two-layer/orphan: pre-commit hook says casting/ belongs on squad-state, but state tools and casting writer keep registry/history on disk #2229

Summary

With stateBackend: "two-layer", three parts of Squad disagree about where .squad/casting/registry.json and history.json should live. As a result, no supported path persists a casting change.

Evidence (source at indexed commit 89d6302)

• packages/squad-cli/src/cli/commands/install-hooks.ts: the pre-commit hook refuses any staged path matching ^\.squad/(decisions\.md|agents/.+/history\.md|casting/|routing/) unless SQUAD_SYNC_ACTIVE is set. Its message says: "These paths belong on the 'squad-state' orphan branch, not in your normal commits". The post-commit comment says it syncs "decisions, histories, casting" onto squad-state.
• packages/squad-sdk/src/tools/index.ts: MUTABLE_STATE_PATHS includes only casting/policy.json. squad_state_write key=casting/history.json is rejected with: "casting registry/history pair must only be changed through the atomic casting protocol".
• packages/squad-sdk/src/casting/durable-registry.ts: commitCastingRegistryPair(castingDir, …) writes the pair to the on-disk .squad/casting/ directory. cast add and preset scaffold both use it.

Observed in a consumer repo

• The squad-state branch had README.md, decisions.md, decisions/inbox/* and agents/*/history.md. It had no casting/ path, so nothing had moved the pair there.
• squad_state_read key=casting/registry.json returned "State key not found". squad_state_list dir=casting returned an empty list.
• To persist a registry model update, we had to call commitCastingRegistryPair and commit with SQUAD_SYNC_ACTIVE=1 to get past the hook.

Separate small bug

squad_state_list with no dir returns "Failed to list state: State key must not contain . or .. path segments". A root listing should either succeed or report a clearer error.

Questions

1. Under the two-layer and orphan backends, where should the canonical casting registry/history pair live: on disk in the working tree, or on the squad-state branch?
2. If on disk, should the pre-commit hook allowlist casting/registry.json, casting/history.json and the commit marker (and fix the hook/post-commit wording)?
3. If on squad-state, should the atomic writer target the state backend, and is a migration needed?

Versions: the source references above are from the indexed main commit 89d6302. The installed CLI (winget squad.exe) version was not checked against it.