docs(p15): add G9D registration controller consensus

2026-08-19 05:36:58 +00:00 · 2026-05-02 20:30:54 -07:00
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+# V3 Phase 15 G9D - Registration / Controller Boundary Consensus
+
+Date: 2026-05-02
+Status: architect consensus for G9D implementation
+Scope: blockmaster registration, heartbeat, inventory, placement, assignment, recovery readiness
+
+## 1. Core rule
+
+Registration and heartbeat are observation facts. They do not grant authority, do not make a replica ready, and do not close recovery.
+
+The controller is the only layer that may turn desired product state plus runtime observations into placement decisions, recovery decisions, and assignment publication requests.
+
+Publisher emits authority only from controller decisions. Frontends consume readiness projections only after the data-plane facts prove serviceability.
+
+## 2. Role split
+
+| Layer | Owns | Must not do |
+| --- | --- | --- |
+| Desired volume registry | User/product intent: volume exists, size, RF, attach intent | Mint primary, mark replica ready, infer placement from heartbeat |
+| Node registration / heartbeat | Node presence, addresses, capacity, labels, local replica inventory | Claim primary, claim replica_ready, close recovery |
+| Placement controller | Select candidate nodes/slots from desired state and inventory | Treat observation as data continuity proof |
+| Assignment controller / publisher | Publish epoch/endpoint-version authority facts | Bypass recovery/ready facts |
+| Recovery feeder | Feed base/WAL and maintain one WAL egress owner per peer | Decide product placement |
+| Durable ack / probe | Report progress facts | Create authority directly |
+| Frontend | Serve only after frontend_primary_ready | Infer readiness from heartbeat |
+
+## 3. Fact vocabulary
+
+### Node registration
+
+A node registration says:
+
+- this server exists;
+- these addresses and labels are visible;
+- these storage pools have capacity;
+- these local replica records already exist.
+
+It is inventory. It is not authority.
+
+### Desired volume registration
+
+A desired volume record says:
+
+- this volume should exist;
+- this is the requested size and replication factor.
+
+It is product intent. It is not placement.
+
+### Replica inventory
+
+A replica inventory record says:
+
+- this node reports a local replica identity;
+- the replica has a local durable identity and progress facts;
+- the replica may be existing, blank, corrupt, unknown, recovering, or ready-candidate.
+
+It is evidence for planner/controller. It is not replica_ready.
+
+### Assignment
+
+Assignment is epoch/endpoint-version authority published after controller decision. Assignment movement alone does not prove data continuity.
+
+### Replica ready
+
+Replica readiness requires recovery/feed/progress facts, including closed recovery window and post-close durable acknowledgement when the replica returned through recovery.
+
+## 4. Anti-patterns
+
+The following are design stops:
+
+1. Heartbeat directly mints primary assignment.
+2. Existing local replica inventory directly becomes replica_ready.
+3. Blank capacity directly becomes primary.
+4. Authority movement alone claims data continuity.
+5. Desired volume creation directly starts frontend service.
+6. One peer has multiple independent WAL feeders.
+7. Delete intent directly drops data-path state without drain/teardown phase.
+
+## 5. G9D implementation boundary
+
+G9D first slice may add durable stores for:
+
+- desired volume intent;
+- node registration;
+- local replica inventory.
+
+G9D first slice must not:
+
+- import `core/adapter`;
+- mention `AssignmentInfo`;
+- construct `AssignmentFact`;
+- publish assignment;
+- update engine mode;
+- claim replica_ready.
+
+Tests must pin these boundaries so future controller work consumes inventory through explicit planner seams instead of reintroducing heartbeat-as-authority.
+
+## 6. Future controller path
+
+The intended future flow is:
+
+```text
+CreateVolume(volume_id, size, RF)
+  -> DesiredVolumeStore
+
+NodeHeartbeat(server_id, pools, local replicas)
+  -> NodeInventoryStore
+
+DesiredVolume + NodeInventory + ReplicaInventory
+  -> PlacementController
+  -> ReplicaCreate / ReplicaStart / Recover decisions
+  -> AssignmentController / Publisher
+  -> blockvolume observes AssignmentFact
+  -> feeder/recovery proves data-plane facts
+  -> replica_ready / frontend_ready projections
+```
+
+This keeps SeaweedFS-style automatic discovery while preserving the V3 anti-pattern boundary: observation facts do not substitute for authority or data-plane proof.