test(feature-model): fuzz the constraint solver (REQ-266)

[avrabe]

REQ-266 — fuzz the constraint solver (v0.29.0)

The proptest strategies hard-coded constraints: vec![], so the solver's
highest-risk code — cross-tree constraint evaluation, implies
propagation, excludes, and REQ-257's fail-loud gate — had zero
property-test coverage. This adds it.

What's covered

• Constraint-generating strategy — implies/excludes/and/or/not
  over real feature-name leaves, kept as a typed TestConstraint so the
  property can evaluate each constraint independently of the solver (an
  oracle, so the solver doesn't grade its own homework).
• prop_ok_means_constraints_actually_hold — the anti-silent-pass
  property: if solve() returns Ok, every constraint genuinely holds
  under the resolved selection. A regression to the pre-REQ-257 _ => true
  blind spot would surface here as an Ok whose selection violates a
  constraint.
• prop_implies_propagation, prop_solver_never_panics_with_constraints.
• Deterministic fail-loud tests: unevaluatable attribute comparison →
  UnevaluatableConstraint (REQ-257); constraint naming a nonexistent
  feature → UnknownConstraintFeature (REQ-259).

Bug surfaced → REQ-269

The shared-child coverage revealed a real latent bug: a feature reachable
through two parents (a diamond / DAG) is mis-reported as a cycle by
validate_tree's BFS (global-visited-as-cycle). Confirmed failing with
cycle detected involving feature shared``. Filed as REQ-269 (v0.29.0)
with a regression test diamond_shared_child_is_not_a_cycle (`#[ignore]`d
until the fix lands, then flip to enforced).

Verification

cargo test -p rivet-core --test proptest_feature_model → 12 passed, 1
ignored. clippy --all-targets (1.97.0) clean. Test-only + artifact
change — the composition core and wasm seam are untouched.

Implements: REQ-266 · Verifies: REQ-257, REQ-259 · Refs: REQ-269, DD-076

🤖 Generated with Claude Code

[github-actions]

📐 Rivet artifact delta

Change	Count
Added	1
Removed	0
Modified	1
Downstream impacted (depth ≤ 5)	0

Graph

graph LR
  REQ_266["REQ-266"]:::modified
  REQ_269["REQ-269"]:::added
  classDef added fill:#d4edda,stroke:#28a745,color:#155724
  classDef removed fill:#f8d7da,stroke:#dc3545,color:#721c24
  classDef modified fill:#fff3cd,stroke:#ffc107,color:#856404
  classDef overflow fill:#e2e3e5,stroke:#6c757d,color:#495057,stroke-dasharray: 3 3

Loading

Added

• REQ-269

Modified

ID	Changes
REQ-266

📎 Full HTML dashboard attached as workflow artifact rivet-delta-pr-715 — download from the workflow run.

_{Posted by rivet-delta workflow. The graph shows only changed artifacts; open the HTML dashboard (above) for full context.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Rivet Criterion Benchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 6480063	Previous: 8abbb62	Ratio
store_insert/100	86586 ns/iter (± 913)	69126 ns/iter (± 437)	1.25
store_insert/1000	928388 ns/iter (± 9279)	740783 ns/iter (± 5800)	1.25
store_lookup/100	1947 ns/iter (± 8)	1522 ns/iter (± 25)	1.28
store_lookup/1000	25050 ns/iter (± 173)	18584 ns/iter (± 46)	1.35
store_lookup/10000	361448 ns/iter (± 9453)	265291 ns/iter (± 954)	1.36
store_by_type/100	96 ns/iter (± 0)	74 ns/iter (± 0)	1.30
store_by_type/1000	95 ns/iter (± 0)	74 ns/iter (± 0)	1.28
store_by_type/10000	95 ns/iter (± 0)	74 ns/iter (± 0)	1.28
schema_load_and_merge	1525307 ns/iter (± 29137)	1181005 ns/iter (± 22486)	1.29
link_graph_build/100	166807 ns/iter (± 1805)	126830 ns/iter (± 655)	1.32
link_graph_build/1000	1985681 ns/iter (± 5978)	1495979 ns/iter (± 9916)	1.33
validate/100	456973 ns/iter (± 6255)	341875 ns/iter (± 3801)	1.34
validate/1000	15016997 ns/iter (± 104351)	11276807 ns/iter (± 269977)	1.33
validate/10000	1101243769 ns/iter (± 20667852)	762756012 ns/iter (± 8858190)	1.44
traceability_matrix/100	4274 ns/iter (± 331)	3215 ns/iter (± 15)	1.33
traceability_matrix/1000	45133 ns/iter (± 271)	34302 ns/iter (± 168)	1.32
traceability_matrix/10000	734981 ns/iter (± 9516)	555669 ns/iter (± 4285)	1.32
diff/100	64047 ns/iter (± 197)	46183 ns/iter (± 131)	1.39
diff/1000	722526 ns/iter (± 13596)	521705 ns/iter (± 2750)	1.38
diff/10000	8238501 ns/iter (± 141364)	6163298 ns/iter (± 202417)	1.34
query/100	1120 ns/iter (± 2)	904 ns/iter (± 2)	1.24
query/1000	15042 ns/iter (± 35)	11284 ns/iter (± 99)	1.33
query/10000	225366 ns/iter (± 3195)	172570 ns/iter (± 970)	1.31
document_parse/10	21752 ns/iter (± 97)	17012 ns/iter (± 124)	1.28
document_parse/100	153972 ns/iter (± 1044)	117738 ns/iter (± 295)	1.31
document_parse/1000	1393310 ns/iter (± 22561)	1102249 ns/iter (± 26378)	1.26

This comment was automatically generated by workflow using github-action-benchmark.