Add disagg_smoke: minimal-Qwen Modal test for pool claim/reset + cookbook consolidation

cookbook/disagg_smoke/README.md

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+# disagg_smoke
+
+A small Modal app that validates the pool-control work end to end on a minimal
+Qwen model (`Qwen/Qwen2.5-0.5B-Instruct`) — no Kimi/large config, no Megatron
+trainer. It exercises both:
+
+1. **PR #5** — explicit pool claim/reset, fresh-run-id ownership, monotonic
+   pointer, 1:1 trainer-call ↔ pool epoch.
+2. **PR #6** — the cookbook consolidation (shared `cookbook.sidecar` /
+   `serving` / `trainer_helpers` / `rollout_control` spine + thin per-trainer
+   adapters, and the whole-cookbook image mount).
+
+Instead of running a real trainer, it synthesizes **real** slime disk-delta
+versions (xor + zstd + xxh3-128) from the base checkpoint (`delta.py`) and
+publishes them through the real bulletin board, so the actual host-side delta
+apply + reconcile path runs.
+
+## Entrypoints
+
+Invoke by **module path** (`-m`), not file path — like the other cookbook apps
+(`modal deploy -m cookbook.slime_disagg.modal_train`). A bare file path names the
+entrypoint module `app`, which the container can't import (`ModuleNotFoundError:
+No module named 'app'`); `-m` resolves it to `cookbook.disagg_smoke.app`, which is
+importable from the mounted cookbook package.
+
+```bash
+# GPU-free control-plane test (primary). Asserts everything itself; raises on failure.
+modal run -m cookbook.disagg_smoke.app::control_plane_test
+
+# 1x GPU live confirmation: real SGLang reload + version-pinned completion.
+modal run -m cookbook.disagg_smoke.app::serving_smoke
+```
+
+### `control_plane_test` (no GPU)
+
+Against a fake SGLang upstream, on the consolidated image:
+
+- `claim` writes the empty pointer `<run_id>/weight_v000000` and resets the pool
+  to base; startup converges there.
+- Publishing a 2-version delta chain and reconciling patches the **local
+  checkpoint** to the exact trainer-intended bytes (slime's real `apply_deltas`),
+  and reloads the engine.
+- A same-run rewind and a reused `run_id` both raise `PointerRewind`
+  (fresh-run-id enforcement).
+- A fresh run re-claims, resets the engine to base, and replays its own chain.
+- Every consolidated module + thin adapter imports off the whole-cookbook mount
+  (the PR #6 regression we fixed: with `include_source=False` a subdir-only mount
+  would `ImportError` here).
+
+### `serving_smoke` (1 GPU)
+
+Runs the **real** consolidated sidecar (`python3 -m cookbook.slime_disagg.sidecar`)
+in front of a real SGLang server on tiny Qwen, publishes one delta, triggers a
+reconcile, and asserts the engine reloaded to v1 (real `update_weights_from_disk`)
+and serves a completion pinned to `min_required_version: 1`.
+
+It uses a vanilla single-GPU SGLang image (not the cookbook's Blackwell fa4 fork
+build, which targets B200s) so it runs on a common 1×GPU; the whole-cookbook
+mount + `--no-deps` decoder layers are identical, so the consolidation/reload
+path is validated the same way.
+
+## Config
+
+Override via env vars when launching:
+
+- `SLIME_SMOKE_REPO` / `SLIME_SMOKE_REF` — the slime checkout for the host-side
+  decoder. `disk_delta` is a **fork feature** (not on upstream `main`), so
+  `SLIME_SMOKE_REF` defaults to the same fork SHA the `slime_disagg` trainer
+  image pins. Override both only to track the trainer if it rolls slime forward
+  (keep encoder == decoder).
+
+## Tests
+
+`delta_test.py` covers the encoder structurally (skips if numpy/zstandard/xxhash
+are absent). The full byte-for-byte round-trip against slime's real decoder is
+asserted by `control_plane_test` on Modal.