🤖 This is an automated pull request from Repo Assist.

Implements a MarkdownProvider type provider that gives statically typed access to YAML front matter in Markdown files, as requested in #1657.

What this adds

type Post = FSharp.Data.MarkdownProvider<"post.md">

// Given a file with YAML front matter:
// ---
// title: Hello World
// date: 2024-01-15
// author: Jane Doe
// tags: [fsharp, data]
// draft: false
// views: 1234
// rating: 4.5
// ---
// # Body content here

let post = Post.Load("post.md")
post.Title   // string:   "Hello World"
post.Date    // DateTime: 2024-01-15
post.Author  // string:   "Jane Doe"
post.Tags    // string[]: [| "fsharp"; "data" |]
post.Draft   // bool:     false
post.Views   // int:      1234
post.Rating  // decimal:  4.5m
post.Body    // string:   "# Body content here\n..."

// Also: Parse, AsyncLoad, With* methods

Implementation

src/FSharp.Data.Json.Core/MarkdownDocument.fs (new)

• MarkdownDocument type that implements IJsonDocument, carrying both the front-matter JsonValue and the Body string
• FrontMatterParser internal module: minimal YAML-lite parser supporting strings, numbers, booleans, null, inline arrays [a, b, c], and block arrays (- item style)
• MarkdownDocument.Load(TextReader) and MarkdownDocument.ParseSample(string) static methods

src/FSharp.Data.DesignTime/Markdown/MarkdownProvider.fs (new)

• MarkdownProvider type provider registered as FSharp.Data.MarkdownProvider
• At design time: parses sample front matter → JsonValue.Record → runs through existing JsonInference + JsonTypeBuilder
• Adds a Body: string property to the root generated type (via IJsonDocument :?> MarkdownDocument downcast — safe because CreateFromTextReader always produces a MarkdownDocument)
• Static parameters: Sample, RootName, Culture, Encoding, ResolutionFolder, EmbeddedResource, InferTypesFromValues, UseOriginalNames, PreferOptionals

Tests & docs

• tests/FSharp.Data.Tests/Data/BlogPost.md — sample file
• tests/FSharp.Data.DesignTime.Tests/expected/Markdown,BlogPost.md,,True.expected — signature snapshot
• tests/FSharp.Data.Tests/MarkdownProvider.fs — integration tests (7 test cases)
• docs/library/MarkdownProvider.fsx — documentation

Design decisions

• Reuse JSON infrastructure: the front matter is treated as a JSON record internally, so all the existing type inference, property generation, With* methods, and InferenceMode support come for free.
• No new dependencies: the YAML parser is a simple ~80-line F# implementation covering the subset of YAML used in markdown front matter.
• Body always available: the Body property is added to the root type after JSON type generation, giving access to the markdown content below the front matter.

Supported front matter patterns

Test Status

✅ Build succeeded
✅ 488 design-time tests pass (including new Markdown signature test)
⚠️ FSharp.Data.Tests OOM on CI runner — pre-existing infrastructure constraint (confirmed by checking out main and observing the same failure without my changes)

Closes #1657

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