diff --git a/packages/rs-platform-wallet-ffi/src/identity_sync.rs b/packages/rs-platform-wallet-ffi/src/identity_sync.rs
index 36bbdfb7115..a05a543185c 100644
--- a/packages/rs-platform-wallet-ffi/src/identity_sync.rs
+++ b/packages/rs-platform-wallet-ffi/src/identity_sync.rs
@@ -18,7 +18,7 @@ use platform_wallet::{IdentityTokenSyncInfo, IdentityTokenSyncState};
 
 use crate::error::*;
 use crate::handle::*;
-use crate::runtime::runtime;
+use crate::runtime::{block_on_worker, runtime};
 use crate::{check_ptr, unwrap_option_or_return};
 
 /// Flattened per-(identity, token) row mirroring
@@ -170,7 +170,12 @@ pub unsafe extern "C" fn platform_wallet_manager_identity_sync_sync_now(
     handle: Handle,
 ) -> PlatformWalletFFIResult {
     let option = PLATFORM_WALLET_MANAGER_STORAGE.with_item(handle, |manager| {
-        runtime().block_on(manager.identity_sync().sync_now());
+        // `block_on_worker`, NOT `runtime().block_on`: the pass
+        // verifies GroveDB proofs whose recursion blows the ~512 KB
+        // stack of the host's dispatch/concurrency calling thread
+        // (same SIGBUS as the shielded/dashpay Sync Now buttons).
+        let mgr = manager.identity_sync_arc();
+        block_on_worker(async move { mgr.sync_now().await });
     });
     unwrap_option_or_return!(option);
     PlatformWalletFFIResult::ok()
diff --git a/packages/rs-platform-wallet-ffi/src/platform_address_sync.rs b/packages/rs-platform-wallet-ffi/src/platform_address_sync.rs
index cfd87cfee0f..e8fcf9febcb 100644
--- a/packages/rs-platform-wallet-ffi/src/platform_address_sync.rs
+++ b/packages/rs-platform-wallet-ffi/src/platform_address_sync.rs
@@ -8,7 +8,7 @@ use dash_sdk::platform::address_sync::AddressSyncMetrics;
 use crate::error::*;
 use crate::handle::*;
 use crate::platform_address_types::AddressSyncConfigFFI;
-use crate::runtime::runtime;
+use crate::runtime::{run_on_big_stack_thread, runtime};
 use crate::{check_ptr, unwrap_option_or_return};
 
 /// Flattened sync metrics for one wallet result in a platform-address sync pass.
@@ -190,9 +190,25 @@ pub unsafe extern "C" fn platform_wallet_manager_platform_address_sync_sync_now(
     handle: Handle,
 ) -> PlatformWalletFFIResult {
     let option = PLATFORM_WALLET_MANAGER_STORAGE.with_item(handle, |manager| {
-        runtime().block_on(manager.platform_address_sync().sync_now());
+        // Big-stack polling, NOT bare `runtime().block_on`: the pass
+        // verifies GroveDB proofs whose recursion blows the ~512 KB
+        // stack of the host's dispatch/concurrency calling thread
+        // (same SIGBUS as the shielded/dashpay Sync Now buttons).
+        // `run_on_big_stack_thread` rather than `block_on_worker`
+        // because this future trips rustc's implied-lifetime-bound
+        // limitation (rust-lang/rust issue #100013) against
+        // `block_on_worker`'s `Send + 'static` bounds.
+        run_on_big_stack_thread(|| {
+            runtime().block_on(manager.platform_address_sync().sync_now());
+        })
     });
-    unwrap_option_or_return!(option);
+    let spawn_result = unwrap_option_or_return!(option);
+    if let Err(e) = spawn_result {
+        return PlatformWalletFFIResult::err(
+            PlatformWalletFFIResultCode::ErrorWalletOperation,
+            format!("failed to spawn big-stack thread for address sync: {e}"),
+        );
+    }
     PlatformWalletFFIResult::ok()
 }
 
diff --git a/packages/rs-platform-wallet-ffi/src/runtime.rs b/packages/rs-platform-wallet-ffi/src/runtime.rs
index 965ef9f5ed5..ee96010db00 100644
--- a/packages/rs-platform-wallet-ffi/src/runtime.rs
+++ b/packages/rs-platform-wallet-ffi/src/runtime.rs
@@ -60,6 +60,70 @@ where
     rt.block_on(async move { rt.spawn(future).await.expect("tokio worker panicked") })
 }
 
