Plan: Property-based tests for cache key canonicalization invariants (5.1.4a)

[leynos]

Summary

Draft ExecPlan for roadmap item 5.1.4a: property-based tests (proptest) for route cache key canonicalization invariants, discharging the TODO left in backend/src/domain/ports/cache_key.rs after 5.1.4 shipped.

Plan document: docs/execplans/backend-5-1-4a-cache-key-canonicalization-property-tests.md

The plan covers:

• Eight properties: theme permutation invariance, coordinate grid-cell equivalence and divergence, normalization idempotence, key-format totality, order materiality for non-canonicalized arrays (two variants), and single-leaf divergence.
• Two example tests: a -0.0 collapse case and a known-answer SHA-256 digest test (the only test that fails if the hash algorithm or pre-hash serialization is swapped).
• Non-vacuity via a scoped cargo mutants --file gate (the repo already runs nightly mutation testing) plus two manual seeded faults cargo-mutants cannot generate.
• Documented exclusions with evidence: object key-order invariance is vacuous in this build (serde_json without preserve_order is BTreeMap-backed), and coordinate generation is bounded to +/-1e6 to stay out of the genuinely non-idempotent extreme-float region.
• A mechanical test-module split (cache_key/tests.rs + tests/properties.rs) following the apalis_route_queue precedent to respect the 400-line file limit.

The draft was reviewed pre-delivery by a six-lens design panel (structure, alternatives, cost, contracts, failure modes, maintainability); all panel conditions are folded in, including two findings that materially changed the design (the unpinned SHA-256 clause and the unbounded idempotence domain).

Per the ExecPlan discipline, implementation starts only after this plan is approved.

References

• Lody session: https://lody.ai/leynos/sessions/e1abce79-3a81-406b-8473-7b288e22b103

🤖 Generated with Claude Code

Summary by Sourcery

Documentation:

• Introduce a detailed ExecPlan documenting the approach, constraints, verification strategy, and milestones for adding property-based tests to route cache key canonicalization invariants in the backend.

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Reviewer's Guide

ExecPlan document for roadmap item 5.1.4a, detailing how to add property-based tests (proptest) for route cache key canonicalization invariants in the backend, including test module splitting, specific properties to implement, verification/non-vacuity strategy, mutation testing gates, and related documentation updates.

File-Level Changes

Change	Details	Files
Introduce an ExecPlan document that specifies how to implement property-based tests for route cache key canonicalization invariants, including module split, test strategies, verification steps, and documentation updates.	Add a detailed planning document under docs/execplans describing the purpose, context, constraints, and risks of adding property-based tests for cache key canonicalization. Define eight specific invariants to be tested using proptest (theme permutation invariance, coordinate grid-cell equivalence/divergence, normalization idempotence, key-format totality, non-canonicalized array order materiality, single-leaf divergence, negative-zero collapse, and known-answer digest). Specify a mechanical split of the existing inline test module in cache_key.rs into cache_key/tests.rs and tests/properties.rs, following existing precedents and line-count constraints. Lay out a verification plan using property tests, example tests, a statistics guard, scoped cargo-mutants runs, and manual negative controls to ensure non-vacuity of the properties. Describe required updates to roadmap, architecture docs, and developers guide to reflect the new property-testing approach and roadmap item 5.1.4a. Define stages, milestones, and concrete shell commands for implementing, validating, and accepting the changes without modifying production behaviour.	docs/execplans/backend-5-1-4a-cache-key-canonicalization-property-tests.md

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