ADR-005 Unified Time Tolerance

Status: Accepted Date: 2025-09 Tags: time, consistency, cross-backend

Problem

The original timeMode design created inconsistent semantics: timeMode: "strict" meant 0ms tolerance on Redis (server-time) but 1000ms on Firestore (client-time minimum safe). This violated predictable cross-backend behavior and created operational risks when switching backends.

Decision

Remove timeMode configuration entirely and use unified 1000ms tolerance across all backends:

• Single TIME_TOLERANCE_MS constant in interface.md
• Same configuration produces identical liveness semantics
• Backend switching preserves lock behavior
• No conditional tolerance mapping needed

Alternatives (brief)

• Keep timeMode with per-backend semantics — confusing, unpredictable behavior
• Zero tolerance for all backends — unrealistic for client-time systems

Impact

• Positive: Predictable behavior, testing simplicity, operational safety during backend migration
• Negative/Risks: Removes fine-grained control (deemed unnecessary complexity)

Links

• Code/Docs: docs/specs/interface.md (TIME_TOLERANCE_MS), common/time-predicates.ts
• Related ADRs: None