diff --git a/web/hwlab-cloud-web/scripts/workbench-r2-session-parity.test.ts b/web/hwlab-cloud-web/scripts/workbench-r2-session-parity.test.ts
index 0c91ca02..ac7fa7b3 100644
--- a/web/hwlab-cloud-web/scripts/workbench-r2-session-parity.test.ts
+++ b/web/hwlab-cloud-web/scripts/workbench-r2-session-parity.test.ts
@@ -21,6 +21,27 @@ test("R2 composer steers only when an active agent message or status exists", ()
   assert.equal(composer.targetTraceId, "trc_running");
 });
 
+test("R2 composer never reuses a stale workspace session during routed selection", () => {
+  const workspace = workspaceRecord({ activeTraceId: null, sessionStatus: "idle" });
+  const withoutTarget = resolveComposerState({ workspace, messages: [], conversations: [], activeConversationId: "cnv_route", chatPending: false });
+  assert.equal(withoutTarget.disabled, true);
+  assert.equal(withoutTarget.disabledReason, "session_required");
+  assert.equal(withoutTarget.conversationId, "cnv_route");
+  assert.equal(withoutTarget.sessionId, null);
+
+  const withTarget = resolveComposerState({
+    workspace,
+    messages: [],
+    conversations: [{ conversationId: "cnv_route", sessionId: "ses_route", threadId: "thr_route" }],
+    activeConversationId: "cnv_route",
+    chatPending: false
+  });
+  assert.equal(withTarget.disabled, false);
+  assert.equal(withTarget.conversationId, "cnv_route");
+  assert.equal(withTarget.sessionId, "ses_route");
+  assert.equal(withTarget.threadId, "thr_route");
+});
+
 test("R2 active trace cleanup preserves workspace and records stale reason", () => {
   const cleared = workspaceWithClearedActiveTrace(workspaceRecord({ activeTraceId: "trc_stale", sessionStatus: "running" }), "trc_stale", "steer-trace-not-found");
   assert.equal(cleared?.activeTraceId, null);
diff --git a/web/hwlab-cloud-web/src/stores/workbench-session.ts b/web/hwlab-cloud-web/src/stores/workbench-session.ts
index 6b1557e1..6b24e107 100644
--- a/web/hwlab-cloud-web/src/stores/workbench-session.ts
+++ b/web/hwlab-cloud-web/src/stores/workbench-session.ts
@@ -61,8 +61,13 @@ export function resolveComposerState(input: { workspace: WorkspaceRecord | null;
   const activeByStatus = isActiveStatus(runningMessage?.status) || isActiveStatus(runningMessage?.runnerTrace?.status) || isActiveStatus(currentRequest?.status) || input.chatPending;
   const terminal = isTerminalStatus(latestMessage?.status) || isTerminalStatus(currentRequest?.status) || (!latestMessage && isTerminalStatus(workspaceStatus));
   const conversationId = input.activeConversationId;
-  const sessionId = firstNonEmptyString(runningMessage?.sessionId, currentRequest?.sessionId, input.workspace?.selectedAgentSessionId, input.workspace?.workspace?.selectedAgentSessionId, activeConversation(input.conversations ?? [], conversationId)?.sessionId);
-  const threadId = firstNonEmptyString(runningMessage?.threadId, currentRequest?.threadId, input.workspace?.workspace?.threadId, activeConversation(input.conversations ?? [], conversationId)?.threadId);
+  const active = activeConversation(input.conversations ?? [], conversationId);
+  const workspaceConversationId = selectedConversationIdFromWorkspace(input.workspace);
+  const workspaceMatchesConversation = !conversationId || !workspaceConversationId || workspaceConversationId === conversationId;
+  const workspaceSessionId = workspaceMatchesConversation ? firstNonEmptyString(input.workspace?.selectedAgentSessionId, input.workspace?.workspace?.selectedAgentSessionId) : null;
+  const workspaceThreadId = workspaceMatchesConversation ? firstNonEmptyString(input.workspace?.workspace?.threadId) : null;
+  const sessionId = firstNonEmptyString(runningMessage?.sessionId, currentRequest?.sessionId, active?.sessionId, workspaceSessionId);
+  const threadId = firstNonEmptyString(runningMessage?.threadId, currentRequest?.threadId, active?.threadId, workspaceThreadId);
   const canSteer = Boolean(conversationId && sessionId && activeTraceId && activeByStatus && !terminal);
   if (canSteer) return { disabled: false, disabledReason: null, submitMode: "steer", route: "/v1/agent/chat/steer", targetTraceId: activeTraceId, conversationId, sessionId, threadId };
   if (!sessionId) return { disabled: true, disabledReason: "session_required", submitMode: "turn", route: "/v1/agent/chat", targetTraceId: null, conversationId, sessionId: null, threadId };
diff --git a/web/hwlab-cloud-web/src/stores/workbench.ts b/web/hwlab-cloud-web/src/stores/workbench.ts
index 34b8b948..ec2dbad9 100644
--- a/web/hwlab-cloud-web/src/stores/workbench.ts
+++ b/web/hwlab-cloud-web/src/stores/workbench.ts
@@ -132,15 +132,18 @@ export const useWorkbenchStore = defineStore("workbench", () => {
     }
     const current = await ensureWorkspace();
     if (!current) return false;
+    if (activeConversationId.value === normalized && messages.value.length > 0) return true;
+    const requestEpoch = beginWorkspaceSelection();
+    switchingConversationId.value = normalized;
     const existing = visibleConversations.value.find((conversation) => conversation.conversationId === normalized) ?? null;
     if (existing && (existing.messages?.length ?? 0) > 0) {
-      if (activeConversationId.value === normalized && messages.value.length > 0) return true;
       await selectConversation(existing);
       return activeConversationId.value === normalized;
     }
     const response = await api.workbench.conversation(normalized);
     const conversation = response.data?.conversation ?? null;
     if (!response.ok || !conversation) {
+      if (isCurrentWorkspaceSelection(requestEpoch, normalized)) clearSwitchingConversation(normalized);
       error.value = response.error ?? "session URL not found";
       return false;
     }