pci-bus registers and reports what it scans (M19.2)

Each function is registered under the bridge with the config-space slice
and BARs sized by the same all-ones probe the kernel uses — byte-for-byte
equal descriptors, so the idempotent register returns the kernel's
existing node ids during coexistence instead of duplicating the tree.
The bridge gained the 16-bit io_port aperture that functions' I/O BARs
need to pass containment. Reports carry the registered device_id, and
the pci-scan scenario drills a forced restart: kill the enumerator after
its reports, watch the respawn re-scan, and assert the broker's PCI node
count never grew. The usb-restart test trigger is pinned to the xHCI
reporter (pci-bus racing it to two reports used to steal the kill).
Harness hardening: failing cases preserve their serial logs; the heavy
scenarios run at 150s.

docs/m19-m20-plan.md

@@ -89,12 +89,13 @@ branch is green; keep branches; push everything.
       manager matches pci_host_bridge → pci-bus per device with the full
       protocol contract; `pci-scan` builds its expected marker from the
       kernel's own count — equivalence on the first run; suite 55/55).
-- [ ] **M19.2** — register + report: each function registered under the bridge
-      (config-space slice + BARs, `pci_class` in the descriptor), reported with
-      `child_added { device_id, identity = class triple }`. Manager mirrors;
-      spawn-from-reports stays **off**. Scenario extends `pci-scan`:
-      registered ids resolve, no duplicates after a forced driver restart
-      (idempotence proven end to end).
+- [x] **M19.2** — register + report (BAR probe mirrored byte-for-byte from the
+      kernel's addBars so dedupe returns the kernel's node ids during
+      coexistence; the bridge gained the io_port aperture I/O BARs need;
+      reports carry the registered device_id; pci-scan drills a forced restart
+      and asserts the PCI node count never grows — plus harness hardening: a
+      failing case now preserves its serial as <case>-failed-serial.log, and
+      the heavy scenarios run at 150s; suite 55/55).
 - [ ] **M19.3** — the flip: kernel `enumeratePci` call removed (bridge node
       stays); manager matches PCI drivers from reports. One commit. The
       existing xHCI scenarios (`driver-restart`, `usb-report`, `device-list`)