diff --git a/fleetd/src/main/java/dev/ltms/fleet/member/CompositePeerLauncher.java b/fleetd/src/main/java/dev/ltms/fleet/member/CompositePeerLauncher.java
index f28f23f..f4eced5 100644
--- a/fleetd/src/main/java/dev/ltms/fleet/member/CompositePeerLauncher.java
+++ b/fleetd/src/main/java/dev/ltms/fleet/member/CompositePeerLauncher.java
@@ -369,8 +369,7 @@ public final class CompositePeerLauncher implements PeerLauncher {
             // CB-547a: route the chosen profile but keep the caller's session identity — dropping it
             // here would silently sever the resume handle on every policy-routed spawn. CB-557: the
             // role rides along for the same reason, or a routed spawn would be labelled as a dev.
-            SpawnRequest routedReq = new SpawnRequest(chosen.profile(), req.requestedCwd(), req.callerCwd(),
-                    req.sessionName(), req.resumeSessionId(), req.role());
+            SpawnRequest routedReq = req.withProfile(chosen.profile());
             try {
                 PeerHandle handle = d.spawn(routedReq);
                 spawnedBy.put(handle.id(), d);
diff --git a/fleetd/src/main/java/dev/ltms/fleet/peer/SpawnRequest.java b/fleetd/src/main/java/dev/ltms/fleet/peer/SpawnRequest.java
index 00f0ffd..943dd37 100644
--- a/fleetd/src/main/java/dev/ltms/fleet/peer/SpawnRequest.java
+++ b/fleetd/src/main/java/dev/ltms/fleet/peer/SpawnRequest.java
@@ -29,4 +29,9 @@ public record SpawnRequest(String profileName, String requestedCwd, String calle
                         String sessionName, String resumeSessionId) {
         this(profileName, requestedCwd, callerCwd, sessionName, resumeSessionId, null);
     }
+
+    /** Return a copy of this request with {@code profileName} replaced by {@code profile}. */
+    public SpawnRequest withProfile(String profile) {
+        return new SpawnRequest(profile, requestedCwd, callerCwd, sessionName, resumeSessionId, role);
+    }
 }
diff --git a/fleetd/src/test/java/dev/ltms/fleet/peer/SpawnRequestWithProfilePreservesEveryComponentTest.java b/fleetd/src/test/java/dev/ltms/fleet/peer/SpawnRequestWithProfilePreservesEveryComponentTest.java
new file mode 100644
index 0000000..a75abe9
--- /dev/null
+++ b/fleetd/src/test/java/dev/ltms/fleet/peer/SpawnRequestWithProfilePreservesEveryComponentTest.java
@@ -0,0 +1,144 @@
+package dev.ltms.fleet.peer;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.RecordComponent;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.TreeSet;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Fleetd #382, the same "defect factory" #357 and #358 guarded on {@code FleetConfig.withDefaults()}
+ * and {@link dev.ltms.fleet.session.MemberSession}'s rebuild sites — reproduced here on
+ * {@link SpawnRequest#withProfile(String)}.
+ *
+ * <p>{@code SpawnRequest} has back-compat constructors at arity 3 and 5 alongside its canonical
+ * arity-6 constructor. Before this ticket, {@code CompositePeerLauncher} routed a profile by
+ * building a fresh {@code SpawnRequest} from a literal {@code new SpawnRequest(...)} call listing
+ * six of the original request's own accessors. That call is only correct because it happens to
+ * name exactly six arguments today — add a 7th component and the established back-compat pattern
+ * (a new constructor at the old, now-shorter arity) and a call one argument short of the new
+ * canonical arity would silently rebind to that back-compat constructor, dropping the new
+ * component on every profile-routed spawn without any compile error. {@link #withProfile} replaces
+ * that literal call, so this test guards the ONE rebuild site instead of a call site scattered
+ * through a launcher.
+ *
+ * <p>The check below builds a {@link SpawnRequest} through the TRUE canonical constructor —
+ * resolved by the record's own component types via {@code getDeclaredConstructor}, never by
+ * argument count, so it can never itself land on a back-compat overload — with a real, distinctive,
+ * non-null value in every component, calls {@link SpawnRequest#withProfile(String)}, and asserts
+ * every component the method is not documented to change survives unchanged, while {@code
+ * profileName} comes back as the new value it was given. A component that comes back anything else
+ * was silently dropped — the shape of the defect this test exists to catch.
+ *
+ * <p>{@link #EXCLUDED_FROM_SURVIVAL_CHECK} is kept deliberately empty and size-pinned by
+ * {@link #exclusionListSizeIsPinned()}, for the same reason the other two guards pin theirs at
+ * zero: a checker whose escape hatch can grow to silence a failure is not a checker. Every one of
+ * {@link SpawnRequest}'s 6 current components has a real, non-null value here and none is excluded.
