diff --git a/Makefile b/Makefile
index 027ed368..15fed889 100644
--- a/Makefile
+++ b/Makefile
@@ -219,6 +219,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_int_cast_signed $(BIN)/test_dot_chain \
 	  $(BIN)/test_amp_dot $(BIN)/test_arr_elem_field \
 	  $(BIN)/test_arr_elem_field_write \
+	  $(BIN)/test_dot_str_chained_arg \
 	  $(BIN)/test_field_signed $(BIN)/test_frame_argcount \
 	  $(BIN)/test_selfhost $(BIN)/test_w6a_ww $(BIN)/test_w6l_ww \
 	  $(BIN)/test_w6c_ww $(BIN)/test_ww_ww $(BIN)/test_self_rebuild \
@@ -311,6 +312,12 @@ $(BIN)/test_arr_elem_field_write: test/wcc/681_arr_elem_field_write.c $(BIN)/ww
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_dot_str_chained_arg: test/wcc/692_dot_str_chained_arg.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_field_signed: test/wcc/660_field_signed.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index 6ccf4c43..2d177d77 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -6063,6 +6063,26 @@ fn nodeisstr(c: *cgen, n: *node) bool = {
 					};
 				};
 			};
+			// Chained dot through value-struct hops (`p.inner.s`):
+			// dotinnerstructptr above only walks *struct fields, so
+			// a value-struct chain falls through and the call-arg
+			// path then pushes only 1 word for the str instead of
+			// 2 (ptr+len), silently dropping the len half.
+			// dotchainresolve handles arbitrary depth through value
+			// struct AND `*T` root, returning the leaf fieldinfo.
+			let rootnm: str = "";
+			let rootoff: i32 = 0;
+			let totaloff: i32 = 0;
+			let lfi: *fieldinfo = nil;
+			let sdelta: i32 = -1;
+			let isglobal: bool = false;
+			let ptrroot: bool = false;
+			let ok: bool = dotchainresolve(c, n,
+			    &rootnm, &rootoff, &totaloff,
+			    &lfi, &sdelta, &isglobal, &ptrroot);
+			if (ok && sdelta < 0 && lfi != nil) {
+				return isstrtype(c, lfi.tnode);
+			};
 		};
 		return false;
 	};
diff --git a/selfhost/cmd/wcc/cgenutil.ww b/selfhost/cmd/wcc/cgenutil.ww
index 0d76b4dd..e485be7d 100644
--- a/selfhost/cmd/wcc/cgenutil.ww
+++ b/selfhost/cmd/wcc/cgenutil.ww
@@ -493,6 +493,26 @@ fn nodeisstr(c: *cgen, n: *node) bool = {
 					};
 				};
 			};
+			// Chained dot through value-struct hops (`p.inner.s`):
+			// dotinnerstructptr above only walks *struct fields, so
+			// a value-struct chain falls through and the call-arg
+			// path then pushes only 1 word for the str instead of
+			// 2 (ptr+len), silently dropping the len half.
+			// dotchainresolve handles arbitrary depth through value
+			// struct AND `*T` root, returning the leaf fieldinfo.
+			let rootnm: str = "";
+			let rootoff: i32 = 0;
+			let totaloff: i32 = 0;
+			let lfi: *fieldinfo = nil;
+			let sdelta: i32 = -1;
+			let isglobal: bool = false;
+			let ptrroot: bool = false;
+			let ok: bool = dotchainresolve(c, n,
+			    &rootnm, &rootoff, &totaloff,
+			    &lfi, &sdelta, &isglobal, &ptrroot);
+			if (ok && sdelta < 0 && lfi != nil) {
+				return isstrtype(c, lfi.tnode);
+			};
 		};
 		return false;
 	};
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index e736c250..6fa76813 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -6063,6 +6063,26 @@ fn nodeisstr(c: *cgen, n: *node) bool = {
 					};
 				};
 			};
+			// Chained dot through value-struct hops (`p.inner.s`):
+			// dotinnerstructptr above only walks *struct fields, so
+			// a value-struct chain falls through and the call-arg
+			// path then pushes only 1 word for the str instead of
+			// 2 (ptr+len), silently dropping the len half.
