kernel: a refusal names its rule, and two bounds stop failing open

An AMD Ryzen booted to a working compositor with no USB and no storage,
and the log said only "register refused". A tree-wide audit of every
compile-time ceiling followed: 235 of them, 139 on quantities the machine
or a file decides rather than us, 5 documented anywhere, 171 silent when
reached. docs/fixed-bounds-audit.md has the inventory.

Errno attribution. The errno space was split between the kernel and the
envelope, free to drift; it is now one list in system/abi.zig, restated on
both sides, with a comptime check in library/device/driver where the two
halves are visible. device_register's six refusals and device_claim's three
are distinct codes, so a bus driver can say which rule stopped it, and
BadParent splits into NoSuchParent and NotYourParent. pci-bus reconciles
found against registered instead of counting refused functions as found.

Idempotency ordering. The child cap was checked before the identity match,
so a restarted bus was refused its own devices — the supervision restart the
system leans on ratcheted toward a degraded machine. A re-registration
consumes no slot and is now admitted first.

IOMMU fail-closed. confineDevice returned success for a device id past the
confinement table, leaving the device outside every domain while the caller
believed it confined — unreachable only while ids stop at 64, which both the
inventory move and a hardware-reported domain count would change. It refuses
now, and the coupling to the broker's device cap is a comptime assert rather
than a sentence in a comment.

PCI apertures. The bridge's MMIO apertures are derived from the holes in the
firmware memory map, and the derivation copied sub-4 GiB entries into a
fixed [64] array and skipped the rest. A skipped region is not merely lost:
the gap finder concludes it is free, so a real machine's 60-200 entry map
yields an aperture over live RAM, and containment then admits a child BAR
covering kernel memory. Rewritten to walk the map in place, with the hole
finder extracted as a pure function and driven by a synthetic 100-entry map
in a new test case. Both new tests were verified to fail on the old code.

parameters.zig gains the rationale it was missing and loses a stale sentence
pointing at the wrong file; vdso.md documents the errno space, including
EPEER, which had no written meaning anywhere.

docs/os-development/bounds.md is how a ceiling is declared from here.
docs/bounds-track-plan.md is the plan to remove the ones we invented.

Suite 114 -> 115.

test/qemu_test.py

@@ -978,9 +978,20 @@ CASES = [
     # device_register containment (in-kernel): registering a child whose MMIO window
     # escapes its parent's grant is refused (NotContained) — else dev_register would map
     # arbitrary physical memory — while an identical re-register stays idempotent.
+    # Also pins the cap ordering: a parent already at maximum_children_per_parent must
+    # still re-admit an identical child (a restarted bus consumes no slot re-reporting
+    # what it rediscovers) while still refusing a genuinely new one.
     {"name": "containment",
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
+    # PCI host-bridge apertures come from the holes in the firmware memory map, and a
+    # registered BAR must fall inside one. The invariant is that an aperture never
+    # covers memory the firmware described - otherwise device_register containment
+    # admits a child BAR over live RAM. Driven with a synthetic 100-entry map, since
+    # OVMF only ever produces 15-25 and real firmware 60-200.
+    {"name": "apertures",
+     "expect": r"DANOS-TEST-RESULT: PASS",
+     "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # IRQ teardown: an exiting driver's line is masked and its slot cleared (so no
     # ISR notifies a freed endpoint), and a sibling owner sharing that endpoint
     # keeps its own binding. A long-running driver never reaches this teardown path.