+ */
+class SpawnRequestWithProfilePreservesEveryComponentTest {
+
+    private static final RecordComponent[] COMPONENTS = SpawnRequest.class.getRecordComponents();
+
+    /** Deliberately empty today; grow it only with a matching justification, and re-pin the size. */
+    private static final Set<String> EXCLUDED_FROM_SURVIVAL_CHECK = Set.of();
+
+    /** One real, distinctive, non-null value per component — none of the 6 is excluded. */
+    private static Map<String, Object> baseValues() {
+        Map<String, Object> v = new LinkedHashMap<>();
+        v.put("profileName", "profile-guard");
+        v.put("requestedCwd", "/wt/requested-guard");
+        v.put("callerCwd", "/wt/caller-guard");
+        v.put("sessionName", "session-guard");
+        v.put("resumeSessionId", "resume-guard");
+        v.put("role", MemberRole.REVIEWER);
+        assertNamesMatchComponents(v);
+        return v;
+    }
+
+    /**
+     * Guards {@link #baseValues()} itself against drifting from the record's real shape — forgetting
+     * to add a new component here fails this assertion by name, rather than silently checking one
+     * component fewer than the record has.
+     */
+    private static void assertNamesMatchComponents(Map<String, Object> values) {
+        Set<String> names = new TreeSet<>();
+        for (RecordComponent rc : COMPONENTS) {
+            names.add(rc.getName());
+        }
+        assertEquals(names, new TreeSet<>(values.keySet()),
+                "this test's value map has drifted from SpawnRequest's actual components — "
+                        + "update baseValues() alongside the record");
+    }
+
+    /**
+     * Builds a {@link SpawnRequest} through the TRUE canonical constructor — resolved by the
+     * record's own component types, not by argument count — so this never accidentally exercises a
+     * back-compat overload the way a literal {@code new SpawnRequest(...)} call risks doing.
+     */
+    private static SpawnRequest requestOf(Map<String, Object> values) throws ReflectiveOperationException {
+        Class<?>[] types = Arrays.stream(COMPONENTS).map(RecordComponent::getType).toArray(Class<?>[]::new);
+        Object[] args = Arrays.stream(COMPONENTS).map(rc -> values.get(rc.getName())).toArray();
+        Constructor<SpawnRequest> ctor = SpawnRequest.class.getDeclaredConstructor(types);
+        return ctor.newInstance(args);
+    }
+
+    @Test
+    void exclusionListSizeIsPinned() {
+        assertEquals(0, EXCLUDED_FROM_SURVIVAL_CHECK.size(),
+                "EXCLUDED_FROM_SURVIVAL_CHECK grew from 0 — every entry needs a justification in "
+                        + "this test class's javadoc AND this assertion re-pinned to the new size; a "
+                        + "growing exclusion list that silences failures on its own is not a guard");
+    }
+
+    @Test
+    void withProfilePreservesEveryOtherComponent() throws ReflectiveOperationException {
+        Map<String, Object> base = baseValues();
+        SpawnRequest request = requestOf(base);
+        SpawnRequest result = request.withProfile("profile-updated");
+
+        Map<String, Object> expectedOverrides = Map.of("profileName", "profile-updated");
+
+        List<String> dropped = new ArrayList<>();
+        int checked = 0;
+        for (RecordComponent rc : COMPONENTS) {
+            String name = rc.getName();
+            if (EXCLUDED_FROM_SURVIVAL_CHECK.contains(name)) {
+                continue;
+            }
+            checked++;
+            Object expected = expectedOverrides.containsKey(name) ? expectedOverrides.get(name) : base.get(name);
+            Object actual;
+            try {
+                actual = rc.getAccessor().invoke(result);
+            } catch (ReflectiveOperationException e) {
+                throw new RuntimeException("failed to read SpawnRequest." + name + "()", e);
+            }
+            if (!Objects.equals(expected, actual)) {
+                dropped.add(String.format(Locale.ROOT,
+                        "%s: withProfile() was expected to carry (%s) for '%s' but returned %s — a "
+                                + "component silently dropped by withProfile(), the shape of the defect "
+                                + "this test exists to catch (its final \"return new SpawnRequest(...)\" "
+                                + "call binding to a back-compat constructor instead of the true "
+                                + "canonical one)",
+                        name, expected, name, actual));
+            }
+        }
+
+        System.out.printf(Locale.ROOT,
+                "SpawnRequest.withProfile() component-survival coverage — %d components, %d checked, "
+                        + "%d excluded, %d survived%n",
+                COMPONENTS.length, checked, EXCLUDED_FROM_SURVIVAL_CHECK.size(), checked - dropped.size());
+        assertEquals(List.of(), dropped,
+                "withProfile() silently dropped these components: " + dropped);
+    }
+}