feat(render): Campaign V slice V10 — Vulkan becomes the default backend

THIS CUTOVER AWAITS THE USER'S VISUAL SIGN-OFF. It is not complete. Section 7
of the campaign plan names the V10 sign-off as the only required user stop
besides gate failures, and it has not been given. This commit flips the default
and runs the battery so that the sign-off has evidence in front of it.

ROLLBACK, one line: `git revert` of this commit. It restores the GL default,
the pre-V10 escape-hatch polarity and the gate scripts' inherited backend
together; nothing else has to move with it.

An unset, empty or unrecognised ACDREAM_RENDER_BACKEND now yields
RenderBackendKind.Vulkan. Only `gl` or `opengl`, case-insensitive, selects
OpenGL. The polarity of the typo case flipped with the default and on purpose:
before V10 an unrecognised token had to land on GL because Vulkan was dark and a
typo must never silently start a backend that cannot draw; after V10 it has to
land on Vulkan for the same reason read the other way, because GL is the backend
V11 deletes. `opengl` is honoured beside `gl` because an escape hatch exists to
be found.

Three gate scripts follow the flip. run-offline-pixel-gate.ps1 gains -Backend
(default vulkan) and now FORCES all four determinism levers — backend, day
group, world day fraction, sky phase — plus ACDREAM_MSAA_SAMPLES=0, instead of
inheriting any of them. run-repeat-connected-gate.ps1 and
run-connected-world-lifecycle-gate.ps1 CLEAR ACDREAM_RENDER_BACKEND rather than
setting it, so what they exercise is the process default and an ambient override
in a caller's shell cannot make a GL run wear the default's report.

TEST PIN UPDATED, flagged as required: RenderBackend_DefaultsToGl becomes
RenderBackend_DefaultsToVulkan, and RenderBackend_AnythingElseStaysOnGl splits
into RenderBackend_SelectsGlOnlyForTheEscapeHatchTokens and
RenderBackend_AnythingElseStaysOnVulkan. Five cases replace two. No other test
is touched, weakened or deleted.

AD-46's divergence-register row moves from "dormant until the V10 cutover" to
live, in this commit, per the same-commit register rule.

Battery, all on the new default:

  complete Release suite    9,222 passed / 5 skipped / 0 failed (9 projects)
                            +5 against the pre-flip 9,217; the +5 are this
                            slice's own escape-hatch cases
  #250 family, singly       4/4 pass (none failed in the whole-suite run)
  repeat connected gate     PASS 3/3 on both columns
  world-lifecycle route     PASS, 0 failures, both sessions graceful at exit 0
  validation layer          inserted at instance AND device level by the loader,
                            zero errors and zero warnings, real frame captured
  GL escape hatch           verified by two offline launches: 4.3.0 Core Profile
                            Context, bindless present, exit 0

Every connected launch in the battery reached Vulkan with no environment
variable set, which is the flip itself under test rather than an assertion
about it.

THE PIXEL GATE IS NOT MET, AND WAS NOT RELAXED. Vulkan against a GL-era capture
taken at this commit through the escape hatch, MSAA off and both clocks pinned:
1.099e-03 masked / 3.764e-02 whole-frame, against a 0.001 threshold. 97.9% of
the difference is in the treeline band, and the masked residual of 619 px — set
against a same-backend control of 10 px — sits entirely on the silhouettes of
distant alpha-blended scenery. That is AD-46's registered population; section
5.5.19 measured the same quantity at 497 px / 8.8e-04. Below the band the two
backends are photometrically identical: mean luminance differs by 0.01 of 255.
No baseline was regenerated and no mask or tolerance was widened.

Two instrument findings are recorded in section 5.5.23. The offline gate's sky
mask is still load-bearing — this slice tried retiring it on the reasoning that
V7's clock pins had made it obsolete, and the control refuted that: two launches
of the same binary still differ by 1,011 px on GL and 482 px on Vulkan, almost
all of it in the band. The default went back to 280 with the measurement written
into the script's help. And the repeat gate's desktop witness needs an
uncontested primary monitor: a first attempt reported 1/3, and the two failing
grabs turn out to be a web browser and Discord composited over the client rect,
not a blank frame — the client's Vulkan capture rendered in all six runs.