+			// dotchainresolve handles arbitrary depth through value
+			// struct AND `*T` root, returning the leaf fieldinfo.
+			let rootnm: str = "";
+			let rootoff: i32 = 0;
+			let totaloff: i32 = 0;
+			let lfi: *fieldinfo = nil;
+			let sdelta: i32 = -1;
+			let isglobal: bool = false;
+			let ptrroot: bool = false;
+			let ok: bool = dotchainresolve(c, n,
+			    &rootnm, &rootoff, &totaloff,
+			    &lfi, &sdelta, &isglobal, &ptrroot);
+			if (ok && sdelta < 0 && lfi != nil) {
+				return isstrtype(c, lfi.tnode);
+			};
 		};
 		return false;
 	};
diff --git a/test/wcc/692_dot_str_chained_arg.c b/test/wcc/692_dot_str_chained_arg.c
new file mode 100644
index 00000000..ad882990
--- /dev/null
+++ b/test/wcc/692_dot_str_chained_arg.c
@@ -0,0 +1,180 @@
+/*
+ * 692_dot_str_chained_arg — pass `<expr>.strfield` as a call argument.
+ *
+ * Task #30: selfhost's `nodeisstr` surface check used `dotinnerstructptr`
+ * to resolve the base of a chained N_DOT, which only walked *struct
+ * fields — value-struct hops fell through. The call-arg path then
+ * pushed only 1 word (`.ptr`) instead of 2 (`.ptr`+`.len`), silently
+ * dropping the str length at the call site.
+ *
+ * Cstage was unaffected because its `node_isstr` reads `n->type` from
+ * the checker rather than re-walking the AST. The bug only bit when
+ * the wwstage was the driver — surfaced via task #29's parallel
+ * slice-field fix when a chained-str test row failed only on wwstage.
+ *
+ * Each fixture passes a str header through a call and reads `.len`
+ * on the callee side to prove both header words round-trip. Rows
+ * cover:
+ *   - chained `*T`-rooted through value-struct hop (`p.inner.s`)
+ *     — the failing shape filed as #30
+ *   - single dot through `*T` root (`p.s`)
+ *     — pre-existing path; baseline / negative control
+ *   - chained local-rooted value-struct (`o.inner.s`)
+ *     — same surface gap as #30 but rooted at a local rather
+ *       than a `*T` param
+ *
+ * Exercises both stages via `ww` (cstage) and `ww_ww` (wwstage).
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return -1;
+}
+
+struct row { const char *label; const char *src; int want; };
+
+static const struct row rows[] = {
+	/* Baseline: single dot through `*T` root. Pre-existing path —
+	 * `nodeisstr` resolves the base local's `*T` tnode directly,
+	 * no dot-chain walker involved. Pinned so a future refactor
+	 * of either branch can't regress it silently. */
+	{ "ptr_root_str_arg",
+	  "type outer = struct { s: str, x: i32 };\n"
+	  "fn slen(s: str) i32 = { return s.len: i32; };\n"
+	  "fn main() i32 = {\n"
+	  "    let o: outer; o.s = \"hello\";\n"
+	  "    let p: *outer = &o;\n"
+	  "    if (slen(p.s) != 5) { return 1; };\n"
+	  "    return 42;\n"
+	  "};\n",
+	  42 },
+	/* #30 repro: chained through `*T` root with a value-struct
+	 * hop. Without the fix, the wwstage pushed only `.ptr` —
+	 * the called function then read whatever was in BX from the
+	 * prior expression as the length. */
+	{ "ptr_root_chained_str_arg",
+	  "type inner = struct { s: str, pad: i32 };\n"
+	  "type outer = struct { i: inner, tag: i32 };\n"
