Fix set_monitor_split never actually reaching srd monitors

Live-tested right after shipping it and caught immediately: srd dispatch
set output split returned ok, but srd monitors kept reporting the whole,
unsplit output. WindowManager::monitors is a passive cache, only
refreshed when a backend re-queries and calls set_monitors again - the
IPC handler mutated the split map directly but never triggered that
requery, unlike set_output_position's own drain site, which already
pushes a "just go recompute" event after applying.

Makes it a proper queued cross-boundary request instead, the same shape
as every other backend-owned effect on this socket: WindowManager::
request_monitor_split/drain_monitor_split_requests, dispatch queues
instead of mutating, the udev backend's poll drains it, applies via
set_monitor_split, and pushes the same recompute event. srd.monitor.
split's Lua config-time path is untouched - it runs before the very
first startup query, so it never had this problem.

2 files changed, 38 insertions, 26 deletions

diff --git a/crates/platform/src/ipc/dispatch.rs b/crates/platform/src/ipc/dispatch.rs
index 665cb59..918b7e0 100644
--- a/crates/platform/src/ipc/dispatch.rs
+++ b/crates/platform/src/ipc/dispatch.rs
@@ -322,17 +322,17 @@ pub(crate) fn handle_request(line: &[u8], wm: &std::rc::Rc<std::cell::RefCell<Wi
         // "rows":<bool, optional, default false>}` - the live CLI/IPC path
         // for `srd.monitor.split(name, parts, direction)` (`crates/config/
         // src/engine/general.rs`'s own `fn_monitor_split`), which until now
-        // only ever ran once at config load. `WindowManager::
-        // set_monitor_split` just mutates `monitor_splits`, and every
-        // backend's own `monitors()` already reads that map fresh on every
-        // single call (see the udev platform's own `monitors()`) - so,
-        // unlike `set_output_position`/`set_output_enabled` above, this
-        // needs no queue-and-drain at all: the very next `monitors()` query
-        // already reflects it. `parts` <= 1 clears an existing split, same
-        // as the Lua function. Same "resolve id to a name first" fallback
-        // `set_output_enabled` above already uses, since a caller working
-        // from a numeric id shouldn't have to look the name up itself
-        // first just to turn around and split it.
+        // only ever ran once at config load. Queued via `request_monitor_
+        // split`, same cross-boundary "core has no way to trigger its own
+        // requery" reasoning as `set_output_position` above - see
+        // `WindowManager::monitor_split_requests`'s own doc comment for the
+        // real, live-reproduced staleness bug that came from calling
+        // `set_monitor_split` directly here on a first attempt. `parts` <=
+        // 1 clears an existing split, same as the Lua function. Same
+        // "resolve id to a name first" fallback `set_output_enabled` above
+        // already uses, since a caller working from a numeric id shouldn't
+        // have to look the name up itself first just to turn around and
+        // split it.
         "set_monitor_split" => {
             let name = match req.get("name").and_then(|v| v.as_str()) {
                 Some(name) => Some(name.to_string()),
@@ -343,7 +343,7 @@ pub(crate) fn handle_request(line: &[u8], wm: &std::rc::Rc<std::cell::RefCell<Wi
                 return (err("missing parts"), false);
             };
             let rows = req.get("rows").and_then(|v| v.as_bool()).unwrap_or(false);
-            wm.borrow_mut().set_monitor_split(name, parts as u32, rows);
+            wm.borrow_mut().request_monitor_split(name, parts as u32, rows);
             (ok(), true)
         }
         // `{"cmd":"capture_workspace","id":<workspace id>,"path":<string>,
diff --git a/crates/platform/src/ipc/tests.rs b/crates/platform/src/ipc/tests.rs
index 591be56..109a9ec 100644
--- a/crates/platform/src/ipc/tests.rs
+++ b/crates/platform/src/ipc/tests.rs
@@ -426,10 +426,15 @@ fn set_output_enabled_with_neither_name_nor_a_resolvable_id_errors() {
 }
 
