diff --git a/docs/protocols/alpha.rst b/docs/protocols/alpha.rst
index 0e02f084baf00c21e164e9d27617a538e3411e61..c9f0f457469fb86d6998767020ae38a63a98da62 100644
--- a/docs/protocols/alpha.rst
+++ b/docs/protocols/alpha.rst
@@ -75,6 +75,14 @@ Minor Changes
 - Relax (pre)endorsements branch condition and allow denunciations of
   a same endorsement on different branches. (MR :gl:`!7828`)
 
+- Relax (pre)endorsement checks during mempool validation. The mempool
+  is now able to propagate (pre)endorsements for blocks in the near
+  past or future, and from close cousin branches. Notably, the
+  preendorsements that the baker is able to inject as soon as a block
+  has been validated (without waiting for its full application) can
+  now be immediately propagated by the mempool, allowing for a much
+  faster PQC. (MR :gl:`!7815`)
+
 Internal
 --------
 
diff --git a/src/proto_alpha/lib_protocol/alpha_context.ml b/src/proto_alpha/lib_protocol/alpha_context.ml
index 99ee157fa42adc48fd30a874bf1fae2b4a65cd56..2a83eb96f1328271166e6a870194219db55ed372 100644
--- a/src/proto_alpha/lib_protocol/alpha_context.ml
+++ b/src/proto_alpha/lib_protocol/alpha_context.ml
@@ -592,17 +592,6 @@ module Consensus = struct
   let store_endorsement_branch ctxt branch =
     let ctxt = set_endorsement_branch ctxt branch in
     Storage.Tenderbake.Endorsement_branch.add ctxt branch
-
-  let load_grand_parent_branch ctxt =
-    Storage.Tenderbake.Grand_parent_branch.find ctxt >>=? function
-    | Some grand_parent_branch ->
-        Raw_context.Consensus.set_grand_parent_branch ctxt grand_parent_branch
-        |> return
-    | None -> return ctxt
-
-  let store_grand_parent_branch ctxt branch =
-    let ctxt = set_grand_parent_branch ctxt branch in
-    Storage.Tenderbake.Grand_parent_branch.add ctxt branch
 end
 
 let prepare_first_block = Init_storage.prepare_first_block
@@ -611,7 +600,6 @@ let prepare ctxt ~level ~predecessor_timestamp ~timestamp =
   Init_storage.prepare ctxt ~level ~predecessor_timestamp ~timestamp
   >>=? fun (ctxt, balance_updates, origination_results) ->
   Consensus.load_endorsement_branch ctxt >>=? fun ctxt ->
-  Consensus.load_grand_parent_branch ctxt >>=? fun ctxt ->
   return (ctxt, balance_updates, origination_results)
 
 let finalize ?commit_message:message c fitness =
diff --git a/src/proto_alpha/lib_protocol/alpha_context.mli b/src/proto_alpha/lib_protocol/alpha_context.mli
index 28d625f8e15adec7d4967d5ec8613064a2a49c77..b280770604c162ed0a5bd40f440fc08bfd7d6c86 100644
--- a/src/proto_alpha/lib_protocol/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/alpha_context.mli
@@ -5348,12 +5348,6 @@ module Consensus : sig
       storage and RAM. *)
   val store_endorsement_branch :
     context -> Block_hash.t * Block_payload_hash.t -> context Lwt.t
-
-  (** [store_grand_parent_branch context branch] sets the "grand-parent branch"
-      (see {!Storage.Tenderbake.Grand_parent_branch} to [branch] in both the
-      disk storage and RAM. *)
-  val store_grand_parent_branch :
-    context -> Block_hash.t * Block_payload_hash.t -> context Lwt.t
 end
 
 (** This module re-exports definitions from {!Token}. *)
diff --git a/src/proto_alpha/lib_protocol/apply.ml b/src/proto_alpha/lib_protocol/apply.ml
index 3c2bf68c3d82c9a62c1243522cf0aee721a6709a..7c281963f85e32f0e20cd77a36adec646c0cc754 100644
--- a/src/proto_alpha/lib_protocol/apply.ml
+++ b/src/proto_alpha/lib_protocol/apply.ml
@@ -2184,9 +2184,16 @@ let record_operation (type kind) ctxt hash (operation : kind operation) :
   | Cons (Manager_operation _, _) ->
       record_non_consensus_operation_hash ctxt hash
 
+let find_in_slot_map consensus_content slot_map =
+  match Slot.Map.find consensus_content.slot slot_map with
+  | Some (consensus_key, power) -> return (consensus_key, power)
+  | None ->
+      (* This should not happen: operation validation should have failed. *)
+      tzfail Faulty_validation_wrong_slot
+
 let record_preendorsement ctxt (mode : mode) (content : consensus_content) :
-    (context * Kind.preendorsement contents_result_list) tzresult =
-  let open Result_syntax in
+    (context * Kind.preendorsement contents_result_list) tzresult Lwt.t =
+  let open Lwt_result_syntax in
   let ctxt =
     match mode with
     | Full_construction _ -> (
@@ -2195,34 +2202,59 @@ let record_preendorsement ctxt (mode : mode) (content : consensus_content) :
         | Some _ -> ctxt)
     | Application _ | Partial_construction _ -> ctxt
   in
-  match Slot.Map.find content.slot (Consensus.allowed_preendorsements ctxt) with
-  | None ->
-      (* This should not happen: operation validation should have failed. *)
-      error Faulty_validation_wrong_slot
-  | Some ({delegate; consensus_pkh; _}, preendorsement_power) ->
-      let* ctxt =
+  let mk_preendorsement_result {Consensus_key.delegate; consensus_pkh; _}
+      preendorsement_power =
+    Single_result
+      (Preendorsement_result
+         {
+           balance_updates = [];
+           delegate;
+           consensus_key = consensus_pkh;
+           preendorsement_power;
+         })
+  in
+  match mode with
+  | Application _ | Full_construction _ ->
+      let* consensus_key, power =
+        find_in_slot_map content (Consensus.allowed_preendorsements ctxt)
+      in
+      let*? ctxt =
         Consensus.record_preendorsement
           ctxt
           ~initial_slot:content.slot
-          ~power:preendorsement_power
+          ~power
           content.round
       in
       return
-        ( ctxt,
-          Single_result
-            (Preendorsement_result
-               {
-                 balance_updates = [];
-                 delegate;
-                 consensus_key = consensus_pkh;
-                 preendorsement_power;
-               }) )
-
-let is_grandparent_endorsement mode content =
-  match mode with
+        (ctxt, mk_preendorsement_result (Consensus_key.pkh consensus_key) power)
   | Partial_construction {predecessor_level; _} ->
-      Raw_level.(succ content.level = predecessor_level)
-  | _ -> false
+      (* In mempool mode, preendorsements are allowed for various levels
+         and rounds. We do not record preendorsements because we could get
+         false-positive conflicts for preendorsements with the same slot
+         but different levels/rounds. We could record just preendorsements
+         for the mempool head's level and round (the most usual
+         preendorsements), but we don't need to, because there is no block
+         to finalize anyway in this mode. *)
+      let* ctxt, consensus_key, power =
+        if Raw_level.(content.level = predecessor_level) then
+          (* We can use the pre-computed slot map, which contains the
+             consensus rights at the predecessor level. *)
+          let* consensus_key, power =
+            find_in_slot_map content (Consensus.allowed_preendorsements ctxt)
+          in
+          return (ctxt, consensus_key, power)
+        else
+          (* We retrieve the key directly, and return a fake voting
+             power of 0 because it doesn't matter for a past or future
+             preendorsement.*)
+          let level = Level.from_raw ctxt content.level in
+          let* ctxt, consensus_key =
+            Stake_distribution.slot_owner ctxt level content.slot
+          in
+          return (ctxt, consensus_key, 0)
+      in
+      return
+        (ctxt, mk_preendorsement_result (Consensus_key.pkh consensus_key) power)
 
 let record_endorsement ctxt (mode : mode) (content : consensus_content) :
     (context * Kind.endorsement contents_result_list) tzresult Lwt.t =
@@ -2238,24 +2270,44 @@ let record_endorsement ctxt (mode : mode) (content : consensus_content) :
            endorsement_power;
          })
   in
-  if is_grandparent_endorsement mode content then
-    let level = Level.from_raw ctxt content.level in
-    let* ctxt, ({delegate; _} as consensus_key) =
-      Stake_distribution.slot_owner ctxt level content.slot
-    in
-    let*? ctxt = Consensus.record_grand_parent_endorsement ctxt delegate in
-    return (ctxt, mk_endorsement_result (Consensus_key.pkh consensus_key) 0)
-  else
-    match Slot.Map.find content.slot (Consensus.allowed_endorsements ctxt) with
-    | None ->
-        (* This should not happen: operation validation should have failed. *)
-        tzfail Faulty_validation_wrong_slot
-    | Some (consensus_key, power) ->
-        let*? ctxt =
-          Consensus.record_endorsement ctxt ~initial_slot:content.slot ~power
-        in
-        return
-          (ctxt, mk_endorsement_result (Consensus_key.pkh consensus_key) power)
+  match mode with
+  | Application _ | Full_construction _ ->
+      let* consensus_key, power =
+        find_in_slot_map content (Consensus.allowed_endorsements ctxt)
+      in
+      let*? ctxt =
+        Consensus.record_endorsement ctxt ~initial_slot:content.slot ~power
+      in
+      return
+        (ctxt, mk_endorsement_result (Consensus_key.pkh consensus_key) power)
+  | Partial_construction {predecessor_level; _} ->
+      (* In mempool mode, endorsements are allowed for various levels
+         and rounds. We do not record endorsements because we could get
+         false-positive conflicts for endorsements with the same slot
+         but different levels/rounds. We could record just endorsements
+         for the predecessor's level and round (the most usual
+         endorsements), but we don't need to, because there is no block
+         to finalize anyway in this mode. *)
+      let* ctxt, consensus_key, power =
+        if Raw_level.(content.level = predecessor_level) then
+          (* We can use the pre-computed slot map, which contains the
+             consensus rights at the predecessor level. *)
+          let* consensus_key, power =
+            find_in_slot_map content (Consensus.allowed_endorsements ctxt)
+          in
+          return (ctxt, consensus_key, power)
+        else
+          (* We retrieve the key directly, and return a fake voting
+             power of 0 because it doesn't matter for a past or future
+             endorsement.*)
+          let level = Level.from_raw ctxt content.level in
+          let* ctxt, consensus_key =
+            Stake_distribution.slot_owner ctxt level content.slot
+          in
+          return (ctxt, consensus_key, 0)
+      in
+      return
+        (ctxt, mk_endorsement_result (Consensus_key.pkh consensus_key) power)
 
