinear. The
+shared `internal/wwpackage/package.ww` coordinator owns public package/test
+diagnostic precedence: its length-aware preflight reports every raw NUL in an
+invalid physical source before its manual package-clause classifier. It is not
+another identity policy. Driver source slurping and synthetic-unit composition
+preserve byte lengths and are not semantic owners.
+
+- **Go-like build:** after fixed-target filename selection, an invalid selected
+  root or dependency rejects during loading, before graph completion and before
+  compiler, assembler, archiver, linker, install, publication, or execution.
+  Source rejection in a root precedes resolution of that root's missing
+  imports. A wrong-target file is excluded before this rule and remains unread
+  by its semantic owners.
+- **Go-like test:** selected production, same-package, external-package, and
+  test-only source each receive the rule before variant construction. Failure
+  emits the established attributable `FAIL\n` without a generated main, test
+  process, accounting, `ok` result, retained binary, or public test product.
+- **Go-like package:** each selected physical file owns its diagnostic and
+  position. Declared package name, source role, package conflict handling,
+  command/test family, physical directory, and exact canonical dotted identity
+  are unchanged.
+- **Go-like import:** invalid bytes create no import edge or graph node. Valid
+  import spelling, aliases, local/vendor/internal resolution, visibility,
+  cycle handling, and initialization order remain unchanged.
+
+Thus raw NUL is never an input to manifest-free package identity, graph/action
+keys, symbols, `.wwi`, archive naming, publication names, or persistence keys.
+It neither changes local dotted-import boundaries nor introduces a manifest.
+
+#### Failure, publication, persistence, and parity
+
+Cold invalid requests create no unit, assembly, object, archive, executable,
+capture, `.new`, `.install`, `.wwtxn.*`, or public output. A warm edit that
+introduces NUL stops before a producer or install action, preserving the prior
+committed unit/interface/assembly/object/archive generation, tool vouchers,
+stamp, and public output byte for byte. Removing the NUL restores the ordinary
+selected-source fingerprint; exact restoration may reuse the earlier generation.
+Existing producer/runtime failure and transaction rollback remain their own
+owners because this branch creates no new rollback mechanism.
+
+Lexer and coordinator state are request/source-local. Concurrent valid and
+invalid requests keep independent workdirs, captures, diagnostics, and
+products; an invalid request cannot contaminate a valid sibling. The rule adds
+no process, wait, or cancellation boundary, so signal, timeout, interruption,
+process-group cleanup, and ordinary scratch cleanup retain their established
+owners. Validation itself leaves no durable residue. Cstage and WWstage are
+semantic twins: diagnostics match exactly, and valid unit/compiler/product
+bytes retain their existing byte-identity contract.
+
+`raw_nul_is_rejected_in_every_selected_source` in
+`test/package/package_test.ww`, with focused C and WW lexer coverage, proves
+literal and comment contexts plus adjacency recovery across escapes,
+identifiers, numbers and typed suffixes, operators, comment delimiters, and
+EOF; it also proves selected/imported builds, wrong-target exclusion, every
+directory-test source role, precedence, cold cleanup, warm rollback and reuse,
+concurrent isolation, valid escaped-NUL behavior, runtime/publication behavior,
+and no-residue/parity observations.
+
+No format bump. This changes invalid-source acceptance and diagnostics only;
+valid source composition and valid `.wwi`, assembly, object, archive,
+executable, and retained-test-product bytes are unchanged. 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 60eaf3c4..e962488e 100644
--- a/docs/spec.md
+++ b/docs/spec.md
@@ -60,6 +60,16 @@ every other source position, including inside string and rune literals and
 comments. Apart from that marker rule, the lexer operates on bytes and
 non-ASCII bytes are legal only inside string and rune literals and comments.
 
+Each raw byte `00` (U+0000) is invalid at every physical source position,
+including in comments and string or rune literal text. It produces one
+positioned `invalid NUL character` error at that byte's source position and
+is omitted from the lexer's logical character stream before token recovery.
+It therefore cannot split an identifier, number, operator, escape, or comment
+boundary into different tokens. This is a source-representation rule, before
+package/import interpretation; it does not make U+0000 a package, import, or
+artifact identity component. An escape spelling such as `"\\x00"` is not a
+raw source byte and remains a legal literal value.
+
 ### 2.2 Comments
 
 Line comments only, introduced by `//` and running to end of line. There
diff --git a/docs/test-system-v2.md b/docs/test-system-v2.md
index 08addab2..53613e20 100644
--- a/docs/test-system-v2.md
+++ b/docs/test-system-v2.md
@@ -429,6 +429,26 @@ before either operation. The marker is source representation only and never
 package/import/action/artifact/publication/persistence identity; no test result
 is cached.
 
+After filename eligibility and before package-clause classification, each raw
+source byte `00` in a selected production, same-package test,
+external-package test, or test-only source is one positioned
+`invalid NUL character` error. Comments and literal text do not hide it. The
+shared coordinator owns that early package/test rejection and reports every
+raw NUL in the invalid physical source. On complete direct
+frontend inputs, the C and WW source decoders diagnose each raw NUL and omit it
+from their logical character streams before token recovery. Thus a NUL cannot
+split an escape, identifier, number or suffix, operator, comment delimiter, or
+EOF boundary into a stage-dependent second error. Test loading maintains a
+stage-equal source-diagnostic stream before import discovery, graph actions,
+producers, test execution, accounting, result output, or retained publication.
+An invalid selected test request emits only the existing attributable
+`FAIL\n`; it does not construct a variant, generated main, test child, or new
+persistent generation. Wrong-target exclusion remains first, so an excluded
+file with a raw NUL has no diagnostic or persistence effect. A `\\x00` escape
+remains a valid literal value. This rule is limited to raw U+0000; malformed
+UTF-8 and the independent per-source BOM rule retain their existing, separate
+contracts.
+
 After that eligibility boundary and the coordinator's required package-clause
 classification and production `@test` validation parses, the delegated loader
 performs selected-basename Go 1.26.5 simple-fold preflight before its graph
diff --git a/internal/wwpackage/package.ww b/internal/wwpackage/package.ww
index d24dd37f..01f68563 100644
--- a/internal/wwpackage/package.ww
+++ b/internal/wwpackage/package.ww
@@ -624,6 +624,16 @@ fn pkgfailpath(path: str, reason: str) void = {
 	pkgputln(os.STDERR_FILENO, reason);
 };
 
+fn pkgfailsource(path: str, line: i32, col: i32, reason: str) void = {
+	pkgput(os.STDERR_FILENO, path);
+	pkgput(os.STDERR_FILENO, ":");
+	pkgput(os.STDERR_FILENO, strconv.i32tos(line, strconv.base.DEC));
+	pkgput(os.STDERR_FILENO, ":");
+	pkgput(os.STDERR_FILENO, strconv.i32tos(col, strconv.base.DEC));
+	pkgput(os.STDERR_FILENO, ": error: ");
+	pkgputln(os.STDERR_FILENO, reason);
+};
+
 fn pkgusage() void = {
 	pkgput(os.STDERR_FILENO,
 		"usage: wwtest package [-c] [-S] [-list] [-j N] [-I DIR] [-L DIR] [-l LIB] [-w DIR] [-run|-filter GLOB] [-timeout-ms=N] [DIR | DIR/... ...] [-- GLOB ...]\n");
@@ -689,6 +699,27 @@ fn pkgident(c: u8) bool = {
 	return c >= '0' && c <= '9';
 };
 
