Design scenario-based sync verification for reproducible convergence testing

[slashv]

Important

This is a stacked draft based on #1406 (schickling/2026-07-15-intent-design) and should be reviewed and merged after it. PR #1406 establishes context/ as the current intent layer and RFCs as the proposal pipeline. This architecture therefore starts as an RFC; once accepted and implemented, its durable contracts should converge into context/02-system/09-verification/.

Problem

LiveStore has targeted sync simulation hooks and tests, but no unified, serializable, reproducible architecture for exercising concurrent clients, network and backend failures, convergence, and trace inspection.

Writing this design directly into context/ would incorrectly describe an unimplemented proposal as current system intent. We need to develop and review the architecture first while preserving a clear path into the intent hierarchy introduced by #1406.

Solution

Add RFC 0003, Scenario-Based Sync Verification, defining a direction for:

• declarative, reproducible scenario specifications;
• a headless runner built around real sync components;
• dynamic creation of clients and additional sessions within a client;
• workloads, network and backend faults, and controlled time;
• participant execution profiles independent of sync-backend realization;
• structured traces, correctness oracles, artifacts, and a separate visualizer;
• initial verification with the SQLite read model while preserving a path toward read-model-independent sync verification.

The RFC deliberately leaves the concrete scenario file syntax open until the runtime model is validated. It changes no runtime behavior. Once the proposal is accepted and implemented, the resulting system contracts should be distilled into the verification section of context/; implementation detail and operating guidance can remain in contributor documentation.

Validation

• git diff --check upstream/pr-1406...HEAD
• Verified that relative Markdown links in the RFC resolve locally.
• Not run: dt lint:full:fix, dt ts:check, or dt test:run. The repository's devenv remained in Nix environment evaluation after warning that the user was not trusted to configure Cachix, and never reached dt. This is a documentation-only draft with no executable changes.
• No changelog entry: this RFC proposes future architecture and does not change shipped behavior or package APIs.

Demo (optional)

scenario specification
         |
         v
       runner ----> participants + sync backend + injected faults
         |
         v
 structured trace ----> correctness oracles / artifacts / visualizer

Related issues

• Stacked on and dependent upon docs: establish hierarchical intent layer (VRS) under context/ #1406