fix(microsoft-fast-build): add depth limit and symlink guard to locator walk

crates/microsoft-fast-build/DESIGN.md

@@ -348,7 +348,7 @@ Each iteration pushes `("$index", JsonValue::Number(i as f64))` into `loop_vars`
 
 For each glob pattern:
 1. Find the **static prefix directory** — the longest directory path before any wildcard character (`*`, `?`). This avoids walking the entire filesystem.
-2. Recursively walk that directory collecting all `.html` files (`walk_html_files`).
+2. Recursively walk that directory collecting all `.html` files (`walk_html_files`). The walk is bounded to a maximum depth of 50 directories (`MAX_DIR_DEPTH`) and skips symlinks to prevent infinite loops from symlink cycles.
 3. Normalise path separators to `/` and strip a leading `./`, then test each file path against the glob pattern.
 4. For each matching file, read its content and call `parse_f_templates` to extract all `<f-template>` elements.
 5. The **element name** is the `name` attribute of each `<f-template>` element (e.g. `name="my-button"`). A single file may declare multiple templates.

crates/microsoft-fast-build/README.md

@@ -250,6 +250,8 @@ locator.add_template("my-button", "<button>{{label}}</button>");
 
 Glob patterns support `*` (any characters within one path segment), `**` (any number of segments), and `?` (any single character).
 
+> **Note:** `Locator::from_patterns` walks the filesystem recursively up to 50 directory levels deep and skips symlinks. Symlinked directories are never followed, guarding against cycles in the directory tree.
+
 ### HTML File Format
 
 Template HTML files must wrap their content in an `<f-template>` element with a `name` attribute identifying the custom element, and an inner `<template>` element containing the template markup:

crates/microsoft-fast-build/src/locator.rs

@@ -195,13 +195,29 @@ fn static_prefix_dir(pattern: &str) -> String {
     base
 }
 
+/// Maximum directory depth walked by `walk_html_files`. This guards against
+/// accidental stack overflows on very deep directory trees and prevents infinite
+/// loops caused by symlink cycles.
+const MAX_DIR_DEPTH: usize = 50;
+
 /// Recursively walk `dir` and collect all `.html` files.
 fn walk_html_files(dir: &Path, result: &mut Vec<std::path::PathBuf>) -> std::io::Result<()> {
+    walk_html_files_inner(dir, result, 0)
+}
+
+fn walk_html_files_inner(dir: &Path, result: &mut Vec<std::path::PathBuf>, depth: usize) -> std::io::Result<()> {
+    if depth > MAX_DIR_DEPTH {
+        return Ok(());
+    }
     for entry in std::fs::read_dir(dir)? {
         let entry = entry?;
         let path = entry.path();
+        // Skip symlinks to avoid following cycles into previously-visited dirs.
+        if path.is_symlink() {
+            continue;
+        }
         if path.is_dir() {
-            walk_html_files(&path, result)?;
+            walk_html_files_inner(&path, result, depth + 1)?;
         } else if path.extension().and_then(|s| s.to_str()) == Some("html") {
             result.push(path);
         }