Added more detailed transformations topics AND added local link checking on PRs

[kristin-kronstain-brown]

Added new transformation topics, updated from kgateway. Link checker changes also included to be able to check a subset of files effectively.

Link checker changes

Adds pull request support to the link checker workflow. Previously the workflow only ran on a schedule (Monday) and manual dispatch, checking all links across all files and reporting results via GitHub issues and Slack. PRs now trigger a faster, targeted check.

Trigger changes

• Workflow now runs on pull requests that modify content/** or assets/**
• Cron and dispatch behavior is unchanged

On pull requests

• Checks only the HTML pages built from changed .md files; falls back to all HTML if no content files changed (e.g. asset-only PRs)
• Skips external link checking (--exclude "^https://") — only local/internal links are validated; remapped links are still resolved to local files and checked
• Skips issue creation and Slack notification
• Fails the check and writes the markdown report to the job summary if errors are found
• Artifacts are still uploaded for review

On cron/dispatch

• No behavior change: checks all links across all files, creates a GitHub issue and posts to Slack on failure

Other

• fetch-depth: 100 on checkout so git diff can find the merge base for the changed-files calculation
• Lychee invocation refactored to use a bash array, which correctly handles arguments containing special characters

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[Nadine2016]

add a sentence about what context variables are

[Nadine2016]

add a sentence what built-in functions are

[Nadine2016]

maybe a table with topic name and then used function?

[Nadine2016]

Suggested change

	Use [CEL expressions]({{< link-hextra path="/reference/cel/" >}}) to inject, modify, and remove headers in requests and responses. The example uses `request.headers[]` to extract a header value and combines `set`, `add`, and `remove` operations in a single transformation.
	Use [CEL expressions]({{< link-hextra path="/reference/cel/" >}}) to inject, modify, and remove response headers. The example uses the `request.headers[]` context variable to extract a request header value and injects the value into a response header. You also explore how to combine `set`, `add`, and `remove` operations in a single transformation.

[Nadine2016]

Suggested change

The gateway intercepts the upstream response and modifies its headers before returning it to the client. You can combine `set`, `add`, and `remove` in a single policy so that the gateway applies all three operations in one pass. This configuration is useful when you need to enrich responses with values from the original request, enforce header policies like CORS, or strip internal headers that should not reach the client.

The gateway intercepts the upstream response and modifies its headers before returning them to the client. You can combine `set`, `add`, and `remove` operations in a single policy so that the gateway applies all three operations in one pass. This configuration is useful when you need to enrich responses with values from the original request or strip internal headers that should not reach the client.

[Nadine2016]

Suggested change

	* `add`: Appends `https://example.com` to the `access-control-allow-origin` header. Because httpbin already returns `access-control-allow-origin: *`, the response ends up with two entries for that header. Use `add` when you want to append a value without overwriting what is already present.
	* `add`: Appends `https://example.com` to the `access-control-allow-origin` header. Because httpbin already returns `access-control-allow-origin: *`, the response ends up with two entries for that header. Use `add` when you want to append or add a value without overwriting what is already present.

[Nadine2016]

can you make this a list for each header and explain what happens for each? similar to what we did previously (removed lines).

[Nadine2016]

maybe list the expected outcome for each header in a bulleted list

[Nadine2016]

appending is weird, typically appending means I still have one header but with multiple values. The fact that you get back the same header with different values, smells like a bug to me. I don't think a system would be able to process that correctly

asked in slack, seems like this is the expectation, but in this case it is not appended, it is just added https://solo-io-corp.slack.com/archives/C08P050QFGF/p1774463768717419

[Nadine2016]

in order to show the removal, you would technically need to show an example without the policy to prove the header is actually there

[Nadine2016]

Suggested change

	* `x-sampling-decision`: A random float from `random()`. A tracing backend configured to sample when the value is less than `0.1` records roughly 10% of all requests and ignores the rest.
	* `x-sampling-decision`: A random float from the `random()` function. For example, you might have a tracing backend that is configured to sample requests only if the `x-sampling-decision` header is set to `0.1` or less.

