**FIXED.** Two parts, both needed for Finder/`open` to work:

1. **cwd-relative assets** — `SdlPlatform.init` now chdir's to
   `SDL_GetBasePath()` when running from inside a `.app` (sx commit
   `b31fbae`, `library/modules/platform/sdl3.sx`), mirroring uikit.sx's iOS
   `chdir_to_bundle`. Gated to the `.app` case so the `sx run` dev flow keeps
   the project CWD.
2. **Gatekeeper-rejected signature** — the bundle was signed with a
   *Development* cert, which `spctl` rejects, so a standalone `open` wouldn't
   launch it. Switched the macOS build to **ad-hoc** signing (the bundler's
   macOS/sim default — just leave the codesign identity empty; game commit
   `d80a350`, `build.sx`).

Verified: a plain `cd game && sx build main.sx` then `open
sx-out/macos/SxChess.app` launches and renders (was: instant `stbtt` segfault
on missing font, or no launch at all). It was NOT App Translocation — the
bundle had no `com.apple.quarantine` xattr.

# Symptom

A bundled macOS `.app` built with `sx build` crashes on launch when started
via Finder double-click or `open Foo.app`, but runs fine when launched from a
shell whose CWD is the bundle directory.

Observed: `open sx-out/macos/SxChess.app` → process exits within ~1s (segfaults
inside `stbtt_ScaleForPixelHeight` because the font buffer is null — the asset
wasn't found).
Expected: double-click / `open` launches the app and it finds its bundled
assets, same as on iOS.

Root: assets are loaded with **CWD-relative** paths (e.g.
`"assets/fonts/default.ttf"`), but Finder/`open` start a GUI app with `CWD=/`,
so the relative path resolves against `/` and the file is missing.

# Reproduction

Any consumer that bundles an `assets/` dir and loads from it by relative path.
Minimal shape (real case: `/Users/agra/projects/game`):

```sx
// main.sx — loads assets by CWD-relative path
g_pipeline.init_font("assets/fonts/default.ttf", 32.0, dpi);   // -> read_file_bytes
g_chess_game.pieces.load("assets/chess/pieces.png", gpu);      // -> read_file_bytes
```

```sh
cd game && sx build main.sx          # produces sx-out/macos/SxChess.app (assets copied in)

# Works (CWD = bundle dir, so "assets/..." resolves):
cd sx-out/macos/SxChess.app && ./SxChess

# Fails (CWD = /, asset not found -> null buffer -> stbtt segfault):
open sx-out/macos/SxChess.app
# or double-click in Finder
```

`add_asset_dir("assets", "assets")` in `build.sx` correctly copies the tree
into the flat `.app` (binary at `SxChess.app/SxChess`, assets at
`SxChess.app/assets/...`), so the files ARE present in the bundle — they're just
not found because the lookup is CWD-relative and CWD isn't the bundle.

# Root cause

The macOS SDL startup never reorients CWD (or the asset root) to the bundle.
`SdlPlatform.init` ([library/modules/platform/sdl3.sx:35](../library/modules/platform/sdl3.sx#L35))
calls `SDL_Init(SDL_INIT_VIDEO)` and creates the window but does no `chdir`,
so `read_file_bytes`
([library/modules/ui/glyph_cache.sx:202](../library/modules/ui/glyph_cache.sx#L202),
and the chess `extern read_file_bytes`) opens paths relative to whatever CWD
the launcher set — `/` under Finder/`open`.

The other platforms already handle this:
- **iOS**: [library/modules/platform/uikit.sx:346](../library/modules/platform/uikit.sx#L346)
  explicitly `chdir`s to the bundle's `resourcePath()` at startup, with the
  comment "iOS apps start with CWD=/. chdir to the bundle's resourcePath so the
  [assets resolve]".
- **Android**: [library/modules/platform/android.sx:71](../library/modules/platform/android.sx#L71)
  routes `read_file_bytes` through `AAssetManager` so paths resolve against the
  APK assets regardless of CWD.

macOS has neither — so it only works by accident when launched from a shell
sitting in the bundle dir.

# Investigation prompt

For a fresh session picking this up:

The fix mirrors the iOS precedent. In `SdlPlatform.init`
([sdl3.sx:35](../library/modules/platform/sdl3.sx#L35)), before any asset is
loaded, reorient to the bundle's resource directory **on macOS only** (leave
wasm/emscripten and the dev `sx run` path alone — those legitimately want the
project CWD).

Recommended approach — `SDL_GetBasePath()`:
- SDL3 `SDL_GetBasePath()` returns the directory containing the executable
  (for a `.app`, that's `SxChess.app/` where the assets were copied). `chdir`
  to it at the top of `init` when `BuildOptions.is_macos` (gate so `sx run`
  during development isn't affected — or gate on "the base path differs from
  CWD and contains an `assets/` dir").
- Add the `extern` decl for `SDL_GetBasePath` (returns `*u8`, SDL-owned) and
  call `chdir` (already used by uikit.sx — reuse the same `extern`).

Alternative (no SDL dependency): `_NSGetExecutablePath` + `dirname`, same as a
plain macOS resolve. SDL_GetBasePath is simpler and already links SDL3.

Things to verify / watch:
- Don't chdir for the `sx run <file>` (JIT) dev flow or for wasm — only the
  bundled AOT macOS app. The cleanest gate is the bundle context; if `init`
  can't see `BuildOptions`, gate on `SDL_GetBasePath()` returning a path that
  ends in `.app/` (bundled) vs the build dir (dev).
- After chdir, the existing `"assets/..."` relative loads resolve unchanged —
  no call-site changes needed in consumers (chess, glyph_cache).
- Confirm the iOS path (uikit, doesn't use SdlPlatform) is untouched.

# Verification

```sh
cd game && sx build main.sx
open sx-out/macos/SxChess.app            # must launch and stay up (board + pieces render)
# screenshot / pgrep -lf sx-out/macos/SxChess  -> alive after a few seconds
```

Before the fix: `open` → exits ~1s (stbtt segfault, null font buffer).
After: `open` and Finder double-click both launch and render, matching the
`cd bundle && ./SxChess` behavior.

Also re-run host + cross suites to confirm no platform-module regression:
`zig build && zig build test && bash tests/run_examples.sh`.