 let apply_manager_contents_list ctxt ~payload_producer chain_id
     fees_updated_contents_list =
@@ -2357,7 +2409,7 @@ let apply_contents_list (type kind) ctxt chain_id (mode : mode)
   in
   match contents_list with
   | Single (Preendorsement consensus_content) ->
-      record_preendorsement ctxt mode consensus_content |> Lwt.return
+      record_preendorsement ctxt mode consensus_content
   | Single (Endorsement consensus_content) ->
       record_endorsement ctxt mode consensus_content
   | Single (Dal_attestation op) ->
@@ -2845,12 +2897,6 @@ let finalize_application ctxt block_data_contents ~round ~predecessor_hash
      accessible. This will not be present before the first two blocks
      of tenderbake. *)
   let level = Level.current ctxt in
-  let*! ctxt =
-    match Consensus.endorsement_branch ctxt with
-    | Some predecessor_branch ->
-        Consensus.store_grand_parent_branch ctxt predecessor_branch
-    | None -> Lwt.return ctxt
-  in
   (* We mark the current payload hash as the predecessor one => this
      will only be accessed by the successor block now. *)
   let*! ctxt =
@@ -3026,6 +3072,10 @@ let finalize_block (application_state : application_state) shell_header_opt =
       in
       return (result, receipt)
   | Partial_construction {predecessor_fitness; _} ->
+      (* Fake finalization to return a correct type, because there is no
+         block to finalize in mempool mode. If this changes in the
+         future, beware that consensus operations are not recorded by
+         {!record_preendorsement} and {!record_endorsement} in this mode. *)
       let* voting_period_info = Voting_period.get_rpc_current_info ctxt in
       let level_info = Level.current ctxt in
       let result = finalize ctxt predecessor_fitness in
diff --git a/src/proto_alpha/lib_protocol/init_storage.ml b/src/proto_alpha/lib_protocol/init_storage.ml
index 2e740d10f93ec2ace297751b932c00fad2f9f4a5..cd1924024a486bdbd77f5bb3892b6ed16b36d2cf 100644
--- a/src/proto_alpha/lib_protocol/init_storage.ml
+++ b/src/proto_alpha/lib_protocol/init_storage.ml
@@ -168,6 +168,7 @@ let prepare_first_block _chain_id ctxt ~typecheck ~level ~timestamp ~predecessor
       Raw_level_repr.of_int32 level >>?= fun level ->
       Storage.Tenderbake.First_level_of_protocol.update ctxt level
       >>=? fun ctxt ->
+      Storage.Legacy.Grand_parent_branch.remove ctxt >>= fun ctxt ->
       (* This needs to be kept in the migration code for every
          protocol, except Genesis. *)
       Sc_rollup_inbox_storage.add_protocol_migration ctxt >>= fun ctxt ->
diff --git a/src/proto_alpha/lib_protocol/main.ml b/src/proto_alpha/lib_protocol/main.ml
index ebb66598b1803e50c138e10c5adaa8dcd6dccf3b..bbc00994427c29da811a6f7bf7b5c9741565ccf8 100644
--- a/src/proto_alpha/lib_protocol/main.ml
+++ b/src/proto_alpha/lib_protocol/main.ml
@@ -156,9 +156,10 @@ let prepare_ctxt ctxt mode ~(predecessor : Block_header.shell_header) =
   (* During block (full or partial) application or full construction,
      endorsements must be for [predecessor_level] and preendorsements,
      if any, for the block's level. In the mempool (partial
-     construction), only consensus operations for [predecessor_level]
-     (that is, head's level) are allowed (except for grandparent
-     endorsements, which are handled differently). *)
+     construction), both endorsements and preendorsements are expected
+     to be for [predecessor_level] (that is, head's level) most of the
+     time, although operations that are one level before or after
+     [predecessor_level] are also accepted. *)
   let preendorsement_level =
     match mode with
     | Application _ | Partial_validation _ | Construction _ ->
@@ -230,16 +231,12 @@ let begin_validation ctxt chain_id mode ~predecessor =
         block_header_data.contents
   | Partial_construction _ ->
       let*? predecessor_round = Fitness.round_from_raw predecessor_fitness in
-      let*? grandparent_round =
-        Fitness.predecessor_round_from_raw predecessor_fitness
-      in
       return
         (Validate.begin_partial_construction
            ctxt
            chain_id
            ~predecessor_level
-           ~predecessor_round
-           ~grandparent_round)
+           ~predecessor_round)
 
 let validate_operation = Validate.validate_operation
 
@@ -411,15 +408,13 @@ module Mempool = struct
         ~predecessor:head
     in
     let*? predecessor_round = Fitness.round_from_raw head.fitness in
-    let*? grandparent_round = Fitness.predecessor_round_from_raw head.fitness in
     return
       (init
          ctxt
          chain_id
          ~predecessor_level:head_level
          ~predecessor_round
-         ~predecessor_hash:head_hash
-         ~grandparent_round)
+         ~predecessor_hash:head_hash)
 end
 
 (* Vanity nonce: TBD *)
diff --git a/src/proto_alpha/lib_protocol/mempool_validation.ml b/src/proto_alpha/lib_protocol/mempool_validation.ml
index 8493f18a7e13f9994ccc55028e453c8b73b2d7f8..e400de8a42bc1d1074ebafcded5dce78b55c5fca 100644
--- a/src/proto_alpha/lib_protocol/mempool_validation.ml
+++ b/src/proto_alpha/lib_protocol/mempool_validation.ml
@@ -64,15 +64,14 @@ let encoding : t Data_encoding.t =
           (Operation_hash.Map.encoding
              (dynamic_size ~kind:`Uint30 Operation.encoding)))
 
-let init ctxt chain_id ~predecessor_level ~predecessor_round ~predecessor_hash
-    ~grandparent_round : validation_info * t =
+let init ctxt chain_id ~predecessor_level ~predecessor_round ~predecessor_hash :
+    validation_info * t =
   let {info; operation_state; _} =
     begin_partial_construction
       ctxt
       chain_id
       ~predecessor_level
       ~predecessor_round
-      ~grandparent_round
   in
   ( info,
     {predecessor_hash; operation_state; operations = Operation_hash.Map.empty}
diff --git a/src/proto_alpha/lib_protocol/mempool_validation.mli b/src/proto_alpha/lib_protocol/mempool_validation.mli
index 6ed036b88545c2155cc00b92934456a720d238d5..dcadef04f5458b4a96597320a59fe01761a85757 100644
--- a/src/proto_alpha/lib_protocol/mempool_validation.mli
+++ b/src/proto_alpha/lib_protocol/mempool_validation.mli
@@ -131,7 +131,6 @@ val init :
   predecessor_level:Level.t ->
   predecessor_round:Round.t ->
   predecessor_hash:Block_hash.t ->
-  grandparent_round:Round.t ->
   validation_info * t
 
 (** Adds an operation to a [mempool] if and only if it is valid and
diff --git a/src/proto_alpha/lib_protocol/raw_context.ml b/src/proto_alpha/lib_protocol/raw_context.ml
index 374d81801ff082498a7cdf3f7ca59603c5955df1..297a17360ce99906e8a7348cf8855404365465b9 100644
--- a/src/proto_alpha/lib_protocol/raw_context.ml
+++ b/src/proto_alpha/lib_protocol/raw_context.ml
@@ -97,9 +97,6 @@ module Raw_consensus = struct
             for the lowest slot in the block can be recorded. The map
             associates to each initial slot the [pkh] associated to this
             slot with its power. *)
-    grand_parent_endorsements_seen : Signature.Public_key_hash.Set.t;
-        (** Record the endorsements already seen for the grand
-            parent. This only useful for the partial construction mode. *)
     endorsements_seen : Slot_repr.Set.t;
         (** Record the endorsements already seen. Only initial slots are indexed. *)
     preendorsements_seen : Slot_repr.Set.t;
@@ -111,7 +108,6 @@ module Raw_consensus = struct
         (** in block construction mode, record the round of preendorsements
             included in a block. *)
     endorsement_branch : (Block_hash.t * Block_payload_hash.t) option;
-    grand_parent_branch : (Block_hash.t * Block_payload_hash.t) option;
   }
 
   (** Invariant:
@@ -129,13 +125,11 @@ module Raw_consensus = struct
       current_endorsement_power = 0;
       allowed_endorsements = Slot_repr.Map.empty;
       allowed_preendorsements = Slot_repr.Map.empty;
-      grand_parent_endorsements_seen = Signature.Public_key_hash.Set.empty;
       endorsements_seen = Slot_repr.Set.empty;
       preendorsements_seen = Slot_repr.Set.empty;
       locked_round_evidence = None;
       preendorsements_quorum_round = None;
       endorsement_branch = None;
-      grand_parent_branch = None;
     }
 
   type error += Double_inclusion_of_consensus_operation
@@ -153,17 +147,6 @@ module Raw_consensus = struct
         | Double_inclusion_of_consensus_operation -> Some () | _ -> None)
       (fun () -> Double_inclusion_of_consensus_operation)
 
-  let record_grand_parent_endorsement t pkh =
-    error_when
-      (Signature.Public_key_hash.Set.mem pkh t.grand_parent_endorsements_seen)
-      Double_inclusion_of_consensus_operation
-    >|? fun () ->
-    {
-      t with
-      grand_parent_endorsements_seen =
-        Signature.Public_key_hash.Set.add pkh t.grand_parent_endorsements_seen;
-    }
-
   let record_endorsement t ~initial_slot ~power =
     error_when
       (Slot_repr.Set.mem initial_slot t.endorsements_seen)
@@ -214,13 +197,8 @@ module Raw_consensus = struct
 
   let endorsement_branch t = t.endorsement_branch
 
-  let grand_parent_branch t = t.grand_parent_branch
-
   let set_endorsement_branch t endorsement_branch =
     {t with endorsement_branch = Some endorsement_branch}
-
-  let set_grand_parent_branch t grand_parent_branch =
-    {t with grand_parent_branch = Some grand_parent_branch}
 end
 
 type dal_committee = {
@@ -1348,9 +1326,6 @@ module type CONSENSUS = sig
     allowed_preendorsements:(consensus_pk * int) slot_map ->
     t
 
-  val record_grand_parent_endorsement :
-    t -> Signature.Public_key_hash.t -> t tzresult
-
   val record_endorsement : t -> initial_slot:slot -> power:int -> t tzresult
 
   val record_preendorsement :
@@ -1367,10 +1342,6 @@ module type CONSENSUS = sig
   val set_endorsement_branch : t -> Block_hash.t * Block_payload_hash.t -> t
 
   val endorsement_branch : t -> (Block_hash.t * Block_payload_hash.t) option
-
-  val set_grand_parent_branch : t -> Block_hash.t * Block_payload_hash.t -> t
-
-  val grand_parent_branch : t -> (Block_hash.t * Block_payload_hash.t) option
 end
 
 module Consensus :
@@ -1411,10 +1382,6 @@ module Consensus :
          ~allowed_endorsements
          ~allowed_preendorsements)
 
-  let[@inline] record_grand_parent_endorsement ctxt pkh =
-    update_consensus_with_tzresult ctxt (fun ctxt ->
-        Raw_consensus.record_grand_parent_endorsement ctxt pkh)
-
   let[@inline] record_preendorsement ctxt ~initial_slot ~power round =
     update_consensus_with_tzresult
       ctxt
@@ -1438,13 +1405,6 @@ module Consensus :
   let[@inline] set_endorsement_branch ctxt branch =
     update_consensus_with ctxt (fun ctxt ->
         Raw_consensus.set_endorsement_branch ctxt branch)
-
-  let[@inline] grand_parent_branch ctxt =
-    Raw_consensus.grand_parent_branch ctxt.back.consensus
-
-  let[@inline] set_grand_parent_branch ctxt branch =
-    update_consensus_with ctxt (fun ctxt ->
-        Raw_consensus.set_grand_parent_branch ctxt branch)
 end
 
 module Tx_rollup = struct
diff --git a/src/proto_alpha/lib_protocol/raw_context.mli b/src/proto_alpha/lib_protocol/raw_context.mli
index e8056a82633d51cc32af33b0e2f4ec83b0da6214..ba4398abf9bae8ad45de15d2505f2f1861a98ff0 100644
--- a/src/proto_alpha/lib_protocol/raw_context.mli
+++ b/src/proto_alpha/lib_protocol/raw_context.mli
@@ -322,12 +322,6 @@ module type CONSENSUS = sig
     allowed_preendorsements:(consensus_pk * int) slot_map ->
     t
 
-  (** [record_grand_parent_endorsement ctx pkh] records an
-      grand_parent_endorsement for the current block. This is only
-      useful for the partial construction mode. *)
-  val record_grand_parent_endorsement :
-    t -> Signature.Public_key_hash.t -> t tzresult
-
   (** [record_endorsement ctx ~initial_slot ~power] records an
      endorsement for the current block.
 
