chore: replace fake protocol story with real harness

.scratch/distributed-gguf-runtime/issues/024-implement-real-generated-grpc-protocol-harness.md

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+<!-- GENERATED FROM prd.json — DO NOT EDIT AS AN INDEPENDENT SOURCE. prd.json IS AUTHORITATIVE. -->
+# DGR-024: Implement real generated-gRPC protocol harness
+
+- **Status / triage:** specification only; `ready-for-agent`; `passes: false`
+- **Execution mode:** `AFK`
+- **Milestone:** `M1`
+- **Dependencies:** `DGR-022`, `DGR-023`
+- **Blocks (derived):** `DGR-033`, `DGR-042`
+- **Labels:** `area:protocol`, `area:testing`, `type:vertical-slice`, `priority:p0`, `ready-for-agent`
+- **Evidence class:** `model-free`
+- **Hardware:** `none`
+- **Model:** `none`
+- **Upstream:** `no`
+
+## Objective / description
+
+Build a real generated-gRPC protocol harness around the versioned shard_runtime.proto contract. Use generated Python and C++ stubs over an actual localhost transport and real process lifecycle; exercise captured deterministic protocol vectors and serialized protobuf bytes before a real model worker exists. Do not implement an in-memory fake transport, synthetic model outputs, or a production-looking stub/demo service.
+
+## Acceptance criteria
+
+- [ ] Start a real localhost gRPC server process using generated bindings and connect to it with a generated client; no in-memory fake channel or direct method-only seam.
+- [ ] Exercise prefill fragments, decode frames, release, cancel, flow-control, deadlines, malformed input, checksum failure, duplicates, and stale epochs using serialized protocol messages and captured deterministic vectors.
+- [ ] Prove direct and opaque-relay paths preserve identical protobuf bytes by recording and comparing actual wire frames at both boundaries.
+- [ ] Use real process/socket lifecycle and fail closed on transport, schema, epoch, size, cache, and deadline violations; do not claim model or accelerator behavior that is not exercised.
+- [ ] Applicable shared quality gates pass, and evidence records exact commands, raw outputs, generated artifact identities, wire-frame hashes, changed files, limitations, and dependency handoff.
+
+## Shared quality gates
+
+- Targeted deterministic tests pass; Python changes also pass `python -m compileall packages tests`.
+- `git diff --check` passes.
+- Default tests are model-download-free, API-credit-free, and GPU-free.
+- Evidence README records exact changed files, commands/results, limitations, and dependency handoff; no fabricated evidence or inherited completion credit.
+- Native changes pass focused out-of-tree CMake build and CTest; patch changes verify clean apply/check/reverse against the exact llama.cpp pin.
+- Runs are opt-in and record exact artifact/split hashes, runtime/upstream pin, backend/driver, hardware, network, commands, and raw metrics. Model artifacts use configured mounted-drive storage and never `/home`.
+- Preserve existing Transformers behavior and backend-agnostic Tracker routing/load balancing/billing/relay semantics unless an explicit versioned contract says otherwise. One scoped story commit is expected during execution, but this specification-materialization change is not committed.
+
+## Evidence handoff
+
+Write and verify `.scratch/distributed-gguf-runtime/evidence/DGR-024/README.md`. Until every criterion and applicable gate has real evidence, this story remains `passes: false`. Legacy evidence is provenance only, not completion credit.