+fn pkgnulerrors(path: str, src: str) bool = {
+	let i: i32 = 0;
+	let ln: i32 = 1;
+	let cl: i32 = 1;
+	let found: bool = false;
+	for (i < src.len) {
+		if (src[i] == 0u8) {
+			pkgfailsource(path, ln, cl, "invalid NUL character");
+			found = true;
+		};
+		if (src[i] == '\n') {
+			ln += 1;
+			cl = 1;
+		} else {
+			cl += 1;
+		};
+		i += 1;
+	};
+	return found;
+};
+
 fn pkgskipspace(src: str, start: i32) i32 = {
 	let i: i32 = start;
 	for (i < src.len) {
@@ -2260,7 +2291,14 @@ export fn packagecommand(args: []str) int = {
 		};
 		let body: str;
 		let pn: str;
-		if (!pkgread(ds.paths[i], &body) || !pkgclause(body, &pn)) {
+		if (!pkgread(ds.paths[i], &body)) {
+			pkgfailpath(ds.paths[i], "invalid or missing package clause");
+			return pkgteststatusfail(explicitstatus, compileonly);
+		};
+		if (pkgnulerrors(ds.paths[i], body)) {
+			return pkgteststatusfail(explicitstatus, compileonly);
+		};
+		if (!pkgclause(body, &pn)) {
 			pkgfailpath(ds.paths[i], "invalid or missing package clause");
 			return pkgteststatusfail(explicitstatus, compileonly);
 		};
diff --git a/lib/ww/syntax/lex.ww b/lib/ww/syntax/lex.ww
index 1103e42f..b424d3dc 100644
--- a/lib/ww/syntax/lex.ww
+++ b/lib/ww/syntax/lex.ww
@@ -51,6 +51,7 @@ export type lex = struct {
 	line:   i32,
 	col:    i32,
 	errs:   i32,
+	nulcount: u64,
 	// a `//ww:module-reset` directive was seen in the last skipped run;
 	// lexnext emits TK_MODRESET before the next real token (#16 opt-B).
 	modreset: i32,
@@ -81,6 +82,7 @@ export fn lexinit(l: *lex, file: str, src: *u8, len: u64) void = {
 	l.line = 1;
 	l.col = 1;
 	l.errs = 0;
+	l.nulcount = 0u64;
 	l.modreset = 0;
 	l.modpathset = 0;
 	l.modresetpathset = 0;
@@ -95,34 +97,101 @@ fn srcb(l: *lex, off: u64) i32 = {
 	return b: i32;
 };
 
+fn lskipnul(l: *lex) void = {
+	for (l.lpos < l.srclen) {
+		if (srcb(l, l.lpos) != 0) { break; };
+		let np: pos;
+		np.file = l.file;
+		np.line = l.line;
+		np.col = l.col;
+		l.lpos += 1u64;
+		l.col += 1;
+		errat(l, &np, "invalid NUL character");
+		l.nulcount += 1u64;
+	};
+};
+
+// Return the raw offset of a logical byte lookahead. Raw NUL bytes do not
+// occupy a slot in the token stream: Go's source.nextch diagnoses them and
+// immediately resumes decoding at the following character.
+fn lrawoff(l: *lex, ahead0: u64) u64 = {
+	let p: u64 = l.lpos;
+	let ahead: u64 = ahead0;
+	for (true) {
+		for (p < l.srclen) {
+			if (srcb(l, p) != 0) { break; };
+			p += 1u64;
+		};
+		if (ahead == 0u64 || p >= l.srclen) { return p; };
+		p += 1u64;
+		ahead -= 1u64;
+	};
+};
+
 fn lpeek(l: *lex, ahead: u64) i32 = {
-	let p: u64 = l.lpos + ahead;
-	if (p >= l.srclen) { return -1; };
-	if (bomat(l.src, l.srclen, p)) { return 0xFEFF; };
-	return srcb(l, p);
+	// Drain NUL at the current decoder position even when it is followed by
+	// EOF; otherwise a trailing NUL could disappear without a diagnostic.
+	for (true) {
+		if (l.lpos >= l.srclen) { return -1; };
+		let c: i32 = srcb(l, l.lpos);
+		if (c == 0) { lskipnul(l); continue; };
+		if (ahead == 0u64) {
+			if (bomat(l.src, l.srclen, l.lpos)) { return 0xFEFF; };
+			return c;
+		};
+		let p: u64 = lrawoff(l, ahead);
+		if (p >= l.srclen) { return -1; };
+		if (bomat(l.src, l.srclen, p)) { return 0xFEFF; };
+		return srcb(l, p);
+	};
 };
 
 fn lget(l: *lex) i32 = {
-	if (l.lpos >= l.srclen) { return -1; };
-	if (bomat(l.src, l.srclen, l.lpos)) {
-		let bp: pos;
-		bp.file = l.file;
-		bp.line = l.line;
-		bp.col = l.col;
-		l.lpos += 3u64;
-		l.col += 3;
-		errat(l, &bp, "invalid BOM in the middle of the file");
-		return 0xFEFF;
+	for (true) {
+		if (l.lpos >= l.srclen) { return -1; };
+		let c: i32 = srcb(l, l.lpos);
+		if (c == 0) { lskipnul(l); continue; };
+		if (bomat(l.src, l.srclen, l.lpos)) {
+			let bp: pos;
+			bp.file = l.file;
+			bp.line = l.line;
+			bp.col = l.col;
+			l.lpos += 3u64;
+			l.col += 3;
+			errat(l, &bp, "invalid BOM in the middle of the file");
+			return 0xFEFF;
+		};
+		l.lpos += 1u64;
+		if (c == '\n') {
+			l.line += 1;
+			l.col = 1;
+		} else {
+			l.col += 1;
+		};
+		return c;
 	};
-	let c: i32 = srcb(l, l.lpos);
-	l.lpos += 1u64;
-	if (c == '\n') {
-		l.line += 1;
-		l.col = 1;
-	} else {
-		l.col += 1;
+};
+
+// Copy one raw source span into token text while omitting diagnosed NUL
+// bytes. This keeps keyword, numeric, suffix, and directive recovery on the
+// same logical character stream as lpeek/lget.
+fn lexspan(l: *lex, begin: u64, end: u64) str = {
+	let buf: []u8 = alloc([], end - begin + 1u64)!;
+	let i: u64 = begin;
+	let j: u64 = 0u64;
+	for (i < end) {
+		let b: i32 = srcb(l, i);
+		if (b != 0) {
+			buf[j] = b: u8;
+			j += 1u64;
+		};
+		i += 1u64;
 	};
-	return c;
+	buf[j] = 0u8;
+	let out: str;
+	out.ptr = buf.ptr;
+	out.len = j: i32;
+	return out;
 };
 
 fn curpos(l: *lex, out: *pos) void = {
@@ -146,6 +215,81 @@ fn errat(l: *lex, p: *pos, msg: str) void = {
 	l.errs += 1;
 };
 
