whitepapers/ccq: add eth_call_by_timestamp

whitepapers/0013_ccq.md

@@ -217,7 +217,7 @@ uint32   query_len
 []byte   query_data
 ```
 
-Currently the only supported query type is `eth_call`. This can be expanded to support other protocols.
+Currently the only supported query types are `eth_call` and `eth_call_by_timestamp`. This can be expanded to support other protocols.
 
 1. eth_call (query type 1)
 
@@ -236,6 +236,30 @@ Currently the only supported query type is `eth_call`. This can be expanded to s
    []byte     call_data
    ```
 
+1. eth_call_by_timestamp (query type 2)
+
+   This query type is identical to `eth_call` but targets a timestamp instead of a specific block_id. This can be useful when forming requests based on uncorrelated data, such as requiring data from another chain based on the block timestamp of a given chain.
+
+   The request MUST include the target timestamp. The request MAY include block hints for the target block and following block. These fields are reserved for the possibility that guardians can optionally perform the timestamp -> block lookup. The resulting block numbers MUST be `1` different and their timestamps MUST be such that the target block is _before_ the target time (inclusive) and the following block is _after_ (exclusive). In other words,
+
+   ```
+   target_block.timestamp <= target_time < following_block.timestamp
+   and
+   following_block_num - 1 == target_block_num
+   ```
+
+   The guardian code MUST enforce the above condition before signing the result.
+
+   ```go
+   u64      target_time_us
+   u32      target_block_id_hint_len
+   []byte   target_block_id_hint
+   u32      following_block_id_hint_len
+   []byte   following_block_id_hint
+   u8       num_batch_call_data
+   []byte   batch_call_data
+   ```
+
 ## Query Response
 
 - Off-Chain
@@ -280,6 +304,24 @@ Currently the only supported query type is `eth_call`. This can be expanded to s
      []byte      result
      ```
 
+  1. eth_call_by_timestamp (query type 2) Response Body
+
+     ```go
+     u64         target_block_number
+     [32]byte    target_block_hash
+     u64         target_block_time_us
+     u64         following_block_number
+     [32]byte    following_block_hash
+     u64         following_block_time_us
+     u8          num_results
+     []byte      results
+     ```
+
+     ```go
+     u32         result_len
+     []byte      result
+     ```
+
 ## REST Service
 
 ### Request