@@ -368,10 +362,6 @@ module type CONSENSUS = sig
   val set_endorsement_branch : t -> Block_hash.t * Block_payload_hash.t -> t
 
   val endorsement_branch : t -> (Block_hash.t * Block_payload_hash.t) option
-
-  val set_grand_parent_branch : t -> Block_hash.t * Block_payload_hash.t -> t
-
-  val grand_parent_branch : t -> (Block_hash.t * Block_payload_hash.t) option
 end
 
 module Consensus :
diff --git a/src/proto_alpha/lib_protocol/storage.ml b/src/proto_alpha/lib_protocol/storage.ml
index b6a09e116daa73fbd3bbf9f6dad1c3f51fa97604..2e1b31102f2ec7abcd7ad0095c5281635bcfe44f 100644
--- a/src/proto_alpha/lib_protocol/storage.ml
+++ b/src/proto_alpha/lib_protocol/storage.ml
@@ -129,13 +129,6 @@ module Tenderbake = struct
         let name = ["endorsement_branch"]
       end)
       (Branch)
-
-  module Grand_parent_branch =
-    Make_single_data_storage (Registered) (Raw_context)
-      (struct
-        let name = ["grand_parent_branch"]
-      end)
-      (Branch)
 end
 
 (** Contracts handling *)
@@ -2095,3 +2088,12 @@ module Zk_rollup = struct
               (option Ticket_hash_repr.encoding))
       end)
 end
+
+module Legacy = struct
+  module Grand_parent_branch =
+    Make_single_data_storage (Registered) (Raw_context)
+      (struct
+        let name = ["grand_parent_branch"]
+      end)
+      (Tenderbake.Branch)
+end
diff --git a/src/proto_alpha/lib_protocol/storage.mli b/src/proto_alpha/lib_protocol/storage.mli
index e1e6f88d7836f7d8e944afbdd399b9f215565319..29bf6cb5335285972bfba1970de37c4d51d208da 100644
--- a/src/proto_alpha/lib_protocol/storage.mli
+++ b/src/proto_alpha/lib_protocol/storage.mli
@@ -654,13 +654,6 @@ module Tenderbake : sig
     Single_data_storage
       with type value = Block_hash.t * Block_payload_hash.t
        and type t := Raw_context.t
-
-  (** [Grand_parent_branch] stores a single value composed of the
-      great-grand parent hash and the grand parent's payload *)
-  module Grand_parent_branch :
-    Single_data_storage
-      with type value = Block_hash.t * Block_payload_hash.t
-       and type t := Raw_context.t
 end
 
 module Tx_rollup : sig
@@ -921,3 +914,12 @@ module Zk_rollup : sig
        and type key = int64
        and type value = Zk_rollup_operation_repr.t * Ticket_hash_repr.t option
 end
+
+module Legacy : sig
+  (** [Grand_parent_branch] stores a single value composed of the
+      great-grand parent hash and the grand parent's payload *)
+  module Grand_parent_branch :
+    Single_data_storage
+      with type value = Block_hash.t * Block_payload_hash.t
+       and type t := Raw_context.t
+end
diff --git a/src/proto_alpha/lib_protocol/test/helpers/consensus_helpers.ml b/src/proto_alpha/lib_protocol/test/helpers/consensus_helpers.ml
index cd198517052d54790894a0689b2cc8ea690078cf..56dce872e73d52899150c8612fa9d0a38cc7f74d 100644
--- a/src/proto_alpha/lib_protocol/test/helpers/consensus_helpers.ml
+++ b/src/proto_alpha/lib_protocol/test/helpers/consensus_helpers.ml
@@ -178,10 +178,5 @@ let test_consensus_op_for_next ~genesis ~kind ~next =
   Incremental.add_operation inc operation >>=? fun inc ->
   delegate_of_slot ~different_slot:true slot (B b2) >>=? fun delegate ->
   dorsement ~endorsed_block:b2 ~delegate >>=? fun operation ->
-  Incremental.add_operation inc operation >>= fun res ->
-  let error_title =
-    match next with
-    | `Level -> "Consensus operation for future level"
-    | `Round -> "Consensus operation for future round"
-  in
-  Assert.proto_error_with_info ~loc:__LOC__ res error_title
+  Incremental.add_operation inc operation >>=? fun (_ : Incremental.t) ->
+  return_unit
diff --git a/src/proto_alpha/lib_protocol/test/integration/consensus/test_endorsement.ml b/src/proto_alpha/lib_protocol/test/integration/consensus/test_endorsement.ml
index a1d12e676c44f88685242058b94d2c832bdfe965..2758d3225de7f4b9c140c19eb7a9b6b7b554d9c0 100644
--- a/src/proto_alpha/lib_protocol/test/integration/consensus/test_endorsement.ml
+++ b/src/proto_alpha/lib_protocol/test/integration/consensus/test_endorsement.ml
@@ -229,16 +229,19 @@ let error_future_level = function
 
 (** Endorsement that is one level in the future (pointing to the same
     level as the block/mempool containing the endorsement instead of
-    its predecessor/head). It should fail in all modes. *)
+    its predecessor/head). It should fail in a block (application or
+    construction) but succeed in a mempool. *)
 let test_one_level_in_the_future () =
   let open Lwt_result_syntax in
   let* _genesis, predecessor = init_genesis () in
   let* next_level_block = Block.bake predecessor in
-  Consensus_helpers.test_consensus_operation_all_modes
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block:next_level_block
     ~predecessor
-    ~error:error_future_level
+    ~application_error:error_future_level
+    ~construction_error:error_future_level
+    ?mempool_error:None
     Endorsement
 
 (** Endorsement that is two levels in the future. It should fail in
@@ -263,30 +266,36 @@ let error_old_round = function
       true
   | _ -> false
 
-(** Endorsement that is one round too old. It should fail in all modes. *)
+(** Endorsement that is one round too old. It should fail in a block
+    (application or construction) but succeed in a mempool. *)
 let test_one_round_too_old () =
   let open Lwt_result_syntax in
   let* _genesis, b = init_genesis () in
   let* round0_block = Block.bake b in
   let* predecessor = Block.bake ~policy:(By_round 1) b in
-  Consensus_helpers.test_consensus_operation_all_modes
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block:round0_block
     ~predecessor
-    ~error:error_old_round
+    ~application_error:error_old_round
+    ~construction_error:error_old_round
+    ?mempool_error:None
     Endorsement
 
-(** Endorsement that is many rounds too old. It should fail in all modes. *)
+(** Endorsement that is many rounds too old. It should fail in a block
+    (application or construction) but succeed in a mempool. *)
 let test_many_rounds_too_old () =
   let open Lwt_result_syntax in
   let* _genesis, b = init_genesis () in
   let* round5_block = Block.bake ~policy:(By_round 5) b in
   let* predecessor = Block.bake ~policy:(By_round 15) b in
-  Consensus_helpers.test_consensus_operation_all_modes
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block:round5_block
     ~predecessor
-    ~error:error_old_round
+    ~application_error:error_old_round
+    ~construction_error:error_old_round
+    ?mempool_error:None
     Endorsement
 
 let error_future_round = function
@@ -295,49 +304,59 @@ let error_future_round = function
       true
   | _ -> false
 
-(** Endorsement that is one round in the future. It should fail in all modes. *)
+(** Endorsement that is one round in the future. It should fail in a
+    block (application or construction) but succeed in a mempool. *)
 let test_one_round_in_the_future () =
   let open Lwt_result_syntax in
   let* _genesis, b = init_genesis () in
   let* predecessor = Block.bake b in
   let* round1_block = Block.bake ~policy:(By_round 1) b in
-  Consensus_helpers.test_consensus_operation_all_modes
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block:round1_block
     ~predecessor
-    ~error:error_future_round
+    ~application_error:error_future_round
+    ~construction_error:error_future_round
+    ?mempool_error:None
     Endorsement
 
-(** Endorsement that is many rounds in the future. It should fail in
-    all modes. *)
+(** Endorsement that is many rounds in the future. It should fail in a
+    block (application or construction) but succeed in a mempool. *)
 let test_many_rounds_future () =
   let open Lwt_result_syntax in
   let* _genesis, b = init_genesis () in
   let* predecessor = Block.bake ~policy:(By_round 5) b in
   let* round15_block = Block.bake ~policy:(By_round 15) b in
-  Consensus_helpers.test_consensus_operation_all_modes
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block:round15_block
     ~predecessor
-    ~error:error_future_round
+    ~application_error:error_future_round
+    ~construction_error:error_future_round
+    ?mempool_error:None
     Endorsement
 
 (** {2 Wrong payload hash} *)
 
-(** Endorsement with an incorrect payload hash. *)
+(** Endorsement with an incorrect payload hash. It should fail in a
+    block (application or construction) but succeed in a mempool. *)
 let test_wrong_payload_hash () =
   let open Lwt_result_syntax in
   let* _genesis, endorsed_block = init_genesis () in
-  Consensus_helpers.test_consensus_operation_all_modes
+  let error_wrong_payload_hash = function
+    | Validate_errors.Consensus.Wrong_payload_hash_for_consensus_operation
+        {kind; _}
+      when kind = Validate_errors.Consensus.Endorsement ->
+        true
+    | _ -> false
+  in
+  Consensus_helpers.test_consensus_operation_all_modes_different_outcomes
     ~loc:__LOC__
     ~endorsed_block
     ~block_payload_hash:Block_payload_hash.zero
-    ~error:(function
-      | Validate_errors.Consensus.Wrong_payload_hash_for_consensus_operation
-          {kind; _}
-        when kind = Validate_errors.Consensus.Endorsement ->
-          true
-      | _ -> false)
+    ~application_error:error_wrong_payload_hash
+    ~construction_error:error_wrong_payload_hash
+    ?mempool_error:None
     Endorsement
 
 (** {1 Conflict tests}
@@ -353,7 +372,11 @@ let assert_conflict_error ~loc res =
 
 (** Test that endorsements conflict with:
     - an identical endorsement, and
-    - an endorsement on the same block with a different branch. *)
+    - an endorsement on the same block with a different branch.
+
+    In mempool mode, also test that they conflict with an endorsement
+    on the same level and round but with a different payload hash
+    (such an endorsement is invalid in application and construction modes). *)
 let test_conflict () =
   let open Lwt_result_syntax in
   let* _genesis, b = init_genesis () in
@@ -376,11 +399,16 @@ let test_conflict () =
   in
   let* () = assert_mempool_conflict __LOC__ op in
   let* () = assert_mempool_conflict __LOC__ op_different_branch in
+  let* op_different_payload_hash =
+    Op.endorsement ~block_payload_hash:Block_payload_hash.zero b
+  in
+  let* () = assert_mempool_conflict __LOC__ op_different_payload_hash in
   return_unit
 
 (** In mempool mode, test that grandparent endorsements conflict with:
-    - an identical endorsement, and
-    - an endorsement on the same block with a different branch.
+    - an identical endorsement,
+    - an endorsement on the same block with a different branch, and
+    - an endorsement on the same block with a different payload hash.
 
     This test would make no sense in application or construction modes,
     since grandparent endorsements fail anyway (as can be observed in
@@ -393,6 +421,33 @@ let test_grandparent_conflict () =
   let* op_different_branch =
     Op.endorsement ~branch:Block_hash.zero grandparent
   in
+  let* op_different_payload_hash =
+    Op.endorsement ~block_payload_hash:Block_payload_hash.zero grandparent
+  in
+  let* inc = Incremental.begin_construction ~mempool_mode:true predecessor in
+  let* inc = Incremental.validate_operation inc op in
+  let assert_conflict loc tested_op =
+    Incremental.validate_operation inc tested_op >>= assert_conflict_error ~loc
+  in
+  let* () = assert_conflict __LOC__ op in
+  let* () = assert_conflict __LOC__ op_different_branch in
+  let* () = assert_conflict __LOC__ op_different_payload_hash in
+  return_unit
+
+(** In mempool mode, test that endorsements with the same future level
+    and same non-zero round conflict. This is not tested in application
+    and construction modes since such endorsements would be invalid. *)
+let test_future_level_conflict () =
+  let open Lwt_result_syntax in
+  let* _genesis, predecessor = init_genesis () in
+  let* future_block = Block.bake ~policy:(By_round 10) predecessor in
+  let* op = Op.endorsement future_block in
+  let* op_different_branch =
+    Op.endorsement ~branch:Block_hash.zero future_block
+  in
+  let* op_different_payload_hash =
+    Op.endorsement ~block_payload_hash:Block_payload_hash.zero future_block
+  in
   let* inc = Incremental.begin_construction ~mempool_mode:true predecessor in
   let* inc = Incremental.validate_operation inc op in
   let assert_conflict loc tested_op =
@@ -400,6 +455,7 @@ let test_grandparent_conflict () =
   in
   let* () = assert_conflict __LOC__ op in
   let* () = assert_conflict __LOC__ op_different_branch in
+  let* () = assert_conflict __LOC__ op_different_payload_hash in
   return_unit
 