+// Consume one // body, then classify the driver's internal module directive
+// from its logical (NUL-filtered) text. A single moving lexer cursor keeps long
+// generated module paths linear. The trailing newline remains for skipws.
+fn linecomment(l: *lex) void = {
+	let begin: u64 = l.lpos;
+	let nulbegin: u64 = l.nulcount;
+	for (true) {
+		let c: i32 = lpeek(l, 0u64);
+		if (c < 0 || c == '\n') { break; };
+		lget(l);
+	};
+	let end: u64 = l.lpos;
+	let body: str;
+	if (l.nulcount == nulbegin) {
+		body.ptr = l.src + begin;
+		body.len = (end - begin): i32;
+	} else {
+		body = lexspan(l, begin, end);
+	};
+
+	let pre: str = "ww:module";
+	if (!strings.hasprefix(body, pre) || body.len == pre.len) { return; };
+	let i: i32 = pre.len;
+	if (body[i] == '-') {
+		let rest: str = "-reset";
+		if (body.len - i < rest.len) { return; };
+		let j: i32 = 0;
+		for (j < rest.len) {
+			if (body[i + j] != rest[j]) { return; };
+			j += 1;
+		};
+		i += rest.len;
+		if (i == body.len) {
+			l.modreset = 1;
+			l.modpathset = 0;	// #9: reset supersedes a pending path
+			return;
+		};
+		if (body[i] != ' ' && body[i] != '\t') { return; };
+		for (i < body.len && (body[i] == ' ' || body[i] == '\t')) {
+			i += 1;
+		};
+		let s: i32 = i;
+		for (i < body.len && body[i] != '\r' && body[i] != ' '
+			&& body[i] != '\t') {
+			i += 1;
+		};
+		l.modreset = 1;
+		l.modpathset = 0;	// #9: see above
+		if (i > s) {
+			let view: str;
+			view.ptr = body.ptr + (s: u64);
+			view.len = i - s;
+			l.modresetpath = strings.dup(view);
+			l.modresetpathset = 1;
+		};
+		return;
+	};
+	if (body[i] != ' ' && body[i] != '\t') { return; };
+	for (i < body.len && (body[i] == ' ' || body[i] == '\t')) {
+		i += 1;
+	};
+	let s: i32 = i;
+	for (i < body.len && body[i] != '\r' && body[i] != ' '
+		&& body[i] != '\t') {
+		i += 1;
+	};
+	if (i > s) {
+		let view: str;
+		view.ptr = body.ptr + (s: u64);
+		view.len = i - s;
+		l.modpath = strings.dup(view);
+		l.modpathset = 1;
+	};
+};
+
 fn skipws(l: *lex) bool = {
 	for (true) {
 		let c: i32 = lpeek(l, 0u64);
@@ -158,111 +302,9 @@ fn skipws(l: *lex) bool = {
 			let c2: i32 = lpeek(l, 1u64);
 			if (c2 == '/') {
 				lget(l); lget(l);
-				// #16 opt-B: recognize the driver's curmod-reset
-				// boundary directive `//ww:module-reset` (whole
-				// line) and flag it; lexnext emits TK_MODRESET.
-				// The body is then skipped like any comment.
-				// Mirrors cstage lex.c skipws. Compare via lpeek
-				// (no consume) so the skip loop below is unchanged.
-				let pre: str = "ww:module";
-				let di: i32 = 0;
-				let matched: bool = true;
-				for (di < pre.len) {
-					if (lpeek(l, di: u64) != pre[di]: i32) {
-						matched = false; break;
-					};
-					di += 1;
-				};
-				if (matched) {
-					let nx: i32 = lpeek(l, pre.len: u64);
-					if (nx == '-') {
-						let rest: str = "-reset";
-						let rj: i32 = 0;
-						let rm: bool = true;
-						for (rj < rest.len) {
-							if (lpeek(l, (pre.len + rj): u64)
-							    != rest[rj]: i32) {
-								rm = false; break;
-							};
-							rj += 1;
-						};
-						if (rm) {
-							let af: i32 = lpeek(l,
-							    (pre.len + rest.len): u64);
-							if (af == '\n') { l.modreset = 1; l.modpathset = 0; } // #9: reset supersedes pending path (empty module body)
-							else { if (af < 0) { l.modreset = 1; l.modpathset = 0; } // #9: see above
-							else { if (af == ' ' || af == '\t') {
-								// `//ww:module-reset <path>` — sep
-								// primary body tagged by its full
-								// dotted import path (#57).
-								let k: u64 =
-								    (pre.len + rest.len): u64;
-								for (true) {
-									let sc: i32 = lpeek(l, k);
-									if (sc == ' ' || sc == '\t') {
-										k += 1u64; continue;
-									};
-									break;
-								};
-								let s0: u64 = k;
-								for (true) {
-									let pc: i32 = lpeek(l, k);
-									if (pc < 0) { break; };
-									if (pc == '\n' || pc == '\r'
-									    || pc == ' '
-									    || pc == '\t') {
-										break;
-									};
-									k += 1u64;
-								};
-								l.modreset = 1;
-								l.modpathset = 0;	// #9: see above — clear pending path
-								if (k > s0) {
-									let view: str;
-									view.ptr =
-									    l.src + l.lpos + s0;
-									view.len = (k - s0): i32;
-									l.modresetpath =
-									    strings.dup(view);
-									l.modresetpathset = 1;
-								};
-							}; }; };
-						};
-					} else { if (nx == ' ' || nx == '\t') {
-						// `//ww:module <path>` — M1 import boundary.
-						let k: u64 = pre.len: u64;
-						for (true) {
-							let sc: i32 = lpeek(l, k);
-							if (sc == ' ' || sc == '\t') {
-								k += 1u64; continue;
-							};
-							break;
-						};
-						let s0: u64 = k;
-						for (true) {
-							let pc: i32 = lpeek(l, k);
-							if (pc < 0) { break; };
-							if (pc == '\n' || pc == '\r'
-							    || pc == ' ' || pc == '\t') {
-								break;
-							};
-							k += 1u64;
-						};
-						if (k > s0) {
-							let view: str;
-							view.ptr = l.src + l.lpos + s0;
-							view.len = (k - s0): i32;
-							l.modpath = strings.dup(view);
-							l.modpathset = 1;
-						};
-					}; };
-				};
-				for (true) {
-					let cx: i32 = lpeek(l, 0u64);
-					if (cx < 0) { return false; };
-					if (cx == '\n') { break; };
-					lget(l);
-				};
+				// #16 opt-B: classify the driver's whole-line internal
+				// module boundary after consuming it once.
+				linecomment(l);
 				continue;
 			};
 			if (c2 == '*') {
@@ -395,6 +437,38 @@ fn escape(l: *lex, out: *i32) bool = {
 	return false;
 };
 
+fn lextypesuffix(l: *lex, out: *str) bool = {
+	let got: [4]u8;
+	let n: u64 = 0u64;
+	for (n < 4u64) {
+		let c: i32 = lpeek(l, n);
+		if (c < 0 || !isidpart(c: rune)) { break; };
+		got[n] = c: u8;
+		n += 1u64;
+	};
+	if (n == 0u64 || n > 3u64) { return false; };
+	let tail: i32 = lpeek(l, n);
+	if (tail >= 0) {
+		if (isidpart(tail: rune)) { return false; };
+	};
+	let names: []str = ["i8", "i16", "i32", "i64",
+		"u8", "u16", "u32", "u64", "f32", "f64"];
+	let i: i32 = 0;
+	for (i < names.len) {
+		if (names[i].len: u64 == n) {
+			let same: bool = true;
+			let j: i32 = 0;
+			for (j < names[i].len) {
+				if (names[i][j] != got[j]) { same = false; break; };
+				j += 1;
+			};
+			if (same) { *out = names[i]; return true; };
+		};
+		i += 1;
+	};
+	return false;
+};
+
 fn scandecimalrun(l: *lex) void = {
 	for (true) {
 		let c: i32 = lpeek(l, 0u64);
@@ -459,6 +533,7 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 	out.line = start.line;
 	out.col  = start.col;
 	let begin: u64 = l.lpos;
+	let nulbegin: u64 = l.nulcount;
 	let base: i32 = 10;
 	let isfloat: bool = false;
 
@@ -507,11 +582,16 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 		};
 	};
 
