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

src/controller/testsuite/test_xcetest_process_entry.c

@@ -16,6 +16,12 @@
  * pty-driven black-box CLI harness that task 1.7 builds separately (that
  * one will live in test_test_cli.c and is needed for interactive-only
  * surfaces like tab completion that a plain pipe can't exercise).
+ *
+ * resolve_xce_test_path() below is deliberately non-static (task 1.7):
+ * test_test_cli.c's pty-driven harness needs the exact same "find the real
+ * built xce_test binary next to this test binary" logic and reuses this
+ * copy via an `extern` declaration rather than duplicating it -- see this
+ * project's own consolidation-over-copy-paste convention.
  */
 #define _GNU_SOURCE
 #include <fcntl.h>
@@ -38,7 +44,7 @@
  * and `controller_unit_test` into the same target dir) -- resolving via
  * /proc/self/exe's directory avoids depending on the caller's cwd or an
  * env var that could go stale. */
-static int resolve_xce_test_path(char* out, size_t outsz)
+int resolve_xce_test_path(char* out, size_t outsz)
 {
     char    self[PATH_MAX];
     ssize_t n;