M2: confirm worker-thread + event-driven gate (architectural wall)

Add a bounded manual stack-scan in the GoOnline detour (FIFA-frame finder).
Result: zero FIFA23.exe frames, sp ~2.4KB below stack top => GoOnline runs on an
anadius worker thread (queued), not FIFA's thread. Three-way corroboration that
the gate is an async "online established" event anadius (offline-only) never
pushes; FIFA waits/retries. No handler-response flip can cross it. Documented in
connection-gate-findings.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

openfut-hook/src/lib.rs

@@ -31,7 +31,7 @@ use windows::Win32::System::ProcessStatus::{GetModuleInformation, MODULEINFO};
 use windows::Win32::System::SystemInformation::GetLocalTime;
 use windows::Win32::System::SystemServices::DLL_PROCESS_ATTACH;
 use windows::Win32::System::Threading::{
-    CreateThread, GetCurrentProcess, Sleep, THREAD_CREATION_FLAGS,
+    CreateThread, GetCurrentProcess, GetCurrentThreadStackLimits, Sleep, THREAD_CREATION_FLAGS,
 };
 
 // ---------------------------------------------------------------------------
@@ -185,6 +185,7 @@ unsafe extern "system" fn hooked(
 unsafe extern "system" fn init_thread(_: *mut c_void) -> u32 {
     // Connection capture first. Listen on the LSX port (gate 1, so the launcher
     // bootstrap succeeds) and on the redirect port (for external TLS/Blaze).
+    store_exe_range();
     start_listener(LSX_PORT, "LSX");
     start_listener(LOCAL_PORT, "BLZ");
     hook_dns();
@@ -418,6 +419,69 @@ unsafe fn install_detour_at(addr: usize, detour: *const (), slot: &AtomicUsize,
 // --- M1 read-only probe: anadius GoOnline handler -------------------------
 
 static ORIG_GOONLINE: AtomicUsize = AtomicUsize::new(0);
+static EXE_BASE: AtomicUsize = AtomicUsize::new(0);
+static EXE_SIZE: AtomicUsize = AtomicUsize::new(0);
+static STACK_LOGGED: AtomicUsize = AtomicUsize::new(0);
+
+/// Record FIFA23.exe's base + size so we can recognise its frames in a backtrace.
+unsafe fn store_exe_range() {
+    if let Ok(h) = GetModuleHandleW(PCWSTR::null()) {
+        let mut mi = MODULEINFO::default();
+        if GetModuleInformation(
+            GetCurrentProcess(),
+            h,
+            &mut mi,
+            core::mem::size_of::<MODULEINFO>() as u32,
+        )
+        .is_ok()
+        {
+            EXE_BASE.store(h.0 as usize, Ordering::SeqCst);
+            EXE_SIZE.store(mi.SizeOfImage as usize, Ordering::SeqCst);
+        }
+    }
+}
+
+/// Scan the raw stack for values that land in FIFA23.exe (the game-side
+/// online-flow return addresses that called into GoOnline). Unwind-free, so it
+/// survives the detour trampolines that break RtlCaptureStackBackTrace.
+/// One-shot to avoid log spam.
+unsafe fn log_fifa_callstack(tag: &str) {
+    if STACK_LOGGED.swap(1, Ordering::SeqCst) != 0 {
+        return;
+    }
+    let base = EXE_BASE.load(Ordering::SeqCst);
+    let size = EXE_SIZE.load(Ordering::SeqCst);
+    if base == 0 || size == 0 {
+        log(&format!("{tag} stack scan skipped (exe range unknown)"));
+        return;
+    }
+    // Address of a local ~= current rsp; the stack grows down, so callers'
+    // return addresses sit at HIGHER addresses. Scan upward, but NEVER past the
+    // committed stack top (reading beyond it faults — that crashed the game).
+    let mut low: usize = 0;
+    let mut high: usize = 0;
+    GetCurrentThreadStackLimits(&mut low, &mut high);
+    let probe: usize = 0;
+    let sp = &probe as *const usize as usize;
+    let end = high; // scan the whole rest of the stack (committed, safe)
+    let mut line = format!(
+        "{tag} stack[low=0x{low:X} high=0x{high:X} sp=0x{sp:X}] FIFA23.exe refs:"
+    );
+    let mut count = 0;
+    let mut p = sp;
+    while p + 8 <= end {
+        let val = *(p as *const usize);
+        if val >= base && val < base + size {
+            line.push_str(&format!(" +0x{:X}", val - base));
+            count += 1;
+            if count >= 40 {
+                break;
+            }
+        }
+        p += 8;
+    }
+    log(&line);
+}
 
 /// M2 flip on anadius's GoOnline handler (anadius64.dll+0x2BB90). The original
 /// handler is `mov rcx,rdx; lea r8,[+0xADD73]; lea rdx,[+0xADE64 = "0"]; call
@@ -425,6 +489,7 @@ static ORIG_GOONLINE: AtomicUsize = AtomicUsize::new(0);
 /// "0" (offline). We replicate it but pass "1" (+0xAF530 = the connected value),
 /// so GoOnline reports online, then return success (al=1).
 unsafe extern "system" fn hooked_goonline(_a: usize, b: usize, _c: usize, _d: usize) -> usize {
+    log_fifa_callstack("GoOnline");
     let base = ANADIUS_BASE.load(Ordering::SeqCst);
     if base != 0 {
         log("FLIP GoOnline -> reporting online (\"1\")");