 (** In mempool mode, test that there is no conflict between an
@@ -440,20 +496,41 @@ let test_no_conflict_with_preendorsement_block () =
   let* (_ : Block.t) = bake_both_ops Baking in
   return_unit
 
-(** In mempool mode, test that there is no conflict between a normal
-    endorsement (for the predecessor) and a grandparent endorsement,
-    both for the same slot (here the first slot). There is no similar
-    test in application and construction modes because grandparent
-    endorsements are not valid then. *)
-let test_no_conflict_with_grandparent () =
+(** In mempool mode, test that there is no conflict between
+    endorsements for the same slot (here the first slot) with various
+    allowed levels and rounds.
+
+    There are no similar tests in application and construction modes
+    because valid endorsements always have the same level and round. *)
+let test_no_conflict_various_levels_and_rounds () =
   let open Lwt_result_syntax in
-  let* _genesis, grandparent = init_genesis () in
+  let* genesis, grandparent = init_genesis () in
   let* predecessor = Block.bake grandparent in
-  let* op_normal = Op.endorsement predecessor in
-  let* op_grandparent = Op.endorsement grandparent in
+  let* future_block = Block.bake predecessor in
+  let* alt_grandparent = Block.bake ~policy:(By_round 1) genesis in
+  let* alt_predecessor = Block.bake ~policy:(By_round 1) grandparent in
+  let* alt_future = Block.bake ~policy:(By_round 10) alt_predecessor in
   let* inc = Incremental.begin_construction ~mempool_mode:true predecessor in
-  let* inc = Incremental.add_operation inc op_normal in
-  let* inc = Incremental.add_operation inc op_grandparent in
+  let add_endorsement inc endorsed_block =
+    let* (op : packed_operation) = Op.endorsement endorsed_block in
+    let (Operation_data protocol_data) = op.protocol_data in
+    let content =
+      match protocol_data.contents with
+      | Single (Endorsement content) -> content
+      | _ -> assert false
+    in
+    Format.eprintf
+      "level: %ld, round: %ld@."
+      (Raw_level.to_int32 content.level)
+      (Round.to_int32 content.round) ;
+    Incremental.add_operation inc op
+  in
+  let* inc = add_endorsement inc grandparent in
+  let* inc = add_endorsement inc predecessor in
+  let* inc = add_endorsement inc future_block in
+  let* inc = add_endorsement inc alt_grandparent in
+  let* inc = add_endorsement inc alt_predecessor in
+  let* inc = add_endorsement inc alt_future in
   let* _inc = Incremental.finalize_block inc in
   return_unit
 
@@ -520,6 +597,7 @@ let tests =
     (* Conflict tests (some negative, some positive) *)
     Tztest.tztest "Conflict" `Quick test_conflict;
     Tztest.tztest "Grandparent conflict" `Quick test_grandparent_conflict;
+    Tztest.tztest "Future level conflict" `Quick test_future_level_conflict;
     Tztest.tztest
       "No conflict with preendorsement (mempool)"
       `Quick
@@ -529,9 +607,9 @@ let tests =
       `Quick
       test_no_conflict_with_preendorsement_block;
     Tztest.tztest
-      "No conflict with grandparent endorsement"
+      "No conflict with various levels and rounds"
       `Quick
-      test_no_conflict_with_grandparent;
+      test_no_conflict_various_levels_and_rounds;
     (* Consensus threshold tests (one positive and one negative) *)
     Tztest.tztest
       "sufficient endorsement threshold"
diff --git a/src/proto_alpha/lib_protocol/test/integration/consensus/test_preendorsement.ml b/src/proto_alpha/lib_protocol/test/integration/consensus/test_preendorsement.ml
index 40b0695d7b54f4a6b3553bbfc3be88daac4085ba..88a60cead11f5a13f141d302aa91aad3dd710ff2 100644
--- a/src/proto_alpha/lib_protocol/test/integration/consensus/test_preendorsement.ml
+++ b/src/proto_alpha/lib_protocol/test/integration/consensus/test_preendorsement.ml
@@ -74,7 +74,8 @@ let test_consensus_operation_preendorsement_for_future_level () =
 
 (** Consensus operation for old level : apply a preendorsement with a level in the past *)
 let test_consensus_operation_preendorsement_for_old_level () =
-  init_genesis () >>=? fun (_genesis, pred) ->
+  init_genesis () >>=? fun (_genesis, grandparent) ->
+  Block.bake grandparent >>=? fun pred ->
   let raw_level = Raw_level.of_int32 (Int32.of_int 0) in
   let level = match raw_level with Ok l -> l | Error _ -> assert false in
   Consensus_helpers.test_consensus_operation
@@ -97,11 +98,6 @@ let test_consensus_operation_preendorsement_for_future_round () =
     ~loc:__LOC__
     ~endorsed_block:pred
     ~round
-    ~error:(function
-      | Validate_errors.Consensus.Consensus_operation_for_future_round {kind; _}
-        when kind = Validate_errors.Consensus.Preendorsement ->
-          true
-      | _ -> false)
     Preendorsement
     Mempool
 
@@ -113,11 +109,6 @@ let test_consensus_operation_preendorsement_for_old_round () =
     ~loc:__LOC__
     ~endorsed_block:pred
     ~round
-    ~error:(function
-      | Validate_errors.Consensus.Consensus_operation_for_old_round {kind; _}
-        when kind = Validate_errors.Consensus.Preendorsement ->
-          true
-      | _ -> false)
     Preendorsement
     Mempool
 
@@ -128,12 +119,6 @@ let test_consensus_operation_preendorsement_on_competing_proposal () =
     ~loc:__LOC__
     ~endorsed_block:pred
     ~block_payload_hash:Block_payload_hash.zero
-    ~error:(function
-      | Validate_errors.Consensus.Wrong_payload_hash_for_consensus_operation
-          {kind; _}
-        when kind = Validate_errors.Consensus.Preendorsement ->
-          true
-      | _ -> false)
     Preendorsement
     Mempool
 
diff --git a/src/proto_alpha/lib_protocol/test/integration/validate/test_mempool.ml b/src/proto_alpha/lib_protocol/test/integration/validate/test_mempool.ml
index 8174a9130213d15c62c5028ae2e21c9ed543bb2a..b4a3ca83dd5f82bb0898dd1b2b831894bf0cb5d3 100644
--- a/src/proto_alpha/lib_protocol/test/integration/validate/test_mempool.ml
+++ b/src/proto_alpha/lib_protocol/test/integration/validate/test_mempool.ml
@@ -47,8 +47,7 @@ let extract_values ctxt (b : Block.t) =
   in
   let predecessor_round = Fitness.round fitness in
   let predecessor_hash = b.header.shell.predecessor in
-  let grandparent_round = Fitness.predecessor_round fitness in
-  (predecessor_level, predecessor_round, predecessor_hash, grandparent_round)
+  (predecessor_level, predecessor_round, predecessor_hash)
 
 let op_with_hash op = (Operation.hash_packed op, op)
 
@@ -102,8 +101,7 @@ let test_simple () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let vs, mempool =
@@ -113,7 +111,6 @@ let test_simple () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   let* op1 = Op.transaction (B block) c1 c2 Tez.one_cent in
   let op1 = op_with_hash op1 in
@@ -137,8 +134,7 @@ let test_imcompatible_mempool () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let (_vs : Mempool.validation_info), mempool1 =
@@ -148,7 +144,6 @@ let test_imcompatible_mempool () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   (* Create a second mempool on a different block *)
   let* block2 = Block.bake block in
@@ -156,8 +151,7 @@ let test_imcompatible_mempool () =
     let+ incr = Incremental.begin_construction block2 in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash2, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash2 =
     extract_values ctxt2 block2
   in
   let (_vs : Mempool.validation_info), mempool2 =
@@ -167,7 +161,6 @@ let test_imcompatible_mempool () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash:predecessor_hash2
-      ~grandparent_round
   in
   let () =
     match Mempool.merge mempool1 mempool2 with
@@ -188,8 +181,7 @@ let test_merge () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let vs, mempool_i =
@@ -199,7 +191,6 @@ let test_merge () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   (* Build two mempool with a conflicting operation and check that the
      merge fails and succeeds when a conflict handler is provided *)
@@ -283,8 +274,7 @@ let test_add_invalid_operation () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let vs, mempool_i =
@@ -294,7 +284,6 @@ let test_add_invalid_operation () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   let* op1 = Op.transaction (B block) c1 c1 ~gas_limit:Zero Tez.one_cent in
   let op1 = op_with_hash op1 in
@@ -311,8 +300,7 @@ let test_add_and_replace () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let info, mempool_i =
@@ -322,7 +310,6 @@ let test_add_and_replace () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   (* Try adding a conflicting operation using both handler strategy *)
   let* op1 = Op.transaction (B block) c1 c2 Tez.one_cent in
@@ -366,8 +353,7 @@ let test_remove_operation () =
     let+ incr = Incremental.begin_construction block in
     Incremental.alpha_ctxt incr
   in
-  let predecessor_level, predecessor_round, predecessor_hash, grandparent_round
-      =
+  let predecessor_level, predecessor_round, predecessor_hash =
     extract_values ctxt block
   in
   let info, mempool_i =
@@ -377,7 +363,6 @@ let test_remove_operation () =
       ~predecessor_level
       ~predecessor_round
       ~predecessor_hash
-      ~grandparent_round
   in
   let* op1 = Op.transaction (B block) c1 c2 Tez.one_cent in
   let op1 = op_with_hash op1 in
diff --git a/src/proto_alpha/lib_protocol/validate.ml b/src/proto_alpha/lib_protocol/validate.ml
index 10515348a5b82bc56a2a0fb9710e66c76e877406..b612393f3aa1a503133112e4812fca94be0ca2c2 100644
--- a/src/proto_alpha/lib_protocol/validate.ml
+++ b/src/proto_alpha/lib_protocol/validate.ml
@@ -41,90 +41,63 @@ let init_consensus_info ctxt (predecessor_level, predecessor_round) =
     endorsement_slot_map = Consensus.allowed_endorsements ctxt;
   }
 
-module Consensus_content_map = Map.Make (struct
-  type t = consensus_content
-
-  let compare {slot; level; round; block_payload_hash}
-      {
-        slot = slot';
-        level = level';
-        round = round';
-        block_payload_hash = block_payload_hash';
-      } =
-    Compare.or_else (Raw_level.compare level level') @@ fun () ->
-    Compare.or_else (Slot.compare slot slot') @@ fun () ->
-    Compare.or_else (Round.compare round round') @@ fun () ->
-    Compare.or_else
-      (Block_payload_hash.compare block_payload_hash block_payload_hash')
-    @@ fun () -> 0
+(** Map used to detect consensus operation conflicts. Each delegate
+    may (pre)endorse at most once for each level and round, so two
+    endorsements (resp. two preendorsements) conflict when they have
+    the same slot, level, and round.
+
+    Note that when validating a block, all endorsements (resp. all
+    preendorsements) must have the same level and round anyway, so only
+    the slot is relevant. Taking the level and round into account is
+    useful in mempool mode, because we want to be able to accept and
+    propagate consensus operations for multiple close
+    past/future/cousin blocks. *)
+module Consensus_conflict_map = Map.Make (struct
+  type t = Slot.t * Raw_level.t * Round.t
+
+  let compare (slot1, level1, round1) (slot2, level2, round2) =
+    Compare.or_else (Raw_level.compare level1 level2) @@ fun () ->
+    Compare.or_else (Slot.compare slot1 slot2) @@ fun () ->
+    Round.compare round1 round2
 end)
 
 type consensus_state = {
-  (* The [predecessor_level] is needed here, despite being also in
-     {!consensus_info}, because it allows to identify grandparent
-     endorsements in [check_endorsement_conflict] where we only have
-     access to the [consensus_state]. *)
-  predecessor_level : Raw_level.t;
-  preendorsements_seen : Operation_hash.t Slot.Map.t;
-  endorsements_seen : Operation_hash.t Slot.Map.t;
-  grandparent_endorsements_seen : Operation_hash.t Slot.Map.t;
+  preendorsements_seen : Operation_hash.t Consensus_conflict_map.t;
+  endorsements_seen : Operation_hash.t Consensus_conflict_map.t;
   dal_attestation_seen : Operation_hash.t Signature.Public_key_hash.Map.t;
 }
 
