fix(editor): strip {json, binary} wrapper on Load-from-execution pin

The pin loader was storing port items verbatim in the on-wire shape
[{json: ..., binary: null}]. The executor's WrapPin treats each pin-array
element as one item's whole payload, so the wrapper leaked in: scripts saw
items[0] == {"json": ..., "binary": null} and items[0]["test"] raised
KeyError instead of returning the value.

Now the loader unwraps each item to its .json payload before storing.
Updated the existing test assertion and added a multi-item regression.

frontend/src/editor/PinnedDataSection.test.tsx

@@ -119,7 +119,40 @@ describe("PinnedDataSection", () => {
       expect(ta.value).toContain(`"loaded": true`);
     });
     const calls = (props.onChange as ReturnType<typeof vi.fn>).mock.calls;
-    expect(calls.some(([v]) => JSON.stringify(v) === `[{"json":{"loaded":true}}]`)).toBe(true);
+    // Wrapper {json, binary} stripped — pin stores raw payloads so scripts see
+    // `items[0]["loaded"]`, not `items[0]["json"]["loaded"]`.
+    expect(calls.some(([v]) => JSON.stringify(v) === `[{"loaded":true}]`)).toBe(true);
+  });
+
+  it("Load from execution strips {json, binary} wrapper across multiple items", async () => {
+    server.use(
+      http.get("/api/workflows/:id/executions", () =>
+        HttpResponse.json([
+          { id: "e1", workflowId: "wf1", trigger: "manual", status: "completed",
+            startedAt: "2025-01-01T00:00:00Z", endedAt: null, error: null } satisfies ExecutionSummary,
+        ])),
+      http.get("/api/executions/e1", () =>
+        HttpResponse.json({
+          id: "e1", workflowId: "wf1", trigger: "manual", status: "completed",
+          startedAt: "", endedAt: "", error: null,
+          nodes: [
+            { nodeId: "n1", status: "completed", startedAt: "", endedAt: "", error: null,
+              inputs: [[
+                { json: { test: "hello" }, binary: null },
+                { json: { test: "world" }, binary: null },
+              ]], outputs: [] },
+          ],
+        } satisfies ExecutionDetail)),
+    );
+    const { props } = renderSection({ value: null });
+    await screen.findByRole("option", { name: /e1/i });
+    await userEvent.selectOptions(screen.getByLabelText(/load from execution/i), "e1");
+    await waitFor(() => {
+      const calls = (props.onChange as ReturnType<typeof vi.fn>).mock.calls;
+      expect(calls.some(([v]) =>
+        JSON.stringify(v) === `[{"test":"hello"},{"test":"world"}]`
+      )).toBe(true);
+    });
   });
 
   it("Load-from-execution for a trigger uses outputs[0] not inputs[0]", async () => {

frontend/src/editor/PinnedDataSection.tsx

@@ -77,8 +77,17 @@ export function PinnedDataSection({
     if (!row) return;
     const source = side === "inputs" ? row.inputs : row.outputs;
     const port0 = Array.isArray(source) ? source[0] : undefined;
-    if (port0 === undefined) return;
-    const pretty = JSON.stringify(port0, null, 2);
+    if (!Array.isArray(port0)) return;
+    // Strip the on-wire {json, binary} wrapper — the executor's WrapPin treats
+    // each pin array element as one item's whole payload. Storing the wrapper
+    // verbatim leaks `items[0] == {json:..., binary:null}` into scripts and
+    // makes property access (`items[0]["test"]`) raise KeyError.
+    const payloads = port0.map((it) =>
+      it && typeof it === "object" && "json" in (it as object)
+        ? (it as { json: unknown }).json
+        : it,
+    );
+    const pretty = JSON.stringify(payloads, null, 2);
     commit(pretty);
     setLoadEid(""); // reset the dropdown to "latest"
   }, [loadEid, loadedExec.data]);