Nothing GL, ImGui or Studio is deleted. That is V11's scope and it is untouched.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/architecture/retail-divergence-register.md

@@ -66,7 +66,7 @@ accepted-divergence entries (#96, #49, #50).
 
 | # | Divergence | Where (file:line) | Why it is safe / justified | Risk if assumption breaks | Retail oracle |
 |---|---|---|---|---|---|
-| AD-46 | **Vulkan-arm only, dormant until the V10 cutover.** Dense alpha-blended distant scenery (the treeline) resolves differently on the Vulkan backend than on GL, by about 15% of the pixels in the band, even though both arms now request identical sampler state — trilinear, clamp-and-repeat, and the device's maximum anisotropy. What remains is the anisotropic TAP PATTERN, which both the GL and Vulkan specifications leave implementation-defined, and AMD's two drivers do not agree. | `src/AcDream.App/Rendering/Wb/WorldTextureArray.cs` (`RhiWorldTextureArray.WorldArrayAnisotropy`); measured in plan §5.5.19 | Not assumed — narrowed by measurement, on an offline capture with no session, no entities and both clocks pinned. Anisotropy 1 → 41,509 differing pixels in the tree band; anisotropy 16 (GL's value, and retail's `m_D3DCaps.MaxAnisotropy`) → 22,266, and the rest of the frame falls to 497 px of 563,200, i.e. 8.8e-04, inside the campaign's 0.001 threshold. The residual is not a sub-pixel shift (an integer shift search finds none), not a sharpness change (high-frequency energy matches within 5%), and not depth precision (forcing Vulkan's window-depth range to GL's compressed [0.5, 1] moved it by 3%). Monotone improvement toward GL's own anisotropy with no knob left is what makes it a driver property rather than a bug. | If it is NOT the tap pattern, some other Vulkan sampler or alpha-path difference is hiding behind this row, and it will present after cutover as distant foliage that shimmers or reads denser than retail's. The class is confined to alpha-blended dense overlap: opaque terrain, roofs, walls, water, statics, the character and the whole retained UI are inside threshold. | `RenderDeviceD3D::SetDefaultD3DStates @ 0x005a3800`, whose `SetSamplerState(stage, 0xA /* D3DSAMP_MAXANISOTROPY */, m_D3DCaps.MaxAnisotropy)` at `0x005a4230` is the value both arms now request |
+| AD-46 | **LIVE as of Campaign V slice V10 (cutover committed, user sign-off pending); previously Vulkan-arm-only and dormant.** Dense alpha-blended distant scenery (the treeline) resolves differently on the Vulkan backend than on GL, by about 15% of the pixels in the band, even though both arms now request identical sampler state — trilinear, clamp-and-repeat, and the device's maximum anisotropy. What remains is the anisotropic TAP PATTERN, which both the GL and Vulkan specifications leave implementation-defined, and AMD's two drivers do not agree. | `src/AcDream.App/Rendering/Wb/WorldTextureArray.cs` (`RhiWorldTextureArray.WorldArrayAnisotropy`); measured in plan §5.5.19 | Not assumed — narrowed by measurement, on an offline capture with no session, no entities and both clocks pinned. Anisotropy 1 → 41,509 differing pixels in the tree band; anisotropy 16 (GL's value, and retail's `m_D3DCaps.MaxAnisotropy`) → 22,266, and the rest of the frame falls to 497 px of 563,200, i.e. 8.8e-04, inside the campaign's 0.001 threshold. The residual is not a sub-pixel shift (an integer shift search finds none), not a sharpness change (high-frequency energy matches within 5%), and not depth precision (forcing Vulkan's window-depth range to GL's compressed [0.5, 1] moved it by 3%). Monotone improvement toward GL's own anisotropy with no knob left is what makes it a driver property rather than a bug. | If it is NOT the tap pattern, some other Vulkan sampler or alpha-path difference is hiding behind this row, and it will present after cutover as distant foliage that shimmers or reads denser than retail's. The class is confined to alpha-blended dense overlap: opaque terrain, roofs, walls, water, statics, the character and the whole retained UI are inside threshold. | `RenderDeviceD3D::SetDefaultD3DStates @ 0x005a3800`, whose `SetSamplerState(stage, 0xA /* D3DSAMP_MAXANISOTROPY */, m_D3DCaps.MaxAnisotropy)` at `0x005a4230` is the value both arms now request |
 | AD-38 | Outgoing teleport viewports retire when retail's quantized animation level exceeds the last captured visible level 1022 (index 96), suppressing levels 1023/1024 up to 20.2 ms before retail's literal `elapsed >= 1.0` state edge. Incoming fades retain the exact timer. | `src/AcDream.Core/World/TeleportAnimSequencer.cs` (`OutgoingViewportReachedTerminalProjection`) | An uncapped 2000 FPS pass can publish the finite tunnel at levels 1023/1024 even though the paired 2013 retail capture switches viewports after 1022. The table-level cutover preserves the captured visible viewport ordering without throttling the application. | Exit sound, viewport replacement, and logout tunnel entry can occur at most two easing-table quanta (about 20.2 ms) earlier than retail's logical timer. | `UIGlobals::GetAnimLevel @ 0x004EE540`; `gmSmartBoxUI::UseTime @ 0x004D6E30`; paired retail/acdream captures documented in `docs/research/2026-07-15-retail-portal-space-pseudocode.md` |