-let slot_map_encoding element_encoding =
+let consensus_conflict_map_encoding =
   let open Data_encoding in
   conv
-    (fun slot_map -> Slot.Map.bindings slot_map)
-    (fun l -> Slot.Map.(List.fold_left (fun m (k, v) -> add k v m) empty l))
-    (list (tup2 Slot.encoding element_encoding))
+    (fun map -> Consensus_conflict_map.bindings map)
+    (fun l ->
+      Consensus_conflict_map.(
+        List.fold_left (fun m (k, v) -> add k v m) empty l))
+    (list
+       (tup2
+          (tup3 Slot.encoding Raw_level.encoding Round.encoding)
+          Operation_hash.encoding))
 
 let consensus_state_encoding =
   let open Data_encoding in
   def "consensus_state"
   @@ conv
-       (fun {
-              predecessor_level;
-              preendorsements_seen;
-              endorsements_seen;
-              grandparent_endorsements_seen;
-              dal_attestation_seen;
-            } ->
-         ( predecessor_level,
-           preendorsements_seen,
-           endorsements_seen,
-           grandparent_endorsements_seen,
-           dal_attestation_seen ))
-       (fun ( predecessor_level,
-              preendorsements_seen,
-              endorsements_seen,
-              grandparent_endorsements_seen,
-              dal_attestation_seen ) ->
-         {
-           predecessor_level;
-           preendorsements_seen;
-           endorsements_seen;
-           grandparent_endorsements_seen;
-           dal_attestation_seen;
-         })
-       (obj5
-          (req "predecessor_level" Raw_level.encoding)
-          (req
-             "preendorsements_seen"
-             (slot_map_encoding Operation_hash.encoding))
-          (req "endorsements_seen" (slot_map_encoding Operation_hash.encoding))
-          (req
-             "grandparent_endorsements_seen"
-             (slot_map_encoding Operation_hash.encoding))
+       (fun {preendorsements_seen; endorsements_seen; dal_attestation_seen} ->
+         (preendorsements_seen, endorsements_seen, dal_attestation_seen))
+       (fun (preendorsements_seen, endorsements_seen, dal_attestation_seen) ->
+         {preendorsements_seen; endorsements_seen; dal_attestation_seen})
+       (obj3
+          (req "preendorsements_seen" consensus_conflict_map_encoding)
+          (req "endorsements_seen" consensus_conflict_map_encoding)
           (req
              "dal_attestation_seen"
              (Signature.Public_key_hash.Map.encoding Operation_hash.encoding)))
 
-let init_consensus_state ~predecessor_level =
+let empty_consensus_state =
   {
-    predecessor_level;
-    preendorsements_seen = Slot.Map.empty;
-    endorsements_seen = Slot.Map.empty;
-    grandparent_endorsements_seen = Slot.Map.empty;
+    preendorsements_seen = Consensus_conflict_map.empty;
+    endorsements_seen = Consensus_conflict_map.empty;
     dal_attestation_seen = Signature.Public_key_hash.Map.empty;
   }
 
@@ -339,14 +312,6 @@ type construction_info = {
   header_contents : Block_header.contents;
 }
 
-(** Information needed to validate grandparent endorsements in
-    [Mempool] mode. *)
-type grandparent = {
-  round : Round.t;
-  hash : Block_hash.t;
-  payload_hash : Block_payload_hash.t;
-}
-
 (** Circumstances in which operations are validated, and corresponding
     specific information.
 
@@ -364,13 +329,10 @@ type mode =
           consensus operations are validated in this mode. *)
   | Construction of construction_info
       (** Used for the construction of a new block. *)
-  | Mempool of grandparent option
+  | Mempool
       (** Used by the mempool ({!module:Mempool_validation}) and by the
           [Partial_construction] mode in {!module:Main}, which may itself be
-          used by RPCs or by another mempool implementation.
-
-          If the option is [None], it means that there cannot be any
-          grandparent endorsements. *)
+          used by RPCs or by another mempool implementation. *)
 
 (** {2 Definition and initialization of [info] and [state]} *)
 
@@ -444,9 +406,9 @@ let empty_voting_state =
     ballots_seen = Signature.Public_key_hash.Map.empty;
   }
 
-let init_operation_conflict_state ~predecessor_level =
+let empty_operation_conflict_state =
   {
-    consensus_state = init_consensus_state ~predecessor_level;
+    consensus_state = empty_consensus_state;
     voting_state = empty_voting_state;
     anonymous_state = empty_anonymous_state;
     manager_state = empty_manager_state;
@@ -477,9 +439,9 @@ module Consensus = struct
       Tez.(frozen_deposits.current_amount > zero)
       (Zero_frozen_deposits delegate_pkh)
 
-  let get_delegate_details slot_map kind consensus_content =
+  let get_delegate_details slot_map kind slot =
     Result.of_option
-      (Slot.Map.find consensus_content.slot slot_map)
+      (Slot.Map.find slot slot_map)
       ~error:(trace_of_error (Wrong_slot_used_for_consensus_operation {kind}))
 
   (** When validating a block (ie. in [Application],
@@ -512,31 +474,43 @@ module Consensus = struct
       (Block_payload_hash.equal expected provided)
       (Wrong_payload_hash_for_consensus_operation {kind; expected; provided})
 
-  (** Check the preendorsement features for both [Application] and
-      [Partial_validation] modes. *)
-  let check_preendorsement_content_preexisting_block vi block_info
-      {level; round; block_payload_hash; _} =
-    let open Result_syntax in
-    let* locked_round =
+  (** Preendorsement checks for both [Application] and
+      [Partial_validation] modes.
+
+      Return the slot owner's consensus key and voting power. *)
+  let check_preexisting_block_preendorsement vi consensus_info block_info
+      {level; round; block_payload_hash = bph; slot} =
+    let open Lwt_result_syntax in
+    let*? locked_round =
       match block_info.locked_round with
-      | Some locked_round -> return locked_round
+      | Some locked_round -> ok locked_round
       | None ->
           (* A preexisting block whose fitness has no locked round
              should contain no preendorsements. *)
           error Unexpected_preendorsement_in_block
     in
     let kind = Preendorsement in
-    let* () = check_round_before_block ~block_round:block_info.round round in
-    let* () = check_level kind vi.current_level.level level in
-    let* () = check_round kind locked_round round in
+    let*? () = check_round_before_block ~block_round:block_info.round round in
+    let*? () = check_level kind vi.current_level.level level in
+    let*? () = check_round kind locked_round round in
     let expected_payload_hash = block_info.header_contents.payload_hash in
-    check_payload_hash kind expected_payload_hash block_payload_hash
+    let*? () = check_payload_hash kind expected_payload_hash bph in
+    let*? consensus_key, voting_power =
+      get_delegate_details consensus_info.preendorsement_slot_map kind slot
+    in
+    let* () =
+      check_frozen_deposits_are_positive vi.ctxt consensus_key.delegate
+    in
+    return (consensus_key, voting_power)
 
-  let check_preendorsement_content_construction vi cons_info
-      {level; round; block_payload_hash; _} =
-    let open Result_syntax in
+  (** Preendorsement checks for Construction mode.
+
+      Return the slot owner's consensus key and voting power. *)
+  let check_constructed_block_preendorsement vi consensus_info cons_info
+      {level; round; block_payload_hash = bph; slot} =
+    let open Lwt_result_syntax in
     let expected_payload_hash = cons_info.header_contents.payload_hash in
-    let* () =
+    let*? () =
       (* When the proposal is fresh, a fake [payload_hash] of [zero]
          has been provided. In this case, the block should not contain
          any preendorsements. *)
@@ -545,27 +519,77 @@ module Consensus = struct
         Unexpected_preendorsement_in_block
     in
     let kind = Preendorsement in
-    let* () = check_round_before_block ~block_round:cons_info.round round in
-    let* () = check_level kind vi.current_level.level level in
+    let*? () = check_round_before_block ~block_round:cons_info.round round in
+    let*? () = check_level kind vi.current_level.level level in
     (* We cannot check the exact round here in construction mode, because
        there is no preexisting fitness to provide the locked_round. We do
        however check that all preendorments have the same round in
        [check_construction_preendorsement_round_consistency] further below. *)
-    check_payload_hash kind expected_payload_hash block_payload_hash
-
-  let check_preendorsement_content_mempool vi (consensus_info : consensus_info)
-      {level; round; block_payload_hash; _} =
-    let open Result_syntax in
-    let kind = Preendorsement in
-    match Consensus.endorsement_branch vi.ctxt with
-    | None ->
-        let expected = consensus_info.predecessor_level in
-        let provided = level in
+    let*? () = check_payload_hash kind expected_payload_hash bph in
+    let*? consensus_key, voting_power =
+      get_delegate_details consensus_info.preendorsement_slot_map kind slot
+    in
+    let* () =
+      check_frozen_deposits_are_positive vi.ctxt consensus_key.delegate
+    in
+    return (consensus_key, voting_power)
+
+  (** Preendorsement/endorsement checks for Mempool mode.
+
+      We want this mode to be very permissive, to allow the mempool to
+      accept and propagate consensus operations even if they point to a
+      block which is not known to the mempool (e.g. because the block
+      has just been validated and the mempool has not had time to
+      switch its head to it yet, or because the block belongs to a
+      cousin branch). Therefore, we do not check the round nor the
+      payload, which may correspond to blocks that we do not know of
+      yet. As to the level, we only require it to be the
+      [predecessor_level] (aka the level of the mempool's head) plus or
+      minus one, that is:
+      [predecessor_level - 1 <= op_level <= predecessor_level + 1]
+      (note that [predecessor_level + 1] is also known as [current_level]).
+
+      Return the slot owner's consensus key and voting power (the
+      latter may be fake because it doesn't matter in Mempool mode, but
+      it is included to mirror the check_..._block_preendorsement
+      functions). *)
+  let check_mempool_consensus vi consensus_info kind {level; slot; _} =
+    let open Lwt_result_syntax in
+    let*? () =
+      if Raw_level.(succ level < consensus_info.predecessor_level) then
+        let expected = consensus_info.predecessor_level and provided = level in
+        error (Consensus_operation_for_old_level {kind; expected; provided})
+      else if Raw_level.(level > vi.current_level.level) then
+        let expected = consensus_info.predecessor_level and provided = level in
         error (Consensus_operation_for_future_level {kind; expected; provided})
-    | Some (_, expected_payload_hash) ->
-        let* () = check_level kind consensus_info.predecessor_level level in
-        let* () = check_round kind consensus_info.predecessor_round round in
-        check_payload_hash kind expected_payload_hash block_payload_hash
+      else ok_unit
+    in
+    if Raw_level.(level = consensus_info.predecessor_level) then
+      (* The operation points to the mempool head's level, which is
+         the level for which slot maps have been pre-computed. *)
+      let slot_map =
+        match kind with
+        | Preendorsement -> consensus_info.preendorsement_slot_map
+        | Endorsement -> consensus_info.endorsement_slot_map
+        | Dal_attestation -> assert false
+      in
+      Lwt.return (get_delegate_details slot_map kind slot)
+    else
+      (* We don't have a pre-computed slot map for the operation's
+         level, so we retrieve the key directly from the context. We
+         return a fake voting power since it won't be used anyway in
+         Mempool mode. *)
+      let* (_ctxt : t), consensus_key =
+        Stake_distribution.slot_owner
+          vi.ctxt
+          (Level.from_raw vi.ctxt level)
+          slot
+      in
+      return (consensus_key, 0 (* Fake voting power *))
+  (* We do not check that the frozen deposits are positive because this
+     only needs to be true in the context of a block that actually
+     contains the operation, which may not be the same as the current
+     mempool's context. *)
 
