diff --git a/Makefile b/Makefile
index a102574a..7f8fa844 100644
--- a/Makefile
+++ b/Makefile
@@ -537,7 +537,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_w6c_ww $(BIN)/test_ww_ww $(BIN)/test_self_rebuild \
 	  $(BIN)/test_dyn_ww $(BIN)/test_selfcheck \
 	  $(BIN)/test_attest_record $(BIN)/test_attest_drop \
-	  $(BIN)/test_declns_sep \
+	  $(BIN)/test_declns_sep $(BIN)/test_wwispread_sep \
 	  $(BIN)/test_fmt_run $(BIN)/test_log_run $(BIN)/test_fnmatch_run \
 	  $(BIN)/test_shlex_run $(BIN)/test_getenv_run $(BIN)/test_dirs_run \
 	  $(BIN)/test_dirs_toolong_run \
@@ -2967,6 +2967,13 @@ $(BIN)/test_declns_sep: test/wcc/989_declns_sep.c $(BIN)/ww $(BIN)/ww_ww \
 		$(BIN)/w6l $(BIN)/w6l_ww $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+# #95 — .wwi producer must preserve the `...` union-spread marker; dir-package
+# `ww build --sep` + run, both driver stages, 2-arm + 3-arm shapes + cs==ww.
+$(BIN)/test_wwispread_sep: test/wcc/989_wwispread_sep.c $(BIN)/ww $(BIN)/ww_ww \
+		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6a_ww \
+		$(BIN)/w6l $(BIN)/w6l_ww $(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_fmt_run: test/wcc/970_fmt_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
diff --git a/cmd/w6c/wwi.c b/cmd/w6c/wwi.c
index 12f1cff2..07e207f1 100644
--- a/cmd/w6c/wwi.c
+++ b/cmd/w6c/wwi.c
@@ -272,6 +272,11 @@ wwi_type(FILE *of, Node *t)
 		fputc('(', of);
 		for (Node *e = t->list; e; e = e->next) {
 			if (e != t->list) fputs(" | ", of);
+			/* #95: re-emit the spread marker purely syntactically;
+			 * the consumer's type-store flattens (ref/hare/hare/
+			 * unparse/type.ha:290-300). */
+			if (e->op == TK_ELLIPSIS)
+				fputs("...", of);
 			wwi_type(of, e);
 		}
 		fputc(')', of);
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index a5a629b2..8d06e1f6 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -45855,6 +45855,10 @@ fn wwitype(fd: i32, t: *syntax.node) void = {
 		let e: *syntax.node = t.list;
 		for (e != nil) {
 			if (e != t.list) { wputs(fd, " | "); };
+			// #95: re-emit the spread marker purely syntactically;
+			// the consumer's type-store flattens
+			// (ref/hare/hare/unparse/type.ha:290-300).
+			if (e.op == syntax.tkind.TK_ELLIPSIS) { wputs(fd, "..."); };
 			wwitype(fd, e);
 			e = e.next;
 		};
diff --git a/selfhost/cmd/wcc/wwi.ww b/selfhost/cmd/wcc/wwi.ww
index 2d2edff9..1bff1722 100644
--- a/selfhost/cmd/wcc/wwi.ww
+++ b/selfhost/cmd/wcc/wwi.ww
@@ -365,6 +365,10 @@ fn wwitype(fd: i32, t: *syntax.node) void = {
 		let e: *syntax.node = t.list;
 		for (e != nil) {
 			if (e != t.list) { wputs(fd, " | "); };
+			// #95: re-emit the spread marker purely syntactically;
+			// the consumer's type-store flattens
+			// (ref/hare/hare/unparse/type.ha:290-300).
+			if (e.op == syntax.tkind.TK_ELLIPSIS) { wputs(fd, "..."); };
 			wwitype(fd, e);
 			e = e.next;
 		};
diff --git a/test/wcc/989_wwispread_sep.c b/test/wcc/989_wwispread_sep.c
new file mode 100644
index 00000000..ca3bc75c
--- /dev/null
+++ b/test/wcc/989_wwispread_sep.c
@@ -0,0 +1,183 @@
+/*
+ * 989_wwispread_sep — #95 .wwi producer must preserve the `...` union-spread
+ * marker when serializing a tagged-union type under `ww build --sep`.
+ *
+ * A spread variant `(...inner | str)` carries Node.op == TK_ELLIPSIS on the
+ * variant node (parse.c:315-324). The N_TTAGGED serializer loop must re-emit
+ * the `...` prefix purely syntactically (cstage wwi.c, selfhost wwi.ww) —
+ * mirroring Hare's unparse (ref/hare/hare/unparse/type.ha:290-300), which
+ * leaves flattening to the consumer's type-store. Before the fix the marker
+ * was dropped: liba.wwi read back as `(inner | str)`, a consumer never
+ * flattened inner's arms, and a bare i32/i64 member was rejected — so fmt /
+ * log / getopt failed under the sep flip. (The old combined.ww path never
+ * round-trips through .wwi, so it accepted; the bug was latent until the flip.)
