[feat] modularized backend with plugin architecture, added module-api, module-host, and summarizer crates, and integrated dynamic module loading into main.rs

backend-rust/crates/module-api/src/lib.rs

@@ -0,0 +1,30 @@
+use std::ffi::{CStr, CString};
+use std::os::raw::c_char;
+
+// Symbols every module must export with `extern "C"` and `#[no_mangle]`.
+// Signature: fn module_name() -> *const c_char
+// Signature: fn module_invoke(op: *const c_char, payload: *const c_char) -> *mut c_char
+pub const SYMBOL_NAME: &str = "module_name";
+pub const SYMBOL_INVOKE: &str = "module_invoke";
+
+// Helper to convert C char* to &str
+pub unsafe fn cstr_to_str<'a>(ptr: *const c_char) -> anyhow::Result<&'a str> {
+    if ptr.is_null() {
+        anyhow::bail!("null pointer");
+    }
+    Ok(CStr::from_ptr(ptr).to_str()?)
+}
+
+// Helper to allocate a CString for return across FFI boundary (module side)
+pub fn string_to_cstring_ptr(s: String) -> *mut c_char {
+    CString::new(s).unwrap().into_raw()
+}
+
+// Helper to take back ownership of a CString (host side), then free by letting CString drop
+pub unsafe fn take_cstring(ptr: *mut c_char) -> anyhow::Result<String> {
+    if ptr.is_null() {
+        anyhow::bail!("null pointer");
+    }
+    let s = CString::from_raw(ptr);
+    Ok(s.into_string()?)
+}