fix: switch prefix ASCII input source on the foreground client (#1016)

* fix: switch prefix ASCII input source on the foreground client

The macOS prefix ASCII-switch ran in the headless server, whose
TISCopyCurrentKeyboardInputSource read is a stale per-process cache
(refreshed only via a main-run-loop notification the server never pumps),
so prefix could leave the terminal on the wrong input source.

Forward it to the foreground client, like clipboard: sync_prefix_input_source
emits AppEvent::PrefixInputSource as an intent; the server forwards it to the
foreground client and the monolithic app applies it in-process via
RealPrefixInputSource, which pumps its main run loop before the stale TIS read.
Key it on Mode::wants_ascii_input so multi-level prefix commands keep ASCII
until returning to the terminal, and restore the IME for rename text entry.

Adds ServerMessage::PrefixInputSource to the already-unreleased protocol 15.

refs #774

* fix: keep prefix input-source switch out of the headless server process

An App-internal drain (the exhaustive drain at the top of
handle_api_request, reachable from prefix-key runtime mutations) can
consume a queued PrefixInputSource intent before the server's
forwarding drain sees it, applying the TIS switch in the headless
server process and stranding the restore state. Gate the in-process
switch on App.local_input_source_switch, disabled by the headless
server alongside the other local side effects, so a swallowed intent
degrades to a skipped switch. Widen the forwarding-bypass maintenance
test to the handle_internal_event_with_prefix_sync wrapper.

refs #774

* docs: clarify prefix input-source comments and flag docs

refs #774

* fix: bump protocol for prefix input source

refs #774

---------

Co-authored-by: Ogulcan Celik <ogulcancelik@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/client/mod.rs b/src/client/mod.rs
index 6a70c79c..da0e4e53 100644
--- a/src/client/mod.rs
+++ b/src/client/mod.rs
@@ -1354,6 +1354,10 @@ async fn run_client_loop(
         .set_nonblocking(false)
         .map_err(ClientError::ConnectionFailed)?;
 
+    // This (foreground) client owns the prefix ASCII input-source switch; a no-op on non-macOS.
+    use crate::platform::PrefixInputSource;
+    let mut prefix_input_source = crate::platform::RealPrefixInputSource::default();
+
     // Main event loop.
     while !should_quit.load(Ordering::Acquire) {
         let event = tokio::select! {
@@ -1560,6 +1564,13 @@ async fn run_client_loop(
                         host_mouse_capture_active.store(desired, Ordering::Release);
                     }
                 }
+                ServerMessage::PrefixInputSource { active } => {
+                    if active {
+                        prefix_input_source.switch_to_ascii();
+                    } else {
+                        prefix_input_source.restore();
+                    }
+                }
                 ServerMessage::Welcome { .. } => {
                     debug!("received unexpected Welcome in main loop");
                 }