feat(foundations): update config for [04.2026] release

foundations/config.mdx

@@ -430,12 +430,18 @@ This parameter provides the configuration for the `Catchain` protocol in the TON
 
 ## Param 29: consensus config
 
-This parameter provides the configuration for the consensus protocol above `Catchain` ([Param 28](#param-28)) in the TON Blockchain. The consensus protocol is a crucial component of a blockchain network, and it ensures that all nodes agree on the state of the distributed ledger.
+This parameter provides the configuration for the consensus protocol above `Catchain` ([Param 28](#param-28-catchain-config)) in the TON Blockchain. The consensus protocol is a crucial component of a blockchain network, and it ensures that all nodes agree on the state of the distributed ledger.
+
+<Aside>
+  `ConfigParam 29` has evolved through several constructors. The latest, `consensus_config_v4#d9`, is defined in [`block.tlb`](https://github.com/ton-blockchain/ton/blob/af252bcdaea357fee21739e984654c2c84e7d61d/crypto/block/block.tlb#L782). It extends `consensus_config_v3#d8` with a new `use_quic:Bool` (taking one bit from `flags`, which shrinks from 7 to 6 bits) and an additional `catchain_max_blocks_coeff:uint32` field at the end.
+</Aside>
 
 ### Configuration parameters
 
 - `flags`: A general field that can be used to set various binary parameters.
 
+- `use_quic`: A Boolean value indicating whether the legacy Catchain consensus path uses QUIC transport instead of RLDP2. Introduced in `consensus_config_v4#d9`; has the same meaning as the `use_quic` field in [Param 30](#param-30-consensus-extension).
+
 - `new_catchain_ids`: A Boolean value indicating whether to generate new `Catchain` identifiers.
 
 - `round_candidates`: The number of candidates to be considered in each round of the consensus protocol.
@@ -458,10 +464,137 @@ This parameter provides the configuration for the consensus protocol above `Catc
 
 - `catchain_max_blocks_coeff`: The coefficient limiting the rate of block generation in `Catchain`, [description](https://github.com/ton-blockchain/ton/blob/master/doc/catchain-dos.md).
 
-For up-to-date values, see [https://tonviewer.com/config](https://tonviewer.com/config).
+For up-to-date values, see [Parameter #29 on mainnet](https://tonviewer.com/config#29).
+
+#### On-chain schema
+
+`ConfigParam 29` is a tagged union: validators must accept any of the legacy constructors so old serialized configs keep parsing, but new on-chain values are written using the latest tag. The current set defined in [`block.tlb`](https://github.com/ton-blockchain/ton/blob/af252bcdaea357fee21739e984654c2c84e7d61d/crypto/block/block.tlb#L782) is:
+
+```tlb
+consensus_config#d6 round_candidates:# { round_candidates >= 1 }
+  next_candidate_delay_ms:uint32 consensus_timeout_ms:uint32
+  fast_attempts:uint32 attempt_duration:uint32 catchain_max_deps:uint32
+  max_block_bytes:uint32 max_collated_bytes:uint32 = ConsensusConfig;
+
+consensus_config_new#d7 flags:(## 7) { flags = 0 } new_catchain_ids:Bool
+  round_candidates:(## 8) { round_candidates >= 1 }
+  next_candidate_delay_ms:uint32 consensus_timeout_ms:uint32
+  fast_attempts:uint32 attempt_duration:uint32 catchain_max_deps:uint32
+  max_block_bytes:uint32 max_collated_bytes:uint32 = ConsensusConfig;
+
+consensus_config_v3#d8 flags:(## 7) { flags = 0 } new_catchain_ids:Bool
+  round_candidates:(## 8) { round_candidates >= 1 }
+  next_candidate_delay_ms:uint32 consensus_timeout_ms:uint32
+  fast_attempts:uint32 attempt_duration:uint32 catchain_max_deps:uint32
+  max_block_bytes:uint32 max_collated_bytes:uint32
+  proto_version:uint16 = ConsensusConfig;
+
+consensus_config_v4#d9 flags:(## 6) { flags = 0 } use_quic:Bool new_catchain_ids:Bool
+  round_candidates:(## 8) { round_candidates >= 1 }
+  next_candidate_delay_ms:uint32 consensus_timeout_ms:uint32
+  fast_attempts:uint32 attempt_duration:uint32 catchain_max_deps:uint32
+  max_block_bytes:uint32 max_collated_bytes:uint32
+  proto_version:uint16 catchain_max_blocks_coeff:uint32 = ConsensusConfig;
+
+_ ConsensusConfig = ConfigParam 29;
+```
+
+<Aside>
+  `consensus_config_v4#d9` was introduced together with the [Catchain 2.0 / Simplex](https://github.com/ton-blockchain/simplex-docs/blob/main/Simplex.md) migration tracked by [Param 30](#param-30-consensus-extension). The `use_quic` toggle in Param 29 controls the transport for the legacy Catchain path; the `use_quic` toggle in Param 30 controls the transport for the new Simplex path. They are configured independently.
+</Aside>
 
