Registers builtin_fcfs at scheduler startup and makes it the default
job_pick_plugin, replacing the hardcoded "xce_sched_fcfs" literal in
sched_job_picker() with a fail-loud lookup through sched_resolve_job_picker().
The picker thread now branches legacy job_elect_fn plugins (delegated
unchanged, preserving their self-contained wbuf-driven loop) from native
xce_job_picker_iface_t pickers (driven by a new per-session loop), and the
allocator now calls on_dispatch/on_pend for every picker as Req 1 AC 4
requires. Closes task 2.3's flagged picker/allocator concurrency race with a
mutex on fcfs_plugin_data_t, and adds cancel points to next_job().
plugin_register() now adapts an old-style job_elect_fn-only plugin to
xce_job_picker_iface_t via legacy_picker_wrapper_iface (next_job()
forwards to job_elect_fn; other hooks are safe no-ops covered elsewhere
in the existing lifecycle), logging a one-time deprecation warning. A
plugin that already sets picker_iface directly skips the wrapper and
the warning. Reuses the existing plugin_register()/key_find() mechanism
-- no parallel registration system.
Requirements: 1.6, 2.5
Add xce_job_picker_iface_t to plugin.h with all 13 hooks across
lifecycle/state-change/session/post-allocation/optional categories,
matching design.md's literal struct. Documents per-category thread
assignment, next_job() cancel-safety, and begin_session() session-reset
requirements. Forward-declares xce_sched_core_t (built in a later task).
Requirements: 1.2, 1.5, 2.6
Wire up 6 previously-stubbed message handlers in the scheduler:
resource dataset, resval dataset, job update notify, queue update
notify, resval update notify, and job rusage notify. Remove the
unreachable pushmsg branch (vtask_entry rewrites all pushmsg to
datamsg before the handler fires).
Changes by component:
- helper.h/helper.c: add xce_notify_event_name() for symbolic log names
- scheduler.h: add 5 new xce_sched_op_t values and matching union fields
- plugin.h/plugin.c: add plugin_job_rusage_hook_t and plugin_job_rusage_update()
- schedobj.c: add sched_update_existing_queue() with NULL/-ENOENT guards
- scheduler.c: wire 5 new dequeue cases; add sched_update_existing_job()
and static sched_op_name(); emit WARN log on handler failure
- handler.c: implement sched_handle_resources/resvals (dataset) and
sched_handle_sched_update_{job,queue,resvals}/job_rusage (notify);
remove dead sched_handle_jobpush/workerpush and pushmsg branch;
update TRACE logs to use symbolic name helpers
- test.c: 5 new unit tests covering notify event names, enum values,
and queue update NULL guard (15/15 pass)
