fix(app): keep live terminals through transient connect failures - #52232

What changed

A failed PTY connect-token request was treated as a dead terminal, so the panel's onConnectError path cloned it into a new PTY even when the server still owned the running one. Route connect failures through the existing bounded-backoff retry instead: it inspects the same PTY's status before deciding it is gone, then reconnects with its original ID. A PTY that is actually exited or missing still takes the existing failure path.

Rebased onto the built-in extensions refactor (#52369): the fix now lives in packages/gui-extensions/src/terminal/terminal.tsx, and the regression test moved to terminal-input.spec.ts on the shared mock workspace. The mock PTY socket gains a close(code, reason) helper so tests can drop a live connection.

The e2e mock now answers an unknown PTY with the server's real PtyNotFoundError instead of a generic MockNotFound. The WSL restart test depended on the old immediate clone-on-connect-failure; with this fix the status check must recognize the PTY as gone, which it only does for the real error tag.

Checks

• New e2e regression: open a terminal, close its socket with 1011, return one 503 for the next connect ticket, then let the mock issue tickets again. Without the fix: the terminal is replaced by a new pty_2. With the fix: three ticket requests, a second socket to the same PTY ID, no rejected sockets, the original terminal DOM node, and only the one PTY create.
• terminal-input, settings-wsl (including the WSL-restart terminal test), side-panels and mobile-session specs (29 pass), gui-extensions terminal unit tests, app and gui-extensions typechecks, oxlint and prettier on changed files. typecheck:e2e reports the same 4 pre-existing errors as v2 in unrelated files.

Persistence boundary

This protects a live backend PTY from a transient client connection failure. It does not keep the same process alive across a backend restart: Pty.Service kills its child PTYs and loses its in-memory map on shutdown, so that needs an independently owned PTY supervisor.

Requested by: @Brendonovich (Brendan via Slack)