`eval` and `echo` supports numbers for knitr engine per documentation, but YAML validation fails

[cderv]

I did not use eval: -2 (in-chunk YAML syntax) because that gets rejected before rendering.

In file test.qmd
(line 8, columns 10--12) Field "eval" has value -2, which must instead be `true` or `false`
7: ```{r}
8: #| eval: -2
           ~~~
9: if (TRUE) {
✖ The value -2 is of type number.
ℹ The error happened in location eval.

ERROR: Validation of YAML cell metadata failed.
ERROR: Render failed due to invalid YAML.

Originally posted by @fkohrt in #12164

quarto-cli/src/resources/schema/cell-codeoutput.yml

Lines 17 to 35 in e8eefd9

	- name: echo
	tags:
	contexts: [document-execute]
	execute-only: true
	schema:
	anyOf:
	- boolean
	- enum: [fenced]
	errorDescription: "be `true`, `false`, or `fenced`"
	description:
	short: Include cell source code in rendered output.
	long: |
	Include cell source code in rendered output.
	- `true` (default in most formats): include source code in output
	- `false` (default in presentation formats like `beamer`, `revealjs`, and `pptx`): do not include source code in output
	- `fenced`: in addition to echoing, include the cell delimiter as part of the output.
	- `[...]`: A list of positive or negative line numbers to selectively include or exclude lines
	(explicit inclusion/excusion of lines is available only when using the knitr engine)

[cderv]

This is related to problem with warning: NA too

• try to add duplicate warning definition only for knitr #11875

[fkohrt]

The following might also be related: #12832

[cderv]

Thanks @fkohrt.

Not directly related.

• YAML validation now fails on valid knitr engine document using multiline knitr option syntax instead of YAML #12832 is about what to do in the document using engine: knitr and not using the expected YAML syntax for comment in-cell options, but using the multiline knitr options syntax. In this case YAML validation can't work for sure.

• eval and echo supports numbers for knitr engine per documentation, but YAML validation fails #12178 (this issue) is about supporting in YAML validation some engine specific values - currently this is not something that Quarto YAML schema can do