chore(pusht): add 5090 repro docs and uv setup

AGENTS.md

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+# Agent Notes
+
+## Purpose
+`~/diffusion_policy` is the Diffusion Policy training repo. The main workflow here is Hydra-driven training via `train.py`, with the canonical PushT image experiment configured by `image_pusht_diffusion_policy_cnn.yaml`.
+
+## Top Level
+- `diffusion_policy/`: core code, configs, datasets, env runners, workspaces.
+- `data/`: local datasets, outputs, checkpoints, run logs.
+- `train.py`: main training entrypoint.
+- `eval.py`: checkpoint evaluation entrypoint.
+- `image_pusht_diffusion_policy_cnn.yaml`: canonical single-seed PushT image config from the README path.
+- `.venv/`: local `uv`-managed virtualenv.
+- `.uv-cache/`, `.uv-python/`: local `uv` cache and Python install state.
+- `README.md`: upstream instructions and canonical commands.
+
+## Canonical PushT Image Path
+- Entrypoint: `python train.py --config-dir=. --config-name=image_pusht_diffusion_policy_cnn.yaml`
+- Dataset path in config: `data/pusht/pusht_cchi_v7_replay.zarr`
+- README canonical device override: `training.device=cuda:0`
+
+## Data
+- PushT archive currently present at `data/pusht.zip`
+- Unpacked dataset used by training: `data/pusht/pusht_cchi_v7_replay.zarr`
+
+## Local Compatibility Adjustments
+- `diffusion_policy/env_runner/pusht_image_runner.py` now uses `SyncVectorEnv` instead of `AsyncVectorEnv`.
+  Reason: avoid shared-memory and semaphore failures on this host/session.
+- `diffusion_policy/gym_util/sync_vector_env.py` has local compatibility changes:
+  - added `reset_async`
+  - seeded `reset_wait`
+  - updated `concatenate(...)` call order for the current `gym` API
+
+## Environment Expectations
+- Use the local `uv` env at `.venv`
+- Verified local Python: `3.9.25`
+- Verified local Torch stack: `torch 2.8.0+cu128`, `torchvision 0.23.0+cu128`
+- Other key installed versions verified in `.venv`:
+  - `gym 0.23.1`
+  - `hydra-core 1.2.0`
+  - `diffusers 0.11.1`
+  - `huggingface_hub 0.10.1`
+  - `wandb 0.13.3`
+  - `zarr 2.12.0`
+  - `numcodecs 0.10.2`
+  - `av 14.0.1`
+- Important note: this shell currently reports `torch.cuda.is_available() == False`, so always verify CUDA access in the current session before assuming GPU is usable.
+
+## Logging And Outputs
+- Hydra run outputs: `data/outputs/...`
+- Per-run files to check first:
+  - `.hydra/overrides.yaml`
+  - `logs.json.txt`
+  - `train.log`
+  - `checkpoints/latest.ckpt`
+- Extra launcher logs may live under `data/run_logs/`
+
+## Practical Guidance
+- Inspect with `rg`, `sed`, and existing Hydra output folders before changing code.
+- Prefer config overrides before code edits.
+- On this host, start from these safety overrides unless revalidated:
+  - `logging.mode=offline`
+  - `dataloader.num_workers=0`
+  - `val_dataloader.num_workers=0`
+  - `task.env_runner.n_envs=1`
+  - `task.env_runner.n_test_vis=0`
+  - `task.env_runner.n_train_vis=0`
+- If a run fails, inspect `.hydra/overrides.yaml`, then `logs.json.txt`, then `train.log`.
+- Avoid driver or system changes unless the repo-local path is clearly blocked.