   let check_preendorsement vi ~check_signature
       (operation : Kind.preendorsement operation) =
@@ -578,33 +602,27 @@ module Consensus = struct
     let (Single (Preendorsement consensus_content)) =
       operation.protocol_data.contents
     in
-    let*? () =
+    let* consensus_key, voting_power =
       match vi.mode with
       | Application block_info | Partial_validation block_info ->
-          check_preendorsement_content_preexisting_block
+          check_preexisting_block_preendorsement
             vi
+            consensus_info
             block_info
             consensus_content
       | Construction construction_info ->
-          check_preendorsement_content_construction
+          check_constructed_block_preendorsement
             vi
+            consensus_info
             construction_info
             consensus_content
-      | Mempool _ ->
-          check_preendorsement_content_mempool
+      | Mempool ->
+          check_mempool_consensus
             vi
             consensus_info
+            Preendorsement
             consensus_content
     in
-    let*? consensus_key, voting_power =
-      get_delegate_details
-        consensus_info.preendorsement_slot_map
-        Preendorsement
-        consensus_content
-    in
-    let* () =
-      check_frozen_deposits_are_positive vi.ctxt consensus_key.delegate
-    in
     let*? () =
       if check_signature then
         Operation.check_signature
@@ -617,12 +635,12 @@ module Consensus = struct
 
   let check_preendorsement_conflict vs oph (op : Kind.preendorsement operation)
       =
-    let (Single (Preendorsement consensus_content)) =
+    let (Single (Preendorsement {slot; level; round; _})) =
       op.protocol_data.contents
     in
     match
-      Slot.Map.find_opt
-        consensus_content.slot
+      Consensus_conflict_map.find_opt
+        (slot, level, round)
         vs.consensus_state.preendorsements_seen
     with
     | Some existing ->
@@ -637,12 +655,12 @@ module Consensus = struct
             Conflicting_consensus_operation {kind = Preendorsement; conflict})
 
   let add_preendorsement vs oph (op : Kind.preendorsement operation) =
-    let (Single (Preendorsement consensus_content)) =
+    let (Single (Preendorsement {slot; level; round; _})) =
       op.protocol_data.contents
     in
     let preendorsements_seen =
-      Slot.Map.add
-        consensus_content.slot
+      Consensus_conflict_map.add
+        (slot, level, round)
         oph
         vs.consensus_state.preendorsements_seen
     in
@@ -652,7 +670,7 @@ module Consensus = struct
       (consensus_content : consensus_content) voting_power =
     let locked_round_evidence =
       match mode with
-      | Mempool _ -> (* The block_state is not relevant in this mode. *) None
+      | Mempool -> (* The block_state is not relevant in this mode. *) None
       | Application _ | Partial_validation _ | Construction _ -> (
           match block_state.locked_round_evidence with
           | None -> Some (consensus_content.round, voting_power)
@@ -671,185 +689,45 @@ module Consensus = struct
   let remove_preendorsement vs (operation : Kind.preendorsement operation) =
     (* As we are in mempool mode, we do not update
        [locked_round_evidence]. *)
-    let (Single (Preendorsement consensus_content)) =
+    let (Single (Preendorsement {slot; level; round; _})) =
       operation.protocol_data.contents
     in
     let preendorsements_seen =
-      Slot.Map.remove
-        consensus_content.slot
+      Consensus_conflict_map.remove
+        (slot, level, round)
         vs.consensus_state.preendorsements_seen
     in
     {vs with consensus_state = {vs.consensus_state with preendorsements_seen}}
 
-  (** Validate an endorsement pointing to the grandparent block. This
-      function will only be called in [Mempool] mode. *)
-  let check_grandparent_endorsement vi ~check_signature grandparent
-      (operation : _ operation) {level; round; block_payload_hash = bph; slot} =
-    let open Lwt_result_syntax in
-    let* (_ctxt : t), consensus_key =
-      Stake_distribution.slot_owner vi.ctxt (Level.from_raw vi.ctxt level) slot
-    in
-    let kind = Grandparent_endorsement in
-    (* This function is only called on endorsements whose level is the
-       grandparent's, so there is no need to check the level. *)
-    let*? () = check_round kind grandparent.round round in
-    let*? () = check_payload_hash kind grandparent.payload_hash bph in
-    let*? () =
-      if check_signature then
-        Operation.check_signature
-          consensus_key.consensus_pk
-          vi.chain_id
-          operation
-      else ok_unit
-    in
-    return_unit
-
-  let add_grandparent_endorsement vs oph (consensus_content : consensus_content)
-      =
-    {
-      vs with
-      consensus_state =
-        {
-          vs.consensus_state with
-          grandparent_endorsements_seen =
-            Slot.Map.add
-              consensus_content.slot
-              oph
-              vs.consensus_state.grandparent_endorsements_seen;
-        };
-    }
-
-  let check_grandparent_endorsement_conflict vs oph
-      (consensus_content : consensus_content) =
-    match
-      Slot.Map.find_opt
-        consensus_content.slot
-        vs.consensus_state.grandparent_endorsements_seen
-    with
-    | None -> ok_unit
-    | Some existing ->
-        Error (Operation_conflict {existing; new_operation = oph})
-
-  let remove_grandparent_endorsement vs (consensus_content : consensus_content)
-      =
-    let grandparent_endorsements_seen =
-      Slot.Map.remove
-        consensus_content.slot
-        vs.consensus_state.grandparent_endorsements_seen
-    in
-    {
-      vs with
-      consensus_state = {vs.consensus_state with grandparent_endorsements_seen};
-    }
-
-  type endorsement_kind = Grandparent_endorsement | Normal_endorsement of int
-
-  (** Retrieve the expected branch and payload_hash for endorsements
-      from the context.
+  (** Endorsement checks for all modes that involve a block:
+      Application, Partial_validation, and Construction.
 
-      [Consensus.endorsement_branch] only returns [None] when the
-      predecessor is the protocol activation block, which is always
-      considered final and should not be endorsed. In that case, return
-      an error depending on the mode. *)
-  let expected_payload_hash vi (consensus_info : consensus_info) op_level =
-    match Consensus.endorsement_branch vi.ctxt with
-    | Some branch_and_payload_hash -> ok branch_and_payload_hash
-    | None ->
-        error
-          (match vi.mode with
-          | Application _ | Partial_validation _ | Construction _ ->
-              (* The block should not contain any endorsements. The
-                 validation of the endorsement fails, and so will the
-                 validation of the whole block. *)
-              Unexpected_endorsement_in_block
-          | Mempool _ ->
-              (* The block that will be built on top on the mempool head
-                 should contain no endorsements, and this is not a
-                 grandparent endorsement (otherwise
-                 [check_normal_endorsement] would not have been called). It
-                 is probably an early endorsement for the next level, hence
-                 the error (and even if this is not the case, hopefully the
-                 levels recorded in the error will provide a hint to what
-                 happened). *)
-              Consensus_operation_for_future_level
-                {
-                  kind = Endorsement;
-                  expected = consensus_info.predecessor_level;
-                  provided = op_level;
-                })
-
-  (** Validate an endorsement pointing to the predecessor, aka a
-      "normal" endorsement. Only this kind of endorsement may be found
-      during block validation or construction (ie. [Application],
-      [Partial_validation], or [Construction] modes). *)
-  let check_normal_endorsement vi consensus_info ~check_signature
-      (operation : Kind.endorsement operation) =
+      Return the slot owner's consensus key and voting power. *)
+  let check_block_endorsement vi consensus_info
+      {level; round; block_payload_hash = bph; slot} =
     let open Lwt_result_syntax in
-    let (Single (Endorsement consensus_content)) =
-      operation.protocol_data.contents
-    in
-    let {level; round; block_payload_hash = bph; _} = consensus_content in
-    let*? _expected_branch, expected_payload_hash =
-      expected_payload_hash vi consensus_info level
+    let*? expected_payload_hash =
+      match Consensus.endorsement_branch vi.ctxt with
+      | Some ((_branch : Block_hash.t), payload_hash) -> ok payload_hash
+      | None ->
+          (* [Consensus.endorsement_branch] only returns [None] when the
+             predecessor is the block that activates the first protocol
+             of the Tenderbake family; this block should not be
+             endorsed. This can only happen in tests and test
+             networks. *)
+          error Unexpected_endorsement_in_block
     in
     let kind = Endorsement in
     let*? () = check_level kind consensus_info.predecessor_level level in
     let*? () = check_round kind consensus_info.predecessor_round round in
     let*? () = check_payload_hash kind expected_payload_hash bph in
     let*? consensus_key, voting_power =
-      get_delegate_details
-        consensus_info.endorsement_slot_map
-        kind
-        consensus_content
+      get_delegate_details consensus_info.endorsement_slot_map kind slot
     in
     let* () =
       check_frozen_deposits_are_positive vi.ctxt consensus_key.delegate
     in
-    let*? () =
-      if check_signature then
-        Operation.check_signature
-          consensus_key.consensus_pk
-          vi.chain_id
-          operation
-      else ok_unit
-    in
-    return voting_power
-
-  let check_normal_endorsement_conflict vs oph
-      (consensus_content : consensus_content) =
-    match
-      Slot.Map.find_opt
-        consensus_content.slot
-        vs.consensus_state.endorsements_seen
-    with
-    | None -> ok_unit
-    | Some existing ->
-        Error (Operation_conflict {existing; new_operation = oph})
-
-  let add_normal_endorsement vs oph (consensus_content : consensus_content) =
-    {
-      vs with
-      consensus_state =
-        {
-          vs.consensus_state with
-          endorsements_seen =
-            Slot.Map.add
-              consensus_content.slot
-              oph
-              vs.consensus_state.endorsements_seen;
-        };
-    }
-
-  (* Hypothesis: this function will only be called in mempool mode *)
-  let remove_normal_endorsement vs (consensus_content : consensus_content) =
-    (* We do not remove the endorsement power because it is not
-       relevant for the mempool mode. *)
-    let endorsements_seen =
-      Slot.Map.remove
-        consensus_content.slot
-        vs.consensus_state.endorsements_seen
-    in
-    {vs with consensus_state = {vs.consensus_state with endorsements_seen}}
+    return (consensus_key, voting_power)
 
   let check_endorsement vi ~check_signature
       (operation : Kind.endorsement operation) =
@@ -862,37 +740,40 @@ module Consensus = struct
     let (Single (Endorsement consensus_content)) =
       operation.protocol_data.contents
     in
-    match vi.mode with
-    | Mempool (Some grandparent)
-      when Raw_level.(
-             succ consensus_content.level = consensus_info.predecessor_level) ->
-        let* () =
-          check_grandparent_endorsement
+    let* consensus_key, voting_power =
+      match vi.mode with
+      | Application _ | Partial_validation _ | Construction _ ->
+          check_block_endorsement vi consensus_info consensus_content
+      | Mempool ->
+          check_mempool_consensus
             vi
-            ~check_signature
-            grandparent
-            operation
-            (consensus_content : consensus_content)
-        in
-        return Grandparent_endorsement
-    | _ ->
-        let* voting_power =
-          check_normal_endorsement vi consensus_info ~check_signature operation
-        in
-        return (Normal_endorsement voting_power)
-
-  let is_normal_endorsement_assuming_valid vs
-      (consensus_content : consensus_content) =
-    Raw_level.equal vs.consensus_state.predecessor_level consensus_content.level
+            consensus_info
+            Endorsement
+            consensus_content
+    in
+    let*? () =
+      if check_signature then
+        Operation.check_signature
+          consensus_key.consensus_pk
+          vi.chain_id
+          operation
+      else ok_unit
+    in
+    return voting_power
 
   let check_endorsement_conflict vs oph (operation : Kind.endorsement operation)
       =
-    let (Single (Endorsement consensus_content)) =
+    let (Single (Endorsement {slot; level; round; _})) =
       operation.protocol_data.contents
     in
-    if is_normal_endorsement_assuming_valid vs consensus_content then
-      check_normal_endorsement_conflict vs oph consensus_content
-    else check_grandparent_endorsement_conflict vs oph consensus_content
+    match
+      Consensus_conflict_map.find_opt
+        (slot, level, round)
+        vs.consensus_state.endorsements_seen
+    with
+    | None -> ok_unit
+    | Some existing ->
+        Error (Operation_conflict {existing; new_operation = oph})
 
   let wrap_endorsement_conflict = function
     | Ok () -> ok_unit
@@ -901,28 +782,40 @@ module Consensus = struct
           Validate_errors.Consensus.(
             Conflicting_consensus_operation {kind = Endorsement; conflict})
 
