fix(pty): close provider cancellation races

docs/core-data-structures/subprocess.md

@@ -240,7 +240,7 @@ interface SubprocessOutcome {
 
 ## Terminal-process primitive
 
-`spawnTerminal(spec)` is the non-pipe process primitive. The provider allocates the controlling terminal and owns UTF-8 text transport, foreground-process-group inspection and signalling, and one awaited TERM-to-KILL operation that reaches whole-session quiescence. The PTY backend remains responsible for prompt detection, readiness inference, scrollback, sandbox policy, and persistent-session ownership; ordinary `spawn()` cannot reconstruct controlling-terminal semantics.
+`spawnTerminal(spec)` is the non-pipe process primitive. The provider allocates the controlling terminal and owns UTF-8 text transport, foreground-process-group inspection and signalling, and one awaited TERM-to-KILL operation that reaches quiescence for every session member the provider can still observe; providers document substrate-specific observability limits. The PTY backend remains responsible for prompt detection, readiness inference, scrollback, sandbox policy, and persistent-session ownership; ordinary `spawn()` cannot reconstruct controlling-terminal semantics.
 
 The terminal spec fully specifies argv, cwd, environment overrides, dimensions, cleanup grace, and optional allocation cancellation. Its handle exposes `pid`, ordered output, `done`, `write`, `inspectForeground`, `signalForeground`, and awaited `terminate`; the exact public shapes are generated into the [`ctx.subprocess` service catalog](../cordis-catalog/services.md#ctxsubprocess--subprocessservice-abstract-seam).