Reusable Claude review workflow

[squaremo]

This takes the Claude workflow definition as it is in nscaledev/uni-region#381, tweaks it a little to make it more robust when files aren't present, and puts it in a workflow_call trigger.

This means you can call it from another repo, and it'll act locally; and that means we can have centralised prompts (as below), but local guidelines (as in CLAUDE.md), which makes it much easier to evolve our reviews.

Fixes INST-545.

[squaremo]

I used one of these (as created in the Anthropic console), but I note that our repos have a CLAUDE_CODE_OAUTH_TOKEN (I don't know how to get one of those) -- they are not interchangeable, so I've made it possible to supply either.

[squaremo]

I've been using a PR in https://github.com/nscaledev/uni-shared-workflow-tester, which calls the workflow here, to experiment.

Some results (most recent to least):

• https://github.com/nscaledev/uni-shared-workflow-tester/actions/runs/21760515725 -- this one was run after separating out specific instructions into rules/*.md (and importing them in the CLAUDE.md here). The prompt -- also here -- says to resolve those imports and use the WebFetch tool to get them. This ends up stringing at least a couple of web fetches together (one to get the CLAUDE.md, then more to get individual files that it imports), which amplifies the non-determinism. But it seems pretty reliable at figuring out the URL to fetch, so that's something.
• https://github.com/nscaledev/uni-shared-workflow-tester/actions/runs/21760004065 this one is interesting because you can see what WebFetch does. The first use gets the CLAUDE.md, which it summarises .. OK .. then you can see it interprets what it wants from the other imports, and chooses which ones. The interpretation exposes the stochastic behaviour -- different runs may or may not decide to fetch guidelines.

[squaremo]

I wanted this to centralise the guidelines (what would go in CLAUDE.md) but I couldn't get this to work reliably. Locally it's possible to put a CLAUDE.md in another directory and use --add-dir to tell Claude to look there (https://code.claude.com/docs/en/memory#load-memory-from-additional-directories).

I tried implementing this in the workflow by checking out this repo (fine) alongside the repo under review (I couldn't get the checkout action to do this in an acceptable way, either you supply .path for the second checkout and it nests it in the first, or you give .path for both checkouts and it fails because github.workspace is set to the default path.) But even in the nested case, it didn't seem to accept the -add-dir argument. But it is 1. difficult to tell, because LLMs, and 2. always possible I got something wrong.

[squaremo]

@peterj-ns After experiments I reduced this to a callable workflow, which at least means we can just call with a secret and keep the (minimal) prompt and other parameters centrally.