diff --git a/frontend/src/components/workflows/AgentCodeInspector.test.tsx b/frontend/src/components/workflows/AgentCodeInspector.test.tsx
index 0ffb68c94..22771dfed 100644
--- a/frontend/src/components/workflows/AgentCodeInspector.test.tsx
+++ b/frontend/src/components/workflows/AgentCodeInspector.test.tsx
@@ -144,6 +144,28 @@ describe("AgentCodeInspector", () => {
     expect(onConfigChange).toHaveBeenCalledWith({ harness: "codex-cli", approvalConversationId: "conv1" });
   });
 
+  it("shows and edits the primary repository's base ref as an expression-capable input", () => {
+    const onInputsChange = vi.fn();
+    render(<AgentCodeInspector {...baseProps} onInputsChange={onInputsChange} config={{ harness: "codex-cli" }} inputs={{ repositoryId: "p1", baseRef: "{{trigger.sourceBranch}}" }} />);
+
+    expect(screen.getByText("Base ref / 基础分支")).toBeInTheDocument();
+    const input = screen.getByLabelText("Default branch");
+    expect(input).toHaveValue("{{trigger.sourceBranch}}");
+
+    fireEvent.change(input, { target: { value: "release/2.x" } });
+
+    expect(onInputsChange).toHaveBeenCalledWith({ repositoryId: "p1", baseRef: "release/2.x" });
+  });
+
+  it("preserves baseRef when the repository workspace changes", () => {
+    const onInputsChange = vi.fn();
+    render(<AgentCodeInspector {...baseProps} onInputsChange={onInputsChange} config={{ harness: "codex-cli" }} inputs={{ repositoryId: "p1", baseRef: "release/2.x" }} />);
+
+    fireEvent.click(screen.getByText("add-row"));
+
+    expect(onInputsChange).toHaveBeenCalledWith(expect.objectContaining({ baseRef: "release/2.x" }));
+  });
+
   // The picker's blank-row channel: "Add a repository" creates a row with an empty id, which neither
   // repositoryId nor relatedRepositories can carry. Both directions of the wiring must therefore survive —
   // feed drafts DOWN, and hand the emitted drafts back UP on onChange. Dropping either end makes the click a
diff --git a/frontend/src/components/workflows/AgentCodeInspector.tsx b/frontend/src/components/workflows/AgentCodeInspector.tsx
index 0ac86f85c..dba360d99 100644
--- a/frontend/src/components/workflows/AgentCodeInspector.tsx
+++ b/frontend/src/components/workflows/AgentCodeInspector.tsx
@@ -40,6 +40,7 @@ export function AgentCodeInspector({ config, inputs, onConfigChange, onInputsCha
   const credentialId = str(config.modelCredentialId);
   const credentialedModelId = str(config.modelCredentialModelId);
   const repositoryId = str(inputs.repositoryId);
+  const baseRef = str(inputs.baseRef);
   const approvalConversationId = str(config.approvalConversationId);
   const timeoutSeconds = typeof config.timeoutSeconds === "number" ? config.timeoutSeconds : undefined;
   const network = config.network === true;
@@ -187,6 +188,17 @@ export function AgentCodeInspector({ config, inputs, onConfigChange, onInputsCha
           <span className="wf-form-help">The first repo is the primary — the writable workspace root the agent runs in. Add more to clone alongside it for a coordinated change (e.g. a frontend + its backend).</span>
         </div>
 
+        <label className="wf-form-row">
+          <span className="wf-form-label">Base ref / 基础分支</span>
+          <VariablePickerInput
+            value={baseRef}
+            onChange={(v) => onInputsChange({ ...inputs, baseRef: v })}
+            suggestions={suggestions}
+            placeholder="Default branch"
+          />
+          <span className="wf-form-help">Branch or ref to clone the primary repository at. Leave empty for its default branch.</span>
+        </label>
+
         <label className="wf-form-row">
           <span className="wf-form-label">Approval conversation</span>
           <ConversationSelector value={approvalConversationId} onChange={(v) => patch({ approvalConversationId: v })} />
diff --git a/frontend/src/styles/ai-code-space.css b/frontend/src/styles/ai-code-space.css
index fdc15d7e5..a6ac70c54 100644
--- a/frontend/src/styles/ai-code-space.css
+++ b/frontend/src/styles/ai-code-space.css
@@ -6309,7 +6309,7 @@ body.chat-resizing .acs-root .app { transition: none; }
 /* execution map */
 .room-exec { border: 1px solid var(--line); border-radius: 12px; background: var(--panel); padding: 15px 18px 14px; }
 .room-exec-label { font-size: 10px; font-weight: 600; letter-spacing: .07em; text-transform: uppercase; color: var(--muted-2); margin-bottom: 13px; }
-.room-exec-flow { display: flex; align-items: flex-start; }
+.room-exec-flow { display: flex; align-items: flex-start; overflow-x: auto; overscroll-behavior-x: contain; }
 .room-exec-note { margin: 13px 0 0; font-size: 11.5px; color: var(--muted); }
 .room-exec-node { flex: 0 0 auto; width: 72px; display: flex; flex-direction: column; align-items: center; gap: 7px; text-align: center; }
 .room-exec-node[data-idle] { opacity: .45; }