docs+ci: document diagnostics, bump to v0.2.0, harden CI

- README: Diagnostics section (severity mapping, .dtx exclusion note,
  settings table), retitled to 'Language Support'
- CHANGELOG: 0.2.0 entry
- package.json: version 0.2.0, @vscode/vsce as devDependency
- ci.yml / release.yml: npm ci + tsc --noEmit + compile before packaging,
  so a type error or broken build fails the pipeline

Author: Liam0205

.github/workflows/ci.yml

@@ -20,8 +20,14 @@ jobs:
       - name: Validate grammar JSON
         run: node -e "JSON.parse(require('fs').readFileSync('syntaxes/expl3.tmLanguage.json','utf8')); console.log('grammar JSON ok')"
 
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type-check
+        run: npx tsc --noEmit
+
+      - name: Compile
+        run: npm run compile
+
       - name: Package (dry run)
-        run: |
-          npm install --no-save @vscode/vsce
-          npx vsce package --no-yarn -o /tmp/expl3-vscode-ci.vsix
-          npx vsce ls
+        run: npx vsce package --no-yarn -o /tmp/expl3-vscode-ci.vsix

.github/workflows/release.yml

@@ -64,8 +64,11 @@ jobs:
           fi
           echo "version check ok: $PKG_VER"
 
-      - name: Install tooling
-        run: npm install --no-save @vscode/vsce
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type-check
+        run: npx tsc --noEmit
 
       - name: Package VSIX
         id: pack

CHANGELOG.md

@@ -1,5 +1,21 @@
 # Changelog
 
+## [0.2.0] - 2026-07-06
+
+### Added
+
+- **explcheck diagnostics.** Runs [`explcheck`](https://ctan.org/pkg/expltools)
+  on expl3 files and reports issues as editor squiggles, mapped by severity
+  (`e`/`t` → Error, `w` → Warning, `s` → Information) with precise ranges.
+  - Triggers: on save (default), on type (debounced), or manual command.
+  - Dirty buffers are linted via a temp file (explcheck reads no stdin).
+  - Graceful one-time prompt when explcheck is missing; highlighting is
+    unaffected.
+  - `.dtx` / `.ins` excluded from linting (explcheck can't process them yet,
+    see explcheck issue #20); highlighting still applies.
+  - Settings: `expl3.check.{enable,path,run,debounce,maxLineLength,ignoredIssues,makeAtLetter}`.
+  - Command: **expl3: Run explcheck on the active file**.
+
 ## [0.1.0] - 2026-07-06
 
 ### Added

README.md

@@ -1,10 +1,13 @@
-# expl3 (LaTeX3) Syntax Highlighting
+# expl3 (LaTeX3) Language Support
 
-Syntax highlighting for **expl3** (the LaTeX3 programming layer) in Visual Studio Code.
+Syntax highlighting **and** static-analysis diagnostics for **expl3** (the
+LaTeX3 programming layer) in Visual Studio Code.
 
-Files full of expl3 code — `xeCJK.dtx`, `expl3.dtx`, your own `.sty`/`.cls` — normally
-render as a wall of undifferentiated `\command` text. This extension adds a semantic
-layer on top so the pieces that actually carry meaning stand out.
+Files full of expl3 code — `xeCJK.dtx`, `expl3.dtx`, your own `.sty`/`.cls` —
+normally render as a wall of undifferentiated `\command` text. This extension
+adds a semantic highlighting layer so the pieces that carry meaning stand out,
+and surfaces [`explcheck`](https://ctan.org/pkg/expltools) lint results directly
+in the editor.
 
 ![expl3 highlighting before / after](https://raw.githubusercontent.com/CTeX-org/expl3-vscode/main/images/before-after.png)
 
@@ -21,6 +24,40 @@ layer on top so the pieces that actually carry meaning stand out.
 Colors come from your active color theme — the extension only assigns scopes, so it
 looks native in Dark+, Light+, Solarized, and everything else.
 
+## Diagnostics (explcheck)
+
+If [`explcheck`](https://ctan.org/pkg/expltools) is available, the extension runs it
+on your expl3 files and shows the results as squiggles, mapped by severity:
+
+| explcheck prefix | meaning | VS Code severity |
+|------------------|---------|------------------|
+| `e`, `t` | errors / type errors | Error |
+| `w` | warnings | Warning |
+| `s` | style warnings | Information |
+
+`explcheck` ships with TeX Live's `expltools` package (`tlmgr install expltools`). If
+it is not found, the extension prompts once and stays quiet otherwise — highlighting
+keeps working regardless.
+
+> **`.dtx` / `.ins` are not linted.** `explcheck` cannot process bundled sources
+> directly yet (see [explcheck issue #20](https://github.com/witiko/expltools/issues/20),
+> planned for v1.1); unpack them to `.sty`/`.tex` first. Highlighting still applies to
+> `.dtx`.
+
+### Settings
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| `expl3.check.enable` | `true` | Enable explcheck diagnostics. |
+| `expl3.check.path` | `explcheck` | Path to the executable. |
+| `expl3.check.run` | `onSave` | `onSave`, `onType` (debounced), or `manual`. |
+| `expl3.check.debounce` | `400` | Debounce (ms) for `onType`. |
+| `expl3.check.maxLineLength` | `0` | Max line length before S103 (0 = explcheck default 80). |
+| `expl3.check.ignoredIssues` | `[]` | Issue ids/prefixes to suppress, e.g. `["s103"]`. |
+| `expl3.check.makeAtLetter` | `false` | Tokenize `@` as a letter (like `.sty` files). |
+
+Command **expl3: Run explcheck on the active file** triggers a check on demand.
+
 ## Requirements
 
 This is an **injection grammar**: it layers on top of an existing LaTeX grammar rather