docs: document SIGINT routing and MCP process-group isolation

Ctrl+C now cancels the turn (or the auto-retry countdown), cancels a poll-based
prompt read such as wait's, and is ignored with a hint for off-loop readline
prompts; it never exits the REPL and never reaches MCP servers, which spawn in
their own session. Also drop ask_into_pty's stale "Ctrl+C cancels" claim: that
prompt is readline-based and empty input is its cancel.

AGENTS.md

@@ -108,12 +108,12 @@ Shared interactive I/O: `ask` / `choose` / `form` / `confirm` with pluggable bac
 
 Click app + readline REPL. Entry: `plyngent` / `python -m plyngent`.
 
-- **`plyngent chat`**: provider/model (flags or interactive; Tab via readline in `prompting`); sessions store `provider_name`/`model` and restore on resume; SQLite via `[database]` (file DB under user data when url unset; explicit `url = ":memory:"` kept + warn); workspace-bound; resume latest for cwd/`--workspace` by default (`--new` / `--session`). One-shot: `-p/--prompt` and non-TTY stdin; exit codes 0/1/2/3; `--yes` (YOLO on), `--auto-continue` (auto-raise limits), `--stream/--no-stream`, `--quiet`. Root `--log-level`. Enabled `[mcp]` servers start before the REPL (`_start_mcp_manager`, per-server failures warn on stderr) and are closed on exit (`McpManager.aclose`).
+- **`plyngent chat`**: provider/model (flags or interactive; Tab via readline in `prompting`); sessions store `provider_name`/`model` and restore on resume; SQLite via `[database]` (file DB under user data when url unset; explicit `url = ":memory:"` kept + warn); workspace-bound; resume latest for cwd/`--workspace` by default (`--new` / `--session`). One-shot: `-p/--prompt` and non-TTY stdin; exit codes 0/1/2/3; `--yes` (YOLO on), `--auto-continue` (auto-raise limits), `--stream/--no-stream`, `--quiet`. Root `--log-level`. Enabled `[mcp]` servers start before the REPL (`_start_mcp_manager`, per-server failures warn on stderr) and are closed on exit (`McpManager.aclose`); each server spawns in its own session/process group (`start_new_session` / `CREATE_NEW_PROCESS_GROUP`), so a terminal Ctrl+C does not kill it.
 - Slash: Click group in `cli/slash.py` + `awaitlet` for async work; Tab completer from registry + ParamType `shell_complete`. Multiline `"""` … `"""`; `/edit` via `$VISUAL`/`$EDITOR` (blocking only). `/yolo on|off|once` for soft destructive confirms. `/model --persist` / `/models --persist` write model catalog entries into TOML. `/todos` for human show/push/pop/clear of the todo stack. `/mcp` (`list` default) prints per-server status/tool counts + an `instructions` preview when the server sent usage guidance, + last stderr lines; `/mcp reconnect` re-reads config, restarts every enabled server, and rebuilds the tool registry. `/grants` lists directory-access grants (`revoke <index|all>`; config grants point at the TOML); `/status` includes the grant count.
 - `/btw` side questions: forked session; main transcript/DB untouched. `--tools=read` (default) exposes only `READ_ONLY` tools under `read_only_context()` (fetch=GET) with the main session view; `--tools=no` off; `--tools=full` whole-registry clone with fresh session. Tools off: default falls back to no tools; explicit `read`/`full` errors. The model gets an `aside` notice as its last message before the question (unsaved exchange + tool scope), shown to the user as `[notice] aside: …`.
 - Explicit `/resume` or `--session` from another workspace prompts: **keep** / **update** / **abort**. A session resumed by a **freshly started process** (`--session` / default latest) also gets a `resume` notice about what a restart drops (PTY sessions, running commands, temp workspaces) — resuming inside a live process pushes nothing.
 - Host notices (`agent/notices.py`): system-level messages appended as trailing `developer` rows, never system-prompt edits — `Notice.to_message()` for the model, `.summary` for the user via `cli.display.echo_notice` (`--quiet` hides the user line only). Durable hosts persist them (`ChatAgent.push_notice`); a side agent without memory keeps its notice local. Trailing developer messages never end a turn, so `/retry` still sees an interrupted turn behind a notice or checkpoint.
-- Failed/cancelled turns: user kept; **committed tool rounds kept** (side effects not re-run on `/retry`); only unfinished assistant rolled back; Ctrl+C cancels; TTY confirms off-loop; auto-retry waits 5s/10s/15s/20s then +10s (10 attempts) and the budget **resets when an attempt completes a model round** (connection recovered); then `/retry`.
+- Failed/cancelled turns: user kept; **committed tool rounds kept** (side effects not re-run on `/retry`); only unfinished assistant rolled back; Ctrl+C cancels the in-flight turn (a session-scoped asyncio SIGINT handler routes it, `cli/interrupt.py` — a stray Ctrl+C while the loop waits never tears the REPL down); TTY confirms/ask prompts run off-loop and register their own SIGINT target, so Ctrl+C there cancels just the poll-based read (`wait` reports `cancelled by user`) or is ignored with a hint for readline prompts (`ask_user_*`, confirms) — never the turn, never the loop; auto-retry waits 5s/10s/15s/20s then +10s (10 attempts), its countdown is Ctrl+C-cancellable, and the budget **resets when an attempt completes a model round** (connection recovered); then `/retry`.
 - Pretty tool lines: known tools (`read_file`, `run_argv`, `grep_files`, …) print their `* Verb 'target' ` prefix as the call starts and append the outcome (`L1-4 (done)`, `(exit code 0)`) when the result lands, so a blocking tool stays visible while it runs. Interactive TTY only (`interactive_terminal()`): piped/plain output and `--verbose` keep whole lines / `[tool ok]`. A second call before the first result (parallel batch) erases the open prefix and falls back to whole lines.
 - **`plyngent providers`**, **`config path|edit`**. Config open: `$VISUAL`/`$EDITOR` (wait), else system default (`xdg-open` / `open` / `startfile`, non-blocking). `/edit` stays blocking-only. No providers → optional edit then reload when waited.
 - Tools default on; workspace defaults to cwd; `--max-rounds` default 32. Readline history under platformdirs (`repl_history`). PTY: `close_all` on chat exit.