-	let n: u64 = l.lpos - begin;
-	let view: str;
-	view.ptr = l.src + begin;
-	view.len = n: i32;
-	out.text = strings.dup(view);
+	let rawend: u64 = l.lpos;
+	if (l.nulcount == nulbegin) {
+		let view: str;
+		view.ptr = l.src + begin;
+		view.len = (rawend - begin): i32;
+		out.text = strings.dup(view);
+	} else {
+		out.text = lexspan(l, begin, rawend);
+	};
+	let n: u64 = out.text.len: u64;
 
 	if (isfloat) {
 		out.kind = tkind.TK_FLOAT;
@@ -522,7 +602,7 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 		let i: u64 = 0u64;
 		let j: u64 = 0u64;
 		for (i < n) {
-			let b: u8 = l.src[begin + i];
+			let b: u8 = out.text[i];
 			if (b != '_') {
 				clean[j] = b;
 				j += 1u64;
@@ -561,7 +641,7 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 		let pu: *u64 = (&fv): *u64;
 		out.uval = *pu;
 	} else {
-		let digs: *u8 = l.src + begin;
+		let digs: *u8 = out.text.ptr;
 		let dn: u64 = n;
 		if (base != 10) {
 			digs = digs + 2u64;
@@ -578,49 +658,11 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 	let pc: i32 = lpeek(l, 0u64);
 	if (pc >= 0) {
 		if (isidstart(pc: rune)) {
-			let sb: u64 = l.lpos;
-			let sc: i32 = l.col;
-			for (true) {
-				let cc: i32 = lpeek(l, 0u64);
-				if (cc < 0) { break; };
-				if (!isidpart(cc: rune)) { break; };
-				lget(l);
-			};
-			let sl: u64 = l.lpos - sb;
-			let p: *u8 = l.src + sb;
-			let isok: bool = false;
-			if (sl == 2u64) {
-				if (p[0] == 'i') {
-					if (p[1] == '8') { isok = true; };	// i8
-				};
-				if (p[0] == 'u') {
-					if (p[1] == '8') { isok = true; };	// u8
-				};
-			};
-			if (sl == 3u64) {
-				if (p[0] == 'i') {
-					if (p[1] == '1') { if (p[2] == '6') { isok = true; }; };	// i16
-					if (p[1] == '3') { if (p[2] == '2') { isok = true; }; };	// i32
-					if (p[1] == '6') { if (p[2] == '4') { isok = true; }; };	// i64
-				};
-				if (p[0] == 'u') {
-					if (p[1] == '1') { if (p[2] == '6') { isok = true; }; };
-					if (p[1] == '3') { if (p[2] == '2') { isok = true; }; };
-					if (p[1] == '6') { if (p[2] == '4') { isok = true; }; };
-				};
-				if (p[0] == 'f') {
-					if (p[1] == '3') { if (p[2] == '2') { isok = true; }; };	// f32
-					if (p[1] == '6') { if (p[2] == '4') { isok = true; }; };	// f64
-				};
-			};
-			if (isok) {
-				let view: str;
-				view.ptr = p;
-				view.len = sl: i32;
-				out.tsuffix = strings.dup(view);
-			} else {
-				l.lpos = sb;
-				l.col = sc;
+			let suffix: str;
+			if (lextypesuffix(l, &suffix)) {
+				let i: i32 = 0;
+				for (i < suffix.len) { lget(l); i += 1; };
+				out.tsuffix = strings.dup(suffix);
 			};
 		};
 	};
@@ -628,14 +670,24 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 
 fn lexident(l: *lex, start: *pos, out: *tok) void = {
 	let begin: u64 = l.lpos;
+	let nulbegin: u64 = l.nulcount;
 	for (true) {
 		let c: i32 = lpeek(l, 0u64);
 		if (c < 0) { break; };
 		if (!isidpart(c: rune)) { break; };
 		lget(l);
 	};
-	let n: u64 = l.lpos - begin;
-	let p: *u8 = l.src + begin;
+	let text: str;
+	if (l.nulcount == nulbegin) {
+		let view: str;
+		view.ptr = l.src + begin;
+		view.len = (l.lpos - begin): i32;
+		text = strings.dup(view);
+	} else {
+		text = lexspan(l, begin, l.lpos);
+	};
+	let n: u64 = text.len: u64;
+	let p: *u8 = text.ptr;
 	out.file = start.file;
 	out.line = start.line;
 	out.col  = start.col;
@@ -643,10 +695,7 @@ fn lexident(l: *lex, start: *pos, out: *tok) void = {
 	if (n == 1u64) {
 		if (p[0] == '_') {
 			out.kind = tkind.TK_UNDER;
-			let view: str;
-			view.ptr = p;
-			view.len = n: i32;
-			out.text = strings.dup(view);
+			out.text = text;
 			return;
 		};
 	};
@@ -656,10 +705,7 @@ fn lexident(l: *lex, start: *pos, out: *tok) void = {
 	} else {
 		out.kind = tkind.TK_IDENT;
 	};
-	let view: str;
-	view.ptr = p;
-	view.len = n: i32;
-	out.text = strings.dup(view);
+	out.text = text;
 };
 
 fn lexstr(l: *lex, start: *pos, out: *tok) void = {
diff --git a/lib/ww/syntax/tok_test.ww b/lib/ww/syntax/tok_test.ww
index 0719e851..7be27e06 100644
--- a/lib/ww/syntax/tok_test.ww
+++ b/lib/ww/syntax/tok_test.ww
@@ -339,6 +339,30 @@ fn checkfloat(src: str, want: u64) void = {
 	assert(!(t.text != "bar"));
 };
 
+@test fn long_module_directive_is_linear() void = {
+	let pre: str = "//ww:module ";
+	let tail: str = "\nfn";
+	let pathlen: i32 = 16384;
+	let total: i32 = pre.len + pathlen + tail.len;
+	let src: []u8 = alloc([], total: u64)!;
+	src.len = total;
+	let i: i32 = 0;
+	for (i < pre.len) { src[i] = pre[i]; i += 1; };
+	for (i < pre.len + pathlen) { src[i] = 'a': u8; i += 1; };
+	let j: i32 = 0;
+	for (j < tail.len) { src[i] = tail[j]; i += 1; j += 1; };
+	let l: syntax.lex;
+	syntax.lexinit(&l, "t", src.ptr, src.len: u64);
+	let t: syntax.tok;
+	syntax.lexnext(&l, &t);
+	assert(t.kind == syntax.tkind.TK_MODPATH);
+	assert(t.text.len == pathlen);
+	assert(t.text[0] == 'a' && t.text[pathlen - 1] == 'a');
+	syntax.lexnext(&l, &t);
+	assert(t.kind == syntax.tkind.TK_FN);
+	assert(l.errs == 0);
+};
+
 fn bomsource(dst: *u8, before: str, after: str) u64 = {
 	let n: u64 = 0u64;
 	let i: i32 = 0;
diff --git a/test/package/package_test.ww b/test/package/package_test.ww
index a67979f3..812c6480 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -130,6 +130,58 @@ fn rewritemidbomfile(path: str, before: str, after: str) void = {
 	putbomfile(path, before, after, true);
 };
 
