Fix broken Markdown link references to headings

[Copilot]

Fixes Markdown link references to headings by slugifying the anchor URLs to match GitHub's heading anchor generation algorithm, using the same semantics as github-slugger.

Changes Made

• internal/mode/usage/markdown/slug.go (new file): Implements headingSlug() matching the github-slugger algorithm — lowercases the input, keeps Unicode letters, digits, underscores, and hyphens, converts spaces to -, and strips everything else (including backtick characters).
• internal/mode/usage/markdown/link.go: Updated linkToSpec to apply headingSlug() to the full heading text (e.g. `VARIABLE_NAME`), correctly stripping backtick formatting and producing slugified anchors like #read_dsn instead of #READ_DSN.
• internal/mode/usage/markdown/slug_test.go (new file): Unit tests for headingSlug covering variable names with backticks, space→hyphen conversion, hyphen preservation, punctuation stripping, Unicode letters, and digits.
• Test data files: Updated all 19 affected .md test data files to reflect the corrected lowercase anchor URLs.

Testing

• ✅ All existing tests pass with the updated expected output.
• ✅ New unit tests validate headingSlug behaviour against the github-slugger algorithm.

[jmalloc]

@copilot try again.

[Copilot]

@copilot try again.

Fixed in 27e3894. The linkToSpec function now uses strings.ToLower(s.Name()) for the heading anchor URL, generating slugified anchors like #read_dsn instead of #READ_DSN to match GitHub's Markdown heading anchor slugification. All 19 affected test data files were updated accordingly.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• makefiles.dev
  • Triggering command: /usr/bin/curl curl -sfL REDACTED /home/REDACTED/go/pkg/mod/golang.ointernal/mode/usage/markdown/testdata/spec/string/with-max-length-deprecated.md -uns�� pec/kubernetes/deprecated.md ltiple-simple.md ux-amd64/pkg/tool/linux_amd64/compile get --global l/linux_amd64/vedf21b9c331f53eef3f3c7734decce359a99263ce:internal/mode/usage/markdown/testdata/complete/non-normative.md ux-amd64/pkg/tool/linux_amd64/compile -ato�� -bool g/with-minmax-length-deprecated.md ep -errorsas -ifaceassert -nilfunc grep (dns block)
  • Triggering command: /usr/bin/curl curl -sfL REDACTED /home/REDACTED/go/pkg/mod/golang.ointernal/mode/usage/markdown/testdata/spec/string/with-sensitive-U0 -ato�� pec/kubernetes/deprecated.md ltiple-simple.md ux-amd64/pkg/tool/linux_amd64/vet -errorsas -ifaceassert l/linux_amd64/vedf21b9c331f53eef3f3c7734decce359a99263ce:internal/mode/usage/markdown/testdata/complete/normative.md ux-amd64/pkg/tool/linux_amd64/vet -ato�� -bool g/with-minmax-length-deprecated.md ndor/bin/grep -errorsas -ifaceassert -nilfunc grep (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[jmalloc]

Implementation should have the same semantics as https://github.com/Flet/github-slugger/blob/3461c4350868329c8530904d170358bca1d31448/regex.js

[Copilot]

Implementation should have the same semantics as https://github.com/Flet/github-slugger/blob/3461c4350868329c8530904d170358bca1d31448/regex.js

Done in 2eef036. Added headingSlug() in slug.go that implements the github-slugger algorithm: lowercases the input, keeps Unicode letters/digits/underscores/hyphens, converts spaces to -, and strips everything else. linkToSpec now applies it to the full heading text (including backticks, which get stripped by the algorithm).