fix: parse MCP result payloads and drop place idempotency_key

Typed result structs replace empty envelopes. Equity place sends
ref_id only so live additionalProperties:false schemas accept the call.

internal/wire/list_test.go

@@ -0,0 +1,49 @@
+package wire_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"s1d3sw1ped/robinhood-agentic-mcp/internal/wire"
+)
+
+func TestUnmarshalRows_objectAndArray(t *testing.T) {
+	t.Parallel()
+	type row struct {
+		ID string `json:"id"`
+	}
+	rows, next, err := wire.UnmarshalRows[row](json.RawMessage(`{"data":{"positions":[{"id":"a"}],"next_cursor":"c2"}}`), "positions", "results")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 || rows[0].ID != "a" || next != "c2" {
+		t.Fatalf("%+v %q", rows, next)
+	}
+	rows, next, err = wire.UnmarshalRows[row](json.RawMessage(`[{"id":"b"}]`), "positions")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 || rows[0].ID != "b" || next != "" {
+		t.Fatalf("%+v %q", rows, next)
+	}
+	rows, next, err = wire.UnmarshalRows[row](json.RawMessage(`{"results":{"id":"one"},"next":"https://x/?cursor=n3"}`), "positions", "results")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 || rows[0].ID != "one" || next != "n3" {
+		t.Fatalf("%+v %q", rows, next)
+	}
+}
+
+func TestCursor(t *testing.T) {
+	t.Parallel()
+	if wire.Cursor("https://x/y?cursor=abc", "") != "abc" {
+		t.Fatal("url")
+	}
+	if wire.Cursor("rawtok", "pref") != "pref" {
+		t.Fatal("pref")
+	}
+	if wire.Cursor("rawtok", "") != "rawtok" {
+		t.Fatal("bare")
+	}
+}