feat(scheduler-sim-repl-verbosity): task 6.2 - implement dynamic REPL prompt

Adds repl_build_prompt(), building the readline() prompt fresh each
loop iteration: the plain "(sim) " before any session begins, else
"(sim session=<N> t=<ISO8601-ts>) " using the bare session count (not
+1, matching info session's convention) and the existing
repl_format_ts_human(). Both of task 6.1's tests pass.

repl.c grew 808->852 lines (6.5% over the 800-line cap). Review
empirically tried extracting repl_build_prompt() into a new
repl_prompt.c: it works, but requires updating 19 sibling white-box
test files' #include lists, and even then repl.c only drops to 814
lines - still over cap. Given the function is a small 15-line
formatter and the split doesn't even achieve compliance, accepted in
place rather than forcing disproportionate churn.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YAWMhfRJFnmmnG8h97yUDd

.kiro/specs/scheduler-sim-repl-verbosity/design.md

@@ -285,6 +285,8 @@ int repl_fmt_jobid_range(char* buf, size_t bufsz,
 - Uses **bare** `rs->session_count`, matching `info session`'s/`info config`'s existing convention (`repl_info.c:848,898`) — **not** `session_count + 1`. That `+1` exists only in `repl_print_event_summary()` (repl_break.c:611) to label events echoed *mid-stream*, before the session containing them has finished and incremented the count; the prompt, by contrast, is only ever shown *after* a `step`/`continue` has returned control (i.e. after `xce_repl_on_begin_round()` for the just-finished session has already run), so the bare count is the session that just completed — the same number `info session` would report if queried at that exact prompt. Copying the `+1` convention here would make the prompt disagree with `info session` by one.
 - Built fresh on every `repl_command_loop()` iteration, immediately before the `readline()` call it feeds — never cached across iterations, since the session/timestamp can change between prompts.
 
+**Accepted residual (post-review, task 6.2)**: this task's `repl_build_prompt()` addition pushed `repl.c` to 852 lines (6.5% over the 800-line cap, up from 1% after task 2.2) — the exact trigger task 2.2's own residual note anticipated. Review empirically tried extracting `repl_build_prompt()` into a new `repl_prompt.c` (matching the `repl_rollup.c` precedent): it links and passes, but 19 sibling white-box test files each `#include "../src/repl.c"` directly and would each need a matching new `#include` line to keep linking, and even after absorbing that churn `repl.c` only drops to 814 lines — still over cap. Given the function is a small, single-purpose 15-line formatter and the split doesn't even achieve compliance, extraction was judged disproportionate and reverted; 852 lines is accepted as this task's residual. Tasks 7-9's `repl_info.c`/`repl_params.c`/`repl.c` (`help`/`BP_KIND_TABLE` accessor) additions are unaffected — revisit `repl.c` specifically only if a later task adds to it again.
+
 **Dependencies**
 - Inbound: `repl_command_loop()` (repl.c) — calls this immediately before its existing `readline(XCE_REPL_PROMPT)` line
 - Outbound: `repl_format_ts_human()` (repl.c, existing), `xce_core_now()` (core_clock.c, existing)

.kiro/specs/scheduler-sim-repl-verbosity/tasks.md

@@ -65,7 +65,7 @@
   - _Requirements: 5.5_
   - _Boundary: REPL Prompt Context_
 
-- [ ] 6.2 (P) Implement the dynamic prompt
+- [x] 6.2 (P) Implement the dynamic prompt
   - Build the prompt fresh on every `repl_command_loop()` iteration from the current session count and `xce_core_now()`/`repl_format_ts_human()`, falling back to the original plain prompt before any session begins
   - Observable: all tests from 6.1 pass; a live `step`/`continue` session shows the session/timestamp in the prompt starting from the first completed session, with no change to any command's own printed output
   - _Requirements: 5.5_

src/scheduler/src/repl.c

@@ -422,6 +422,42 @@ static bool repl_dispatch(xce_sched_sim_driver_t* sim, const char* line)
     return false;
 }
 
+/*
+ * repl_build_prompt (scheduler-sim-repl-verbosity spec, task 6.2, design.md's
+ * "REPL Prompt Context" component, Req 5.5) - builds this iteration's
+ * readline() prompt into `buf` (bufsz-bounded): the plain XCE_REPL_PROMPT
+ * ("(sim) ") if no session has completed yet (rs->session_count == 0, the
+ * same zero-initialized value repl_state_ensure()'s calloc already
+ * guarantees), else "(sim session=<N> t=<ISO8601-ts>) " using the BARE
+ * rs->session_count -- deliberately NOT +1, unlike repl_print_event_summary()
+ * (repl_break.c)'s unrelated mid-stream convention, which labels events
+ * echoed before the session containing them has finished/incremented the
+ * count. This prompt is only ever shown AFTER a step/continue has already
+ * returned control (i.e. after xce_repl_on_begin_round() for the
+ * just-finished session has run), so the bare count is the session that
+ * just completed -- the same number `info session` would report right now.
+ * The timestamp reuses xce_core_now(&sim->core)/repl_format_ts_human()
+ * verbatim (no new time source, no raw-epoch-ns component). A read-only
+ * formatter -- never blocks, never mutates sim/sim->repl_state -- so it is
+ * safe to call fresh on every loop iteration (never cached).
+ */
+static void repl_build_prompt(xce_sched_sim_driver_t* sim, char* buf,
+                              size_t bufsz)
+{
+    xce_sched_repl_state_t* rs = sim->repl_state;
+    char                     ts_human[32];
+
+    if ((rs == NULL) || (rs->session_count == 0)) {
+        snprintf(buf, bufsz, "%s", XCE_REPL_PROMPT);
+        return;
+    }
+
+    repl_format_ts_human(xce_core_now(&(sim->core)), ts_human,
+                         sizeof(ts_human));
+    snprintf(buf, bufsz, "(sim session=%llu t=%s) ",
+             (unsigned long long)rs->session_count, ts_human);
+}
+
 /*
  * repl_command_loop - the blocking prompt loop itself: readline() the
  * `(sim) ` prompt, add_history() on non-blank input (same convention
@@ -433,11 +469,19 @@ static bool repl_dispatch(xce_sched_sim_driver_t* sim, const char* line)
  * that case either. Non-static (repl_internal.h) -- repl_break.c's
  * breakpoint-hit hooks re-enter it directly, the same way
  * xce_repl_post_session_check() below already does for a `step N` pause.
+ * The prompt itself is rebuilt fresh (repl_build_prompt()) immediately
+ * before every readline() call, never cached across iterations, since the
+ * session count/timestamp it shows can change between prompts (task 6.2,
+ * Req 5.5).
  */
 void repl_command_loop(xce_sched_sim_driver_t* sim)
 {
     for (;;) {
-        char* line = readline(XCE_REPL_PROMPT);
+        char prompt[64];
+        char* line;
+
+        repl_build_prompt(sim, prompt, sizeof(prompt));
+        line = readline(prompt);
 
         if (line == NULL) {
             repl_cmd_quit(sim); /* never returns */