feat: define shard lifecycle status contract

.scratch/distributed-gguf-runtime/evidence/DGR-022/README.md

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+# DGR-022 evidence — Shard lifecycle and structured status RPC contract
+
+**Completed:** 2026-07-17
+**Branch:** `ralph/distributed-gguf-runtime`
+**Authority:** `.scratch/distributed-gguf-runtime/prd.json`
+
+## Outcome
+
+Implemented the versioned, backend-neutral lifecycle/status contract consumed by a future generated gRPC binding. The contract keeps Meshnet routing, identity, authentication policy, billing, and llama.cpp ownership outside the worker contract.
+
+## Implemented
+
+- `packages/node/meshnet_node/shard_lifecycle.py`
+  - capability, health, session, cancellation, release, and metrics RPC names
+  - schema version negotiation and fail-closed unsupported-version handling
+  - structured status/error taxonomy with retryability and details
+  - lifecycle state machine for prefill/decode/cancel/release transitions
+  - monotonic idempotency-step enforcement and duplicate rejection
+  - bounded frame/byte flow control with cancellation-aware waits
+  - explicit cache expectation/result types
+  - deadline policy and TLS/auth transport hooks
+  - deterministic contract serialization round-trip
+- `tests/test_shard_lifecycle.py`
+  - contract round-trip and RPC coverage
+  - unsupported-version rejection
+  - malformed transition and idempotency rejection
+  - cancellation/release behavior
+  - bounded flow-control behavior
+  - TLS hook and incomplete-contract fail-closed behavior
+
+## Verification
+
+```text
+$ PYTHONPATH=packages/node pytest -q tests/test_shard_lifecycle.py tests/test_activation_envelope.py
+17 passed in 0.10s
+```
+
+The existing DGR-021 activation-envelope tests remain green alongside DGR-022.
+
+## Scope limitation
+
+This story defines the lifecycle/status contract only. Generated Python/C++ protobuf bindings and the concrete `shard_runtime.proto` generation pipeline are DGR-023 and remain separate.
+
+## Dependency handoff
+
+DGR-023 may consume the RPC names, status taxonomy, version identity, deadlines, flow-control limits, and TLS/auth hooks when the canonical `.proto` schema and toolchain are provisioned.