 [Parameter #29 on mainnet](https://tonviewer.com/config#29)
 
+## Param 30: consensus extension
+
+<Aside type="note">
+  - [TON v2026.03](https://github.com/ton-blockchain/ton/releases/tag/v2026.03): `ConfigParam 30` introduced on testnet.
+  - [TON v2026.04](https://github.com/ton-blockchain/ton/releases/tag/v2026.04): `ConfigParam 30` enabled on mainnet.
+</Aside>
+
+This parameter configures [Catchain 2.0](https://github.com/ton-blockchain/simplex-docs/blob/main/Simplex.md) — the Simplex-based consensus protocol that succeeds the original Catchain. The settings are optional and can be supplied independently for each chain. Block-size limits are not duplicated here: the node continues to read `max_block_bytes` and `max_collated_bytes` from [`ConfigParam 29`](/foundations/config#param-29-consensus-config).
+
+The `crypto/block/block.tlb` [defines](https://github.com/ton-blockchain/ton/blob/v2026.04/crypto/block/block.tlb#L782) the following schema:
+
+```tlb
+simplex_config#21 flags:(## 7)
+  use_quic:Bool
+  target_rate_ms:uint32
+  slots_per_leader_window:uint32
+  first_block_timeout_ms:uint32
+  max_leader_window_desync:uint32
+  = NewConsensusConfig;
+
+simplex_config_v2#22 flags:(## 7)
+  use_quic:Bool
+  slots_per_leader_window:uint32
+  noncritical_params:(HashmapE 8 uint32)
+  = NewConsensusConfig;
+
+new_consensus_config_all#10
+  mc:(Maybe ^NewConsensusConfig)
+  shard:(Maybe ^NewConsensusConfig)
+  = NewConsensusConfigAll;
+
+_ NewConsensusConfigAll = ConfigParam 30;
+```
+
+The `simplex_config_v2#22` constructor moves noncritical configuration parameters into a sparse dictionary.
+There are two optional refs in `new_consensus_config_all#10`. If a ref is absent, then the pre-2.0 Catchain config is active for the corresponding class of chains:
+
+| Field   | Type                        | Meaning                                                 |
+| ------- | --------------------------- | ------------------------------------------------------- |
+| `mc`    | `Maybe ^NewConsensusConfig` | Config for the masterchain (`workchain = -1`)           |
+| `shard` | `Maybe ^NewConsensusConfig` | Config for shardchains (all non-masterchain workchains) |
+
+The `NewConsensusConfig` has two constructors:
+
+- `simplex_config#21` is the legacy fixed-layout format; scheduled for removal.
+- `simplex_config_v2#22` is the current extensible format, which supports arbitrary `noncritical_params` without changes to the `block.tlb` layout.
+
+### Configuration parameters of `simplex_config_v2`
+
+- `flags`: A general field that can be used to set various binary parameters.
+- `use_quic`: Whether the QUIC transport is used instead of RLDP2. Set to **True** in mainnet.
+- `slots_per_leader_window`: Number of consecutive slots assigned to one leader. Set to **4** in mainnet.
+- `noncritical_params`: A `HashmapE 8 uint32` map from parameter IDs to raw 32-bit values.
+
+Inherited from [Param 29](https://tonviewer.com/config#29):
+
+- `max_block_bytes` — maximum block size.
+- `max_collated_bytes` — maximum size of serialized block correctness proofs.
+
+The `noncritical_params` dictionary contains tunable timing and DoS-protection parameters that might differ between validators:
+
+- The key is an 8-bit parameter ID.
+- The value is always a raw 32-bit word.
+- Unknown IDs are ignored by the current implementation.
+- Missing IDs use default values.
+- Duration-like parameters store milliseconds directly.
+- Floating-point parameters store `float32` bits according to the [IEEE-754](https://en.wikipedia.org/wiki/IEEE_754) standard in a `uint32` value. The loader then reinterprets these bits as a floating-point numeric value.
+
+IDs from `0` through `14` are recognized and supported. On the mainnet, only IDs `0`, `1`, and `13` are explicitly set. All other IDs are normally absent and use defaults.
+
+| ID   | Name                                   | Stored as                  | Default                  | Meaning                                                                                                    |
