_remote_write branched on getattr(env, "_stdin_mode", "pipe") and only
passed stdin_data on pipe backends, echoing base64 into argv elsewhere.
BaseEnvironment.execute already embeds stdin_data as a heredoc for
heredoc-mode backends (modal/daytona/vercel), and managed_modal forwards
it as stdinData; _write_to_sandbox already relies on that for every
backend. The branch duplicated base-class logic, and its defensive
getattr default meant a fake env with neither _stdin_mode nor a
stdin_data parameter raised TypeError on every RPC response write. The
poll loop swallowed the error, so no res_* file appeared and
test_code_execution_file_rpc hung forever (it passes on base).
Collapse to one path that always passes stdin_data, and teach the
file-RPC Shell fake to accept it and feed it as input. ScriptedEnv no
longer needs its _stdin_mode stub.
The four CI reds from #41225:
- persist_on_release is a background-only terminal modifier: join the
sandbox blocked sets (precedent: heartbeat, 9acd0d33b6) in
_TERMINAL_BLOCKED_PARAMS and the stub-drift tests' mirrors.
- The gateway shutdown sweep passes source="gateway_shutdown" so
persisted jobs are still killed on host exit; the two shutdown tests'
kill_all fakes now accept and assert that kwarg instead of raising
TypeError that _quiet_step silently swallowed.
Update stale test assumptions for PM install hints and terminal heartbeat,
keep Unix socket fixtures below AF_UNIX path limits, and remove timing and
host-process races from gateway tests. Read systemd units with BOM-tolerant
UTF-8 so the Windows footgun scan remains clean.
