fix(pty): retain send ownership through cancellation

packages/pty/pty-local/README.md

@@ -10,7 +10,7 @@ The plugin injects `pty`, `sandbox`, `sandboxPolicy`, and `subprocess`, then reg
 
 Readiness combines a foreground-verified private bash prompt marker, provider-reported foreground stdin-wait facts, silence fallback, and absolute timeout. A marker is not ready until the printable tail after the latest owned marker exactly equals the controlled `PS1`, including when the OSC marker and prompt are split across data callbacks; echoed input or output following a delayed earlier prompt therefore cannot settle the current send. Prompt and silence evidence collected before the provider write, including while pre-write foreground inspection is pending, is discarded at the write boundary. When bash prints the marker before the terminal provider publishes its return to the foreground process group, polling retains the candidate for `handoffGraceMs` past the ordinary silence bound so a coincident handoff can win. An interactive child that inherits `PROMPT_COMMAND` therefore cannot suppress inferred-idle readiness until the absolute timeout. Unknown foreground state is never a positive exact-idle signal. A foreground group's stdin wait that existed before a send is likewise not post-write readiness: the same group must be observed outside that wait before a later wait can settle the send, while a changed foreground group is new evidence. During unpublished startup, a fallback requires observed output; zero-output silence cannot publish an empty session, and timeout rejects the spawn. Cancellation closes the unpublished shell and rejects with the caller's exact abort reason; `PtyBackendCleanupError` separately preserves a cleanup failure. The terminal-allocation signal is detached when allocation returns, while readiness initialization keeps the setup signal, so later cancellation cannot terminate a published persistent session. Incomplete terminal-control sequences are bounded by `maxReadBytes` and discarded through their terminator after crossing that limit; a trailing carriage return is carried across callbacks so split CRLF becomes one newline.
 
-Send cancellation marks queued input as canceled before asking the terminal handle to signal the current foreground process group with a real `SIGINT`; if asynchronous pre-write inspection later settles, it cannot execute that input. Cancellation never emulates interruption by writing `\x03`, so raw-mode programs remain cancellable. A send that times out during an asynchronous provider write, or whose cancellation signal fails while that write remains pending, reports its result but retains the session's send slot until the write settles, so late bytes cannot interleave with a successor. Close starts provider-owned TERM-to-KILL whole-session cleanup and awaits quiescence after the terminal outcome. A cleanup failure does not cache a permanently rejected close; a later close retries the provider operation.
+Send cancellation marks queued input as canceled before asking the terminal handle to signal the current foreground process group with a real `SIGINT`; if asynchronous pre-write inspection later settles, it cannot execute that input. The canceled send retains its slot until foreground signalling settles, so a successor cannot become that signal's target. Cancellation never emulates interruption by writing `\x03`, so raw-mode programs remain cancellable. A send that times out during an asynchronous provider write, or whose cancellation signal fails while that write remains pending, reports its result but retains the slot until the write settles, so late bytes cannot interleave with a successor. Close starts provider-owned TERM-to-KILL whole-session cleanup and awaits quiescence after the terminal outcome. A cleanup failure does not cache a permanently rejected close; a later close retries the provider operation.
 
 ## Model Experience