docs: revise specs for padding shares (#1359)

Context: #1353
Closes #1344

## Screenshot

<img width="746" alt="Screenshot 2023-02-08 at 11 55 07 AM"
src="https://user-images.githubusercontent.com/3699047/217598202-15737680-d81b-4771-9940-75aa1830eaa2.png">

specs/src/specs/consensus.md

@@ -71,7 +71,7 @@
 | `TRANSACTION_NAMESPACE_ID`              | `NamespaceID` | `0x0000000000000001` | Transactions: requests that modify the state.                                              |
 | `INTERMEDIATE_STATE_ROOT_NAMESPACE_ID`  | `NamespaceID` | `0x0000000000000002` | Intermediate state roots, committed after every transaction.                               |
 | `EVIDENCE_NAMESPACE_ID`                 | `NamespaceID` | `0x0000000000000003` | Evidence: fraud proofs or other proof of slashable action.                                 |
-| `TAIL_TRANSACTION_PADDING_NAMESPACE_ID` | `NamespaceID` | `0x00000000000000FF` | Tail padding for transactions: padding after all transactions but before messages.         |
+| `RESERVED_PADDING_NAMESPACE_ID`         | `NamespaceID` | `0x00000000000000FF` | Padding after all reserved namespaces but before blobs.                                    |
 | `TAIL_PADDING_NAMESPACE_ID`             | `NamespaceID` | `0xFFFFFFFFFFFFFFFE` | Tail padding for messages: padding after all messages to fill up the original data square. |
 | `PARITY_SHARE_NAMESPACE_ID`             | `NamespaceID` | `0xFFFFFFFFFFFFFFFF` | Parity shares: extended shares in the available data matrix.                               |
 

specs/src/specs/data_structures.md

@@ -32,7 +32,7 @@
     - [Compact Share](#compact-share)
     - [Sparse Share](#sparse-share)
     - [Parity Share](#parity-share)
-    - [Namespaced Padding Share](#namespaced-padding-share)
+    - [Namespace Padding Share](#namespace-padding-share)
     - [Tail Padding Share](#tail-padding-share)
   - [Arranging Available Data Into Shares](#arranging-available-data-into-shares)
 - [Available Data](#available-data)
@@ -543,19 +543,27 @@ For shares **with a namespace ID equal to [`PARITY_SHARE_NAMESPACE_ID`](./consen
 
 - Bytes carry no special meaning.
 
-#### Namespaced Padding Share
+#### Namespace Padding Share
 
-A namespaced padding share acts as padding between blobs so that the subsequent blob may begin at an index that conforms to the [non-interactive default rules](../rationale/message_block_layout.md#non-interactive-default-rules). A namespaced padding share contains the namespace ID of the blob that precedes it in the data square so that the data square can retain the property that all shares are ordered by namespace.
+A namespace padding share acts as padding between blobs so that the subsequent blob may begin at an index that conforms to the [non-interactive default rules](../rationale/message_block_layout.md#non-interactive-default-rules). A namespace padding share contains the namespace ID of the blob that precedes it in the data square so that the data square can retain the property that all shares are ordered by namespace.
 
-The first [`NAMESPACE_ID_BYTES`](./consensus.md#constants) of a share's raw data `rawData` is the namespace ID of the blob that precedes this padding share. The next [`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are for share information. The sequence start indicator is always `0`. The version bits are filled with the share version. The remaining [`SHARE_SIZE`](./consensus.md#constants)`-`[`NAMESPACE_ID_BYTES`](./consensus.md#constants)`-`[`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are filled with `0`.
+The first [`NAMESPACE_ID_BYTES`](./consensus.md#constants) of a share's raw data `rawData` is the namespace ID of the blob that precedes this padding share. The next [`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are for share information. The sequence start indicator is always `1`. The version bits are filled with the share version. The sequence length is zeroed out. The remaining [`SHARE_SIZE`](./consensus.md#constants)`-`[`NAMESPACE_ID_BYTES`](./consensus.md#constants)`-`[`SHARE_INFO_BYTES`](./consensus.md#constants) `-` [`SEQUENCE_BYTES`](./consensus.md#constants) bytes are filled with `0`.
+
+#### Reserved Padding Share
+
+Reserved padding shares are placed after the last reserved namespace share in the data square so that the first blob can start at an index that conforms to non-interactive default rules. Clients can safely ignore the contents of these shares because they don't contain any significant data.
+
+For shares **with a namespace ID equal to [`RESERVED_PADDING_NAMESPACE_ID`](./consensus.md#constants)** (i.e. reserved padding shares):
+
+The first [`NAMESPACE_ID_BYTES`](./consensus.md#constants) of a share's raw data `rawData` is the namespace ID of that share, `namespaceID`. The next [`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are for share information. The sequence start indicator is always `1`. The version bits are filled with the share version. The sequence length is zeroed out. The remaining [`SHARE_SIZE`](./consensus.md#constants)`-`[`NAMESPACE_ID_BYTES`](./consensus.md#constants)`-`[`SHARE_INFO_BYTES`](./consensus.md#constants) `-` [`SEQUENCE_BYTES`](./consensus.md#constants) bytes are filled with `0`.
 
 #### Tail Padding Share
 
 Tail padding shares are placed after the last blob in the data square so that the number of shares in the data square is a perfect square. Clients can safely ignore the contents of these shares because they don't contain any significant data.
 
 For shares **with a namespace ID equal to [`TAIL_PADDING_NAMESPACE_ID`](./consensus.md#constants)** (i.e. tail padding shares):
 
-The first [`NAMESPACE_ID_BYTES`](./consensus.md#constants) of a share's raw data `rawData` is the namespace ID of that share, `namespaceID`. The next [`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are for share information. The sequence start indicator is always `0`. The version bits are filled with the share version. The remaining [`SHARE_SIZE`](./consensus.md#constants)`-`[`NAMESPACE_ID_BYTES`](./consensus.md#constants)`-`[`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are filled with `0`.
+The first [`NAMESPACE_ID_BYTES`](./consensus.md#constants) of a share's raw data `rawData` is the namespace ID of that share, `namespaceID`. The next [`SHARE_INFO_BYTES`](./consensus.md#constants) bytes are for share information. The sequence start indicator is always `1`. The version bits are filled with the share version. The sequence length is zeroed out. The remaining [`SHARE_SIZE`](./consensus.md#constants)`-`[`NAMESPACE_ID_BYTES`](./consensus.md#constants)`-`[`SHARE_INFO_BYTES`](./consensus.md#constants) `-` [`SEQUENCE_BYTES`](./consensus.md#constants) bytes are filled with `0`.
 
 ### Arranging Available Data Into Shares