neuron-tai/.scratch/distributed-gguf-runtime/issues/13-harden-failure-cancellation-and-restart-semantics.md

13 — Harden failure, cancellation, and restart semantics

Status: ready-for-agent

Mandatory fresh-session context

• Read RALPH-CONTEXT.md completely before changing code.
• This issue is DGR-013 in prd.json.
• Read the evidence README for every dependency listed below.
• Inspect current code and git status; historical text and previous agent claims are not evidence.

Description

As a client, I need failures to be bounded and explicit so that distributed speed does not come with hanging or corrupted generations.

Expected durable outputs

• Failure/cancel/restart test matrix
• Resource cleanup and billing-state evidence
• evidence/DGR-013/README.md

Acceptance criteria

• Deadlines and heartbeat/health loss terminate blocked stream operations.
• Cancellation propagates across every Shard and releases local KV and queued buffers.
• Duplicate steps are idempotent; uncertain mutations are never replayed silently.
• Alpha failover restarts from token zero on a newly compatible route rather than importing unverified KV.
• Worker death, stream reset, malformed bundle, stale epoch, and cache miss tests pass.
• Billing/work records distinguish completed, cancelled, failed, and unverified work.
• Targeted pytest tests pass
• python -m compileall packages tests passes for Python changes
• git diff --check passes
• Default tests remain deterministic, model-download-free, API-credit-free, and GPU-free
• Full deterministic pytest -q passes, or the exact pre-existing unrelated failure is recorded with a clean-tree reproduction
• Pinned native C++ target builds and focused CTest/protocol tests pass where native code is touched
• llama.cpp patch stack applies cleanly to the exact pinned commit where patch code is touched
• Read .scratch/distributed-gguf-runtime/RALPH-CONTEXT.md and this story issue completely before changing code
• Read and verify every dependency evidence README before relying on dependency behavior
• Preserve all pre-existing working-tree changes and stage only files belonging to this story
• Write .scratch/distributed-gguf-runtime/evidence/DGR-013/README.md with files changed, exact commands and real results, limitations, compatibility notes, and dependent-story handoff
• Update only this story issue to Status: done after every acceptance criterion and quality gate passes

Dependency handoff

• DGR-008 must have passes: true; read ../evidence/DGR-008/README.md and verify its referenced files/commands.
• DGR-009 must have passes: true; read ../evidence/DGR-009/README.md and verify its referenced files/commands.
• DGR-012 continuous batching is post-alpha; this story must harden single-session failure/cancellation first and later extend the same invariants to batched sessions.

Finish contract

• Create the task evidence directory and durable handoff required above.
• Preserve real failures and blockers; never fabricate benchmark, model, test or hardware output.
• Change this issue to Status: done only after all criteria pass.
• Emit <promise>COMPLETE</promise> only after the evidence handoff exists.

References

• Ralph execution context
• PRD
• Implementation strategy
• Current architecture
• Architecture decision