Run harness adapters (Claude Code, Codex, OpenCode) INSIDE isolated sandboxes via defineSandbox + withSandbox + a provider (localProcessSandbox / dockerSandbox). Covers declarative provisioning: createSecrets + secret/bearer, skills (agentSkill/gitSkill/mcpSkill/ fileSkill), plugins, instructions → canonical AGENTS.md + symlinks projected per harness; shallow-clone default with depth opt-out; serial/parallel setup callback over a persistent shell; snapshot-after-setup default with snapshotMaxAge TTL; defineWorkspace (git/setup/scripts/skills/secrets/ instructions/plugins), defineSandboxPolicy (allow/ask/deny), lifecycle/resume, the SandboxHandle (fs/git/process/ports), capability tokens, defineSandbox hooks (onFile/onFileCreate/onFileChange/onFileDelete/onReady/onError/ onDestroy) + fileEvents flag, chat middleware sandbox group (defineChatMiddleware sandbox hooks), the sandbox debug category, watchWorkspace as a low-level building block, the file.changed / sandbox.file / claude-code.session-id events, and the run journal (spawnNdjson journal option, runId uniqueness, follow vs bounded-poll reading, alignToStoredLog replay alignment, chunkFingerprint, createRunScopedIdGen), and takeover of detached runs (withSandbox runs+durability as one opt-in, detach vs cancel via requestRunCancel / RUN_CANCEL_REASON, sandboxRunDriver on the resume path, single-writer fencing of BOTH the event log and the run record, replay-from-zero with JournalReplayDivergedError, the distributed LockStore requirement). Use whenever a harness adapter needs a sandbox or when building sandbox providers.