+ *
+ * TABLE-DRIVEN over two spread shapes (2-arm `inner` and 3-arm `three`). For
+ * each shape and each driver stage (cs `ww`, ww `ww_ww`) the test:
+ *   (a) builds the consumer via `ww build --sep` and runs it — clean compile
+ *       + exit 0 proves the imported alias's arms flattened into the spread
+ *       type (the consumer assigns BARE members the spread must expose);
+ *   (b) greps the produced <pkg>.wwi and asserts the spread marker survived;
+ *   (c) cs==ww (rule 10): the .wwi from `ww` vs `ww_ww` must be byte-identical.
+ *
+ * NON-VACUITY: reverting the wwi.c/.ww edit reddens BOTH legs — the consumer
+ * build fails with `init i32 not assignable to declared outer` AND the marker
+ * grep finds nothing (verified by hand at fix time).
+ *
+ * Light wwstage-driver test (CLAUDE.md rule 14): every build's intermediates
+ * are `-o`-redirected to a private /tmp dir, so it is phase-1 parallel-safe.
+ * Models 989_declns_sep conventions; 989 prefix per the sep-gate precedent.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return 1;
+}
+
+static const char *
+absbin(void)
+{
+	const char *b = getenv("BIN");
+	if (!b) b = "out/bin";
+	if (b[0] == '/') return b;
+	static char buf[2048];
+	char cwd[1024];
+	if (getcwd(cwd, sizeof cwd) == NULL) return NULL;
+	snprintf(buf, sizeof buf, "%s/%s", cwd, b);
+	return buf;
+}
+
+static int
+slurp(const char *path, char **outbuf, size_t *outlen)
+{
+	FILE *f = fopen(path, "rb");
+	if (!f) return -1;
+	fseek(f, 0, SEEK_END);
+	long n = ftell(f);
+	fseek(f, 0, SEEK_SET);
+	if (n < 0) { fclose(f); return -1; }
+	char *b = malloc((size_t)n + 1);
+	if (!b) { fclose(f); return -1; }
+	if (fread(b, 1, (size_t)n, f) != (size_t)n) { free(b); fclose(f); return -1; }
+	b[n] = '\0';
+	fclose(f);
+	*outbuf = b;
+	*outlen = (size_t)n;
+	return 0;
+}
+
+static int
+files_eq(const char *a, const char *b)
+{
+	char *ba = NULL, *bb = NULL;
+	size_t na = 0, nb = 0;
+	if (slurp(a, &ba, &na) < 0 || slurp(b, &bb, &nb) < 0) {
+		free(ba); free(bb);
+		return -1;
+	}
+	int eq = (na == nb && memcmp(ba, bb, na) == 0);
+	free(ba); free(bb);
+	return eq ? 0 : 1;
+}
+
+/* 0 if `needle` occurs in the file at `path`, else 1 (or -1 on read err). */
+static int
+file_contains(const char *path, const char *needle)
+{
+	char *b = NULL;
+	size_t n = 0;
+	if (slurp(path, &b, &n) < 0) return -1;
+	int found = (strstr(b, needle) != NULL);
+	free(b);
+	return found ? 0 : 1;
+}
+
+struct shape {
+	const char *name;	/* label */
+	const char *main;	/* consumer main.ww (imports the spread package) */
+	const char *wwi;	/* produced interface basename for the imported pkg */
+	const char *marker;	/* the spread marker that must survive serialization */
+};
+static const struct shape shapes[] = {
+	{ "twoarm",   "test/wcc/data/wwispread/main.ww",  "liba.wwi", "...inner" },
+	{ "threearm", "test/wcc/data/wwispread3/main.ww", "libb.wwi", "...three" },
+};
+
+static const struct { const char *drv; const char *tag; } drivers[] = {
+	{ "ww",    "cs" },
+	{ "ww_ww", "ww" },
+};
+
+int
+main(void)
+{
+	const char *bin = absbin();
+	if (!bin) { fprintf(stderr, "wwispread FAIL: getcwd\n"); return 1; }
+
+	char td[64], cmd[4096];
+	snprintf(td, sizeof td, "/tmp/wwwwispread_%d", getpid());
+	snprintf(cmd, sizeof cmd, "rm -rf %s", td);
+	runwait(cmd);
+	mkdir(td, 0755);
+
+	int fail = 0;
+	for (size_t s = 0; s < sizeof shapes / sizeof shapes[0]; s++) {
+		char wwi[2][256];
+		for (size_t d = 0; d < sizeof drivers / sizeof drivers[0]; d++) {
+			char prog[160];
+			snprintf(prog, sizeof prog, "%s/%s.%s", td, shapes[s].name,
