fix(pty): close provider cancellation races

.agents/notes/implemented/architecture/2026-07-28-portable-execution-world-consumers.md

@@ -16,13 +16,13 @@ Ordinary pipes do not cover one requirement. A persistent terminal needs PTY all
 
 The filesystem interface owns the path facts that another capability needs without exposing its opaque target identity: a canonical process path, canonical `file:` URI, and containment. Existing whole and streaming text operations remain filesystem-owned; protocol consumers enforce their own retention limits while consuming the stream.
 
-The subprocess interface owns the process coordinates and primitives: canonical cwd, private runtime storage, executable lookup, ordinary raw or collected process spawning, and `spawnTerminal()`. The terminal operation is one deep primitive whose handle owns text I/O, foreground groups, signalling, and one awaited TERM-to-KILL operation that settles in-flight handle calls and reaches whole-session quiescence. Its signal cancels allocation only; the published handle owns its lifetime. Prompt detection, idle inference, scrollback, sandbox policy, and owner lifecycle remain in the PTY consumer.
+The subprocess interface owns the process coordinates and primitives: canonical cwd, private runtime storage, executable lookup, ordinary raw or collected process spawning, and `spawnTerminal()`. The terminal operation is one deep primitive whose handle owns text I/O, foreground groups, signalling, and one awaited TERM-to-KILL operation that settles in-flight handle calls and reaches quiescence for every session member the provider can still observe. Its signal cancels allocation only; the published handle owns its lifetime. Prompt detection, idle inference, scrollback, sandbox policy, and owner lifecycle remain in the PTY consumer.
 
 Generic consumers use that execution world:
 
 - `dsh-bash-local` continues to map Bash semantics onto ordinary `ctx.subprocess.spawn()`.
 - `dsh-lsp-local` reads and contains source through `ctx.fs`, resolves and launches language servers through `ctx.subprocess`, and carries provider-owned file URIs through initialization and result rendering. One provider-lifetime signal aborts filesystem and protocol work during disposal, including workspace lookup before queue ownership; its JSON-RPC, pooling, synchronization, and normalization stay unchanged.
-- `dsh-pty-local` maps persistent-shell semantics onto `ctx.subprocess.spawnTerminal()`. The local `node-pty` and process-inspection implementation moves into `dsh-subprocess-local`; another subprocess provider supplies the same primitive. `danger-full-access` needs no `ctx.sandbox`; a confined mode requires a same-world sandbox provider and fails before spawn when none is mounted. Prompt and silence evidence collected during asynchronous pre-write inspection is discarded when the provider write begins. Cancellation retains the send reservation while an in-flight write settles and then signals the foreground group, so late bytes or the signal cannot target a successor; a rejected write sends no signal. The absolute deadline remains armed throughout cancellation. A signal failure becomes terminal transport failure. Completion of a stale inspection resumes polling for the current send. Close rejects new public signals and delegates complete-session quiescence to the handle's awaited termination operation.
+- `dsh-pty-local` maps persistent-shell semantics onto `ctx.subprocess.spawnTerminal()`. The local `node-pty` and process-inspection implementation moves into `dsh-subprocess-local`; another subprocess provider supplies the same primitive. `danger-full-access` needs no `ctx.sandbox`; a confined mode requires a same-world sandbox provider and fails before spawn when none is mounted. Prompt and silence evidence collected during asynchronous pre-write inspection is discarded when the provider write begins. Cancellation retains the send reservation while an in-flight write settles and then signals the foreground group, so late bytes or the signal cannot target a successor; an in-flight readiness poll cannot release that reservation, and a rejected write sends no signal. The absolute deadline remains armed throughout cancellation. A signal failure becomes terminal transport failure. Completion of a stale inspection resumes polling for the current send. Startup cancellation begins terminal rollback without waiting for a stalled readiness or signalling call. Close rejects new public signals and delegates provider-observable session quiescence to the handle's awaited termination operation.
 - `dsh-code-runtime-subprocess` materializes a dependency-free runner through `ctx.fs` and launches it through `ctx.subprocess`, preserving the Code Runtime binding and output contract across local or remote worlds. The fixed runner is adapter-owned infrastructure below `ctx.subprocess.runtimeRoot`, so its write carries an explicit `danger-full-access` policy instead of inheriting the model-facing filesystem mode. It shares host-side worker mechanics through the non-plugin `dsh-code-runtime-worker/runtime-host` subpath instead of copying them. Preparation carries one lifecycle signal through filesystem resolution, materialization, and executable lookup so disposal can abort a stalled provider. The heap-bounded worker rejects oversized binding frames before transfer, each outer hop enforces the same bound before forwarding, and raw subprocess pipes carry newline-delimited UTF-8 JSON without a redundant base64 representation. The launcher publishes an accepted terminal frame before reaping its controller so a descendant that inherits controller pipes cannot suppress completion; the host still awaits process-group quiescence.
 
 `dsh-code-runtime-worker` remains a separate implementation. It is the smaller in-process backend and works in single-file distributions that cannot assume an installed Node executable. Remote filesystem/process compositions select `dsh-code-runtime-subprocess`; they do not need a provider-specific Code Runtime package.