Protect decimal quantities from implicit numeric coercion
The warehouse adapter rounds fractional unit quantities after a provider changes strings to numbers.
- Focused work estimate
- 2h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Data contracts · Numeric correctness
Estimated field mix
- Quality engineering60%
- API design40%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional fulfillment API serves a web checkout and warehouse adapter. Provider tests pass while consumers fail on subtle response and error changes.
Setup prerequisites
- Author two small local consumers and one mock provider with versioned synthetic responses.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Specify quantity representation and allowed scale.
- Reject excess precision and non-finite values.
- Verify consumer arithmetic preserves the declared quantity.
Implementation constraints
- Use exact decimal arithmetic or integer units.
Verification to include
- Process a supported fractional quantity.
- Reject scientific-notation and overprecision examples where unsupported.
Deliverables
- Quantity contract regression.
Rollout and recovery
Treat representation changes as reviewed compatibility changes.
Value of the work
For the engineer: Practice executable contracts, meaningful negative tests, and compatibility triage.
For the team: Expose integration regressions before deployment without requiring every system to run together.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.