chore(ffi-linkage): post-stream polish — vscode keywords + vestigial param + extension metadata

Two post-stream follow-ups flagged in CHECKPOINT-EXTERN-EXPORT.md, plus a
reproducible vscode-extension packaging setup:

- parser: drop the vestigial `RuntimeClassPrefix.is_extern` field and
  `parseRuntimeClassDecl`'s `is_extern` param. Always false since the
  `#foreign` token was deleted; the postfix `extern`/`export` keyword is the
  sole reference-vs-define decider. No behavior change (644 corpus / 442 unit).
- vscode grammar: highlight `extern`/`export` as `storage.modifier.sx`.
- vscode packaging: declare `@vscode/vsce` as a devDep + add `package` /
  `vscode:prepublish` scripts so the vsix rebuilds reproducibly (was an
  ambient tool). Add repository/homepage/bugs (Gitea), icon (swipelab logo,
  256x256), galleryBanner, README with cover banner. Rebuilt the vsix.

editors/vscode/README.md

@@ -0,0 +1,25 @@
+![sx](cover.png)
+
+# sx for Visual Studio Code
+
+Language support for the [sx programming language](https://git.swipelab.com/lab/sx).
+
+## Features
+
+- **Syntax highlighting** for `.sx` files, including embedded GLSL, SQL, HTML, and JSON blocks.
+- **Language server integration** — the extension launches the `sx` binary's language server (`sx lsp`) to provide editor intelligence.
+- **Breakpoints** registered for the `sx` language.
+
+## Requirements
+
+The `sx` compiler must be installed and on your `PATH` (or point the extension at it via the setting below). The extension shells out to it for the language server.
+
+## Settings
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| `sx.lspPath` | `sx` | Path to the `sx` binary used to start the language server (`sx lsp`). |
+
+## License
+
+See the repository for license details.

editors/vscode/package.json

@@ -4,6 +4,19 @@
   "description": "Language support for the sx programming language",
   "version": "0.0.1",
   "publisher": "swipelab",
+  "icon": "icon.png",
+  "galleryBanner": {
+    "color": "#000000",
+    "theme": "dark"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://git.swipelab.com/lab/sx.git"
+  },
+  "homepage": "https://git.swipelab.com/lab/sx",
+  "bugs": {
+    "url": "https://git.swipelab.com/lab/sx/issues"
+  },
   "engines": {
     "vscode": "^1.75.0"
   },
@@ -73,13 +86,16 @@
   },
   "scripts": {
     "build": "tsc -p .",
-    "watch": "tsc -watch -p ."
+    "watch": "tsc -watch -p .",
+    "vscode:prepublish": "npm run build",
+    "package": "vsce package --baseContentUrl https://git.swipelab.com/lab/sx/src/branch/master/editors/vscode --baseImagesUrl https://git.swipelab.com/lab/sx/raw/branch/master/editors/vscode"
   },
   "dependencies": {
     "vscode-languageclient": "^9.0.1"
   },
   "devDependencies": {
     "@types/vscode": "^1.75.0",
+    "@vscode/vsce": "^3.9.2",
     "typescript": "^5.0.0"
   }
 }

editors/vscode/syntaxes/sx.tmLanguage.json

@@ -193,6 +193,10 @@
           "name": "keyword.other.sx",
           "match": "\\b(enum|struct)\\b"
         },
+        {
+          "name": "storage.modifier.sx",
+          "match": "\\b(extern|export)\\b"
+        },
         {
           "name": "keyword.operator.cast.sx",
           "match": "\\bxx\\b"