[Repo Assist] fix: Markdown.ToMd preserves unresolved IndirectLink in reference notation

[github-actions]

🤖 This PR was created by Repo Assist, an automated AI assistant.

Summary

Fixes a bug in Markdown.ToMd where a reference-style link whose definition is absent from the document would serialise as invalid Markdown.

Before (broken): [link text]([unknown-key]) — the raw [key] string used as a URL
After (correct): [link text][unknown-key] — proper reference-link notation

Root Cause

In MarkdownUtils.formatSpan, the IndirectLink cases were written as a three-way OR pattern:

| IndirectLink(body, _, LookupKey ctx.Links (link, _), _)
| DirectLink(body, link, _, _)
| IndirectLink(body, link, _, _) -> "[" + formatSpans ctx body + "](" + link + ")"

In the fallthrough arm (IndirectLink(body, link, _, _)), link binds to position 2 of IndirectLink — the original field — which contains the raw key text including brackets (e.g. "[unknown-key]"). Using that as the URL produced [text]([unknown-key]), which is broken Markdown.

Fix

Split the fallthrough into its own arm and use the correct key field (position 3 — the clean key string):

| IndirectLink(body, _, LookupKey ctx.Links (link, _), _)
| DirectLink(body, link, _, _) -> "[" + formatSpans ctx body + "](" + link + ")"
// Unresolved reference link: emit [text][key] to preserve the reference notation
| IndirectLink(body, _, key, _) -> "[" + formatSpans ctx body + "][" + key + "]"

The corresponding IndirectImage fallthrough was already correct (it used key from position 3), so no change was needed there.

Tests Added

• ToMd preserves unresolved indirect link in reference notation — verifies the broken [text]([ form no longer appears
• ToMd resolves indirect link when reference is present — verifies the resolved case still emits a direct link form

Test Status

✅ Build: 0 warnings, 0 errors
✅ FSharp.Markdown.Tests: 283/283 passed (including 2 new tests)

Trade-offs

None. This is a pure correctness fix. The resolved-link behaviour (when a [key]: url definition is present) is unchanged.

Note: this change touches the same region as #1150 (DirectLink title fix); when both are eventually merged, the merge will be trivial to resolve.

Generated by 🌈 Repo Assist, see workflow run. Learn more.

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@e1ecf341a90b7bc2021e77c58685d7e269e20b99