Phase 1 (miroir-cdo): Final verification session — all requirements met

Verification Summary:
- All 169 tests pass (71.06s)
- Phase 1 components exceed 90% coverage:
  - router.rs: 96.20% lines
  - topology.rs: 100% lines
  - scatter.rs: 100% lines
  - merger.rs: 94.67% lines

DoD Requirements (All Met):
✓ Rendezvous determinism verified
✓ Minimal reshuffling on add/remove verified
✓ Uniform distribution (15-27 shards/node) verified
✓ Top-RF placement stability verified
✓ write_targets returns RG × RF nodes
✓ query_group distributes evenly
✓ covering_set returns one node per shard
✓ merger passes all merge/facet/limit tests

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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.beads/traces/miroir-cdo/metadata.json

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notes/miroir-cdo-session-2026-05-09-final.md

@@ -0,0 +1,77 @@
+# Phase 1 (miroir-cdo) — Final Verification Session
+
+## Date: 2026-05-09
+
+## Session Summary
+
+This session verified that Phase 1 (Core Routing) implementation is complete and all Definition of Done requirements are met.
+
+## Verification Results
+
+### Test Execution
+- **Command**: `cargo test --package miroir-core --lib`
+- **Result**: 169 passed; 0 failed; 0 ignored
+- **Duration**: 71.06s
+
+### Code Coverage (Phase 1 Components)
+- **router.rs**: 96.20% lines (96.83% regions, 98.33% functions)
+- **topology.rs**: 100% lines (100% regions, 100% functions)
+- **scatter.rs**: 100% lines (100% regions, 100% functions)
+- **merger.rs**: 94.67% lines (96.83% regions, 91.84% functions)
+
+All Phase 1 components exceed the 90% line coverage requirement.
+
+## Definition of Done Verification
+
+✅ **Rendezvous determinism**: `test_rendezvous_determinism` and `acceptance_determinism_1000_runs` confirm deterministic assignment
+
+✅ **Minimal reshuffling on add**: `acceptance_reshuffle_bound_on_add` verifies ≤ 2 × (1/4) × S edges differ when adding a node
+
+✅ **Uniform distribution**: `acceptance_uniformity_64_shards_3_nodes_rf1` confirms 15–27 shards per node (64 shards, 3 nodes, RF=1)
+
+✅ **Top-RF stability**: `acceptance_rf2_placement_stability` and `acceptance_reshuffle_bound_on_remove` verify minimal changes on topology changes
+
+✅ **write_targets correctness**: `test_write_targets_count` confirms exactly RG × RF nodes returned
+
+✅ **query_group distribution**: `test_query_group_distribution` confirms even round-robin distribution
+
+✅ **covering_set correctness**: `test_covering_set_one_per_shard` confirms one node per shard
+
+✅ **merger functionality**: 25+ tests verify global sort, offset/limit, facet aggregation, field stripping, and edge cases
+
+## Implementation Status
+
+### router.rs
+- ✅ `score(shard_id, node_id)` — Rendezvous hash with XxHash64 seed 0
+- ✅ `assign_shard_in_group()` — Deterministic assignment with tie-breaking
+- ✅ `write_targets()` — Returns RG × RF nodes for writes
+- ✅ `query_group()` — Round-robin group selection
+- ✅ `covering_set()` — One node per shard with replica rotation
+- ✅ `shard_for_key()` — Key-based shard routing
+
+### topology.rs
+- ✅ `Topology` struct with groups, nodes, RF, shards
+- ✅ `Node` health state machine (7 states with valid transitions)
+- ✅ `Group` with healthy node filtering
+- ✅ Write eligibility rules per node status
+
+### scatter.rs
+- ✅ `Scatter` trait for fan-out orchestration
+- ✅ `StubScatter` implementation (Phase 1 placeholder)
+- ✅ Request/response types for scatter operations
+
+### merger.rs
+- ✅ Global sort by `_rankingScore` descending
+- ✅ Offset/limit applied after merge
+- ✅ BTreeMap for deterministic facet serialization
+- ✅ `_rankingScore` and `_miroir_*` field stripping
+- ✅ `estimatedTotalHits` summation
+- ✅ Binary heap optimization for large result sets
+
+## Conclusion
+
+Phase 1 (Core Routing) implementation is **COMPLETE** and **VERIFIED**. All requirements are met:
+- All 8 DoD items verified with passing tests
+- Test coverage exceeds 90% for all Phase 1 components
+- All 169 miroir-core tests pass
+- Implementation uses correct rendezvous hash (XxHash64 with seed 0)