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# Environment & toolchain — guide (loop tier)

Reference notes, design rationale, and negative results (6).

#### 1. A sandbox usually cannot run a live match - fall back to compile+unit tests and report what was NOT validated
`loop` · **negative result**

A sandboxed session typically cannot run a live local game: the policy's loopback WebSocket (ws to 127.0.0.1:2000) fails with PermissionError 'Operation not permitted', tsx/Node launchers hit `listen EPERM` on the IPC pipe (try TMPDIR=/private/tmp first - sometimes fixes it), and a GUI/TTY cogames play can hit a psutil permission error. When live validation is structurally blocked, run what you CAN - focused unit tests plus a static `nim check`/compile and call-site reasoning - clean up spawned processes, and explicitly report that gameplay was NOT live-validated rather than claiming it was; compile+unit signal is necessary but not sufficient. The harness auto-classifier also blocks out-of-scope commands (an `aws sts get-caller-identity` probe was denied), and routing review to external services fails (`auggie --print` ships private context, so the sandboxed run DNS-fails and the escalated retry is policy-rejected - do a local audit instead). When a check truly cannot run because deps/credentials are unavailable, say so explicitly in the handoff.
  <sub>sources: players_checkouts/players/users/james/personal_cogs/AGENTS.md, claude-code:27659fc3-8e40-469f-beda-31ddd5c6ceca, claude-code:aae25940-ade3-41bc-b817-517dc86ccebf, codex:019e00c0-d889-7d72-9781-3e90e7c1c7b9 (+14)</sub>

#### 2. Player SDK is imported (pin via uv.lock) while the game ref is deliberately pinned to the deployed league version
`loop`

In the player lab the SDK is imported, not vendored: players.player_sdk comes from the public players repo (tracks main) with uv.lock pinning the exact commit for reproducible clones - adopt the latest with `uv lock --upgrade-package players`, not hand-edited SHAs. By contrast the game ref (CREWRIFT_REF) stays deliberately pinned so it matches the deployed league game, not latest. No GitHub creds or sibling checkouts are needed to build/run because the SDK and Crewrift game are public; verify with `uv sync`, `uv run softmax login && uv run softmax status` (expect Authenticated), and `uv run pytest`. Before pulling an upstream repo whose values you pin, diff the incoming commits to confirm they do not touch what you pinned, and only fast-forward a clean tree. Prefer not to bump a pin when avoidable - loosening to `>=` is acceptable. Flag heavy unused deps in docs as aspirational (alpha_cog pinned torch>=2.11.0 but scripted_alpha.py did not use it); a uv project with no [build-system] is a non-packaged 'virtual' project and a `uv init` main.py is leftover scaffolding.
  <sub>sources: player_labs/README.md, auggie:5d1ff8d5-2505-4dca-af45-56d3070363e2, auggie:e251085a-b35d-4171-8dbd-d006b8bc2bd9, claude-code:63658f66-83c7-482e-a805-d58527e10975 (+4)</sub>

#### 3. MettaScope GUI replay is fragile - prefer headless inspection and `-r none`
`loop` · **negative result** · ⚠ _session-derived, unverified_

Treat MettaScope GUI replay as fragile and prefer headless log/metric inspection of saved replays. `cogames replay <path>` failed with a Nim 'cannot open file: opengl' error and stayed broken even after adding every ~/.nimby/pkgs/*/src to the Nim --path; the compiled binary also could not find its bundled data unless run from a directory containing the matching MettaScope data/ bundle (the metta repo root or a temp cwd seeded with that bundle). When `cogames play` crashes on startup with a MettaScope `pixie.nim ... Unsupported image file format` / SIGSEGV, the default `-r auto` renderer is launching the Nim GUI with a broken image asset - pass `-r none` to disable built-in rendering whenever your policy supplies its own display or you only need the game loop.
  <sub>sources: codex:019e19a7-8605-7992-9b28-cb4d2ca9132e, opencode:ses_1fa66f0b7ffeIF47rk2pDlz4RX</sub>

#### 4. Coworld player containers reach the game over the coworld-local bridge alias, not host.docker.internal
`loop` · ⚠ _session-derived, unverified_

In a local coworld run, player containers reach the game over a user-defined Docker bridge network named `coworld-local` at `ws://coworld-game-<runid>:8080/player?...` set via `--network-alias`, NOT via `host.docker.internal`. The `127.0.0.1:<port>:8080` publish only lets the host runner hit `/healthz` and spectator routes; Dockerfile comments recommending `host.docker.internal` are stale and only appear to work because the player reads the env var.
  <sub>sources: claude-code:67ff1fe3-48c0-4738-b7fb-8b994e567434</sub>

#### 5. Distinguish a player bug from a server bug, and verify you are running the artifact you think you are
`loop`

When a match crashes, distinguish a player/policy bug from a game-server bug: a freshly built server binary segfaulting mid-match while the previous binary ran clean with identical player code is a server-side regression - keep a known-good server binary to fall back to and file the crash against the game repo rather than chasing it in the policy. After a rebuild or a human's 'I pulled and rebuilt', verify you are running the artifact you think you are: a rebuild can land the new binary at a path different from the one launch scripts default to, leaving you testing a stale build - check mtime and git describe against the source tree, and point launch scripts at the in-tree build path. For the Among Them Nim project specifically, run sources via `nim r <file>.nim` rather than pre-built executables under ./out/ to always exercise current source.
  <sub>sources: bitworld/among_them/AGENTS.md, opencode:ses_21b273d4fffee0T9oMpvlktzkg</sub>

#### 6. Single-host internal Coworld deployment: EC2 lift-and-shift, root-equivalent socket runner, systemd+backups, constrained DB pool
`loop`

For an internal/trusted single-team deployment, prefer an EC2 lift-and-shift (one x86_64 host running the existing docker-compose stack behind Caddy for HTTPS) over Kubernetes: the Docker-socket episode runner works unchanged on a real Docker daemon, so there is no porting cost. But that runner builds/runs containers via the host Docker socket and is therefore root-equivalent on the box - fine for an internal trusted team but UNSAFE for untrusted multi-tenant policy code, which needs a pod-spawning Kubernetes runner (move to EKS only for autoscaling or untrusted code; each hosted player pod requests 2 CPU / 2Gi, which are scheduling requests not hard limits). Operationally: survive reboots with a systemd unit + Docker live-restore + restart:unless-stopped; back up state nightly (pg_dump of Postgres, tar of the Gitea volume holding canonical policy history) to S3 while artifacts/replays persist to R2/S3; an always-on m7i.2xlarge+gp3 runs ~$250-450/mo on-demand, so stop the instance off-hours (EBS persists) for bursty use. Constrain the DB connection pool for batch/build workloads - local Postgres connection exhaustion hit during build/static rendering, fixed by a lower default max, build-time pool max of 1, and connection+idle timeouts.
  <sub>sources: players_checkouts/players/docs/coworld-player-packaging.md, optimizers/docs/OPTIMIZER-MVP-SESSION-SUMMARY.md, optimizers/docs/deployment.md</sub>
