Adds 2 tests in a new test_repl_prompt_context.c covering the dynamic
prompt's plain-before-first-session baseline and its session/timestamp
content in both step and continue modes (Requirement 5.5).
Required genuinely new test infrastructure: libedit's readline() only
writes its prompt text when both stdin and stdout are real ptys, which
no existing REPL test in this codebase's freopen()-from-file harness
can observe. Built a PTY-based capture technique (openpty(), ECHO
disabled via termios) instead - independently reproduced via a
standalone probe and stress-tested 15x with zero flakiness during
review.
New file rather than extending test_repl_execution_control.c (already
at 948 lines, over the 800-line cap), per this spec's established
split precedent.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YAWMhfRJFnmmnG8h97yUDd
Rongsong Shen
99fa45c41a