+fn putnulfile(path: str, before: str, after: str, rewrite: bool) void = {
+	let flags: os.flag = os.flag.WRONLY;
+	if (rewrite) { flags |= os.flag.TRUNC; }
+	else { flags |= os.flag.CREATE | os.flag.EXCL; };
+	let fd: i32 = os.open(path, flags, 384i32);
+	assert(fd >= 0);
+	match (os.writeall(fd, before.ptr, before.len: u64)) {
+	case let n: i64 => assert(n == before.len: i64);
+	case let e: os.oserror => abort("write before NUL failed");
+	};
+	let nul: [1]u8;
+	nul[0] = 0u8;
+	match (os.writeall(fd, nul.ptr, 1u64)) {
+	case let n: i64 => assert(n == 1i64);
+	case let e: os.oserror => abort("write NUL failed");
+	};
+	match (os.writeall(fd, after.ptr, after.len: u64)) {
+	case let n: i64 => assert(n == after.len: i64);
+	case let e: os.oserror => abort("write after NUL failed");
+	};
+	assert(os.close(fd) == 0);
+};
+
+fn writenulfile(path: str, before: str, after: str) void = {
+	putnulfile(path, before, after, false);
+};
+
+fn rewritenulfile(path: str, before: str, after: str) void = {
+	putnulfile(path, before, after, true);
+};
+
+fn writedoublenulfile(path: str, before: str, after: str) void = {
+	let fd: i32 = os.open(path,
+		os.flag.WRONLY | os.flag.CREATE | os.flag.EXCL, 384i32);
+	assert(fd >= 0);
+	match (os.writeall(fd, before.ptr, before.len: u64)) {
+	case let n: i64 => assert(n == before.len: i64);
+	case let e: os.oserror => abort("write before NUL pair failed");
+	};
+	let pair: [2]u8;
+	pair[0] = 0u8; pair[1] = 0u8;
+	match (os.writeall(fd, pair.ptr, 2u64)) {
+	case let n: i64 => assert(n == 2i64);
+	case let e: os.oserror => abort("write NUL pair failed");
+	};
+	match (os.writeall(fd, after.ptr, after.len: u64)) {
+	case let n: i64 => assert(n == after.len: i64);
+	case let e: os.oserror => abort("write after NUL pair failed");
+	};
+	assert(os.close(fd) == 0);
+};
+
 fn writeexecutable(path: str, content: str) void = {
 	let fd: i32 = os.open(path,
 		os.flag.WRONLY | os.flag.CREATE | os.flag.EXCL, 448i32);
@@ -16968,3 +17020,479 @@ fn runtimepath(relative: str) str = {
 		&& !directoryhasnew(root));
 	clean(root);
 };
+
+// Go 1.26.5's physical-source reader rejects U+0000 before token context can
+// turn it into comment or literal payload. Selected roots, dependencies, and
+// every test-source role share that rule; target-excluded files do not.
+@test fn raw_nul_is_rejected_in_every_selected_source() void = {
+	let root: str = fresh();
+	let source: str = strings.concat(root, "/source");
+	mkdirall(source);
+
+	// Direct frontend ownership and exact C/WW recovery parity.
+	let leading: str = strings.concat(root, "/leading.ww");
+	let comment: str = strings.concat(root, "/comment.ww");
+	let stringlit: str = strings.concat(root, "/string.ww");
+	let runelit: str = strings.concat(root, "/rune.ww");
+	let between: str = strings.concat(root, "/between.ww");
+	let escapechar: str = strings.concat(root, "/escape-char.ww");
+	let escapedigit: str = strings.concat(root, "/escape-digit.ww");
+	let identifier: str = strings.concat(root, "/identifier.ww");
+	let lineend: str = strings.concat(root, "/line-end.ww");
+	let blockend: str = strings.concat(root, "/block-end.ww");
+	let operator: str = strings.concat(root, "/operator.ww");
+	let number: str = strings.concat(root, "/number.ww");
+	let suffix: str = strings.concat(root, "/suffix.ww");
+	let trailing: str = strings.concat(root, "/trailing.ww");
+	writenulfile(leading, "",
+		"package main;\nfn main() void = {};\n");
+	writenulfile(comment, "package main;\n// NUL: ",
+		" here\nfn main() void = {};\n");
+	writenulfile(stringlit,
+		"package main;\nfn main() void = { let value: str = \"NUL: ",
+		"\"; };\n");
+	writenulfile(runelit,
+		"package main;\nfn main() void = { let value: rune = '",
+		"A'; };\n");
+	writenulfile(between, "package main;\n",
+		"\nfn main() void = {};\n");
+	writenulfile(escapechar,
+		"package main;\nfn main() void = { let value: str = \"\\",
+		"n\"; };\n");
+	writenulfile(escapedigit,
+		"package main;\nfn main() void = { let value: str = \"\\x0",
+		"0\"; };\n");
+	writenulfile(identifier, "pack",
+		"age main;\nfn main() void = {};\n");
+	writenulfile(lineend, "package main;\n// comment",
+		"\nfn main() void = {};\n");
+	writenulfile(blockend, "package main;\n/* end *",
+		"/\nfn main() void = {};\n");
+	writenulfile(operator,
+		"package main;\nfn main() void = { let value: bool = true =",
+		"= true; };\n");
+	writenulfile(number,
+		"package main;\nfn main() void = { let value: i32 = 1",
+		"_0; };\n");
+	writenulfile(suffix,
+		"package main;\nfn main() void = { let value: i32 = 1i",
+		"32; };\n");
+	writenulfile(trailing,
+		"package main;\nfn main() void = {};\n", "");
+	let direct: []str = [leading, comment, stringlit, runelit, between,
+		escapechar, escapedigit, identifier, lineend, blockend, operator,
+		number, suffix, trailing];
+	let positions: []str = [":1:1: error: invalid NUL character\n",
+		":2:9: error: invalid NUL character\n",
+		":2:43: error: invalid NUL character\n",
+		":2:39: error: invalid NUL character\n",
+		":2:1: error: invalid NUL character\n",
+		":2:39: error: invalid NUL character\n",
+		":2:41: error: invalid NUL character\n",
+		":1:5: error: invalid NUL character\n",
+		":2:11: error: invalid NUL character\n",
+		":2:9: error: invalid NUL character\n",
+		":2:44: error: invalid NUL character\n",
+		":2:38: error: invalid NUL character\n",
+		":2:39: error: invalid NUL character\n",
+		":3:1: error: invalid NUL character\n"];
+	let compilers: []str = ["w6c", "w6c_ww"];
+	let stages: []str = ["ww", "ww_ww"];
+	let tags: []str = ["c", "ww"];
+	let di: i32 = 0;
+	for (di < direct.len) {
+		let reference: str = "";
+		let si: i32 = 0;
+		for (si < compilers.len) {
+			let asmout: str = strings.concat(root, "/direct-", tags[si], "-",
+				boundarypkgname(di), ".s");
+			let av: []str = [driver(compilers[si]), "-c", "--command-package",
+				"-o", asmout, direct[di]];
+			let out: commandout;
+			runcommand(root, strings.concat("nul-direct-", tags[si], "-",
+				boundarypkgname(di)), av,
+				(30i64 * (time.second: i64)): time.duration, &out);
+			expectexit(&out, 1);
+			assert(out.stdout.len == 0 && has(out.stderr, positions[di]));
+			assert(occurrences(out.stderr, "invalid NUL character") == 1);
+			assert(!os.exists(asmout));
+			if (si == 0) { reference = strings.dup(out.stderr); }
+			else { assert(same(reference, out.stderr)); };
+			si += 1;
+		};
+		di += 1;
+	};
+
+	// Decoder recovery is also exact for repeated bytes and the internal
+	// module-boundary directive used by package-unit composition.
+	let repeated: str = strings.concat(root, "/repeated.ww");
+	let directive: str = strings.concat(root, "/directive.ww");
+	writedoublenulfile(repeated, "pack",
+		"age main;\nfn main() void = {};\n");
+	writenulfile(directive, "//ww:module-reset ma",
+		"in\npackage main;\nfn main() void = {};\n");
+	let recoverypaths: []str = [repeated, directive];
+	let recoverycounts: []i32 = [2, 1];
+	let recoverypositions: []str = [
+		":1:5: error: invalid NUL character\n",
+		":1:21: error: invalid NUL character\n"];
+	let ri: i32 = 0;
+	for (ri < recoverypaths.len) {
+		let reference: str = "";
+		let rsi: i32 = 0;
+		for (rsi < compilers.len) {
