miroir/notes/miroir-cdo-final-verification.md

Phase 1 — Core Routing Final Verification (2026-05-09)

Bead ID: miroir-cdo Date: 2026-05-09

Summary

Phase 1 Core Routing implementation verified as complete. All 151 tests pass with 91.80% line coverage, exceeding the 90% requirement.

Verification Results

Test Execution

running 151 tests
test result: ok. 151 passed; 0 failed; 0 ignored; finished in 70.70s

Coverage (cargo-llvm-cov)

Filename                      Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
router.rs                      1016                26    97.44%          60                 1    98.33%         500                19    96.20%
topology.rs                     776                 0   100.00%          70                 0   100.00%         421                 0   100.00%
scatter.rs                      214                 0   100.00%          11                 0   100.00%         121                 0   100.00%
merger.rs                       977                31    96.83%          49                 4    91.84%         582                31    94.67%
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                           5672               423    92.54%         396                33    91.67%        3770               309    91.80%

Definition of Done Compliance

Requirement	Status	Test
Rendezvous assignment is deterministic	✅	test_rendezvous_determinism, acceptance_determinism_1000_runs
Adding 4th node moves ≤ 2×(1/4) of shards	✅	test_minimal_reshuffling_on_add, acceptance_reshuffle_bound_on_add
64 shards / 3 nodes / RF=1 → 18-26 shards each	✅	test_shard_distribution_64_3_rf1, acceptance_uniformity_64_shards_3_nodes_rf1
Top-RF placement changes minimally	✅	test_top_rf_stability, acceptance_rf2_placement_stability
write_targets returns RG × RF nodes	✅	test_write_targets_count
query_group distributes evenly	✅	test_query_group_distribution
covering_set returns one node per shard	✅	test_covering_set_one_per_shard, test_covering_set_replica_rotation
Merger passes merge/facet/limit tests	✅	19 comprehensive merger tests
miroir-core ≥ 90% line coverage	✅	91.80%

Implementation Summary

router.rs

• score(shard_id, node_id): Rendezvous hashing with XxHash64::with_seed(0)
• assign_shard_in_group(): Deterministic shard assignment within a group
• write_targets(): Returns RG × RF nodes for writes
• query_group(): Round-robin group selection for queries
• covering_set(): One node per shard within chosen group
• shard_for_key(): Key-to-shard mapping

topology.rs

• Topology: Cluster topology with nodes grouped by replica_group
• NodeStatus: Health state machine (Healthy/Active/Degraded/Joining/Draining/Failed/Removed)
• Group: Replica group with node list
• NodeId: Unique node identifier

scatter.rs

• Scatter trait: Fan-out orchestration interface
• StubScatter: Stub implementation (wired in Phase 2)

merger.rs

• merge(): Global sort by _rankingScore, offset/limit, facet aggregation
• _rankingScore stripping when not requested
• _miroir_* fields always stripped
• Binary heap optimization for large fan-out
• BTreeMap for stable facet serialization

Retrospective

What worked

• All core routing primitives implemented correctly
• Comprehensive test coverage with deterministic tests
• Rendezvous hashing provides minimal reshuffling on topology changes
• Group-scoped assignment ensures replica isolation
• Pure-function design enables thorough unit testing

What didn't

• No issues encountered during verification

Surprise

• Coverage exceeded 90% requirement without additional work

Reusable pattern

• Rendezvous hashing with XxHash64::with_seed(0) for deterministic assignment
• Group-scoped assignment for replica isolation
• Pure-function design for testability
• Node health state machine for cluster management