diff --git a/test/wcc/989_septest_run.c b/test/wcc/989_septest_run.c
index 508963fa..12eb1dcc 100644
--- a/test/wcc/989_septest_run.c
+++ b/test/wcc/989_septest_run.c
@@ -15,6 +15,13 @@
  *     fails. The failing row is the non-vacuity teeth: it proves the @tests
  *     genuinely RUN under sep (a no-op --sep that linked an empty main would
  *     exit 0 on the failing fixture and the gate would catch it).
+ *     This same RUN-EXIT path also hosts the @test user-facing reject +
+ *     coexist legs ported from 910/997 (C2a, #83), which die at the M4 flip
+ *     that deletes 910/997: `userman` (explicit user main collides with the
+ *     -T synth entry) and `badsig` (non-`fn() void` @test) must reject
+ *     (exit != 0) on both stages; `collide_run` (user `fn run` coexists with
+ *     lib/test's bound runner) must accept and run to exit 0 — under sep the
+ *     two land in distinct units, so a regressed collision fails the link.
  *  2. cs==ww (rule 10): the cstage `ww` and wwstage `ww_ww` sep-drivers emit
  *     byte-identical per-package .s/.wwi for the passing fixture — including
  *     __root.s, which carries the synth `CALL test.run`.
@@ -153,8 +160,10 @@ cmp_sepwork(const char *csdir, const char *wwdir, const char *label)
 struct tcase {
 	const char *label;
 	const char *src;	/* inline fixture written to <td>/<label>.ww */
-	int expect;		/* expected `ww test --sep` run-exit */
+	const char *path;	/* when set, use this on-disk fixture instead of src */
+	int expect;		/* expected `ww test --sep` run-exit (when !reject) */
 	int byteid;		/* run the cs==ww + synth-presence checks */
+	int reject;		/* @test user-facing reject: assert run-exit != 0 */
 };
 
 static struct tcase cases[] = {
@@ -168,15 +177,35 @@ static struct tcase cases[] = {
 	  "@test fn t_again() void = {\n"
 	  "  let s: str = \"ok\";\n"
 	  "  if (len(s) != 2) { abort(); };\n"
-	  "};\n", 0, 1 },
+	  "};\n", NULL, 0, 1, 0 },
 	/* a failing @test → run-exit 1: proves the tests actually RUN under
 	 * sep (the non-vacuity teeth). */
 	{ "fail",
 	  "package septest;\n"
 	  "@test fn t_bad() void = {\n"
 	  "  if (1 + 1 == 2) { abort(); };\n"
-	  "};\n", 1, 0 },
-	{ NULL, NULL, 0, 0 },
+	  "};\n", NULL, 1, 0, 0 },
+	/* C2a (#83): the @test user-facing reject + coexist paths, re-hosted
+	 * from 910/997 (deleted at the M4 flip) onto the live `ww test --sep`
+	 * gate. Fixtures are the unchanged 910/997 flat @test fixtures, reused
+	 * in place (single source of truth) — they survive the flip; only the
+	 * .c gates move. */
+
+	/* an explicit user `main` collides with the -T synth entry → reject. */
+	{ "userman", NULL, "test/wcc/data/attest_userman.ww", 0, 0, 1 },
+	/* a non-`fn() void` @test signature must loud-reject, not be coerced. */
+	{ "badsig", NULL, "test/wcc/data/attest_badsig.ww", 0, 0, 1 },
+	/* a user `fn run` COEXISTS with lib/test's bound runner (post-#80 synth
+	 * `use test;` keys the runner under "test", #84 mangles the user `run`
+	 * bare) → accept and run to exit 0. Under sep the two land in distinct
+	 * units (`run` in __root.s, `test.run` in test.s), so a regressed #84
+	 * collision re-mangles the user `run` to `test.run` and the force-loaded
+	 * root `.o` + test's `.a` both define `test.run` → w6l duplicate-symbol
+	 * → non-zero; exit 0 is the teeth (empirically confirmed). byteid=1 also
+	 * pins this coexist path's cs==ww per-pkg asm + synth presence — the
+	 * rule-10 leg the ported 997 `coexist_run` carried over the #84 mangle. */
+	{ "collide_run", NULL, "test/wcc/data/attest_userrun.ww", 0, 1, 0 },
+	{ NULL, NULL, NULL, 0, 0, 0 },
 };
 
 int
@@ -195,8 +224,12 @@ main(void)
 	for (int i = 0; cases[i].label; i++) {
 		struct tcase *t = &cases[i];
 		char rootww[1024];
-		snprintf(rootww, sizeof rootww, "%s/%s.ww", td, t->label);
-		if (write_file(rootww, t->src)) { fail++; continue; }
+		if (t->path) {
+			snprintf(rootww, sizeof rootww, "%s", t->path);
+		} else {
+			snprintf(rootww, sizeof rootww, "%s/%s.ww", td, t->label);
+			if (write_file(rootww, t->src)) { fail++; continue; }
+		}
 
 		struct { const char *drv, *tag; int rc; }
 		stg[] = { { "ww", "cs", -1 }, { "ww_ww", "ww", -1 } };
@@ -216,8 +249,17 @@ main(void)
 			stg[s].rc = runwait(cmd);
 		}
 
-		/* 1. RUN-EXIT: both stages exit with the expected code. */
-		if (stg[0].rc != t->expect || stg[1].rc != t->expect) {
+		/* 1. RUN-EXIT: a reject row must exit non-zero on BOTH stages (the
+		 * user-facing path is how `ww test` surfaces the diagnostic; the
+		 * exact code is a driver detail, so assert != 0 not == N). An
+		 * accept row exits with the exact expected code. */
+		if (t->reject) {
+			if (stg[0].rc == 0 || stg[1].rc == 0) {
+				fprintf(stderr, "septest FAIL: %s accepted cs=%d ww=%d "
+				    "(expected reject)\n", t->label, stg[0].rc, stg[1].rc);
+				fail++;
+			}
+		} else if (stg[0].rc != t->expect || stg[1].rc != t->expect) {
 			fprintf(stderr, "septest FAIL: %s exits cs=%d ww=%d (expected %d)\n",
 			    t->label, stg[0].rc, stg[1].rc, t->expect);
 			fail++;