Add lychee link checker config and CI workflow

Adds a lychee configuration and a Links GitHub Actions workflow so that
stale or redirecting links are caught automatically going forward. The
checker runs on push, pull request, and weekly to catch external link
rot. max_redirects is 0 so links that have moved are surfaced and can be
updated to their canonical destination.

The configured globs cover Markdown docs plus C sources and headers,
which is where links appear in this repository. Vendored submodules
(maxmind-db, t/libtap), the test harness under t/, build/generated
directories, the Hugo site output, and the Changes.md changelog are
excluded.

Part of STF-557.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: oschwald

.github/workflows/links.yml

@@ -0,0 +1,32 @@
+name: Links
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: "0 13 * * 1" # weekly, to catch external link rot without a commit
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  linkChecker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Setup mise
+        uses: jdx/mise-action@6d1e696aa24c1aa1bcc1adea0212707c71ab78a8 # v3.6.1
+        with:
+          install: false
+
+      # Install only lychee (not the repo's full toolchain) and run the check.
+      - name: Check links
+        env:
+          MISE_AUTO_INSTALL: "false"
+        run: |
+          mise install lychee
+          mise run check-links

.gitignore

@@ -46,3 +46,4 @@ Makefile.in
 Testing/
 install_manifest.txt
 build/
+.lycheecache

lychee.toml

@@ -0,0 +1,60 @@
+# Lychee link checker configuration
+# https://lychee.cli.rs/#/usage/config
+#
+# Run locally with:
+#   lychee './**/*.md' './src/**/*.c' './include/**/*.h'
+
+# Include URL fragments in checks
+include_fragments = true
+
+# Don't allow any redirects, so links that have moved are surfaced and updated
+# to their canonical destination.
+max_redirects = 0
+
+# Accept these HTTP status codes
+# 100-103: Informational responses
+# 200-299: Success responses
+# 403: Forbidden (some sites use this for rate limiting)
+# 429: Too Many Requests
+# 500-599: Server errors (temporary issues shouldn't fail CI)
+# 999: LinkedIn's custom status code
+accept = ["100..=103", "200..=299", "403", "429", "500..=599", "999"]
+
+# Exclude URL patterns from checking (treated as regular expressions)
+exclude = [
+    # Local / template file URLs (e.g. Hugo layout placeholders)
+    '^file://',
+    # Live / auth-gated endpoints that require login or are queried at runtime
+    '^https://geoip\.maxmind\.com',
+    '^https://geolite\.info',
+    '^https://updates\.maxmind\.com',
+    '^https://www\.maxmind\.com/en/accounts/',
+    # Placeholders / local
+    '^https?://example\.(com|org|net)',
+    '^http://localhost',
+    '127\.0\.0\.1',
+]
+
+# Exclude file paths from getting checked (treated as regular expressions)
+exclude_path = [
+    '(^|/)\.git/',
+    # Build / generated directories
+    '(^|/)build/',
+    '(^|/)\.libs/',
+    '(^|/)autom4te\.cache/',
+    '(^|/)generated/',
+    # Generated Hugo site output
+    '(^|/)docs/public/',
+    # Vendored submodules and test harness/fixtures
+    '(^|/)maxmind-db/',
+    '(^|/)t/',
+    # Changelog: historical entries are preserved as-is, not rewritten
+    '(^|/)Changes\.md$',
+]
+
+# Cache results for 1 day to speed up repeated checks
+cache = true
+max_cache_age = "1d"
+
+# Skip missing input files instead of erroring
+skip_missing = true

mise.lock

@@ -9,6 +9,7 @@ disable_backends = [
 
 [tools]
 hugo = "latest"
+lychee = "0.23.0"
 node = "latest"
 "pipx:clang-format" = "21.1.8"
 "github:houseabsolute/precious" = "latest"
@@ -21,3 +22,7 @@ run = "hugo --source docs --minify"
 [tasks.serve-docs]
 description = "Serve the docs site locally with Hugo dev server"
 run = "hugo server --source docs"
+
+[tasks.check-links]
+description = "Check links with lychee"
+run = "lychee --no-progress './**/*.md' './src/**/*.c' './include/**/*.h'"