+			let asmout: str = strings.concat(root, "/recovery-", tags[rsi],
+				"-", boundarypkgname(ri), ".s");
+			let av: []str = [driver(compilers[rsi]), "-c",
+				"--command-package", "-o", asmout, recoverypaths[ri]];
+			let out: commandout;
+			runcommand(root, strings.concat("nul-recovery-", tags[rsi], "-",
+				boundarypkgname(ri)), av,
+				(30i64 * (time.second: i64)): time.duration, &out);
+			expectexit(&out, 1);
+			assert(out.stdout.len == 0
+				&& has(out.stderr, recoverypositions[ri])
+				&& occurrences(out.stderr,
+					"invalid NUL character") == recoverycounts[ri]
+				&& !os.exists(asmout));
+			if (ri == 0) {
+				assert(has(out.stderr,
+					":1:6: error: invalid NUL character\n"));
+			};
+			if (rsi == 0) { reference = strings.dup(out.stderr); }
+			else { assert(same(reference, out.stderr)); };
+			rsi += 1;
+		};
+		ri += 1;
+	};
+
+	// An escape denotes a literal value; it is not a raw source NUL.
+	let escaped: str = strings.concat(root, "/escaped.ww");
+	writefile(escaped, strings.concat(
+		"package main;\n",
+		"fn main() i32 = { let value: str = \"\\x00\"; return value.len - 1; };\n"));
+	let escapedasm: []str = [strings.concat(root, "/escaped-c.s"),
+		strings.concat(root, "/escaped-ww.s")];
+	let si: i32 = 0;
+	for (si < compilers.len) {
+		let av: []str = [driver(compilers[si]), "-c", "--command-package",
+			"-o", escapedasm[si], escaped];
+		let out: commandout;
+		runcommand(root, strings.concat("nul-escaped-", tags[si]), av,
+			(30i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0);
+		si += 1;
+	};
+	assert(same(readfile(escapedasm[0]), readfile(escapedasm[1])));
+
+	let dep: str = strings.concat(source, "/dep");
+	let app: str = strings.concat(source, "/app");
+	let bad: str = strings.concat(source, "/bad");
+	let good: str = strings.concat(source, "/good");
+	mkdirall(dep); mkdirall(app); mkdirall(bad); mkdirall(good);
+	writenulfile(strings.concat(dep, "/dep.ww"),
+		"package dep;\n// NUL: ",
+		" dependency\nexport fn value() i32 = { return 42; };\n");
+	writefile(strings.concat(app, "/main.ww"), strings.concat(
+		"package main;\nimport dep;\n",
+		"fn main() i32 = { return dep.value() - 42; };\n"));
+	writefile(strings.concat(bad, "/a.ww"),
+		"package main;\nfn helper() i32 = { return 1; };\n");
+	writenulfile(strings.concat(bad, "/main.ww"),
+		"package main;\n// NUL: ", strings.concat(
+		" root\nimport missing;\n",
+		"fn main() i32 = { return 0; };\n"));
+	writefile(strings.concat(good, "/main.ww"),
+		"package main;\nfn main() i32 = { return 0; };\n");
+	writenulfile(strings.concat(good, "/ignored_windows.ww"),
+		"not package NUL: ", " and not WW\n");
+
+	// Invalid root and dependency sources stop before graph actions and public
+	// output. The wrong-target source remains outside the semantic input set.
+	let goodbins: []str = [strings.concat(root, "/good-c"),
+		strings.concat(root, "/good-ww")];
+	let invaliddiags: []str = ["", ""];
+	let rootdiags: []str = ["", ""];
+	si = 0;
+	for (si < stages.len) {
+		let depwork: str = strings.concat(root, "/dep-work-", tags[si]);
+		let depout: str = strings.concat(root, "/dep-output-", tags[si]);
+		mkdirall(depwork);
+		let depav: []str = [driver(stages[si]), "build", "-w", depwork,
+			"-I", source, "-o", depout, "app"];
+		let out: commandout;
+		runcommand(root, strings.concat("nul-dependency-", tags[si]), depav,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& has(out.stderr, "/dep/dep.ww:2:9: error: invalid NUL character\n"));
+		assert(occurrences(out.stderr, "invalid NUL character") == 1
+			&& !has(out.stderr, "w6c failed"));
+		assert(!os.exists(depout) && directoryisempty(depwork));
+		invaliddiags[si] = strings.dup(out.stderr);
+
+		let badwork: str = strings.concat(root, "/bad-work-", tags[si]);
+		let badout: str = strings.concat(root, "/bad-output-", tags[si]);
+		mkdirall(badwork);
+		let badav: []str = [driver(stages[si]), "build", "-w", badwork,
+			"-I", source, "-o", badout, "bad"];
+		runcommand(root, strings.concat("nul-root-", tags[si]), badav,
+			(60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& has(out.stderr, "/bad/main.ww:2:9: error: invalid NUL character\n"));
+		assert(!has(out.stderr, "cannot find import")
+			&& occurrences(out.stderr, "invalid NUL character") == 1);
+		assert(!os.exists(badout) && directoryisempty(badwork));
+		rootdiags[si] = strings.dup(out.stderr);
+
+		let goodwork: str = strings.concat(root, "/good-work-", tags[si]);
+		mkdirall(goodwork);
+		let goodav: []str = [driver(stages[si]), "build", "-w", goodwork,
+			"-I", source, "-o", goodbins[si], "good"];
+		runcommand(root, strings.concat("nul-wrong-target-", tags[si]), goodav,
+			(120i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& !directoryhasnew(goodwork)
+			&& !directoryhasfragment(goodwork, ".wwtxn."));
+		let runav: []str = [goodbins[si]];
+		runcommand(root, strings.concat("nul-good-run-", tags[si]), runav,
+			time.second, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0);
+		si += 1;
+	};
+	assert(same(invaliddiags[0], invaliddiags[1])
+		&& same(rootdiags[0], rootdiags[1])
+		&& same(readfile(goodbins[0]), readfile(goodbins[1])));
+
+	// Production, same-package, external-package, and test-only sources all
+	// reject before product construction, execution, accounting, and retention.
+	let prodcase: str = strings.concat(source, "/prodcase");
+	let samecase: str = strings.concat(source, "/samecase");
+	let externalcase: str = strings.concat(source, "/externalcase");
+	let onlycase: str = strings.concat(source, "/onlycase");
+	let repeatcase: str = strings.concat(source, "/repeatcase");
+	mkdirall(prodcase); mkdirall(samecase); mkdirall(externalcase);
+	mkdirall(onlycase); mkdirall(repeatcase);
+	writefile(strings.concat(prodcase, "/more.ww"),
+		"package prodcase;\nfn more() i32 = { return 2; };\n");
+	writenulfile(strings.concat(prodcase, "/prod.ww"),
+		"package prodcase;\n// NUL: ",
+		" production\nexport fn value() i32 = { return 1; };\n");
+	writefile(strings.concat(prodcase, "/same_test.ww"),
+		"package prodcase;\n@test fn must_not_run() void = { abort(); };\n");
+	writefile(strings.concat(samecase, "/prod.ww"),
+		"package samecase;\nfn value() i32 = { return 1; };\n");
+	writenulfile(strings.concat(samecase, "/same_test.ww"),
+		"package samecase;\n// NUL: ",
+		" same\n@test fn must_not_run() void = { abort(); };\n");
+	writefile(strings.concat(externalcase, "/prod.ww"),
+		"package externalcase;\nexport fn value() i32 = { return 1; };\n");
+	writenulfile(strings.concat(externalcase, "/external_test.ww"),
+		"package externalcase_test;\n// NUL: ", strings.concat(
+		" external\nimport externalcase;\n",
+		"@test fn must_not_run() void = { abort(); };\n"));
+	writenulfile(strings.concat(onlycase, "/only_test.ww"), "",
+		"package onlycase;\n@test fn must_not_run() void = { abort(); };\n");
+	writedoublenulfile(strings.concat(repeatcase, "/prod.ww"),
+		"package repeatcase;\n// pair ",
+		" here\nfn value() i32 = { return 1; };\n");
+	let testids: []str = ["prodcase", "samecase", "externalcase", "onlycase",
+		"repeatcase"];
+	let testpositions: []str = ["/prodcase/prod.ww:2:9: error: invalid NUL character\n",
