Actors: std/actor wrapper and tests/actor, in Go

[malcolmredheron]

Summary

Implements the actor design, which was proposal-only on this branch. Actors are a user-level layer on top of caos, so the design doc now lives with the tool as std/actor/README.md rather than under design/.

• std/actor: a single Go program on std/go. Start reads the branch head, passes the state tree to the inner request and tail-calls it with itself as the callback. Finish mints the new commit with caos put-commit and moves the branch with a compare-and-swap. A lost race fails the request, which is never cached, so the caller retries. std/actor/README.md is the design doc (moved from design/actors.md).
• tests/actor: a reference key-value inner plus a staged test covering put, get, idempotent re-apply, a forced lost race that fails uncached and succeeds on retry, 12 concurrent writers converging to a linear chain, the inner's lazy view of the state, and the inner's cache hit.
• tests/actor-ref: a spike that proves the write path described below.
• Docs: std/actor/README.md (spike results, open question 6, status), design/runner-protocol.md (status line, link to the actor README) and std/README.md.

How finish moves the branch

Finish does not use git push. A push is a command <old> <new> <ref> plus a pack, and the pack can be empty when the server already has the new object, which it does after caos put-commit. So finish POSTs that one command and an empty pack to $CAOS_SERVER_URL/git-receive-pack and the server does the compare-and-swap. This needs no scratch repository, no fetch of the parent and no history.

git push cannot do this. It resolves the new commit in a local repository and walks its ancestry to build a pack, which needs every ancestor commit (a deep checkout). A partial clone with a promisor remote does not avoid that: with a depth-1 promisor pack and the shallow file removed, the push fails with Could not read <parent>. This is written up in open question 6 of std/actor/README.md and in the header of std/actor/worker.go.

Test plan

• Merged current main (b57d285) cleanly
• Full caos-test suite on the merged tree: 53/53 pass, including actor, actor-ref and lint

Known gaps

• A real crash between the move and the reply is not injected; a re-applied message gives the same observable result.
• Laziness is checked from inside the inner, not by counting server object reads.
• Start still reads the head with a depth-1 tree:0 fetch into a scratch repo; a caos verb could replace it.
• Not converted to Go: std/run-and-update-ref and its tests, which predate this work.

🤖 Generated with Claude Code

https://claude.ai/code/session_01TdKoYwiDbeZeVgVz12BFVS