Improve copilot instructions

[achamayou]

Goals:

1. Expand instruction coverage of the repo, but:
2. Split more into skills
3. Condense top-level instructions

[cjen1-msft]

I think pointing the robot at the docs here is likely more effective, from a 'go read these whenever you need to learn about a thing'.

[achamayou]

It could be, but this GitHub blog suggests it's worthwhile: https://github.blog/ai-and-ml/github-copilot/5-tips-for-writing-better-custom-instructions-for-copilot/

Perhaps it is good to have a relatively context-efficient dispatch early on? I don't know for sure.

[cjen1-msft]

As a generic review. I think we should restrict these kind of files to things that the robot often gets wrong (see norms and standards for how to build and run tests).
It seems to be pretty good at getting context for most cases, so unless its often entirely misunderstanding our architecture I'm not sure what the value is.

[achamayou]

As a generic review. I think we should restrict these kind of files to things that the robot often gets wrong (see norms and standards for how to build and run tests). It seems to be pretty good at getting context for most cases, so unless its often entirely misunderstanding our architecture I'm not sure what the value is.

That was also my hunch, but then I read https://github.blog/ai-and-ml/github-copilot/5-tips-for-writing-better-custom-instructions-for-copilot/. I think it's an early dispatch optimisation that leaves more context for the task rather than a "gets things wrong measurably" situation. Same for pushing stuff to skills.

I would be better if there was a way to measure this properly, all suggestions welcome.

[Copilot]

Pull request overview

This PR expands and restructures Copilot guidance by adding a dedicated Testing skill doc and enriching the main repository instructions with architectural and contributor workflow details.

Changes:

• Added a new “Testing” skill document describing how to run unit/e2e/SDK tests, labels, coverage, and e2e test patterns.
• Expanded .github/copilot-instructions.md with architecture details, key directories, build/test/lint pointers, and C++ conventions (naming, JSON, endpoints, logging, KV).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/skills/testing.md	New testing skill guide (how to run tests, coverage, and e2e infra/patterns).
.github/copilot-instructions.md	Adds architecture overview and links to skill docs; consolidates build/test/lint sections and C++ conventions.