 #[test]
-fn set_monitor_split_accepts_a_name_directly_and_applies_immediately() {
-    // Unlike `set_output_position`/`set_output_enabled`, this one is a
-    // plain `WindowManager` mutation with nothing to drain - the very
-    // next `monitor_split` read already reflects it.
+fn set_monitor_split_accepts_a_name_directly_and_queues_a_request() {
+    // Queued, not applied directly - see `WindowManager::monitor_split_
+    // requests`'s own doc comment for why a direct mutation here left
+    // `srd monitors` reporting the stale, unsplit layout indefinitely
+    // (nothing re-triggers `monitors`' own passive cache). Only the
+    // backend that owns real output hardware can call `set_monitor_split`
+    // and push the matching recompute event, so this test - run from the
+    // platform crate alone, with no such backend - can only observe the
+    // queued request, not the applied state.
     let dir = tempfile::tempdir().unwrap();
     let mut server = IpcServer::bind_in(dir.path(), "test").unwrap();
     let wm = Rc::new(RefCell::new(WindowManager::new()));
@@ -441,9 +446,7 @@ fn set_monitor_split_accepts_a_name_directly_and_applies_immediately() {
     server.poll(&wm);
     let _ = read_line(&mut reader);
 
-    let split = wm.borrow().monitor_split("eDP-1").unwrap();
-    assert_eq!(split.parts, 2);
-    assert!(!split.rows);
+    assert_eq!(wm.borrow_mut().drain_monitor_split_requests(), vec![("eDP-1".to_string(), 2, false)]);
 }
 
 #[test]
@@ -459,26 +462,35 @@ fn set_monitor_split_resolves_an_id_to_its_name() {
     server.poll(&wm);
     let _ = read_line(&mut reader);
 
-    let split = wm.borrow().monitor_split("HDMI-A-1").unwrap();
-    assert_eq!(split.parts, 3);
-    assert!(split.rows);
+    assert_eq!(wm.borrow_mut().drain_monitor_split_requests(), vec![("HDMI-A-1".to_string(), 3, true)]);
 }
 
 #[test]
-fn set_monitor_split_with_one_part_clears_an_existing_split() {
+fn set_monitor_split_replaces_a_still_pending_request_for_the_same_name() {
+    // Same "last write wins per name" semantics as `request_output_
+    // position` - only the latest requested split for a given output
+    // matters if several arrive before the backend's next drain.
     let dir = tempfile::tempdir().unwrap();
     let mut server = IpcServer::bind_in(dir.path(), "test").unwrap();
     let wm = Rc::new(RefCell::new(WindowManager::new()));
     wm.borrow_mut().set_monitors(vec![srdwm_core::Monitor::new(0, "eDP-1", srdwm_core::Rect::new(0, 0, 1920, 1080))]);
-    wm.borrow_mut().set_monitor_split("eDP-1".to_string(), 2, false);
 
     let mut client = UnixStream::connect(&server.path).unwrap();
     let mut reader = std::io::BufReader::new(client.try_clone().unwrap());
-    client.write_all(b"{\"cmd\":\"set_monitor_split\",\"name\":\"eDP-1\",\"parts\":1}\n").unwrap();
+    client.write_all(b"{\"cmd\":\"set_monitor_split\",\"name\":\"eDP-1\",\"parts\":2,\"rows\":false}\n").unwrap();
     server.poll(&wm);
     let _ = read_line(&mut reader);
 
-    assert!(wm.borrow().monitor_split("eDP-1").is_none());
+    // A fresh connection - each `srd dispatch` is its own one-shot socket
+    // connection in practice, not a second write on an already-answered
+    // one (which the server closes after replying).
+    let mut client2 = UnixStream::connect(&server.path).unwrap();
+    let mut reader2 = std::io::BufReader::new(client2.try_clone().unwrap());
+    client2.write_all(b"{\"cmd\":\"set_monitor_split\",\"name\":\"eDP-1\",\"parts\":1}\n").unwrap();
+    server.poll(&wm);
+    let _ = read_line(&mut reader2);
+
+    assert_eq!(wm.borrow_mut().drain_monitor_split_requests(), vec![("eDP-1".to_string(), 1, false)]);
 }
 
 #[test]