+/// Run `f` to completion on a freshly spawned scoped OS thread with the
+/// same 8 MB stack the runtime workers get, blocking the caller until it
+/// returns. Errors (instead of panicking) if the OS refuses to spawn
+/// the thread, so `extern "C"` callers can surface the failure through
+/// their `PlatformWalletFFIResult` rather than aborting the host.
+///
+/// Escape hatch for call sites that need big-stack polling but whose
+/// future cannot satisfy [`block_on_worker`]'s `Send + 'static` bounds
+/// (e.g. rustc's implied-lifetime-bound limitation, rust-lang/rust
+/// issue #100013). The closure typically wraps
+/// `runtime().block_on(...)` — the future is then created *and* polled
+/// entirely on the big-stack thread, so no `Send`/`'static` proof is
+/// needed for the future itself. Prefer [`block_on_worker`] where it
+/// compiles: it reuses pooled runtime workers instead of paying a
+/// thread spawn per call.
+///
+/// A panic inside `f` is propagated as a panic here, matching
+/// [`block_on_worker`]'s "tokio worker panicked" convention — a panic
+/// in the pass is a bug, not a recoverable condition.
+pub(crate) fn run_on_big_stack_thread<T: Send>(f: impl FnOnce() -> T + Send) -> std::io::Result<T> {
+    std::thread::scope(|scope| {
+        let handle = std::thread::Builder::new()
+            .name("pw-ffi-bigstack".into())
+            .stack_size(WORKER_STACK_BYTES)
+            .spawn_scoped(scope, f)?;
+        Ok(handle.join().expect("big-stack FFI thread panicked"))
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn run_on_big_stack_thread_round_trips_return_value() {
+        let out = run_on_big_stack_thread(|| 41 + 1).expect("spawn should succeed");
+        assert_eq!(out, 42);
+    }
+
+    /// The whole point of the helper: recursion far past the ~512 KB
+    /// host-thread stacks (and the 2 MB default test-thread stack)
+    /// must complete on the 8 MB thread.
+    #[test]
+    fn run_on_big_stack_thread_survives_deep_recursion() {
+        #[inline(never)]
+        fn recurse(depth: u32) -> u64 {
+            // ~1 KB frame the optimizer can't elide.
+            let frame = std::hint::black_box([depth as u64; 128]);
+            if depth == 0 {
+                frame[0]
+            } else {
+                recurse(depth - 1) + std::hint::black_box(frame[127])
+            }
+        }
+
+        // ~1000 frames * >1 KB each (debug frames run several KB with
+        // the black_box copies) lands well past the ~512 KB iOS host
+        // stacks this helper exists for, while staying comfortably
+        // under WORKER_STACK_BYTES.
+        let out = run_on_big_stack_thread(|| recurse(1_000)).expect("spawn should succeed");
+        assert!(out > 0);
+    }
+}
+
 #[cfg(feature = "tokio-metrics")]
 mod metrics {
     use std::time::Duration;
diff --git a/packages/rs-platform-wallet-ffi/src/shielded_sync.rs b/packages/rs-platform-wallet-ffi/src/shielded_sync.rs
index 2d58d8165f6..2424e0cc2d0 100644
--- a/packages/rs-platform-wallet-ffi/src/shielded_sync.rs
+++ b/packages/rs-platform-wallet-ffi/src/shielded_sync.rs
@@ -20,7 +20,7 @@ use zeroize::Zeroizing;
 use crate::error::*;
 use crate::handle::*;
 use crate::identity_keys_from_mnemonic::parse_mnemonic_any_language;
-use crate::runtime::runtime;
+use crate::runtime::{block_on_worker, runtime};
 use crate::shielded_types::ShieldedSyncWalletResultFFI;
 use crate::{check_ptr, unwrap_option_or_return};
 use rs_sdk_ffi::{
@@ -170,7 +170,15 @@ pub unsafe extern "C" fn platform_wallet_manager_shielded_sync_sync_now(
     handle: Handle,
 ) -> PlatformWalletFFIResult {
     let option = PLATFORM_WALLET_MANAGER_STORAGE.with_item(handle, |manager| {
-        runtime().block_on(manager.shielded_sync().sync_now(true));
+        let mgr = manager.shielded_sync_arc();
+        // `block_on_worker`, NOT `runtime().block_on`: the host calls
+        // this from a dispatch/concurrency thread with ~512 KB of
+        // stack, and polling the whole notes-sync future there blows
+        // it (SIGBUS "Thread stack size exceeded" observed on-device
+        // and on-sim 2026-07-07 from the Sync Now button). The worker
+        // dispatch moves the compute onto the runtime's 8 MB-stack
+        // threads (see runtime.rs) — same fix as dashpay_sync.
+        block_on_worker(async move { mgr.sync_now(true).await });
     });
     unwrap_option_or_return!(option);
     PlatformWalletFFIResult::ok()
@@ -548,9 +556,11 @@ pub unsafe extern "C" fn platform_wallet_manager_shielded_sync_wallet(
 
     let option = PLATFORM_WALLET_MANAGER_STORAGE.with_item(handle, |manager| {
         // Per-wallet sync_wallet is exclusively a user-initiated
-        // entry point — same `force=true` reasoning as
+        // entry point — same `force=true` reasoning and same
+        // `block_on_worker` stack-size requirement as
         // `platform_wallet_manager_shielded_sync_sync_now`.
-        runtime().block_on(manager.shielded_sync().sync_wallet(&wallet_id, true))
+        let mgr = manager.shielded_sync_arc();
+        block_on_worker(async move { mgr.sync_wallet(&wallet_id, true).await })
     });
     let result = unwrap_option_or_return!(option);
     match result {