+		"/samecase/same_test.ww:2:9: error: invalid NUL character\n",
+		"/externalcase/external_test.ww:2:9: error: invalid NUL character\n",
+		"/onlycase/only_test.ww:1:1: error: invalid NUL character\n",
+		"/repeatcase/prod.ww:2:9: error: invalid NUL character\n"];
+	let testcounts: []i32 = [1, 1, 1, 1, 2];
+	let testdiags: []str = ["", "", "", "", ""];
+	si = 0;
+	for (si < stages.len) {
+		let ti: i32 = 0;
+		for (ti < testids.len) {
+			let testwork: str = strings.concat(root, "/test-work-", tags[si], "-",
+				boundarypkgname(ti));
+			let testout: str = strings.concat(root, "/test-output-", tags[si], "-",
+				boundarypkgname(ti));
+			mkdirall(testwork);
+			let av: []str = [driver(stages[si]), "test", "-w", testwork,
+				"-I", source, "-o", testout, testids[ti]];
+			let out: commandout;
+			runcommand(root, strings.concat("nul-test-", tags[si], "-",
+				boundarypkgname(ti)), av,
+				(60i64 * (time.second: i64)): time.duration, &out);
+			expectexit(&out, 1);
+			assert(same(out.stdout, "FAIL\n")
+				&& has(out.stderr, testpositions[ti]));
+			assert(occurrences(out.stderr,
+				"invalid NUL character") == testcounts[ti]
+				&& !has(out.stdout, "must_not_run")
+				&& !has(out.stdout, "discovered") && !has(out.stdout, "ok   "));
+			if (ti == 4) {
+				assert(has(out.stderr,
+					"/repeatcase/prod.ww:2:10: error: invalid NUL character\n"));
+			};
+			assert(!os.exists(testout) && directoryisempty(testwork));
+			if (si == 0) { testdiags[ti] = strings.dup(out.stderr); }
+			else { assert(same(testdiags[ti], out.stderr)); };
+			ti += 1;
+		};
+		si += 1;
+	};
+
+	// A warm invalid edit commits nothing and preserves prior public and action
+	// bytes. Exact restoration reuses the committed generation without a tool.
+	let warm: str = strings.concat(source, "/warm");
+	mkdirall(warm);
+	let warmpath: str = strings.concat(warm, "/main.ww");
+	let warmvalid: str =
+		"package main;\nfn main() i32 = { return 0; };\n";
+	writefile(warmpath, warmvalid);
+	let wrapper: str = strings.concat(root, "/nul-compiler-wrapper.sh");
+	writeexecutable(wrapper, strings.concat(
+		"#!/bin/sh\n",
+		"printf 'compile\\n' >> \"$WW_NUL_TRACE\"\n",
+		"exec \"$WW_NUL_REAL\" \"$@\"\n"));
+	let commandsuffixes: []str = [".unit.ww", ".wwi", ".s", ".o", ".a",
+		".init.unit.ww", ".init.s", ".init.o"];
+	si = 0;
+	for (si < stages.len) {
+		let warmwork: str = strings.concat(root, "/warm-work-", tags[si]);
+		let warmout: str = strings.concat(root, "/warm-output-", tags[si]);
+		let trace: str = strings.concat(root, "/warm-trace-", tags[si]);
+		mkdirall(warmwork); writefile(trace, "");
+		let env: []str = os.getenvs();
+		append(env, strings.concat("WW_W6C=", wrapper));
+		append(env, strings.concat("WW_NUL_TRACE=", trace));
+		append(env, strings.concat("WW_NUL_REAL=", driver(compilers[si])));
+		let av: []str = [driver(stages[si]), "build", "-w", warmwork,
+			"-I", source, "-o", warmout, "warm"];
+		let out: commandout;
+		runcommandenv(root, strings.concat("nul-warm-cold-", tags[si]), av,
+			env, (120i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& readfile(trace).len != 0);
+		let refs: []str = alloc([], commandsuffixes.len: u64)!;
+		let fi: i32 = 0;
+		for (fi < commandsuffixes.len) {
+			append(refs, strings.dup(readfile(strings.concat(warmwork,
+				"/warm", commandsuffixes[fi]))));
+			fi += 1;
+		};
+		let toolpaths: []str = ["/.wwtool.ww", "/.wwtool.w6c",
+			"/.wwtool.w6a", "/.wwtool.stamp"];
+		let toolrefs: []str = alloc([], toolpaths.len: u64)!;
+		fi = 0;
+		for (fi < toolpaths.len) {
+			append(toolrefs, strings.dup(readfile(strings.concat(warmwork,
+				toolpaths[fi]))));
+			fi += 1;
+		};
+		let binref: str = strings.dup(readfile(warmout));
+		rewritefile(trace, "");
+		rewritenulfile(warmpath, "package main;\n// NUL: ",
+			" invalid\nfn main() i32 = { return 0; };\n");
+		runcommandenv(root, strings.concat("nul-warm-invalid-", tags[si]), av,
+			env, (60i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 1);
+		assert(out.stdout.len == 0
+			&& has(out.stderr, ":2:9: error: invalid NUL character\n"));
+		assert(readfile(trace).len == 0 && same(binref, readfile(warmout)));
+		fi = 0;
+		for (fi < commandsuffixes.len) {
+			assert(same(refs[fi], readfile(strings.concat(warmwork,
+				"/warm", commandsuffixes[fi]))));
+			fi += 1;
+		};
+		fi = 0;
+		for (fi < toolpaths.len) {
+			assert(same(toolrefs[fi], readfile(strings.concat(warmwork,
+				toolpaths[fi]))));
+			fi += 1;
+		};
+		assert(!directoryhasnew(warmwork)
+			&& !directoryhasfragment(warmwork, ".wwtxn."));
+		rewritefile(warmpath, warmvalid);
+		runcommandenv(root, strings.concat("nul-warm-restored-", tags[si]), av,
+			env, (120i64 * (time.second: i64)): time.duration, &out);
+		expectexit(&out, 0);
+		assert(out.stdout.len == 0 && out.stderr.len == 0
+			&& readfile(trace).len == 0 && same(binref, readfile(warmout)));
+		fi = 0;
+		for (fi < commandsuffixes.len) {
+			assert(same(refs[fi], readfile(strings.concat(warmwork,
+				"/warm", commandsuffixes[fi]))));
+			fi += 1;
+		};
+		fi = 0;
+		for (fi < toolpaths.len) {
+			assert(same(toolrefs[fi], readfile(strings.concat(warmwork,
+				toolpaths[fi]))));
+			fi += 1;
+		};
+		si += 1;
+	};
+
+	// Source validation is request-local under overlapping valid and invalid
+	// builds, including independent work, outputs, diagnostics, and cleanup.
+	let pcwork: str = strings.concat(root, "/parallel-c-work");
+	let pwwork: str = strings.concat(root, "/parallel-ww-work");
+	let pcout: str = strings.concat(root, "/parallel-c-output");
+	let pwout: str = strings.concat(root, "/parallel-ww-output");
+	mkdirall(pcwork); mkdirall(pwwork);
+	let pcav: []str = [driver("ww"), "build", "-w", pcwork,
+		"-I", source, "-o", pcout, "good"];
+	let pwav: []str = [driver("ww_ww"), "build", "-w", pwwork,
+		"-I", source, "-o", pwout, "bad"];
+	let pc: exec.command;
+	pc.path = pcav[0]; pc.argv = pcav; pc.env = os.getenvs(); 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),
+		(120i64 * (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 = os.getenvs(); 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),
+		(120i64 * (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);
+	assert(pwp.result.errno == 0 && pwp.result.cleanuperrno == 0
+		&& pwp.result.termination == exec.termination.EXIT
+		&& pwp.result.code == 1);
+	assert(readfile(pc.stdoutpath).len == 0 && readfile(pc.stderrpath).len == 0);
+	assert(readfile(pw.stdoutpath).len == 0
+		&& has(readfile(pw.stderrpath), "invalid NUL character"));
+	assert(same(readfile(pcout), readfile(goodbins[0])) && !os.exists(pwout));
+	assert(directoryisempty(pwwork) && !directoryhasnew(pcwork)
+		&& !directoryhasfragment(pcwork, ".wwtxn."));
+	let runav: []str = [pcout];
+	let out: commandout;
+	runcommand(root, "nul-parallel-run", runav, time.second, &out);
+	expectexit(&out, 0);
+	assert(out.stdout.len == 0 && out.stderr.len == 0);
+	assert(!directoryhasfragment(root, ".wwtxn.")
+		&& !directoryhasfragment(root, ".install")
+		&& !directoryhasnew(root));
+	clean(root);
+};
diff --git a/test/wcc/100_lex.c b/test/wcc/100_lex.c
index 969b6444..3a4990d5 100644
--- a/test/wcc/100_lex.c
+++ b/test/wcc/100_lex.c
@@ -18,11 +18,11 @@ toklit(Arena *a, Tok t)
 }
 
