Merge branch 'cache-lwip-sock-pointers' into integration

# Conflicts:
#	esphome/core/lwip_fast_select.c
#	esphome/core/lwip_fast_select.h

esphome/core/lwip_fast_select.c

@@ -150,6 +150,10 @@ _Static_assert(offsetof(struct netconn, callback) % sizeof(netconn_callback) ==
 _Static_assert(offsetof(struct lwip_sock, rcvevent) % sizeof(((struct lwip_sock *) 0)->rcvevent) == 0,
                "lwip_sock.rcvevent must be naturally aligned for atomic access");
 
+// Verify the hardcoded offset used in the header's inline esphome_lwip_socket_has_data().
+_Static_assert(offsetof(struct lwip_sock, rcvevent) == ESPHOME_LWIP_SOCK_RCVEVENT_OFFSET,
+               "lwip_sock.rcvevent offset changed — update ESPHOME_LWIP_SOCK_RCVEVENT_OFFSET in lwip_fast_select.h");
+
 // Task handle for the main loop — written once in init(), read from TCP/IP and background tasks.
 static TaskHandle_t s_main_loop_task = NULL;
 
@@ -198,17 +202,6 @@ struct lwip_sock *esphome_lwip_get_sock(int fd) {
   return get_sock(fd);
 }
 
-// Hot path: caller has already cached the lwip_sock pointer at registration time.
-// No fd lookup, no null checks — just a volatile 16-bit load of rcvevent.
-bool esphome_lwip_socket_has_data(struct lwip_sock *sock) {
-  // volatile prevents the compiler from caching/reordering this cross-thread read.
-  // The write side (TCP/IP thread) commits via SYS_ARCH_UNPROTECT which releases a
-  // FreeRTOS mutex (ESP32) or resumes the scheduler (LibreTiny), ensuring the value
-  // is visible. Aligned 16-bit reads are single-instruction loads (L16SI/LH/LDRH) on
-  // Xtensa/RISC-V/ARM and cannot produce torn values.
-  return *(volatile s16_t *) &sock->rcvevent > 0;
-}
-
 void esphome_lwip_hook_socket(struct lwip_sock *sock) {
   // Save original callback once — all LwIP sockets share the same static event_callback
   // (DEFAULT_SOCKET_EVENTCB in sockets.c, used for SOCK_RAW, SOCK_DGRAM, and SOCK_STREAM).

esphome/core/lwip_fast_select.h

@@ -4,6 +4,16 @@
 // Replaces lwip_select() with direct rcvevent reads and FreeRTOS task notifications.
 
 #include <stdbool.h>
+#include <stdint.h>
+
+// Forward declare lwip_sock for C++ callers that store cached pointers.
+// The full definition is only available in the .c file (lwip/priv/sockets_priv.h
+// conflicts with C++ compilation units).
+struct lwip_sock;
+
+// Byte offset of rcvevent (s16_t) within struct lwip_sock.
+// Verified at compile time in lwip_fast_select.c via _Static_assert.
+#define ESPHOME_LWIP_SOCK_RCVEVENT_OFFSET 8
 
 // Forward declare lwip_sock for C++ callers that store cached pointers.
 // The full definition is only available in the .c file (lwip/priv/sockets_priv.h
@@ -26,8 +36,17 @@ struct lwip_sock *esphome_lwip_get_sock(int fd);
 /// Check if a cached LwIP socket has data ready via direct rcvevent read.
 /// The sock pointer must have been obtained from esphome_lwip_get_sock() and must
 /// remain valid (caller owns socket lifetime — no concurrent close).
-/// Hot path: no fd lookup, no null checks — just a volatile 16-bit load.
-bool esphome_lwip_socket_has_data(struct lwip_sock *sock);
+/// Hot path: inlined volatile 16-bit load — no function call overhead.
+/// Uses offset-based access because lwip/priv/sockets_priv.h conflicts with C++.
+/// The offset is verified at compile time in lwip_fast_select.c.
+static inline bool esphome_lwip_socket_has_data(struct lwip_sock *sock) {
+  // volatile prevents the compiler from caching/reordering this cross-thread read.
+  // The write side (TCP/IP thread) commits via SYS_ARCH_UNPROTECT which releases a
+  // FreeRTOS mutex (ESP32) or resumes the scheduler (LibreTiny), ensuring the value
+  // is visible. Aligned 16-bit reads are single-instruction loads (L16SI/LH/LDRH) on
+  // Xtensa/RISC-V/ARM and cannot produce torn values.
+  return *(volatile int16_t *) ((char *) sock + ESPHOME_LWIP_SOCK_RCVEVENT_OFFSET) > 0;
+}
 
 /// Hook a socket's netconn callback to notify the main loop task on receive events.
 /// Wraps the original event_callback with one that also calls xTaskNotifyGive().