fix(ui): OP5 review fixes — thumb sync, batched opacity writes, cull register row, tests

Fixes the OP5 (Chat tab) dual-lens review findings against e71e5a96:

- M1 (MUST-FIX): each opacity row's own apply closure now pushes its OWN
  slider's thumb from the post-link truth (bindings.Current*Opacity()),
  mirroring the OP4 binding pattern. Before this, a single-slider drag
  followed by Reset reverted the live value/link but left that slider's
  own thumb stuck at the dragged position.

- S1 (SHOULD-FIX): the Chat tab's two opacity sliders no longer round-trip
  the whole settings.json on every drag MouseMove tick. UiScrollbar gains
  IsDragging + a DragCompleted callback (fires once, at the MouseUp that
  ends an actual thumb drag); the opacity apply closures flush immediately
  when not mid-drag (Reset/Defaults/discrete edits, same as before) and
  defer to DragCompleted otherwise, collapsing dozens of per-tick writes
  into exactly one per drag gesture. Live opacity still applies every tick.

- S2 (SHOULD-FIX): filed register row AP-201 and issue #371 for the
  UiScrollablePanel whole-row-cull-vs-clip divergence the review found
  (predates OP5, made user-visible by OP5's 240-260px filter blocks). Not
  fixed in this round (a renderer-level scissor stack is out of scope
  here) — corrected the OP5 connected-gate script instead so a straddling
  block's disappear-then-reappear-whole is no longer reported as a
  self-sizing regression.

- S3 (SHOULD-FIX): the chatWindowMainFilter round-trip test already
  existed in e71e5a96 (the review missed it scrolling past line 330);
  added the genuinely missing coverage instead — a composed test pinning
  RetailUiRuntime.MountChat's window-0 SettingsStore -> ChatWindowState
  seed (MountChat itself needs live DAT access and isn't unit-testable
  directly).

- N11: ScrollbarLinkage_ModelPointsAtTheChatListBoxScroll now asserts
  through the scoped page-slot lookup (UiElement.FindDescendant) instead
  of the flat layout.FindElement, which passed for the wrong reason given
  the shared scrollbar id 0x10000201 — matches OP6's own scrollbar-linkage
  test pattern.

Also updated ConfigOptionsPageControllerTests' local ChatOptionsPageController
Bindings fake for the new FlushOpacity parameter.

Full Release suite: 13,117 passed / 4 skipped / 0 failed (baseline 13,107/4/0
post-OP6 — 10 tests added, zero skips added, zero failures).

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

docs/ISSUES.md

@@ -24,6 +24,28 @@ 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.
 
+## #371 — Options-panel row viewport culls whole rows instead of clipping; tall filter blocks can vanish entirely at some scroll offsets
+
+**Status:** OPEN — filed 2026-08-11 at the OP5 review-fix round (S2).
+`UiScrollablePanel.LayoutScrollableChildren` (`src/AcDream.App/UI/UiScrollablePanel.cs:69`)
+has no scissor stack, so a row that straddles the viewport's visible edge is
+hidden WHOLE (`child.Visible = top >= -0.5f && top + child.Height <=
+Height + 0.5f`) rather than clipped to its visible portion. Every row in
+this viewport (used by `UiTemplateListBox`, the Character/Chat/Config
+Options-panel tabs) was 8-36px until Campaign OP slice OP5 added five
+self-sized filter blocks (240-260px, AP-195's self-sizing) to the Chat
+tab — a block that size straddling the viewport edge now disappears
+entirely for a range of scroll offsets instead of clipping, a visible pop
+that the pre-OP5 small rows never made noticeable. Register row AP-201.
+
+**Fix:** add a real per-row clip rect (scissor test, or per-row UV/geometry
+clip in the draw path) to `UiScrollablePanel.OnDraw`/`LayoutScrollableChildren`
+so a straddling row renders its visible slice instead of being culled
+outright. Deliberately NOT attempted in the OP5 fix round (out of scope —
+a renderer-level change, not a Chat-tab content fix); see AP-201 for the
+full analysis and the OP5 gate script's step 2 for the exact observable
+symptom.
+
 ## #360 — @allegiance/@house management dispatchers only port their simple subcommands
 
 **Status:** OPEN — filed 2026-08-09, Campaign CH slice CH4; corrected