 | AD-1 | Lost-cell machinery replaced by recoverable outdoor demote (**#107** safety net) + outdoor-restore `max(terrainZ, z)` under-terrain lift; retail goes `GotoLostCell` | `src/AcDream.Core/Physics/PhysicsEngine.cs:553` (+ :808) | acdream has no lost-cell state machine; outdoor landcell is the recoverable equivalent; the #107 auto-entry hold should make the demote branch unreachable | Gap in the hold → player committed to outdoor terrain inside/under a building (fake-grounded spawn, fall-through); a legit below-heightmap server restore is silently lifted — upward warp vs server | `GotoLostCell` pc:283418; `SetPositionInternal` 0x00515bd0, pc:283892-283945 |
 | AD-2 | Async readiness gates replace retail's synchronous destination cell load. **#229 refinement (2026-07-20):** login and F751 portal-space exit now share `WorldRevealReadinessBarrier`, so neither path can expose the normal viewport until the same render-publication, composite-texture, and collision domains converge. A hydratable indoor claim requires its owning Near-tier static/EnvCell mesh set, destination composites, and exact EnvCell physics (`IsSpawnCellReady`); an outdoor claim requires those render domains plus terrain/collision residency for the required Near ring. Hard-recenter generations and tier-aware completion application prevent stale overlapping loads/unloads or Far/Near jobs from opening or erasing the gate; mesh upload remains separate from balanced landblock ownership. Claims beyond NumCells still take the loud unhydratable-placement path. `RuntimeWorldTransitState` owns the shared reveal generation, accepted readiness, transit correlation, and exact generation/cell-scoped host-acknowledgement suffix. `WorldRevealCoordinator` is a graphical adapter holding only App resource receipts; normalized Runtime checkpoints observe ownership without defining another readiness path. **Slice E3 refinement (2026-07-24):** the same generation now publishes an immediate `WorldGenerationQuiescence` edge: old-world drawing/spatial queries, simulation/effect clocks, reconciliation, targeting, and 3-D audio stop while retained physical teardown advances through metered cursors and destination network/UI/streaming/readiness remain live. **Slice E4 refinement (2026-07-24):** accepted render/physics/static publication may span update frames through retained exact cursors, but reveal still consumes only the completed spatial/render-ready generation; building and EnvCell snapshots remain invisible until complete and the final spatial identity swap stays observer-atomic. **Slice E5 refinement (2026-07-24):** the reveal generation owns one exact destination reservation across every typed budget dimension. Stale completion cannot consume or clear its replacement, and hydratable incomplete content is never force-revealed; portal transit retains the DAT tunnel and centered retail wait cue until readiness converges. The hold→materialize→regain-control lifecycle remains owned by `TeleportAnimSequencer`. | `src/AcDream.Runtime/World/RuntimeWorldTransitState.cs`; `src/AcDream.App/Streaming/WorldRevealCoordinator.cs`; `src/AcDream.App/Streaming/WorldGenerationQuiescence.cs`; `src/AcDream.App/Streaming/WorldRevealReadinessBarrier.cs`; `src/AcDream.App/Streaming/StreamingOriginRecenterCoordinator.cs`; `src/AcDream.App/Streaming/LandblockPresentationPipeline.cs`; `src/AcDream.App/Streaming/StreamingController.cs`; `src/AcDream.App/Rendering/PortalTunnelPresentation.cs`; `src/AcDream.App/UI/PortalWaitNoticeController.cs`; `src/AcDream.App/Streaming/GpuWorldState.cs` (`IsRenderReady`); `src/AcDream.App/Rendering/Wb/LandblockSpawnAdapter.cs`; `src/AcDream.Core/Physics/PhysicsEngine.cs` (`IsSpawnCellReady`, `IsNeighborhoodTerrainResident`) | This is the asynchronous equivalent of retail leaving `SmartBox::position_update_complete` false while `CellManager::blocking_for_cells` is set: neither initial login nor portal arrival may reveal or continue simulating an old/partial collision world, a terrain-only Far shell, or a published-but-not-drawable GPU landblock. Indoor does not require a terrain heightmap, only the owning render landblock and exact EnvCell. | Gate opens early → grey/untextured first login or portal reveal, free-fall, wrong-cell rooting, missing scenery, or a still-active old generation; predicate never satisfies (streamer/DAT/upload failure) → login remains behind the world render gate, while portal transit remains in the authored tunnel and presents the centered wait cue after five seconds. | `SmartBox::UseTime` 0x00455410; `gmSmartBoxUI::UseTime` 0x004D6E30; `gmSmartBoxUI::EndTeleportAnimation` 0x004D65A0 |