daemon: sched/scheduler — governor <-> store <-> engine, against an EnginePort seam

The Scheduler that D4 was waiting on. Built against CORE's engine
HEADERS (now in main); the real EnginePort and the veloxd wiring wait
for lane/core's stage-8 bodies to reach main (deferrals.md D4a/D4b) —
core/src/task/ is still .gitkeep there, so linking vdm::Engine now
would be an unresolved symbol.

- sched/engine_port — the abstract seam: start/pause/resume/cancel/
  provide_auth/decide/refresh_url + the ADR 0011 admission config
  (set_task_order / set_max_active_segments / set_host_segment_cap).
  Keeps the Scheduler testable without a live engine and the daemon
  unbound from the concrete vdm::Engine.
- sched/fake_engine_port — a recording impl for tests.
- sched/scheduler:
  * owns the wire-UUID <-> vdm::TaskId map.
  * tick(): snapshot queues (schedule window evaluated with an
    injectable clock) + non-terminal tasks -> governor.evaluate ->
    apply. to_start builds a vdm::task::DownloadSpec from the row and
    calls EnginePort::start; to_resume -> resume(); to_pause ->
    pause() + writes the pause_reason; priority_order -> set_task_order
    over the mapped engine ids. `new` tasks are parked (startMode
    manual) and skipped.
  * on_engine_state(wire_id, state, err): projects an engine
    transition onto the store row (state, pause_reason='auto' when an
    error rides a paused transition per ADR 0013 §2, flattened error
    columns) so the next tick sees ground truth. This is also the hook
    event.task.state will fire from (D5).
  * reconcile_after_restart(): CORE-owned states -> queued, paused
    keeps its reason (ADR 0013 §5).
  * reload_config(): reads connection.maxConcurrentDownloads /
    maxActiveSegments + a daemon-local host-cap map, pushes caps to
    the engine, updates the governor.
  * Deps: injectable local-now clock and a post_to_loop marshaller
    (engine callbacks arrive on engine threads; default runs inline
    for tests).

Test veloxd.sched_scheduler (ASan+UBSan and TSan clean): admission +
ordering, a slot freeing on completion, queue-stop -> pause
(queue_stopped) then queue-restart -> resume (not a fresh start),
engine auto-pause -> pause_reason 'auto' + never auto-resumed,
reconcile_after_restart, reload_config caps push. 35 daemon/cli tests
green.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Upd9WhG9oppieig5nRDLig

daemon/CMakeLists.txt

@@ -59,12 +59,13 @@ target_compile_options(veloxd_fs PRIVATE -Wall -Wextra -Wpedantic -Werror)
 add_library(veloxd_sched STATIC
     src/sched/schedule_window.cpp
     src/sched/governor.cpp
+    src/sched/scheduler.cpp
 )
 add_library(velox::daemon_sched ALIAS veloxd_sched)
 target_include_directories(veloxd_sched PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
 target_compile_features(veloxd_sched PUBLIC cxx_std_23)
 target_compile_options(veloxd_sched PRIVATE -Wall -Wextra -Wpedantic -Werror)
-target_link_libraries(veloxd_sched PUBLIC velox::proto nlohmann_json::nlohmann_json)
+target_link_libraries(veloxd_sched PUBLIC velox::proto velox::core veloxd_store nlohmann_json::nlohmann_json)
 
 # --- veloxd_rpc — the RPC transports + dispatcher ------------------------------------
 add_library(veloxd_rpc STATIC