test(scheduler-sim-step-verbosity): task 1.1 - RED tests for preamble dedup

Adds 6 failing tests for the Event Echo Preamble Deduplicator
(Requirements 1.1-1.4, 2.2): a second echoed event sharing its
predecessor's rendered timestamp+session omits its preamble; two
events across a session boundary both print their own preamble; the
critical raw-vs-rendered nuance (Requirement 1.3) - two events whose
raw nanosecond timestamps genuinely differ but whose rendered,
second-granularity timestamp and session are identical still dedupe,
with a fixture-premise self-check proving the two raw values really
do render identically; the first echoed event in a fresh session
always prints its preamble; a structural event under continue mode
after suppressed routine events follows the same rule; event content
and ordering are unaffected regardless of the preamble decision.

Lands in a new test_repl_step_verbosity.c (1010 lines, 6 tests) rather
than extending test_repl_event_echo.c (705 lines) - proactive split
per this file family's established practice, since appending would
have pushed that file well past the project's ~1000-line trigger.
Registered in testsuite/meson.build. No production code touched.

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

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

@@ -1,7 +1,7 @@
 # Implementation Plan
 
 - [ ] 1. Core: event echo preamble deduplication
-- [ ] 1.1 Write failing tests for preamble deduplication across consecutive echoed events
+- [x] 1.1 Write failing tests for preamble deduplication across consecutive echoed events
   - Cover: two consecutive echoed events with identical rendered timestamp and session omit the second's preamble; two consecutive events with a different session both print their own preamble; two consecutive events whose raw high-resolution timestamps differ but whose rendered timestamp and session are identical still dedupe; the first echoed event in a fresh REPL session always prints its preamble; a structural event echoed under continue mode after a stretch of suppressed routine events follows the same rule; every event's own content line and ordering remain present and unaffected regardless of the preamble decision
   - Observable: the new test cases fail against today's REPL, which prints the timestamp/session preamble unconditionally before every echoed event
   - After adding the new test cases, check `test_repl_event_echo.c`'s resulting line count against this project's ~1000-line split trigger (design.md's File Structure Plan); if approached or exceeded, split the preamble-dedup tests into a new `test_repl_step_verbosity.c` (duplicating shared fixture helpers per this file family's established convention) and register the new file's test target in `testsuite/meson.build`

src/scheduler/testsuite/meson.build

@@ -965,6 +965,42 @@ sched_repl_event_echo_test = executable(
     dependencies: [scheduler_test_deps, libedit_dep],
     install: false)
 
+# Contract test for the interactive simulation REPL's Event Echo Preamble
+# Deduplicator component (scheduler-sim-step-verbosity spec, task 1.1,
+# Requirements 1 and 2 "collapse the repeated timestamp/session preamble
+# across consecutive same-context echoed events"): two consecutive echoed
+# events sharing the same rendered (second-granularity) timestamp and
+# displayed session omit the second's preamble line while still printing
+# its own content line; events spanning a session boundary each print their
+# own full preamble; two events whose raw high-resolution timestamps differ
+# but whose rendered timestamp and session are identical still dedupe (the
+# design's central "rendered value, not raw ns" nuance); the first echoed
+# event of a fresh REPL session always prints its preamble; the same rule
+# applies to a structural event echoed under `continue` mode after a
+# stretch of suppressed routine events; and event content/ordering stay
+# unaffected by the preamble decision at N=3 consecutive same-context
+# events. THIS TASK (1.1) IS RED-PHASE ONLY -- see this file's own header
+# comment. Same white-box #include pattern and forked-child/real-stdout-
+# capture technique as sched_repl_event_echo_test above (core.c,
+# core_clock.c, core_events.c, core_session.c, decision.c, plugin.c,
+# plugins/builtin_fcfs.c, recording.c, recording_session.c, sim.c,
+# sim_loop.c, sim_record.c, sim_verify.c,
+# snapshot.c/snapshot_wire.c/snapshot_load.c, repl.c, repl_fmt.c,
+# repl_rollup.c, repl_break.c, repl_info.c, repl_params.c). Split into its
+# own file from the start rather than appended to test_repl_event_echo.c
+# (705 lines before this feature) -- design.md's File Structure Plan flags
+# this file's ~1000-line split trigger, and this task's six behavioral
+# cases plus their own preamble-construction helper would have pushed it
+# well past that threshold; the same reasoning that already split
+# test_repl_round_rollup.c/test_repl_event_echo.c/test_repl_prompt_context.c/
+# test_sim_print_decision_gate.c out of test_repl_execution_control.c.
+sched_repl_step_verbosity_test = executable(
+    'sched_repl_step_verbosity_test',
+    ['test_repl_step_verbosity.c'],
+    include_directories:[incdir],
+    dependencies: [scheduler_test_deps, libedit_dep],
+    install: false)
+
 # Contract test for the interactive simulation REPL's Prompt Context
 # component (scheduler-sim-repl-verbosity spec, task 6.1, Requirement 5.5
 # "REPL prompt shows session/timestamp"): the readline() prompt is the
@@ -1563,6 +1599,9 @@ test('scheduler repl round rollup test',
 test('scheduler repl event echo test',
      sched_repl_event_echo_test, suite: 'scheduler',
      env: ['ASAN_OPTIONS=detect_leaks=0'])
+test('scheduler repl step verbosity test',
+     sched_repl_step_verbosity_test, suite: 'scheduler',
+     env: ['ASAN_OPTIONS=detect_leaks=0'])
 test('scheduler repl prompt context test',
      sched_repl_prompt_context_test, suite: 'scheduler',
      env: ['ASAN_OPTIONS=detect_leaks=0'])