test(xce-test-cli-ux): build reusable pty-driven black-box CLI harness

clitest_spawn/send_line/send_partial/send_tab/send_signal/wait_for_text/
wait_for_exit/kill_and_reap launch the real compiled xce_test behind a
genuine pty (so isatty/g_interactive/libedit behave as a real terminal),
with stderr routed to a separate pipe for real stream-separation testing.
All waits are poll()-bounded with an explicit timeout so a future
regression can't hang the whole test suite. This is the shared
infrastructure tasks 2.3, 3.5, and all of Validation phase (4.1-4.4)
will build their black-box scenarios on top of. One smoke test proves
launch/send/capture/exit-code/stream-separation end to end.
1290/1290 controller suite passing (+1).

Task 1.7 of .kiro/specs/xce-test-cli-ux/tasks.md.
Foundation phase (1.1-1.7) now complete.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019jaMf9QEwpugH2W9KAuc7f

.kiro/specs/xce-test-cli-ux/tasks.md

@@ -46,7 +46,7 @@
   - _Requirements: 4.1, 4.2, 4.3_
   - _Boundary: Process Entry_
 
-- [ ] 1.7 Build the black-box CLI test harness
+- [x] 1.7 Build the black-box CLI test harness
   - Add a subprocess/pty-driven test harness capable of launching the built client, sending input lines (including partial input followed by a tab keypress and raw signals), and capturing its stdout/stderr/exit code separately
   - Observable completion: a smoke test using the new harness launches the client, sends a trivial command, and confirms the expected output arrives on the correct stream with the expected exit code
   - _Boundary: Testing Infrastructure_
@@ -178,6 +178,7 @@
 ## Implementation Notes
 - `src/tools/xce-build.sh controller asan xce.build --incremental` writes its build dir at `src/xce.build/` (relative to the script's own location), not a repo-root `xce.build/` — meson logs are at `src/xce.build/meson-logs/testlog.txt`. (task 1.1)
 - New Unity test files need two wiring points, not just meson.build's source list: also register an `extern void test_<module>(void);` + `TEST(test_<module>);` in `src/controller/testsuite/controller_test.c`, mirroring the existing `test_rcfile` registration, or the suite silently never runs. (task 1.1)
+- The `test_test_cli.c` black-box harness (`clitest_*` functions) is file-static and single-file by design (matching design.md's File Structure Plan and this directory's own no-split norm) — tasks 2.3, 3.5, 4.1-4.4 should add their black-box test functions directly into this same file rather than a new one. `clitest_wait_for_text()` is generic (arbitrary needle/stream) and safe to call repeatedly mid-session; `clitest_send_signal()` targets the child's real pid via `kill()`. (task 1.7)
 - `argp` has no built-in `-h` alias (its default short help flag is `-?`) — Requirement 4.1 literally names `-h`, so it needed an explicit `OPTION_HIDDEN` option added, not just verification of existing defaults. Task 1.6's new `test_xcetest_process_entry.c` already covers "`-h`/`--help`/`--version` exit without entering the REPL" end-to-end against the real binary; task 1.7's `test_test_cli.c` should either skip re-adding this exact scenario or consolidate the two rather than duplicating coverage. (task 1.6)
 - The per-connection lock is a POSIX semaphore (`sem_t`), not a `pthread_mutex_t` — a mutex was tried first but rejected on review (POSIX classifies a non-owning-thread `pthread_mutex_unlock()` as UB for every mutex type, not just error-checking ones, and this design needs the worker thread to release a lock the caller thread acquired). `sem_t` has no ownership concept and is fully POSIX-defined for this pattern. See bug-1791. (task 1.5)
 - `interruptcall.c`'s forced-abandonment test proves `-EINTR` via return-value disambiguation against a slow `fn`, not a direct wall-clock elapsed-time assertion — sound today (poll interval is 50ms, matching design.md) but a future regression widening the poll interval wouldn't be caught unless the test also asserts an elapsed-time bound. Non-blocking; noted for task 4.1's end-to-end Ctrl-C validation to consider. (task 1.4)