-  let add_endorsement vs oph (op : Kind.endorsement operation) endorsement_kind
-      =
-    let (Single (Endorsement consensus_content)) = op.protocol_data.contents in
-    match endorsement_kind with
-    | Grandparent_endorsement ->
-        add_grandparent_endorsement vs oph consensus_content
-    | Normal_endorsement _voting_power ->
-        add_normal_endorsement vs oph consensus_content
-
-  let may_update_endorsement_power block_state = function
-    | Grandparent_endorsement -> block_state
-    | Normal_endorsement voting_power ->
+  let add_endorsement vs oph (op : Kind.endorsement operation) =
+    let (Single (Endorsement {slot; level; round; _})) =
+      op.protocol_data.contents
+    in
+    let endorsements_seen =
+      Consensus_conflict_map.add
+        (slot, level, round)
+        oph
+        vs.consensus_state.endorsements_seen
+    in
+    {vs with consensus_state = {vs.consensus_state with endorsements_seen}}
+
+  let may_update_endorsement_power vi block_state voting_power =
+    match vi.mode with
+    | Mempool -> (* The block_state is not relevant. *) block_state
+    | Application _ | Partial_validation _ | Construction _ ->
         {
           block_state with
           endorsement_power = block_state.endorsement_power + voting_power;
         }
 
-  let remove_endorsement vs (op : Kind.endorsement operation) =
-    let (Single (Endorsement consensus_content)) = op.protocol_data.contents in
-    if is_normal_endorsement_assuming_valid vs consensus_content then
-      remove_normal_endorsement vs consensus_content
-    else remove_grandparent_endorsement vs consensus_content
+  (* Hypothesis: this function will only be called in mempool mode *)
+  let remove_endorsement vs (operation : Kind.endorsement operation) =
+    (* We do not remove the endorsement power because it is not
+       relevant for the mempool mode. *)
+    let (Single (Endorsement {slot; level; round; _})) =
+      operation.protocol_data.contents
+    in
+    let endorsements_seen =
+      Consensus_conflict_map.remove
+        (slot, level, round)
+        vs.consensus_state.endorsements_seen
+    in
+    {vs with consensus_state = {vs.consensus_state with endorsements_seen}}
 
   let check_dal_attestation vi (operation : Kind.dal_attestation operation) =
     (* DAL/FIXME https://gitlab.com/tezos/tezos/-/issues/3115
@@ -1014,7 +907,7 @@ module Consensus = struct
             (* Other preendorsements have already been validated: we check
                that the current operation has the same round as them. *)
             check_round Preendorsement expected consensus_content.round)
-    | Application _ | Partial_validation _ | Mempool _ -> return_unit
+    | Application _ | Partial_validation _ | Mempool -> return_unit
 
   let validate_preendorsement ~check_signature info operation_state block_state
       oph (operation : Kind.preendorsement operation) =
@@ -1047,13 +940,13 @@ module Consensus = struct
   let validate_endorsement ~check_signature info operation_state block_state oph
       operation =
     let open Lwt_result_syntax in
-    let* kind = check_endorsement info ~check_signature operation in
+    let* power = check_endorsement info ~check_signature operation in
     let*? () =
       check_endorsement_conflict operation_state oph operation
       |> wrap_endorsement_conflict
     in
-    let block_state = may_update_endorsement_power block_state kind in
-    let operation_state = add_endorsement operation_state oph operation kind in
+    let block_state = may_update_endorsement_power info block_state power in
+    let operation_state = add_endorsement operation_state oph operation in
     return {info; operation_state; block_state}
 end
 
@@ -2219,7 +2112,7 @@ module Manager = struct
   let may_trace_gas_limit_too_high info =
     match info.mode with
     | Application _ | Partial_validation _ | Construction _ -> fun x -> x
-    | Mempool _ ->
+    | Mempool ->
         (* [Gas.check_limit] will only
            raise a "temporary" error, however when
            {!validate_operation} is called on a batch in isolation
@@ -2436,7 +2329,7 @@ module Manager = struct
           Gas.Arith.(sub block_state.remaining_block_gas operation_gas_used)
         in
         {block_state with remaining_block_gas}
-    | Mempool _ -> block_state
+    | Mempool -> block_state
 
   let remove_manager_operation (type kind) vs
       (operation : kind Kind.manager operation) =
@@ -2474,15 +2367,7 @@ end
 
 let init_validation_state ctxt mode chain_id ~predecessor_level_and_round =
   let info = init_info ctxt mode chain_id ~predecessor_level_and_round in
-  let predecessor_level =
-    match predecessor_level_and_round with
-    | Some (predecessor_level, _) -> predecessor_level
-    | None ->
-        (* Fake predecessor level that will not be used since the
-           validation of all consensus operations will fail. *)
-        info.current_level.level
-  in
-  let operation_state = init_operation_conflict_state ~predecessor_level in
+  let operation_state = empty_operation_conflict_state in
   let block_state = init_block_state info in
   {info; operation_state; block_state}
 
@@ -2617,17 +2502,11 @@ let begin_full_construction ctxt chain_id ~predecessor_level ~predecessor_round
   return validation_state
 
 let begin_partial_construction ctxt chain_id ~predecessor_level
-    ~predecessor_round ~grandparent_round =
-  let grandparent =
-    Option.map
-      (fun (hash, payload_hash) ->
-        {round = grandparent_round; hash; payload_hash})
-      (Alpha_context.Consensus.grand_parent_branch ctxt)
-  in
+    ~predecessor_round =
   let validation_state =
     init_validation_state
       ctxt
-      (Mempool grandparent)
+      Mempool
       chain_id
       ~predecessor_level_and_round:
         (Some (predecessor_level.Level.level, predecessor_round))
@@ -2635,11 +2514,7 @@ let begin_partial_construction ctxt chain_id ~predecessor_level
   validation_state
 
 let begin_no_predecessor_info ctxt chain_id =
-  init_validation_state
-    ctxt
-    (Mempool None)
-    chain_id
-    ~predecessor_level_and_round:None
+  init_validation_state ctxt Mempool chain_id ~predecessor_level_and_round:None
 
 let check_operation ?(check_signature = true) info (type kind)
     (operation : kind operation) : unit tzresult Lwt.t =
@@ -2651,7 +2526,7 @@ let check_operation ?(check_signature = true) info (type kind)
       in
       return_unit
   | Single (Endorsement _) ->
-      let* (_kind : Consensus.endorsement_kind) =
+      let* (_voting_power : int) =
         Consensus.check_endorsement info ~check_signature operation
       in
       return_unit
@@ -2769,20 +2644,8 @@ let add_valid_operation operation_conflict_state oph (type kind)
   match operation.protocol_data.contents with
   | Single (Preendorsement _) ->
       Consensus.add_preendorsement operation_conflict_state oph operation
-  | Single (Endorsement consensus_content) ->
-      let endorsement_kind =
-        if
-          Consensus.is_normal_endorsement_assuming_valid
-            operation_conflict_state
-            consensus_content
-        then Consensus.Normal_endorsement 0
-        else Grandparent_endorsement
-      in
-      Consensus.add_endorsement
-        operation_conflict_state
-        oph
-        operation
-        endorsement_kind
+  | Single (Endorsement _) ->
+      Consensus.add_endorsement operation_conflict_state oph operation
   | Single (Dal_attestation _) ->
       Consensus.add_dal_attestation operation_conflict_state oph operation
   | Single (Proposals _) ->
@@ -2860,7 +2723,7 @@ let remove_operation operation_conflict_state (type kind)
 let check_validation_pass_consistency vi vs validation_pass =
   let open Lwt_result_syntax in
   match vi.mode with
-  | Mempool _ | Construction _ -> return vs
+  | Mempool | Construction _ -> return vs
   | Application _ | Partial_validation _ -> (
       match (vs.last_op_validation_pass, validation_pass) with
       | None, validation_pass ->
@@ -2908,7 +2771,7 @@ let validate_operation ?(check_signature = true)
       (* Do not validate non-consensus operations in
          [Partial_validation] mode. *)
       return {info; operation_state; block_state}
-  | (Application _ | Partial_validation _ | Construction _ | Mempool _), _ -> (
+  | (Application _ | Partial_validation _ | Construction _ | Mempool), _ -> (
       match operation.protocol_data.contents with
       | Single (Preendorsement _) ->
           Consensus.validate_preendorsement
@@ -3162,6 +3025,6 @@ let finalize_block {info; block_state; _} =
           ~fitness_locked_round:(Option.map fst locked_round_evidence)
       in
       return_unit
-  | Mempool _ ->
+  | Mempool ->
       (* There is no block to finalize in mempool mode. *)
       return_unit
diff --git a/src/proto_alpha/lib_protocol/validate.mli b/src/proto_alpha/lib_protocol/validate.mli
index 19050496379bc8e815b0ec1cb98aacb6773f30b1..00afeaa8448ca3c8745a1fd531265b8b77eaa368 100644
--- a/src/proto_alpha/lib_protocol/validate.mli
+++ b/src/proto_alpha/lib_protocol/validate.mli
@@ -239,7 +239,6 @@ val begin_partial_construction :
   Chain_id.t ->
   predecessor_level:Level.t ->
   predecessor_round:Round.t ->
-  grandparent_round:Round.t ->
   validation_state
 
 (** Similar to [begin_partial_construction] but do not require
diff --git a/src/proto_alpha/lib_protocol/validate_errors.ml b/src/proto_alpha/lib_protocol/validate_errors.ml
index 0eb8bdee3343bde0533014ec0f3ca6372e4bfacd..b6026458fa9f223623acb746e32c328333493fc5 100644
--- a/src/proto_alpha/lib_protocol/validate_errors.ml
+++ b/src/proto_alpha/lib_protocol/validate_errors.ml
@@ -72,7 +72,6 @@ module Consensus = struct
   type consensus_operation_kind =
     | Preendorsement
     | Endorsement
-    | Grandparent_endorsement
     | Dal_attestation
 
   let consensus_operation_kind_encoding =
@@ -80,14 +79,12 @@ module Consensus = struct
       [
         ("Preendorsement", Preendorsement);
         ("Endorsement", Endorsement);
-        ("Grandparent_endorsement", Grandparent_endorsement);
         ("Dal_attestation", Dal_attestation);
       ]
 
   let consensus_operation_kind_pp fmt = function
     | Preendorsement -> Format.fprintf fmt "Preendorsement"
     | Endorsement -> Format.fprintf fmt "Endorsement"
-    | Grandparent_endorsement -> Format.fprintf fmt "Grandparent endorsement"
     | Dal_attestation -> Format.fprintf fmt "Dal_attestation"
 
   (** Errors for preendorsements and endorsements. *)
@@ -308,7 +305,18 @@ module Consensus = struct
       (fun (block_round, provided) ->
         Preendorsement_round_too_high {block_round; provided}) ;
     register_error_kind
-      `Permanent
+      (* TODO: https://gitlab.com/tezos/tezos/-/issues/5061
+
+         The classification of this error has been changed to Branch
+         because it is possible for a previously valid operation to
+         trigger this error during reclassification on a new
+         head. This could lead to the unwarranted kicking of a peer if
+         this error were Permanent.
+
+         The classification should be set back to Permanent once the
+         mempool checks the slot normalization more consistently
+         across all levels. *)
+      `Branch
       ~id:"validate.wrong_slot_for_consensus_operation"
       ~title:"Wrong slot for consensus operation"
       ~description:"Wrong slot used for a preendorsement or endorsement."
diff --git a/src/proto_alpha/lib_protocol/validate_errors.mli b/src/proto_alpha/lib_protocol/validate_errors.mli
index 4d1b3485afb6914a2cad819ac0f50cf48a8d19f5..ec07efbc44cf78466918de8761b9fc312210b64f 100644
--- a/src/proto_alpha/lib_protocol/validate_errors.mli
+++ b/src/proto_alpha/lib_protocol/validate_errors.mli
@@ -37,7 +37,6 @@ module Consensus : sig
   type consensus_operation_kind =
     | Preendorsement
     | Endorsement
-    | Grandparent_endorsement
     | Dal_attestation
 