+	  "fn slen(s: str) i32 = { return s.len: i32; };\n"
+	  "fn main() i32 = {\n"
+	  "    let o: outer; o.i.s = \"abcdef\";\n"
+	  "    let p: *outer = &o;\n"
+	  "    if (slen(p.i.s) != 6) { return 1; };\n"
+	  "    return 42;\n"
+	  "};\n",
+	  42 },
+	/* Local value-struct rooted, chained value-struct hop —
+	 * same surface gap as the #30 repro above, but rooted on a
+	 * local rather than a `*T` param. dotchainresolve walks
+	 * both shapes; both go through the same fallback in
+	 * `nodeisstr`. */
+	{ "local_root_chained_str_arg",
+	  "type inner = struct { s: str, pad: i32 };\n"
+	  "type outer = struct { i: inner, tag: i32 };\n"
+	  "fn slen(s: str) i32 = { return s.len: i32; };\n"
+	  "fn main() i32 = {\n"
+	  "    let o: outer; o.i.s = \"qrstuvw\";\n"
+	  "    if (slen(o.i.s) != 7) { return 1; };\n"
+	  "    return 42;\n"
+	  "};\n",
+	  42 },
+};
+
+static int
+run_driver(const char *driver, const struct row *r, int i)
+{
+	char src[64], tmpdir[64], cmd[1024];
+	snprintf(src, sizeof src, "/tmp/wdsc_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/wdsc_%d_d_%d", getpid(), i);
+
+	FILE *f = fopen(src, "wb");
+	if (!f) return -1;
+	fputs(r->src, f);
+	fclose(f);
+
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s",
+	    tmpdir, driver, src);
+	if (runwait(cmd) != 0) {
+		fprintf(stderr, "row[%s]: build via %s failed\n",
+		    r->label, driver);
+		unlink(src); rmdir(tmpdir);
+		return -1;
+	}
+
+	const char *base = strrchr(src, '/');
+	base = base ? base + 1 : src;
+	char outbin[128];
+	snprintf(outbin, sizeof outbin, "%s/%s", tmpdir, base);
+	char *dot = strrchr(outbin, '.');
+	if (dot && strcmp(dot, ".ww") == 0) *dot = '\0';
+	int got = runwait(outbin);
+
+	unlink(src); unlink(outbin); rmdir(tmpdir);
+	return got;
+}
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char absbin[1024];
+	if (bin[0] != '/') {
+		char cwd[1024];
+		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	char cdrv[1024];
+	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
+	char wdrv[1024];
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
+
+	struct { const char *name; const char *path; int gated_on_existence; }
+	drivers[] = {
+		{ "cstage", cdrv, 0 },
+		{ "wwstage", wdrv, 1 },
+		{ NULL, NULL, 0 },
+	};
+
+	int n = (int)(sizeof rows / sizeof rows[0]);
+	int total = 0, fail = 0;
+	for (int d = 0; drivers[d].name; d++) {
+		if (drivers[d].gated_on_existence
+		    && access(drivers[d].path, X_OK) != 0) {
+			fprintf(stderr, "dot_str_chained_arg: skip %s (no %s)\n",
+			    drivers[d].name, drivers[d].path);
+			continue;
+		}
+		for (int i = 0; i < n; i++) {
+			int got = run_driver(drivers[d].path, &rows[i], i);
+			total++;
+			if (got != rows[i].want) {
+				fprintf(stderr,
+				    "dot_str_chained_arg[%s][%s]: exit=%d want=%d\n",
+				    drivers[d].name, rows[i].label,
+				    got, rows[i].want);
+				fail++;
+			}
+		}
+	}
+	if (fail) {
+		fprintf(stderr,
+		    "dot_str_chained_arg: %d/%d fixtures failed\n", fail, total);
+		return 1;
+	}
+	printf("dot_str_chained_arg: %d/%d ok\n", total, total);
+	return 0;
+}