add: devnet-4 plan

breakout-rooms/leanConsensus/pq-interop/pq-devnet-4.md

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+# pq-devnet-4: High Level Plan
+
+## Objectives
+
+1. Enable recursive PQ signature aggregation using `leanVm`
+2. Coalesce multiple aggregates for the same message into one final aggregate
+3. Ensure blocks contain a single aggregate per message instead of multiple aggregates with different `participantValidators`
+
+## Key functionalities & targets
+
+- **Existing**
+  - **Slot duration:** 4 seconds
+  - **Consensus mechanism:** Modified [3SF-mini](https://github.com/ethereum/research/tree/master/3sf-mini)
+  - **PQ signature:** [leanSig](https://github.com/leanEthereum/leanSig)
+  - **Signature aggregation base:** [leanMultisig](https://github.com/leanEthereum/leanMultisig)
+- **Changes**
+  - **`validator-config.yaml`:**
+    - New optional field: `log_inv_rate` (integer, aggregator-only).
+    - Valid values: `1` to `4`.
+    - This field is set only when `is_aggregator: true`.
+    - Semantics:
+      - `1`: biggest proof size, fastest proof construction.
+      - `4`: smallest proof size, slowest proof construction / most compute intensive.
+    - If omitted for aggregators, clients use default as 2.
+    - Non-aggregator validators MUST ignore this field.
+  - **Recursive aggregation via `leanVm`:**
+    - `leanVm` performs recursive aggregation over partial aggregates that correspond to the same message.
+    - Aggregates are progressively merged until a single aggregate remains per message.
+  - **Aggregate coalescing rules:**
+    - Multiple aggregates with different `participantValidators` sets for the same message are merged into one aggregate.
+    - The final aggregate MUST represent the union of all non-equivocating participant validators included in valid partial aggregates.
+  - **Block contents:**
+    - Proposers include exactly one aggregate per message in block body.
+    - Duplicate aggregates for the same message MUST be rejected at block validation time.
+  - **Networking and mempool behavior:**
+    - Nodes MAY receive multiple partial aggregates for the same message over gossip.
+    - Aggregators SHOULD coalesce compatible partial aggregates before forwarding and propagate.
+    - Conflicting or invalid aggregates are ignored according to existing attestation validity rules.
+  - **Role behavior updates:**
+    - **Aggregator:** Continues collecting attestations/partial aggregates and recursively merges them.
+    - **Proposer:** Prioritizes the best available coalesced aggregate per message for inclusion.
+    - **Verifier:** Validates that each message has at most one aggregate in block and that the aggregate verifies against its participant set.
+
+## Notable exclusions
+
+- Dynamic committee assignment changes
+- Changes to validator churn/activation logic
+- Multi-message proof batching beyond one aggregate-per-message semantics
+
+## Completion target
+
+2026-03-25 (TBC)
+
+## Specification targets
+
+| Specification | Target | Remarks |
+| ------------- | ------ | ------- |
+| leanSpec      | TBD | - For specification-related changes, see [all pq-devnet-4 spec PRs](https://github.com/leanEthereum/leanSpec/pulls?q=is%3Apr+is%3Amerged+label%3Aspecs+milestone%3Apq-devnet-4) <br />- For all changes including tests and framework, see [all pq-devnet-4 PRs](https://github.com/leanEthereum/leanSpec/pulls?q=is%3Apr+is%3Amerged+label%3Aspecs+milestone%3Apq-devnet-4) |
+| leanSig       | TBD | |
+| leanMultisig  | TBD | |
+| leanVm        | TBD | |
+| leanMetrics   | TBD | |
+
+## Configurations
+
+- `validator-config.yaml`: TBD
+  - Example aggregator entry:
+
+    ```yaml
+    - name: node_0
+      privkey: 0000000000000000010000000000000002000000000000000300000000000000
+      enrFields:
+        ip: 10.0.0.0
+        quic: 10000
+        is_aggregator: true
+      log_inv_rate: 4
+    ```
+
+## Interop toolings
+
+| Tool | Link |
+| ---- | ---- |
+| lean-quickstart | TBD |
+
+## Client support status
+
+| Client | Implementation | Spec tests | Interop | Code      | Docker |
+| ------ | -------------- | ---------- | ------- | --------- | ------ |
+| Ream   | ⏳ | ⏳ | ⏳ | | |
+| Zeam   | ⏳ | ⏳ | ⏳ | | |
+| Qlean  | ⏳ | ⏳ | ⏳ | | |
+| Lantern | ⏳ | ⏳ | ⏳ | | |
+| Lighthouse | ⏳ | ⏳ | ⏳ | | |
+
+## Benchmarks
+
+- Hardware specs: TBD (based on [EIP-7870](https://eips.ethereum.org/EIPS/eip-7870) full node specs)
+- Configurations: TBD
+- Results
+  - [leanMetrics](https://github.com/leanEthereum/leanMetrics) collected and analyzed. Links to results to be added here once completed.
+
+## Summary and learnings
+
+- To be added once devnet is complete