   (** Errors for preendorsements and endorsements. *)
diff --git a/tezt/tests/prevalidator.ml b/tezt/tests/prevalidator.ml
index c00cb54bf4495e82c50604f712808eaac5b06547..2967a52bbffc174b78a23ff574746d30f521b0b8 100644
--- a/tezt/tests/prevalidator.ml
+++ b/tezt/tests/prevalidator.ml
@@ -2148,36 +2148,8 @@ let pp_mempool_count fmt
     outdated
     unprocessed
 
-(** Matches events which contain an injection request.
-   For example:
-
-  {[
-    { "event": {
-       "request": {
-         "request": "inject",
-         "operation": {
-           "branch": "BL2FDpiSbzxkXpefiSRCpBHGhZ1kDpEUzWswSCABvGKr3hF6xre",
-           "data": "6c0002298c03ed7d454a101eb7022bc95f7e5f41ac78940a0280bd3f00e8070000e7670f32038107a59a2b9cfefae36ea21f5aa63c00cf958f834a8d89a88068d7da1209db3c8dc6f5a0c88fb7df0fc8b910f5e100c1179e0862993fd2abadcc47eb4710ad41b68603983559b5fb68bb98499aa1800d"
-         }
-       },
-       "status": {
-         "pushed": "2021-05-03T17:16:03.826-00:00",
-         "treated": 3.0033e-05,
-         "completed": 0.00190934
-       }
-     },
-     "level": "info"
-   }
-  ]}
- *)
-let wait_for_injection node =
-  let filter json =
-    match JSON.(json |-> "view" |-> "request" |> as_string_opt) with
-    | Some s when s = "inject" -> Some s
-    | Some _ | None -> None
-  in
-  let* _ = Node.wait_for node "request_completed_info.v0" filter in
-  return ()
+(** Wait for an injection request event. *)
+let wait_for_injection = Node.wait_for_request ~request:`Inject
 
 (** Matches events which contain an flush request.
    For example:
@@ -2381,64 +2353,27 @@ let get_endorsement_as_bytes client =
   in
   Lwt.return (wrapped_bytes, hash)
 
-let wait_for_synch node =
-  let filter json =
-    match JSON.(json |-> "view" |-> "request" |> as_string_opt) with
-    | Some s when s = "notify" -> Some s
-    | Some _ | None -> None
-  in
-  let* _ = Node.wait_for node "request_completed_debug.v0" filter in
-  return ()
-
 let mempool_synchronisation client node =
-  let waiter = wait_for_synch node in
+  let waiter = Node.wait_for_request ~request:`Notify node in
   let* _ =
     RPC.Client.call client @@ RPC.post_chain_mempool_request_operations ()
   in
   waiter
 
-(** This test checks that future endorsement are still propagated when
-    the head is  incremented *)
+(** This test checks that future endorsements are correctly
+    propagated, either immediately or when the head is sufficiently
+    incremented. *)
 let propagation_future_endorsement =
-  let step1_msg =
-    "Step 1: 3 nodes are initialised, chain connected and the protocol is \
-     activated."
-  in
-  let step2_msg = "Step 2: disconnect the nodes" in
-  let step3_msg = "Step 3: bake one block on node_1" in
-  let step4_msg = "Step 4: Endorsement on node_1 injected" in
-  let step5_msg =
-    "Step 5: recover hash endorsement and bytes representing the endorsement"
-  in
-  let step6_msg =
-    "Step 6: ban the endorsement on node_1 to ensure it will not be propagated \
-     from this node"
-  in
-  let step7_msg = "Step 7: Endorsement has been inject on node_2" in
-  let step8_msg =
-    "Step 8: Reconnect node_2 and node_3 and synchronise their mempool"
-  in
-  let step9_msg =
-    "Step 9: ensure that endorsement is in node_2 mempool and classified as \
-     branch_delayed"
-  in
-  let step10_msg =
-    "Step 10: ensure that endorsement is not in node_3 mempool"
-  in
-  let step11_msg = "Step 11: Reconnect node_1 and node_2, new head on node_2" in
-  let step12_msg =
-    "Step 12: Synchronise mempool on node_2 and check that endorsement is now \
-     applied"
-  in
-  let step13_msg =
-    "Step 13: Synchronise mempool on node_3 and check that endorsement has \
-     been propagated"
-  in
   Protocol.register_test
     ~__FILE__
-    ~title:"Ensure that future endorsement are propagated"
+    ~title:"Ensure that future endorsements are propagated"
     ~tags:["endorsement"; "mempool"; "branch_delayed"]
   @@ fun protocol ->
+  (* For this test to be moved to {!Revamped}, we need to update its
+     auxiliary functions. Notably, {!get_endorsement_as_bytes} should
+     use the {!Operation} module to build the endorsement bytes. *)
+  let log_step = Revamped.log_step in
+  log_step 1 "Initialize 3 nodes, connect them, and activate the protocol." ;
   let* node_1 = Node.init [Synchronisation_threshold 0; Private_mode]
   and* node_2 =
     Node.init
@@ -2460,7 +2395,7 @@ let propagation_future_endorsement =
   and* () = Client.Admin.connect_address client_2 ~peer:node_3 in
   let* () = Client.activate_protocol_and_wait ~protocol client_1 in
   let* _ = Node.wait_for_level node_2 1 and* _ = Node.wait_for_level node_3 1 in
-  Log.info "%s" step1_msg ;
+  log_step 2 "Disconnect all the nodes from each other." ;
   let* node_1_id = Node.wait_for_identity node_1
   and* node_2_id = Node.wait_for_identity node_2
   and* node_3_id = Node.wait_for_identity node_3 in
@@ -2468,56 +2403,107 @@ let propagation_future_endorsement =
   and* () = Client.Admin.kick_peer client_2 ~peer:node_1_id
   and* () = Client.Admin.kick_peer client_2 ~peer:node_3_id
   and* () = Client.Admin.kick_peer client_3 ~peer:node_2_id in
-  Log.info "%s" step2_msg ;
+  log_step
+    3
+    "Bake a block on node_1 then inject an endorsement, which is one level in \
+     the future from the perspective of nodes 2 and 3. Retrieve the hash and \
+     bytes representing this endorsement, called future1 from now on." ;
   let* () = Node_event_level.bake_wait_log node_1 client_1 in
-  Log.info "%s" step3_msg ;
-  let endorser_waiter = wait_for_injection node_1 in
+  let injection_waiter = wait_for_injection node_1 in
   let* () = Client.endorse_for client_1 ~force:true ~protocol in
-  let* () = endorser_waiter in
-  Log.info "%s" step4_msg ;
-  let* bytes, hash = get_endorsement_as_bytes client_1 in
-  Log.info "%s" step5_msg ;
-  let* _ =
-    RPC.Client.call client_1
-    @@ RPC.post_chain_mempool_ban_operation ~data:(Data (`String hash)) ()
-  in
-  Log.info "%s" step6_msg ;
-  let (`Hex bytes) = Hex.of_bytes bytes in
-  let injection_waiter = wait_for_injection node_2 in
-  let* _ =
-    RPC.Client.call client_2
-    @@ RPC.post_private_injection_operation (Data (`String bytes))
-  in
   let* () = injection_waiter in
-  Log.info "%s" step7_msg ;
+  let* bytes_future1, oph_future1 = get_endorsement_as_bytes client_1 in
+  log_step
+    4
+    "Bake another block on node_1 then inject another endorsement, which is \
+     two levels in the future from the perspective of nodes 2 and 3. Retrieve \
+     the hash and bytes representing this endorsement, called future2." ;
+  let* () = Node_event_level.bake_wait_log node_1 client_1 in
+  let injection_waiter2 = wait_for_injection node_1 in
+  let* () = Client.endorse_for client_1 ~force:true ~protocol in
+  let* () = injection_waiter2 in
+  let* bytes_future2, oph_future2 = get_endorsement_as_bytes client_1 in
+  log_step 5 "Inject both endorsements in node_2." ;
+  let inject_bytes_in_node_2 bytes =
+    let (`Hex bytes) = Hex.of_bytes bytes in
+    let injection_waiter = wait_for_injection node_2 in
+    let* (_ : JSON.t) =
+      RPC.Client.call client_2
+      @@ RPC.post_private_injection_operation (Data (`String bytes))
+    in
+    injection_waiter
+  in
+  let* () = inject_bytes_in_node_2 bytes_future1 in
+  let* () = inject_bytes_in_node_2 bytes_future2 in
+  log_step 6 "Reconnect node_2 and node_3, and synchronize their mempools." ;
   let* () = Client.Admin.trust_address client_2 ~peer:node_3
   and* () = Client.Admin.trust_address client_3 ~peer:node_2 in
   let* () = Client.Admin.connect_address client_2 ~peer:node_3 in
-  let* _ = mempool_synchronisation client_3 node_3 in
-  Log.info "%s" step8_msg ;
-  let* _ =
-    check_if_op_is_in_mempool
-      client_2
-      ~classification:(Some "branch_delayed")
-      hash
+  let* () = mempool_synchronisation client_3 node_3 in
+  log_step
+    7
+    "Check that both endorsements are in the mempool of node_2: future1 is \
+     branch_delayed for protocols 016 and before, and applied for protocol 017 \
+     on; future2 is branch_delayed for all protocols." ;
+  (* From protocol N on, consensus operations that are one level in
+     the future are accepted and propagated by the mempool. *)
+  let accept_one_level_in_future = Protocol.number protocol >= 017 in
+  let* () =
+    let classification =
+      Some (if accept_one_level_in_future then "applied" else "branch_delayed")
+    in
+    check_if_op_is_in_mempool client_2 ~classification oph_future1
   in
-  Log.info "%s" step9_msg ;
-  let* _ = check_if_op_is_in_mempool client_3 ~classification:None hash in
-  Log.info "%s" step10_msg ;
-  let* () = Client.Admin.trust_address client_1 ~peer:node_2
-  and* () = Client.Admin.trust_address client_2 ~peer:node_1 in
-  let* () = Client.Admin.connect_address client_1 ~peer:node_2 in
-  Log.info "%s" step11_msg ;
-  let* _ = mempool_synchronisation client_2 node_2 in
-  let* _ =
-    check_if_op_is_in_mempool client_2 ~classification:(Some "applied") hash
+  let* () =
+    let classification = Some "branch_delayed" in
+    check_if_op_is_in_mempool client_2 ~classification oph_future2
+  in
+  log_step
+    8
+    "Check that none of the endorsements is in node_3 mempool for protocols \
+     016 and before. For protocol 017 on, only future1 is present (and \
+     applied) in node_3 mempool." ;
+  let* () =
+    let classification =
+      if accept_one_level_in_future then Some "applied" else None
+    in
+    check_if_op_is_in_mempool client_3 ~classification oph_future1
   in
-  Log.info "%s" step12_msg ;
-  let* _ = mempool_synchronisation client_3 node_3 in
-  let* _ =
-    check_if_op_is_in_mempool client_3 ~classification:(Some "applied") hash
+  let* () =
+    check_if_op_is_in_mempool client_3 ~classification:None oph_future2
+  in
+  log_step
+    9
+    "Bake one block on node_2 and synchronize its mempool. Check that future1 \
+     is now applied for all protocols, and future2 is also applied for \
+     protocol 017 on." ;
+  let* () = Node_event_level.bake_wait_log node_2 client_2 in
+  let* () = mempool_synchronisation client_2 node_2 in
+  let* () =
+    let classification = Some "applied" in
+    check_if_op_is_in_mempool client_2 ~classification oph_future1
+  in
+  let* () =
+    let classification =
+      Some (if accept_one_level_in_future then "applied" else "branch_delayed")
+    in
+    check_if_op_is_in_mempool client_2 ~classification oph_future2
+  in
+  log_step
+    10
+    "Synchronize the mempool of node_3. Check that future1 is present and \
+     applied for both protocols, and so is future2 for protocol 017 on." ;
+  let* () = mempool_synchronisation client_3 node_3 in
+  let* () =
+    let classification = Some "applied" in
+    check_if_op_is_in_mempool client_3 ~classification oph_future1
+  in
+  let* () =
+    let classification =
+      if accept_one_level_in_future then Some "applied" else None
+    in
+    check_if_op_is_in_mempool client_3 ~classification oph_future2
   in
-  Log.info "%s" step13_msg ;
   unit
 
 let check_empty_operation__ddb ddb =