Expand CLAUDE.md with build constraints, hooking model, and conventions

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -28,6 +28,12 @@ cmake --build build --config Release
 - Output: `bin/` (gMod.dll, TpfConvert.exe)
 - Version: set in `CMakeLists.txt` (`VERSION_MAJOR/MINOR/PATCH/TWEAK`)
 
+> **Cannot be built or run in this agent environment** (Linux, no MSVC, no 32-bit
+> D3D9, no Guild Wars to inject into). Don't burn turns attempting `cmake`/builds
+> here — validate changes by reading and matching existing patterns, and lean on
+> Windows CI (`ci.yaml`) for the real build. When an actual compile/test is needed,
+> ask the user to do it in Visual Studio rather than trying locally.
+
 ## Key dependencies (via vcpkg)
 
 - `minhook` — D3D9 function hooking
@@ -42,6 +48,47 @@ cmake --build build --config Release
 3. `ModfileLoader` — reads `modlist.txt`, loads .tpf/.zip mod archives
 4. `TextureClient` / `TextureFunction` — matches and replaces textures by hash at runtime
 
+### Hooking model (read before touching D3D9 code)
+
+gMod uses **MinHook vtable hooks**, not proxy/subclass wrappers (the old uMod model
+was replaced — see `git log` "Replace D3D9 proxy wrappers with vtable hooks"). The
+game keeps the **real** `IDirect3D9` / `IDirect3DDevice9` / texture objects byte-for-byte
+untouched; gMod patches only the individual vtable slots it cares about (CreateDevice,
+CreateTexture/Volume/Cube, UpdateTexture, BeginScene, Set/GetTexture, Release).
+
+- Per-texture side-state lives **out of band** in `header/D3D9State.h` (`TexState`,
+  keyed by the real texture pointer), so reverting the hooks fully detaches gMod.
+- `RemoveAllD3D9Hooks()` must leave the host process pristine — preserve that invariant.
+- A vtable is shared by all instances of a class, so each slot is hooked once; texture
+  Release slots are hooked lazily on first instance. Don't double-hook.
+
+## Conventions
+
+- **Formatting is CI-enforced** by clang-format `22.1.5` (`.clang-format`, applied by
+  `lint.yaml` on push to `dev`). Don't hand-reformat or "tidy" whole files — it just
+  churns the diff. Notable rules: `ColumnLimit: 0` (never reflow long D3D signatures /
+  vtable typedefs), `SortIncludes: Never` (include order is load-bearing in Windows
+  headers — never reorder), 4-space indent, braces on their own line after functions.
+- **C++23 named modules** (`modules/*.ixx`). Editing a module *interface* triggers wide
+  rebuilds; prefer changing implementation over interface when possible.
+- **Public exported API is a fixed surface** — four `extern "C" __declspec(dllexport)`
+  functions in `dll_main.cpp`: `SetDevice`, `AddFile`, `RemoveFile`, `GetFiles`. These
+  are consumed by GW Launcher and Daybreak; do **not** change their names, signatures,
+  or calling convention (`__cdecl`) without coordinating downstream.
+- **Commits**: short imperative summaries, lowercase, no trailing period
+  (e.g. "Keep loaded_files in load order so GetFiles returns priority order").
+- **Branching**: `dev` is the integration branch; PRs target `master`. CI builds on
+  push to `dev` and on PRs to `master`.
+
+### Where things live (by size / how often they change)
+
+- `modules/TextureClient.ixx` (~670 lines) — texture match/replace bookkeeping, hot
+- `source/D3D9Hooks.cpp` (~580) — the vtable detours and install/remove
+- `modules/TextureFunction.ixx` (~380) — texture creation/conversion helpers
+- `source/dll_main.cpp` (~345) — entry point + exported C API
+- `modules/ModfileLoader*.ixx` — .tpf/.zip parsing
+- `header/Defines.h` — shared structs/constants (`TextureFileStruct`, `HashTuple`, etc.)
+
 ## Notes
 
 - Must be injected before d3d9.dll loads, or renamed to d3d9.dll in the GW folder