prscs: proxy response status code setter

[bneradt]

In complex setups where there are multiple plugins that can be setting
an error response, it can be non-trival to determine which component
intervened for any given transaction. This adds the prscs log field,
proxy response status code setter, which provides an identifying string
for the component (a plugin name, or ip_allow, for instance) that set
the transaction's response status.

[Copilot]

Pull Request Overview

This PR introduces a plugin status setter (plss) feature to help identify which plugin or component set a transaction's HTTP response status. This is valuable for debugging complex setups with multiple plugins that may modify response status codes.

• Adds a new logging field 'plss' (Plugin Last Set Status) to track which entity set the transaction's status
• Enhances TSHttpTxnStatusSet and TSHttpHdrStatusSet APIs with optional setter parameter
• Updates all plugins and internal components to use the new setter tracking functionality

Reviewed Changes

Copilot reviewed 57 out of 57 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
include/ts/ts.h	Adds new API functions with setter parameters and documentation
src/api/InkAPI.cc	Implements the core setter tracking functionality
include/proxy/http/HttpTransact.h	Adds status setter name field to transaction state
src/proxy/logging/Log.cc, LogAccess.cc	Implements plss log field for status setter tracking
src/proxy/http/*.cc	Updates core components to set "ip_allow" as setter
plugins/*/**.cc	Updates all plugins to pass their names as setter parameters
tests/gold_tests/*	Adds tests to verify the new logging functionality
doc/*	Adds comprehensive documentation for new API functions

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[cmcfarlen]

Setting the new setter field in TSHttpTxnStatusSet makes sense, but setting it in TSHttpHdrStatusSet seems strange to me. Also, wasn't there some discussion about removing proxy from the log field name?

[bneradt]

Thanks for the review. A quick answer to this question:

Also, wasn't there some discussion about removing proxy from the log field name?

The concern was not with "proxy" but with my previous "plugin" terminology. "plugin" is wrong because aspects of ATS core can set the response, not just plugins. This now uses "proxy". I think that's better. "proxy" in prscs fits well with the other p* log fields which are also proxy related.