vms-0044: directory-logical resolution over the ACP (SYS$SYSTEM:/rooted logicals → ODS-2 directory FID, flip-blocker, epic vms-208)

[baron-3dl]

What

Flip-blocker for epic vms-208 (Files-11 ODS-2 ACP in the executive). The boot-to-Username path (LOGINOUT reading SYS$SYSTEM:SYSUAF.DAT) could not resolve rooted/concealed directory logicals to a concrete on-volume ODS-2 directory the ACP can walk to a FID — the reroute proofs sidestepped it with a concrete DKA0:[DIR] spec. This lands the two genuinely-missing pieces and proves the full chain on a real /dev/vms.

1. Composition (product code, pure) — vmsfs_compose_ods2_candidates()

src/vmsfs/vmsfs_translate.c. The VMS-spec sibling of vmsfs_to_linux_path(): same concealed-rooted machinery (vmsfs_device_concealed_rooted / merge_rooted_root, honouring LNM$M_CONCEALED and the trailing-dot rooted rule), but it stops at the resolved VMS spec instead of a host path:

SYS$SYSTEM:SYSUAF.DAT
  → DKA0:[SYS0.SYSEXE]SYSUAF.DAT            (node-specific member, first)
  → DKA0:[SYS0.SYSCOMMON.SYSEXE]SYSUAF.DAT  (common member, second)

in search-list order. Fail-honest (INV-6): an unresolvable chain composes nothing.

2. ACP directory walk

The composed [SYSn.SYSCOMMON.SYSEXE] path is walked MFD → [SYS0] → [SYSCOMMON] → [SYSEXE] via IO$_ACCESS-by-name (each level's <comp>.DIR entry gives the next directory FID), then the file within → the file FID. A search-list candidate that misses falls through to the next.

Proof (Rule 9 / INV-6)

• tests/vmsrms/test_dirlogical_compose.c (host): composition to the ordered candidates + live relocation + fail-honest — 11/11.
• tests/qemu/test_syssvc_dirlogical_acp.c (real /dev/vms): SYS$SYSTEM:SYSUAF.DAT resolves through lnm+$PARSE+ACP to the file FID (falling through the empty node member to the common member), $GET/IO$_READVBLK reads it byte-exact (no vmsfs_to_linux_path), fail-honest RMS$_FNF (file absent) / RMS$_DNF (missing directory level) — 9/9.
• Fixture tests/qemu/mkimage_ods2_sysvol.c masters a genuine ODS-2 system-disk tree on a new DKA300: (vdd); harness + Dockerfile wire the fourth disk.
• Negctl anchor dirlogical-compose-drops-common-member added (floor unchanged). test_kmod_disk / test_kmod_vmsfs_mountvis updated for the fourth unit.

Full QEMU kernel-executive harness run locally: 90 suites passed, 0 suites failed.

Mergeability

Incrementally mergeable — NOT a red-by-design flip-group. Purely additive; host ctest stays green because resolve_filename's default is not flipped. Wiring the ACP walk as RMS $OPEN's default (which forces the rms → libvmssys native-link --use LIBVMSSYS$SHR edge, and is red-by-design without /dev/vms) is the held capstone flip — this PR delivers the composition + walk that flip consumes.

Note: the item referenced rms_acp_spec_from_fab (#649) as on main; that PR was unrelated and no RMS-over-ACP $OPEN path exists on main yet — hence the composition ships as reusable vmsfs product code and the walk is proven in the harness (the footing every ACP-QIO rung sits on today).

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