Adds xce_core_now() (new core_clock.c, kept separate from core.c so
test_core_isolation.c's wall-clock scan still enforces zero direct
clock_gettime()/time() calls elsewhere in the core): the two-anchor
plus speed formula (virtual_clock_base + (elapsed * speed_num) /
speed_den), covering all four modes (normal, discrete/real-time/fast-
slow simulation) via four new atomic fields on xce_sched_core_t,
defaulted to normal-mode (1/1 speed) in xce_sched_core_init().
requirements.md's literal tlog_reg_format_func(fn, core_ptr) call
shape doesn't exist in the real vendored tlog library (registration
takes only the callback; userptr is per-call-site, not bindable at
registration) -- resolved with a module-level active-core pointer read
by a new core-scoped format function, not wired into mylog_init()/
main.c yet. xce_core_go()/xce_core_end_session() (task 4.4) now stamp
session_start/compute session_duration_ns via xce_core_now(), with
their existing session-active/reentrancy behavior untouched.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019dw5WnN3DXStaEaPYfACU1
Adds xce_core_go()/xce_core_end_session() (new core_session.c):
xce_core_go() is non-blocking, performs begin-session state reset
(select-eval-ctx, resval resets), signals the picker thread via wbuf,
and returns -EINVAL on a reentrant call while a session is already
active (proven a true no-op, not just an early return). Draining
core->decisions and invoking the driver's on_decision callback is the
driver's own responsibility between core_go() and core_end_session()
(confirmed driver-owned, not core-owned, per the Driver <-> Core
protocol). xce_core_set_decision_cb() registers the callback + driver
context as a separate setter, keeping xce_sched_core_init()'s live
sched_init() call site untouched. Adds XCE_DECISION_PREEMPT to
decision.h (jobid/victims[]/reason) alongside the existing DISPATCH/
PEND types. Additive only — sched_go/sched_begin_session/
sched_end_session/sched_allocator/main.c remain untouched.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019dw5WnN3DXStaEaPYfACU1
