Add agent config with project guide

.claude/CLAUDE.md

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+playscii - ascii art and game creation tool (v9.18)
+
+desktop GUI app using SDL2 + OpenGL. NOT a web app, no server component.
+originally from https://heptapod.host/jp-lebreton/playscii (mercurial).
+we maintain our own git repo.
+
+
+running
+-------
+  just run          launch the app (uv run python playscii.py)
+  just check        lint gate (ruff check + format)
+  just lint         ruff check --fix + ruff format
+  just typecheck    ty check (601 errors, legacy code, not in check gate)
+  just test         pytest (no tests yet, not in check gate)
+
+
+project structure
+-----------------
+  all python source lives at the repo root (no src/ layout)
+  ~50 .py files, flat structure, no packages
+
+  playscii.py       main entry point, app init, SDL2/OpenGL setup
+  art.py            art/canvas management, the core data model
+  ui*.py            ~20 UI modules (dialogs, panels, menus, toolbar, etc.)
+  game_*.py         game engine (objects, rooms, world, HUD)
+  renderable*.py    rendering pipeline (sprites, lines, framebuffer)
+  formats/          import/export handlers (ANS, ATA, BMP, EDSCII, PNG, GIF, TXT)
+  games/            bundled example games (crawler, fireplace, flood, maze, shmup, etc.)
+  charsets/         30+ classic computer character sets (.char + .png)
+  palettes/         color palette definitions
+  shaders/          GLSL shader files
+  artscripts/       art animation scripts (.arsc files)
+  art/              sample ASCII art (.psci files)
+  docs/             documentation and design notes
+  ui/               UI image resources
+
+
+dependencies
+------------
+  runtime: appdirs, numpy, Pillow, PyOpenGL, PySDL2, packaging
+  system:  libSDL2, libSDL2_mixer (must be installed on the OS)
+  dev:     ruff, pytest
+
+
+gotchas
+-------
+  art scripts and exec():
+    art.py imports random at module level with a noqa comment. art scripts
+    (.arsc files) are loaded via exec() in art.py's scope. they use random
+    without importing it themselves. do NOT remove that import even though
+    ruff flags it as unused. same pattern may apply to other "unused" imports
+    in art.py — check before removing anything.
+
+  pdoc detection:
+    playscii.py has a contextlib.suppress block that tries to import pdoc.
+    the import MUST stay inside the suppress block. if it gets moved or
+    removed, pdoc_available becomes unconditionally True and the help menu
+    breaks when pdoc isn't installed.
+
+  SDL2 init ordering:
+    many modules import from playscii.py's namespace or expect SDL2 to be
+    initialized before they run. import order in playscii.py matters — E402
+    is disabled for this reason.
+
+  mutable default arguments:
+    B006 is disabled. many functions use mutable defaults (lists, dicts).
+    changing these could alter behavior since some code may rely on the
+    shared mutable state. do not "fix" these without testing.
+
+  variable naming:
+    E741 is disabled. single-letter vars (l, x, y, z, i, r, g, b) are
+    everywhere in the math/rendering/game code. this is intentional.
+
+
+ruff config
+-----------
+  rules: E, F, I, UP, B, SIM
+  13 rules are explicitly ignored (see pyproject.toml for rationale)
+  line-length: 88, formatter handles what it can
+
+  when adding new code, write it clean. the ignored rules are concessions
+  to legacy code, not a style guide for new work.