docs: define implementation-ready distributed GGUF roadmap

.scratch/distributed-gguf-runtime/issues/056-enforce-bounded-admission-queues-and-backpressure.md

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+<!-- GENERATED FROM prd.json — DO NOT EDIT AS AN INDEPENDENT SOURCE. prd.json IS AUTHORITATIVE. -->
+# DGR-056: Enforce bounded admission, queues, and backpressure
+
+- **Status / triage:** specification only; `ready-for-agent`; `passes: false`
+- **Execution mode:** `AFK`
+- **Milestone:** `M4`
+- **Dependencies:** `DGR-055`
+- **Blocks (derived):** `DGR-057`, `DGR-058`, `DGR-060`
+- **Labels:** `area:scheduler`, `area:backpressure`, `type:performance`, `priority:p1`, `ready-for-agent`
+- **Evidence class:** `fixture`
+- **Hardware:** `none`
+- **Model:** `generic`
+- **Upstream:** `no`
+
+## Objective / description
+
+Fresh Ralph session: read `.scratch/distributed-gguf-runtime/RALPH-CONTEXT.md`, source issue `.scratch/distributed-gguf-runtime/issues/056-enforce-bounded-admission-queues-and-backpressure.md`, and evidence READMEs for dependencies (DGR-055) before changing code. Inspect live source/tests rather than trusting legacy pass states. Objective: Prevent weight, KV, state, scratch, and stream buffers from exceeding admitted capacity.
+
+## Acceptance criteria
+
+- [ ] Admission accounts separately for weights, KV/state, scratch, in-flight fragments, and queue slots.
+- [ ] Queue and stream limits produce structured retryable or terminal responses.
+- [ ] Prefill cannot starve decode and one route session cannot monopolize queue capacity.
+- [ ] Telemetry reports active sessions, queue depth/time, batch occupancy, memory pressure, and rejects.
+- [ ] Applicable shared quality gates in `prd.json` pass, and the evidence handoff records exact commands/results, 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-056/README.md`. Until every criterion and applicable gate has real evidence, this story remains `passes: false`. Legacy evidence is provenance only, not completion credit.