Bootstrap DD3 Rust port workspace with host-first compatibility tests

crates/dd3_firmware/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "dd3_firmware"
+version = "0.1.0"
+edition = "2021"
+
+[features]
+default = []
+esp-idf = []
+esp-hal = []
+
+[dependencies]
+dd3_core = { path = "../dd3_core" }

crates/dd3_firmware/src/main.rs

@@ -0,0 +1,29 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum DeviceRole {
+    Sender,
+    Receiver,
+}
+
+#[cfg(any(feature = "esp-idf", feature = "esp-hal"))]
+fn detect_role_from_gpio14() -> DeviceRole {
+    // Placeholder: wire real GPIO14 read in hardware integration phase.
+    DeviceRole::Receiver
+}
+
+#[cfg(not(any(feature = "esp-idf", feature = "esp-hal")))]
+fn detect_role_from_gpio14() -> DeviceRole {
+    // Host placeholder so crate compiles in non-embedded environments.
+    DeviceRole::Receiver
+}
+
+fn main() {
+    let role = detect_role_from_gpio14();
+    match role {
+        DeviceRole::Sender => {
+            println!("dd3_firmware placeholder: sender mode");
+        }
+        DeviceRole::Receiver => {
+            println!("dd3_firmware placeholder: receiver mode");
+        }
+    }
+}