docs(render): close Campaign V slice V4a and file #249

V4a landed on the second attempt at 096dd203, verified independently: offline pixel gate passing at 22 differing pixels against an 8-26 same-commit noise band, App suite at exactly the 3,843/3 baseline, 26 files touched, no encoding damage. Three audits of the reverted first attempt found defects that outlive it - resident bindless handles never released, no test coverage for the Multisample state dimension, and no encoding guard - now tracked as #249.

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

docs/ISSUES.md

@@ -97,6 +97,45 @@ Copy this block when adding a new issue:
 
 ---
 
+## #249 — Bindless handles stay resident after their table slot is released
+
+**Status:** OPEN
+**Severity:** MEDIUM
+**Filed:** 2026-07-27
+**Component:** rendering / GPU resource lifetime
+
+**Description:** `GlGpuDevice.ReleaseTextureSlot` zeroes the table entry and
+returns the index to the free list, but never calls
+`BindlessSupport.MakeNonResident`. Two consequences:
+
+1. Callers go on to `glDeleteTexture` a texture whose bindless handle is still
+   resident, which `GL_ARB_bindless_texture` leaves undefined. Six other caches in
+   the tree (`TextureCache`, `CompositeTextureArrayCache`,
+   `StandaloneBindlessTextureCache`, `TerrainAtlas`) do call `MakeNonResident`
+   first, so the omission is inconsistent as well as unsafe.
+2. Every released slot leaks a resident handle for the process lifetime, even
+   though the index itself is recycled.
+
+**Provenance:** found by the Campaign V slice V4a audits. Introduced in V1
+(`4f94ad7d`), not in either V4a attempt; present on the current tree.
+
+**Also in scope for this issue** (same audits, same class of "no gate would have
+caught it"):
+- No test covers the `Multisample` dimension of `GlRenderStateCache`. Mistyping
+  that comparison would leave the whole suite green — that is exactly the
+  regression that forced the V4a revert (`9aaf97e7`). Add a positive test plus
+  `Assert.False(changes.Multisample)` in the existing negative cases.
+- Add an encoding guard: an `.editorconfig` with `charset = utf-8` and a
+  `.gitattributes` text rule, plus a check that rejects newly introduced BOMs or
+  mojibake. The first V4a attempt re-encoded 259 files and corrupted non-ASCII
+  characters in 116 of them, and no existing gate noticed.
+
+**Acceptance:** released slots make their handle non-resident before the texture
+is deleted; a test proves the `Multisample` dimension is diffed; an encoding
+guard fails on a reintroduced BOM.
+
+---
+
 ## #248 — FrustumCuller extracts the near plane with the GL-convention formula
 
 **Status:** OPEN