feat: port CTaskFilter::HandleMessage to Rust

Replace the message subscription filter (vtable slot 2, 0x54F4A0).
Original is just 8 instructions — checks subscription_table[msg_type]
and either drops the message or tail-calls CTask::HandleMessage.

Rust replacement uses the typed subscription_table field directly:
messages with type < 98 are forwarded only if subscribed, messages
>= 98 always pass through. Unsubscribed messages are silently dropped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/openwa-wormkit/src/replacements/task/filter.rs

@@ -0,0 +1,48 @@
+//! CTaskFilter vtable hooks.
+//!
+//! Replaces CTaskFilter::HandleMessage (vtable slot 2).
+//! Gate-keeps message propagation via a per-instance subscription table.
+
+use openwa_core::address::va;
+use openwa_core::log::log_line;
+use openwa_core::task::filter::CTaskFilter;
+use openwa_core::task::{CTask, Task};
+
+/// CTaskFilter::HandleMessage replacement.
+///
+/// Messages with `msg_type < 98` are only forwarded if
+/// `subscription_table[msg_type] != 0`. Messages >= 98 always pass through.
+/// Forwarding means tail-calling base CTask::HandleMessage, which propagates
+/// the message down to child tasks.
+unsafe extern "thiscall" fn filter_handle_message(
+    this: *mut CTaskFilter,
+    sender: *mut CTask,
+    msg_type: u32,
+    size: u32,
+    data: *const u8,
+) {
+    let filter = &*this;
+
+    // Check subscription table — messages >= 98 always pass through
+    if (msg_type as usize) < filter.subscription_table.len()
+        && filter.subscription_table[msg_type as usize] == 0
+    {
+        return; // message not subscribed — drop silently
+    }
+
+    // Forward to base CTask::HandleMessage (propagates to children)
+    let base_handler: unsafe extern "thiscall" fn(*mut CTask, *mut CTask, u32, u32, *const u8) =
+        core::mem::transmute(openwa_core::rebase::rb(va::CTASK_VT2_HANDLE_MESSAGE) as usize);
+    base_handler(filter.as_task_ptr() as *mut CTask, sender, msg_type, size, data);
+}
+
+pub fn install() -> Result<(), String> {
+    use openwa_core::vtable_replace;
+
+    vtable_replace!(openwa_core::task::filter::CTaskFilterVTable, va::CTASK_FILTER_VTABLE, {
+        handle_message => filter_handle_message,
+    })?;
+
+    let _ = log_line("[Filter] HandleMessage hooked via vtable_replace");
+    Ok(())
+}

crates/openwa-wormkit/src/replacements/task/mod.rs

@@ -1,6 +1,8 @@
 mod cloud;
+mod filter;
 
 pub fn install() -> Result<(), String> {
     cloud::install()?;
+    filter::install()?;
     Ok(())
 }