Add links to Quarto documentation for extensions, includes, filters, and freeze

Author: gordonwoodhull

posts/2026-03-xx/index.qmd

@@ -39,7 +39,7 @@ This creates a project with two pieces: an `_extension.yml` that declares the en
 
 ### `_extension.yml`
 
-The extension metadata lives in `_extensions/{name}/_extension.yml`. For an engine extension, the important part is `contributes.engines`:
+The extension metadata lives in [`_extensions/{name}/_extension.yml`](https://quarto.org/docs/extensions/). For an engine extension, the important part is `contributes.engines`:
 
 ```yaml
 title: My Engine
@@ -137,7 +137,7 @@ interface ExecutionTarget {
 
 Most engines do the same thing here — read the file as a `MappedString` and extract its YAML. `MappedString` is a string that carries source location mapping so that error messages can point back to the right line in the original file. Use `quarto.mappedString.fromFile()` to create one.
 
-`{{< include >}}` shortcodes can appear inside code blocks to import code. Call `context.resolveFullMarkdownForFile()` here to expand them before `execute()` sees the document — see [`EngineProjectContext`](#engineprojectcontext). Both knitr and Jupyter do this.[^2]
+[`{{< include >}}` shortcodes](https://quarto.org/docs/authoring/includes.html) can appear inside code blocks to import code. Call `context.resolveFullMarkdownForFile()` here to expand them before `execute()` sees the document — see [`EngineProjectContext`](#engineprojectcontext). Both knitr and Jupyter do this.[^2]
 
 [^2]: Currently, neither marimo nor the Julia engine calls `resolveFullMarkdownForFile`.
 
@@ -158,7 +158,7 @@ The most important fields of `ExecuteResult`:
 
 - `markdown` — the processed markdown (this is the main output)
 - `supporting` — paths to supporting files like figures
-- `filters` — pandoc filters to apply
+- `filters` — [pandoc filters](https://quarto.org/docs/extensions/filters.html) to apply
 - `includes` — content to inject into the document header, footer, etc.
 
 Other fields include `metadata`, `pandoc`, `engine`, `engineDependencies`, `preserve`, `postProcess`, and `resourceFiles`.
@@ -288,7 +288,7 @@ This is the top-level interface your engine exports as its default export. It ha
 : File extensions this engine supports beyond `.qmd` — for example, Jupyter returns `[".ipynb"]`. Most engine extensions return `[]`.
 
 `canFreeze`
-: Whether your engine supports freezing (caching execution results so they aren't re-run).
+: Whether your engine supports [freezing](https://quarto.org/docs/projects/code-execution.html#freeze) (caching execution results so they aren't re-run).
 
 `generatesFigures`
 : Whether your engine produces figure output.