HtmlScreenshot: honour OFFICECLI_BROWSER as an explicit chrome-family executable

README.md

@@ -256,7 +256,7 @@ OfficeCLI is self-contained. The capabilities below ship inside the binary — *
 
 #### Rendering engine — high-fidelity, built-in
 
-OfficeCLI's keystone: a from-scratch, high-fidelity HTML rendering engine that lets an AI agent *see* the rendered document instead of guessing from the DOM. It covers shapes, charts (trendlines, error bars, waterfall, candlestick, sparklines), equations (OMML → LaTeX, rendered with KaTeX), 3D `.glb` models via Three.js, morph transitions, slide zoom, and shape effects. Per-page PNG screenshots are produced by piping the rendered HTML through a headless browser. Three modes:
+OfficeCLI's keystone: a from-scratch, high-fidelity HTML rendering engine that lets an AI agent *see* the rendered document instead of guessing from the DOM. It covers shapes, charts (trendlines, error bars, waterfall, candlestick, sparklines), equations (OMML → LaTeX, rendered with KaTeX), 3D `.glb` models via Three.js, morph transitions, slide zoom, and shape effects. Per-page PNG screenshots are produced by piping the rendered HTML through a headless browser — found on PATH or in a platform-standard install location, or set `OFFICECLI_BROWSER=/path/to/chrome-family-binary` to point OfficeCLI at an explicit Chrome/Chromium/Edge executable outside those locations (e.g. a Chrome for Testing build a host manages itself). Three modes:
 
 - **`view html`** — standalone HTML file, assets inlined. Open in any browser.
 - **`view screenshot`** — per-page PNG, ready for multimodal agents to read.

src/officecli/Core/HtmlScreenshot.cs

@@ -411,6 +411,13 @@ private static (bool, string?) TryChrome(string url, string outPath, int w, int
 
     private static string? FindChrome()
     {
+        // Explicit override first: lets hosts that ship their own Chromium
+        // (e.g. a Chrome for Testing build outside the standard install
+        // paths) point OfficeCLI at it without touching PATH.
+        var explicitBrowser = Environment.GetEnvironmentVariable("OFFICECLI_BROWSER");
+        if (!string.IsNullOrWhiteSpace(explicitBrowser) && File.Exists(explicitBrowser))
+            return explicitBrowser;
+
         string[] names = ["google-chrome", "google-chrome-stable", "chromium", "chromium-browser",
                           "chrome", "microsoft-edge", "microsoft-edge-stable", "msedge"];
         var pathHit = WhichFirst(names);