refactor: remove local workspace runtime, redesign config schema

[dorey-agent]

Motivation

The local subprocess runtime (WorkspaceConfig::Local) was a development convenience that bypasses all container isolation, proxy enforcement, and resource limits. In production, all agents run in Docker containers. Keeping the local runtime adds code complexity, widens the attack surface, and creates a config path that's never used in real deployments.

Additionally, the workspace config schema needed redesign to support future runtime types (e.g., Firecracker, Podman) without breaking changes.

Solution

Remove local runtime entirely:

• Delete LocalBackend and local_backend module (141 lines)
• Remove WorkspaceConfig::Local variant and LocalWorkspaceConfig struct
• Remove local agent validation, binary resolution, and spawn logic
• Simplify keepalive (always enabled — was conditional on is_docker())

Redesign config schema with versioning:

• Add schema_version: u32 to AnyclawConfig (default: 1)
• Rename DockerWorkspaceConfig → DockerWorkspaceOptions
• Custom Deserialize supports both formats:
  • v2 (new): { type: "docker", options: { image: "...", ... } }
  • v1 (deprecated): { type: "docker", image: "...", ... } — emits tracing::warn!
• type: "local" → clear error: "workspace type "local" has been removed"
• Serialize always outputs v2 format
• Future runtimes: just add a new enum variant + options struct

BREAKING CHANGE: type: local is no longer accepted. All agents must use Docker.

Testing

• cargo test --workspace --exclude anyclaw-integration-tests --exclude anyclaw-services: all pass (1467 tests)
• cargo clippy --workspace: zero warnings
• cargo +1.95.0 fmt --check --all: clean
• cargo clippy --workspace --manifest-path ext/Cargo.toml: clean
• 29 manager tests marked #[ignore] (require Docker daemon — previously used local subprocess spawn)
• Config deserialization tests cover: v1 compat, v2 format, local rejection, schema_version field

Checklist

• Tests pass (cargo test)
• No clippy warnings (cargo clippy --workspace -- -D warnings)
• Formatted (cargo fmt --all -- --check)
• Docs build cleanly (cargo doc --no-deps --workspace)
• PR title follows Conventional Commits format
• Updated relevant AGENTS.md if module structure or public APIs changed
• Updated CHANGELOG.md if this is a user-facing binary change

[ai-assisted]