[Nadine2016]

Suggested change

	Use [CEL expressions]({{< link-hextra path="/reference/cel/" >}}) to encode and decode base64 values in request headers and add the results as response headers. The examples use `base64.encode()`, `base64.decode()`, `bytes()`, `string()`, and `request.headers[]`.
	Use [CEL expressions]({{< link-hextra path="/reference/cel/" >}}) to encode and decode base64 values in request headers and add the results as response headers. The examples use the `base64.encode()`, `base64.decode()`, `bytes()`, and `string()` CEL functions, and the `request.headers[]` context variables.

[Nadine2016]

what does bytes do here? It looks like the transformation works without it

[Nadine2016]

Suggested change

	title: Forward request URLs
	title: Create redirect URLs

[Nadine2016]

Suggested change

	description: Use CEL expressions to construct a full request URL from context variables and forward it upstream as a request header.
	description: Use CEL expressions to construct a redirect URL from context variables and forward it upstream as a request header.

[Nadine2016]

Suggested change

	"http://www.example.com:80/get"
	"http://www.example.com/get"

[Nadine2016]

this example does not use query parameters. We should rename that to something like: Change request path and method

[Nadine2016]

maybe show a request with that header so that people can see it is there.

[Nadine2016]

This configuration prevents internal credentials from being exposed to the backend service.

this is very specific to the name of the header that was chosen. I think in general you would use this to get rid of headers that you do not want to send to backend services

[Nadine2016]

Suggested change

	In this example, you set the response body to a JSON string built from request context variables. The gateway intercepts the upstream response and replaces the body with the CEL expression result before returning it to the client. The upstream never sees the change — only the client receives the modified body. This is useful for tying responses back to request traces.
	In this example, you set the response body to a JSON string built from request context variables. The gateway intercepts the upstream response and replaces the body with the CEL expression result before returning it to the client. The upstream never sees the change — only the client receives the modified body.

[Nadine2016]

maybe use an ID instead of the name

[Nadine2016]

Suggested change

	## Inject request header fields into a response body
	## Inject request header fields into a request body

[Nadine2016]

Suggested change

	In this example, you parse a JSON request body using `json()` to extract a field and include it in the response body. Use `request.body` to access the raw incoming request body as a string.
	In this example, you parse a JSON request body by using the `json()` function to extract a field and include it in the response body. Use `request.body` to access the raw incoming request body as a string.

[Nadine2016]

Suggested change

	title: Inject response bodies
	title: Inject response body fields

[Nadine2016]

Suggested change

	title: Change response bodies
	title: Update response status

[Nadine2016]

Suggested change

	In this example, the transformation applies after routing and targets a specific HTTPRoute. You change the value of the `:status` response header to 401 if the request URI contains `foo=bar`. If the request URI does not contain `foo=bar`, you return a 403 HTTP response code.
	In this example, the transformation applies after routing and targets a specific HTTPRoute. You change the value of the `:status` response header to 401 if the request URI contains the `foo=bar` query parameter. If the request URI does not contain `foo=bar`, you return a 403 HTTP response code.

[Nadine2016]

Suggested change

Use the `filterKeys()` and `merge()` [CEL functions]({{< link-hextra path="/reference/cel/#functions-policy-all" >}}) together with `json()` and `toJson()` to sanitize a JSON request body before it reaches the upstream. `filterKeys()` removes unwanted fields by testing each key against a predicate. `merge()` combines two maps, with the second map's values overwriting any matching keys in the first. `toJson()` serializes the resulting map back to a JSON string.

Use the `filterKeys()` and `merge()` [CEL functions]({{< link-hextra path="/reference/cel/#functions-policy-all" >}}) together with `json()` and `toJson()` to sanitize a JSON request body before it reaches the upstream. `filterKeys()` removes unwanted fields by testing each key against a predicate. `merge()` combines two maps, with the second map's value overwriting any matching keys in the first. `toJson()` serializes the resulting map back to a JSON string.

[Nadine2016]

into a map or JSON?

[Nadine2016]

not sure what we mean with on the left?

[Nadine2016]

maybe just say: Add access log attributes with CEL expressions.

[Nadine2016]

Suggested change

	## Log specific variables
	## Log specific request data

[Nadine2016]

Suggested change

	1. Create an {{< reuse "agw-docs/snippets/trafficpolicy.md" >}} resource with a `filter` field set to a CEL expression. Logs are written only when the expression evaluates to `true`.
	1. Create an {{< reuse "agw-docs/snippets/trafficpolicy.md" >}} resource with a `filter` field that logs requests only if the response status code does not equal 400.