+| ---- | -------------------------------------- | -------------------------- | ------------------------ | ---------------------------------------------------------------------------------------------------------- |
+| `0`  | `target_rate`                          | `uint32` milliseconds      | `2400 ms`                | Target slot or block interval; used for leader pacing, block production timing, and skip scheduling.       |
+| `1`  | `first_block_timeout`                  | `uint32` milliseconds      | `1000 ms`                | Base timeout before skip voting starts for the first missing block in a leader window.                     |
+| `2`  | `first_block_timeout_multiplier`       | `float32` bits in `uint32` | `1.2`                    | Multiplier applied to `first_block_timeout` after a window that had skips.                                 |
+| `3`  | `first_block_timeout_cap`              | `uint32` milliseconds      | `100,000 ms`             | Cap for the adaptive `first_block_timeout` growth.                                                         |
+| `4`  | `candidate_resolve_timeout`            | `uint32` milliseconds      | `1000 ms`                | Initial timeout for candidate or notarization resolution requests.                                         |
+| `5`  | `candidate_resolve_timeout_multiplier` | `float32` bits in `uint32` | `1.2`                    | Backoff multiplier for candidate resolution retries.                                                       |
+| `6`  | `candidate_resolve_timeout_cap`        | `uint32` milliseconds      | `10,000 ms`              | Cap for candidate resolution timeout growth.                                                               |
+| `7`  | `candidate_resolve_cooldown`           | `uint32` milliseconds      | `10 ms`                  | Cooldown between candidate resolution attempts.                                                            |
+| `8`  | `standstill_timeout`                   | `uint32` milliseconds      | `10,000 ms`              | No-progress timeout before standstill recovery or rebroadcast logic triggers.                              |
+| `9`  | `standstill_max_egress_bytes_per_s`    | `uint32` number            | `6,553,600` (`50 << 17`) | Egress rate cap used during standstill rebroadcast.                                                        |
+| `10` | `max_leader_window_desync`             | `uint32` number            | `250`                    | Maximum tolerated future leader-window distance for inbound Simplex traffic.                               |
+| `11` | `bad_signature_ban_duration`           | `uint32` milliseconds      | `5000 ms`                | Temporary ban duration after receiving bad signatures from a peer.                                         |
+| `12` | `candidate_resolve_rate_limit`         | `uint32` number            | `10`                     | Per-peer rate limit for candidate resolution requests.                                                     |
+| `13` | `min_block_interval`                   | `uint32` milliseconds      | `0 ms`                   | Minimum interval between parent block time and the next locally generated block.                           |
+| `14` | `no_empty_blocks_on_error_timeout`     | `uint32` milliseconds      | `15,000 ms`              | How long empty-block fallback is allowed after the last finalized block when collation fails or times out. |
+
+[Parameter #30 on mainnet](https://tonviewer.com/config#30)
+
 ## Param 31: fee-exempt contracts
 
 This parameter represents the configuration of smart contract addresses from which no fees are charged for either gas or storage, and where **tick-tock** transactions can be created. The list usually includes governance contracts. The parameter is presented as a binary tree structure — a tree (HashMap 256), where the keys are a 256-bit representation of the address. Only addresses in the masterchain can be present in this list.