fix #451: stabilize portal seam rendering

docs/ISSUES.md

@@ -24,6 +24,48 @@ What does NOT go here:
 - Every session: scan OPEN issues at start; promote/close anything we touched during the session before ending.
 - Promoting to a Phase: mark as `DONE (promoted to Phase X)` + commit SHA where the Phase entry landed.
 
+## #451 — Sanctuary cathedral portal seam leaks exterior world and particles
+
+**Status:** DONE — OWNER-ACCEPTED 2026-08-27 ("Looks good! Gate pass now!").
+**Component:** Vulkan PView / nested building look-ins / landscape alpha ordering.
+
+At the open-air Sanctuary cathedral seam between `0xF4180104` and
+`0xF4180106`, small player or chase-camera movements could make cathedral
+halves, their shadows, or floor textures flap; expose the world background,
+trees, a nearby building, and waterfall/steam particles through opaque
+geometry; or clip the local player in half. Camera zoom alone reproduced the
+failure. The final particle repro was
+`0xF4180104 [31.111177 57.648911 169.804993]`.
+
+This was a renderer contract failure, not bad Sanctuary data. The correction:
+
+- classifies exterior building seeds with retail's `F_EPSILON` instead of the
+  ordinary 1 cm EnvCell traversal tolerance and retains the exact accepted
+  `CBldPortal` aperture;
+- appends every nested look-in cell's own `portal_view` to the frame clip
+  buffer, punches only the accepted seed portal, and clips shells plus static
+  and particle alpha to that view;
+- pairs each look-in with only its own exterior building shell and reproduces
+  retail's per-building alpha barriers;
+- keeps dynamic objects whole after the CPU PortalList sphere test, matching
+  retail `DrawMesh` and preventing the player-slicing regression;
+- submits attached and ownerless exterior particles inside `LScape::draw` for
+  every PView root, eliminating the late post-world replay that let waterfall
+  alpha repaint already-drawn cathedral cells; and
+- treats authored `SeenOutside` open-air cells as atmospheric outdoor cells so
+  sky/shadow activation no longer flips merely because the camera acquired an
+  EnvCell root.
+
+The fix is renderer-wide: no Sanctuary coordinate or asset special case is
+present in production. Installed-DAT regressions retain the reported camera
+handoff, lateral transition, and exact steam-seam views. The temporary live
+emitter/shell trace was removed at closeout.
+
+**Acceptance:** owner swept both cells, moved across the seam, and zoomed the
+camera through the former trigger positions. Cathedral/world flapping, shadow
+toggle, player clipping, exterior geometry, and waterfall/particle bleed were
+absent in the accepted build.
+
 ## #450 — Fast character re-entry after logout can remain in portal space at `lb 0/0`
 
 **Status:** DONE — OWNER-ACCEPTED 2026-08-26 in the combined client-parity gate.
@@ -18959,6 +19001,13 @@ DrawDynamicsParticles only sees dynamics-last cone survivors.
 **Gate:** stand inside, look out the doorway at the town portal — the
 swirl renders through the door.
 
+**2026-08-27 ordering correction (#451):** the old "once per frame after the
+look-ins" placement was sufficient for this gate but did not preserve the
+installed `outside_view` and could repaint an already-drawn open-air building.
+Ownerless emitters now submit once per outside-view slice with that slice's
+clip slot. When building look-ins exist they enter the pre-building alpha
+barrier; otherwise they drain at the end of `LScape::draw`.
+
 ---
 
 ## #132 — Candle flame disappears when the through-opening background is behind it
@@ -18999,6 +19048,13 @@ against interiors). The owner-id filter carries over; cell-pass and
 dynamics-pass emitters keep their own passes (owners never in the
 outdoor-static set → no double-draw).
 
+**2026-08-27 correction (#451):** the post-frame placement fixed this narrow
+flame-overpaint case but was too late for nested open-air cathedral cells: an
+exterior waterfall could repaint their completed opaque floor. Outdoor-static
+and ownerless particles now submit inside `LScape::draw` under the exact
+outside-view clip slot, with retail's pre-building/per-building alpha barriers;
+the post-world PView replay is deleted.
+
 **Gate:** both sides — indoors with the opening behind the candle, and
 outdoors at the angle that previously erased it.