 static int
-runrow(const char *src, const char *expect)
+runrown(const char *src, size_t len, const char *expect, int expecterrs)
 {
 	Arena *a = newarena();
 	Lex l;
-	lexinit(&l, a, "<test>", src, strlen(src));
+	lexinit(&l, a, "<test>", src, len);
 
 	char *got = amalloc(a, 1);
 	got[0] = '\0';
@@ -48,15 +48,23 @@ runrow(const char *src, const char *expect)
 		got[n] = '\0';
 	}
 
-	int ok = strcmp(got, expect) == 0;
+	int ok = strcmp(got, expect) == 0
+	    && (expecterrs < 0 || l.errs == expecterrs);
 	if (!ok) {
-		fprintf(stderr, "lex mismatch:\n  src:    %s\n"
-		    "  want:   %s\n  got:    %s\n", src, expect, got);
+		fprintf(stderr, "lex mismatch:\n  want:   %s (%d errors)\n"
+		    "  got:    %s (%d errors)\n", expect, expecterrs, got,
+		    l.errs);
 	}
 	freearena(a);
 	return ok;
 }
 
+static int
+runrow(const char *src, const char *expect)
+{
+	return runrown(src, strlen(src), expect, -1);
+}
+
 struct row { const char *src, *expect; };
 
 static const struct row rows[] = {
@@ -133,11 +141,11 @@ static const struct row rows[] = {
  * not the token stream. The verbatim Hare messages live at lexunicode
  * in cmd/wcc/lex.c. */
 static int
-runerr(const char *src)
+runerrn(const char *src, size_t len)
 {
 	Arena *a = newarena();
 	Lex l;
-	lexinit(&l, a, "<test>", src, strlen(src));
+	lexinit(&l, a, "<test>", src, len);
 	for (;;) {
 		Tok t = lexnext(&l);
 		if (t.kind == TK_EOF)
@@ -151,6 +159,12 @@ runerr(const char *src)
 	return ok;
 }
 
+static int
+runerr(const char *src)
+{
+	return runerrn(src, strlen(src));
+}
+
 static int
 runrewind(void)
 {
@@ -205,6 +219,93 @@ static const char *const errrows[] = {
 	"'\\uDFFF'",		/* top of the UTF-16 surrogate range */
 };
 
+static const struct {
+	const char *src;
+	size_t len;
+	const char *expect;
+	int errs;
+} nulrows[] = {
+	{ "\0package main;", sizeof "\0package main;" - 1,
+	  "package IDENT(main) ;", 1 },
+	{ "pack\0age main;", sizeof "pack\0age main;" - 1,
+	  "package IDENT(main) ;", 1 },
+	{ "1\0_0", sizeof "1\0_0" - 1, "INT(10)", 1 },
+	{ "1f\0oo", sizeof "1f\0oo" - 1, "INT(1) IDENT(foo)", 1 },
+	{ "=\0=", sizeof "=\0=" - 1, "==", 1 },
+	{ "/\0/ comment\nfn", sizeof "/\0/ comment\nfn" - 1, "fn", 1 },
+	{ "/* end *\0/ fn", sizeof "/* end *\0/ fn" - 1, "fn", 1 },
+	{ "\"a\0b\"", sizeof "\"a\0b\"" - 1, "STR(ab)", 1 },
+	{ "'\0A'", sizeof "'\0A'" - 1, "RUNE(65)", 1 },
+	{ "fn\0", sizeof "fn\0" - 1, "fn", 1 },
+	{ "f\0\0n", sizeof "f\0\0n" - 1, "fn", 2 },
+};
+
+static int
+runescapenul(void)
+{
+	static const char line[] = "\"\\\0n\"";
+	static const char hex[] = "\"\\x0" "\0" "0\"";
+	Arena *a = newarena();
+	Lex l;
+	lexinit(&l, a, "<test>", line, sizeof line - 1);
+	Tok t = lexnext(&l);
+	int ok = t.kind == TK_STR && t.tlen == 1 && t.text[0] == '\n'
+	    && l.errs == 1 && lexnext(&l).kind == TK_EOF;
+	lexinit(&l, a, "<test>", hex, sizeof hex - 1);
+	t = lexnext(&l);
+	ok = ok && t.kind == TK_STR && t.tlen == 1 && t.text[0] == '\0'
+	    && l.errs == 1 && lexnext(&l).kind == TK_EOF;
+	if (!ok)
+		fprintf(stderr, "NUL escape recovery failed\n");
+	freearena(a);
+	return ok;
+}
+
+static int
+runsuffixnul(void)
+{
+	static const char src[] = "1i" "\0" "8";
+	Arena *a = newarena();
+	Lex l;
+	lexinit(&l, a, "<test>", src, sizeof src - 1);
+	Tok t = lexnext(&l);
+	int ok = t.kind == TK_INT && t.v.uval == 1 && t.tsuffix != NULL
+	    && strcmp(t.tsuffix, "i8") == 0 && l.errs == 1
+	    && lexnext(&l).kind == TK_EOF;
+	if (!ok)
+		fprintf(stderr, "NUL typed-suffix recovery failed\n");
+	freearena(a);
+	return ok;
+}
+
+static int
+runlongdirective(void)
+{
+	static const char pre[] = "//ww:module ";
+	static const char tail[] = "\nfn";
+	const size_t pathlen = 16384;
+	const size_t len = sizeof pre - 1 + pathlen + sizeof tail - 1;
+	char *src = malloc(len);
+	if (!src)
+		return 0;
+	memcpy(src, pre, sizeof pre - 1);
+	memset(src + sizeof pre - 1, 'a', pathlen);
+	memcpy(src + sizeof pre - 1 + pathlen, tail, sizeof tail - 1);
+	Arena *a = newarena();
+	Lex l;
+	lexinit(&l, a, "<test>", src, len);
+	Tok m = lexnext(&l);
+	Tok f = lexnext(&l);
+	int ok = m.kind == TK_MODPATH && m.tlen == pathlen
+	    && m.text[0] == 'a' && m.text[pathlen - 1] == 'a'
+	    && f.kind == TK_FN && l.errs == 0;
+	if (!ok)
+		fprintf(stderr, "long module directive failed\n");
+	freearena(a);
+	free(src);
+	return ok;
+}
+
 int
 main(void)
 {
@@ -225,6 +326,19 @@ main(void)
 			fail++;
 		}
 	}
+	for (size_t i = 0; i < sizeof nulrows / sizeof nulrows[0]; i++) {
+		if (!runrown(nulrows[i].src, nulrows[i].len,
+		    nulrows[i].expect, nulrows[i].errs)) {
+			fprintf(stderr, "NUL row %zu failed\n", i);
+			fail++;
+		}
+	}
+	if (!runescapenul())
+		fail++;
+	if (!runsuffixnul())
+		fail++;
+	if (!runlongdirective())
+		fail++;
 	if (fail) {
 		fprintf(stderr, "%d/%zu lex tests failed\n", fail,
 		    sizeof rows / sizeof rows[0]);