feat: add DGR-001 performance contract

.scratch/distributed-gguf-runtime/evidence/DGR-001/README.md

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+# DGR-001 — performance contract baseline
+
+## Files changed
+
+- `packages/node/meshnet_node/performance_contract.py`
+- `tests/test_performance_contract.py`
+- `.scratch/distributed-gguf-runtime/issues/01-lock-the-safetensors-versus-gguf-performance-contract.md`
+- `.scratch/distributed-gguf-runtime/evidence/DGR-001/performance-contract.json`
+
+## What this slice does
+
+- Locks the DGR-001 benchmark contract in code.
+- Pins the architecture-aligned baseline to **DeepSeek-V2-Lite-Chat** (`deepseek2`).
+- Uses the smallest DeepSeek-family GGUF target selected for this story: **Q2_K** via `second-state/DeepSeek-V2-Lite-Chat-GGUF`.
+- Exposes a machine-readable JSON contract with:
+  - benchmark lanes for `transformers` safetensors and `llama.cpp` GGUF
+  - concurrency levels `1` and `4`
+  - the required metrics list
+  - an explicit stop condition for “no meaningful speed or fit benefit”
+
+## Exact commands and real results
+
+### Targeted tests
+
+```bash
+pytest -q tests/test_performance_contract.py tests/test_route_session_benchmark.py
+```
+
+Result: `9 passed in 0.14s`
+
+### Contract artifact generation
+
+```bash
+PYTHONPATH=packages/node python -m meshnet_node.performance_contract --json-out .scratch/distributed-gguf-runtime/evidence/DGR-001/performance-contract.json
+```
+
+Result: wrote `.scratch/distributed-gguf-runtime/evidence/DGR-001/performance-contract.json`
+
+### Python compile check
+
+```bash
+python -m compileall packages/node/meshnet_node/performance_contract.py tests/test_performance_contract.py
+```
+
+Result: passed
+
+## Limitations
+
+- This slice captures the DGR-001 contract and baseline selection only.
+- It does **not** download or run a real model yet.
+- Real safetensors vs GGUF execution, TTFT/prefill/decode measurements, RSS/VRAM capture, and output-drift comparison are still to be implemented against the contract.
+
+## Compatibility notes
+
+- The contract stays on the DeepSeek2 family to remain close to the DeepSeek-V4-Flash end goal.
+- A smaller non-DeepSeek model can still be used later for loader-plumbing smoke tests, but it does not replace this baseline.
+- Model artifacts must stay on the mounted drive and not under `/home`.
+
+## Dependent-story handoff
+
+Next implementation work should attach to this contract and add the live benchmark runner that actually compares:
+
+1. current Transformers/safetensors recipe
+2. whole-model llama.cpp GGUF recipe
+
+using the same model architecture/revision and the same prompt/context/concurrency settings.