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