Add opt-in .md→.html link rewriting to the markdown bundle action

[stevenchalem]

Summary

Add an opt-in capability to the markdown bundle action that rewrites local .md links to .html in the rendered output, so that converting a Markdown doc to HTML also fixes its intra-doc links in a single action.

Motivation

Today the markdown action only renders Markdown to HTML — it does not touch links. To make links work in the rendered HTML, bundle authors must follow every markdown action with a separate move/copy action carrying a regex replace like:

replace:
  from: "((\./|(?:\.\./)+).+)\.md"
  to: "\g<1>.html"

In the gist repo's bundle.yaml this exact block is copy-pasted 6 times (docs, docs/models, migration v11–v14). That duplication is error-prone: a real bug shipped in the gist 14.1.0 web-download bundle because the replace block got attached to the wrong action (the *.md move instead of the *.html move), simultaneously skipping the conversion where it was needed and applying it where it was wrong. See gist issues semanticarts/gist#1443 (redesign request) and semanticarts/gist#1467 (the narrow bug fix).

Pushing the .md→.html relink into the markdown action itself eliminates all six duplicated blocks downstream and removes the entire class of "wrong action" bugs, because there is no longer a separate, mis-attachable step. This is "Option A" from semanticarts/gist#1443.

Proposed change

Add an opt-in boolean option to the markdown action (proposed name: relinkHtml, matching the existing camelCase options like versionedDefinedBy, retainDefinedBy). When true, after rendering Markdown to HTML, rewrite local relative links ending in .md to .html.

- action: markdown
  source: "{output}/docs/"
  target: "{output}/docs/html/"
  includes: ["*.md"]
  relinkHtml: true        # NEW: render AND fix .md -> .html links

Rewrite semantics (must get these right)

• Only rewrite local relative link targets — skip absolute URLs (http:, https:, mailto:, protocol-relative //, and root-absolute /...).
• Operate on href/src attribute values of the rendered HTML, not arbitrary text — so .md mentioned in prose or code spans is not touched. (This is stricter/safer than the current regex, which matched anywhere in the file.)
• Preserve any #fragment or ?query suffix: ./Foo.md#section → ./Foo.html#section.
• More general than the current regex (which required an explicit ./ or ../ prefix): bare relative targets like Foo.md should also be relinked.

Implementation pointers (branch already created)

A branch feature/markdown-relink-html is already checked out off develop.

• onto_tool/bundle.py:292 — __bundle_markdown__ (the markdown action). Currently renders via md2html and writes output; ignores replace. Read the option here (use the existing __boolean_option__ helper at onto_tool/bundle.py:849) and pass it through to the renderer.
• onto_tool/mdutils.py:44 — md2html(md). Add an optional relink=False parameter; when set, post-process the rendered HTML to rewrite local .md links in href/src attributes to .html. A focused regex on attribute values (with the scheme/anchor handling above) is acceptable for the prototype; a real HTML parser is the robust version if needed.
• onto_tool/bundle_schema.yaml — the markdown action validates against #/definitions/bulk_file_operation (def at line 32; markdown wired at lines 394–396). Add the new relinkHtml property so the option passes schema validation. (Confirm whether additionalProperties is restricted — this was the last unchecked item before the session paused.)

Tests

There is an existing markdown test harness to extend:

• tests/bundle/test_markdown.py, tests/bundle/markdown.yaml, tests/bundle/bulk_md.yaml, tests/bundle/Table.md
• Add a fixture Markdown file containing a mix of links: a local ./foo.md, a bare foo.md, a ../bar.md#frag, an external https://example.com/x.md, and a .md reference inside a code span. Assert that only the local relative ones are rewritten to .html, fragments preserved, external and code-span untouched.
• Runner is pytest (see setup.py tests_require).

Acceptance criteria

• markdown action accepts relinkHtml: true and rewrites local .md links to .html in rendered output.
• External URLs, absolute paths, code-span text, and fragments are handled per the semantics above.
• Schema validates the new option.
• New test covers the link cases and passes; existing tests still pass.
• (Follow-up, separate) Update gist bundle.yaml to use relinkHtml and delete the six duplicated move … replace blocks — tracked in gist, not here.

Out of scope

The relative-path depth fixes (e.g. ../docs/ → ./, ../migration/ → ../../migration/) are a separate concern ("Option B" in semanticarts/gist#1443) and are not part of this issue.

[stevenchalem]

@bpelakh What do you think of this proposal as part of the solution to semanticarts/gist#1443 ?