+			    drivers[d].tag);
+			snprintf(cmd, sizeof cmd, "%s/%s build --sep -o %s %s 2>/dev/null",
+			    bin, drivers[d].drv, prog, shapes[s].main);
+			if (runwait(cmd) != 0) {
+				fprintf(stderr, "wwispread FAIL: %s build --sep %s "
+				    "(spread member not assignable → marker dropped?)\n",
+				    drivers[d].drv, shapes[s].name);
+				fail++;
+				continue;
+			}
+			int got = runwait(prog);
+			if (got != 0) {
+				fprintf(stderr, "wwispread FAIL: %s %s run exit=%d want=0\n",
+				    drivers[d].drv, shapes[s].name, got);
+				fail++;
+			}
+			snprintf(wwi[d], sizeof wwi[d], "%s/%s.%s.sepwork/%s", td,
+			    shapes[s].name, drivers[d].tag, shapes[s].wwi);
+			if (file_contains(wwi[d], shapes[s].marker) != 0) {
+				fprintf(stderr, "wwispread FAIL: %s %s — %s missing `%s` "
+				    "(spread marker dropped in serializer)\n", drivers[d].drv,
+				    shapes[s].name, shapes[s].wwi, shapes[s].marker);
+				fail++;
+			}
+		}
+		/* cs==ww (rule 10): both stages emit the same interface text. */
+		if (files_eq(wwi[0], wwi[1]) != 0) {
+			fprintf(stderr, "wwispread FAIL: %s cs!=ww for %s (rule 10)\n",
+			    shapes[s].name, shapes[s].wwi);
+			fail++;
+		}
+	}
+
+	snprintf(cmd, sizeof cmd, "rm -rf %s", td);
+	runwait(cmd);
+
+	if (fail) {
+		fprintf(stderr, "wwispread: %d check(s) failed\n", fail);
+		return 1;
+	}
+	printf("wwispread: `...` union-spread marker survives .wwi serialization "
+	    "(2-arm + 3-arm, both stages cs==ww), consumer flattens bare members "
+	    "→ exit 0 (#95)\n");
+	return 0;
+}
diff --git a/test/wcc/data/wwispread/liba/lib.ww b/test/wcc/data/wwispread/liba/lib.ww
new file mode 100644
index 00000000..b10d6556
--- /dev/null
+++ b/test/wcc/data/wwispread/liba/lib.ww
@@ -0,0 +1,8 @@
+package liba;
+
+// `outer` spreads the named alias `inner` (a 2-arm union). The `...` marker
+// must survive serialization to liba.wwi so a consumer flattens inner's arms
+// into outer (#95). Without it, outer reads back as (inner | str) and a bare
+// i32/i64 is not assignable.
+export type inner = (i32 | i64);
+export type outer = (...inner | str);
diff --git a/test/wcc/data/wwispread/main.ww b/test/wcc/data/wwispread/main.ww
new file mode 100644
index 00000000..05428bda
--- /dev/null
+++ b/test/wcc/data/wwispread/main.ww
@@ -0,0 +1,13 @@
+package main;
+
+import liba;
+
+// Each assignment binds a BARE member of inner (i32, i64) or the outer-direct
+// arm (str) to liba.outer — typechecks ONLY if the spread flattened inner's
+// arms into outer across the liba.wwi round-trip (#95).
+export fn main() void = {
+	let x: liba.outer = 42i32;
+	x = 99i64;
+	x = "hi";
+	return;
+};
diff --git a/test/wcc/data/wwispread3/libb/lib.ww b/test/wcc/data/wwispread3/libb/lib.ww
new file mode 100644
index 00000000..3dde5a42
--- /dev/null
+++ b/test/wcc/data/wwispread3/libb/lib.ww
@@ -0,0 +1,6 @@
+package libb;
+
+// 3-arm spread: proves ALL of three's arms (i32, i64, rune) flatten into
+// wide, not just the first (#95).
+export type three = (i32 | i64 | rune);
+export type wide = (...three | str);
diff --git a/test/wcc/data/wwispread3/main.ww b/test/wcc/data/wwispread3/main.ww
new file mode 100644
index 00000000..8c8d9352
--- /dev/null
+++ b/test/wcc/data/wwispread3/main.ww
@@ -0,0 +1,13 @@
+package main;
+
+import libb;
+
+// Bind each of three's arms (i32, i64, rune) plus the str arm to libb.wide:
+// typechecks ONLY if all three flattened across the libb.wwi round-trip (#95).
+export fn main() void = {
+	let a: libb.wide = 1i32;
+	a = 2i64;
+	a = 9i32: rune;
+	a = "z";
+	return;
+};