diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index 83151052..d60bfa77 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -24,6 +24,40 @@ 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.
 
+## #393 — Texture detail options: retail's "High Resolution Textures" toggle + Landscape/Environment TextureDetail mip-skip
+
+**Status:** OPEN — filed 2026-08-14 from the highres-texture verification
+(post-M4 nice-to-have; perf/nostalgia option, no gameplay impact).
+acdream today loads `client_highres.dat` unconditionally and always picks
+`Textures[0]` — retail's MAXIMUM texture detail, verified end-to-end (live
+path AND the baked `acdream.pak`; the 2026-08-14 investigation's evidence
+chain). Retail additionally offers two knobs acdream has no equivalent for:
+
+1. **"High Resolution Textures" toggle** (change-notice string
+   `ID_Option_HighResChange`; `CLCache::LoadHighResDat @0x004FA250` only
+   runs when armed). Off = `client_highres.dat` never loads; lookups use
+   the portal-resident versions. acdream shape: a Config-tab option that
+   skips the highres fallback in `DatCollectionAdapter.TryGet` (portal
+   class: `_portal || _highRes`, `DatCollectionAdapter.cs:90`) and
+   `MeshExtractor`'s explicit highres fallbacks (`MeshExtractor.cs:399,767`
+   — which currently THROW on a miss; the off-path must degrade the way
+   retail does, NOT throw). **Research prerequisite:** what retail falls
+   back to for surfaces whose ONLY copy lives in highres.
+2. **Texture detail levels** (`Render_LandscapeTextureDetail` /
+   `Render_EnvironmentTextureDetail` UIPreferences; the pick
+   `@0x0044C3C8`): the enum is an INDEX into the texture's source-level
+   (mip) chain — detail 0 keeps every level, detail N drops the N largest
+   (`i_1 = m_num - esi_1` keeps levels from index N;
+   `RenderTexture::ShouldDropHighDetail` can force it under memory
+   pressure). acdream shape: skip/downsample the top N levels at Vulkan
+   texture upload — works for live uploads and pak payloads alike (the
+   downsample is at upload, not bake; NO re-bake needed).
+
+Also carried from the same investigation: a one-off enumeration proving
+portal/highres id sets are disjoint (the "portal wins on overlap"
+`TryResolvePreferred` corner — no overlap evidence exists, a ~20-line
+tool run closes it).
+
 ## #392 — A refused/failed fullscreen enter leaves `fullscreen: true` persisted against a windowed client
 
 **Status:** OPEN — filed 2026-08-13 from the #376/#388 blast review (M4).