- [x] Add `packages/server/src/simulation/` as the home for all simulation layer replacements, exported from `index.ts` as `simulationReplacements`.
- [x] Wire simulation replacements through the server's `makeRoutes` via `Layer.unwrap` + dynamic `import("./simulation")` gated on `OPENCODE_SIMULATION`, so the simulation module is never loaded eagerly and `makeRoutes` stays synchronous.
- [x] Implement in-memory `FileSystem.FileSystem` (`simulation/filesystem.ts`) replacing the `NodeFileSystem` platform node. Backed by a flat path map; implements the operations the app uses (stat, access, chmod, realPath, read/write file, make/read directory, remove, rename, copy, copyFile, temp dirs, read-only open handles); unused operations die with a clear defect; `watch` fails as unsupported.
- [x] Root the fake filesystem at `OPENCODE_SIMULATION_ROOT` (falling back to `process.cwd()` at layer-build time). The anchor is a real, empty host directory the runner creates and cds into.
- [x] Deny host filesystem escapes loudly: content/mutation operations outside the root fail with `PermissionDenied` simulation errors. Probe operations (`stat`/`access`/`exists`) report `NotFound` outside the root so walk-up loops (project discovery, `findUp`, `globUp`) terminate naturally.
- [x] Add `SimulationFSUtil` replacement (`simulation/fs-util.ts`): wraps the real `FSUtil` layer and reroutes `readDirectoryEntries`, `glob`, and `globUp` — which bypass the injected `FileSystem` via node `fs/promises` and the `glob` package — through the simulated filesystem.
- [x] Fix `LayerNode.hoist` conflict detection to compare node implementations instead of object identity; replacement rewriting produces dependency-rewritten copies of the same node, which previously false-positived as "conflicting implementations".
- [x] Add snapshot seeding from `OPENCODE_SIMULATION_STATE`: `project/` contents of the snapshot directory are read from the host once at layer-build time and seeded into the in-memory tree joined onto the anchor root.
- [x] Verify end to end: `opencode serve` boots with `OPENCODE_SIMULATION=1` + `OPENCODE_SIMULATION_ROOT` + path/DB env seams (`OPENCODE_CONFIG_DIR`, `OPENCODE_TEST_HOME`, `OPENCODE_DB=:memory:`); `fs.list`/`fs.read` observe only seeded in-memory files; the anchor directory on the host remains empty after the run.
- [ ] Create the anchor directory + `chdir` + env seam setup automatically in CLI startup when simulation mode is enabled (currently set manually by the runner).
- [ ] Assert the anchor directory is still empty at the end of the run.
- [ ] Add simulated network registry and deny unknown external network by default (design: `simulated-network-llm.md`).
- [ ] Add driver-scripted LLM as an OpenAI route in the simulated network; the driver answers `llm.request` notifications over the control WebSocket and streams chunks back — no enqueue store (design: `simulated-network-llm.md`).
- [ ] Add simulated process registry (shell via `just-bash`, minimal fake `git`, deny unsupported spawns).
- [ ] Add simulation-gated backend control routes proxied through the frontend WebSocket.
- [ ] Trace filesystem, network, LLM, process, and backend control activity.
- Wire simulation replacements through `AppNodeBuilder.build(...)` and `AppNodeBuilderV1.build(...)`.
- Create a real, empty anchor directory (`mkdtemp`) and `process.chdir` into it before any command resolves its working directory; skip creation when the runner already spawned the app inside an anchor.
- Root the in-memory filesystem at `process.cwd()` (the anchor). No cwd monkey-patching: cwd, `$PWD`, and `path.resolve()` stay truthful.
- Add snapshot loading from `OPENCODE_SIMULATION_STATE`: read the snapshot directory once at startup and seed the in-memory filesystem (snapshot `project/` paths joined onto the anchor root), config, env, and optional LLM/network state from it.
- Route config/data/state/cache/temp paths into the simulated space using existing env seams (`OPENCODE_CONFIG_DIR`, `OPENCODE_TEST_HOME`, `OPENCODE_DB=:memory:`), set before `packages/core/src/global.ts` import-time path setup runs.
- Deny host filesystem escapes loudly (paths outside the anchor root fail with typed simulation errors).
- Assert the anchor directory on the host is still empty at the end of the run; anything written there means a code path bypassed the simulated filesystem.
- Add simulated network registry and deny unknown external network by default.
- Add scriptable LLM boundary.
- Add simulated process registry:
- shell through `just-bash` against the simulated filesystem.
- minimal fake `git` support for discovery/status paths.
- deny unsupported process spawns.
- Add simulation-gated backend control routes, proxied only through the frontend WebSocket.
- Expose backend methods through the frontend server: filesystem seed/write, network register, LLM enqueue, backend snapshot.
- Trace filesystem, network, LLM, process, and backend control activity.
Done when:
- Unknown network fails with a simulation error.
- Host filesystem escape fails with a simulation error.
- The anchor directory on the host is empty after a run.
- The app boots from a snapshot directory via `OPENCODE_SIMULATION_STATE` and observes the seeded project files, config, and env through normal app paths.
- A driver can seed a project filesystem.
- A driver can enqueue an LLM script and submit a prompt through the TUI.
- The real session/tool path consumes the scripted LLM behavior.
- Shell commands use `just-bash`; unsupported process spawns fail.
- Trace contains backend activity and snapshots.
Out of scope:
- Model-based generation.
- Generated plugin config state.
- Shrinking.
## Phase 3: Generated Config And Model-Based Runner
Goal: explore different app states using generated commands and plugin-provided config state.
Scope:
- Add generated simulation plugins as the primary config-state generation mechanism.
- Support generated plugin domains for:
- agents and defaults.
- provider/model availability.
- tool definitions and scripted tool behavior.
- MCP-like capabilities or endpoints.
- permission policies.
- instructions/system-context-like inputs where supported.
- workspace/project adapters where supported.
- Add runner commands to generate, enable, disable, and inspect generated plugin state.
- Build a custom external model-based runner, not `fast-check` yet.
- Runner command shape: precondition, execute, model update, postcondition.
