docs: provide genesis-start for testnet 71

Refs #4087. Also lists an archive URL for `pd testnet join`.

docs/guide/src/pd/chain-upgrade.md

@@ -23,7 +23,6 @@ After the node is restarted on the new version, it should be able to talk to the
 Once enough validators with sufficient stake weight have upgraded, the network
 will resume generating blocks.
 
-
 ## Genesis time
 
 In order for the chain to start again after the upgrade, all nodes must be using the same genesis information,
@@ -39,6 +38,11 @@ until the `--genesis-start` time is reached, at which point it will resume proce
 the community of validators can coordinate resumption of chain activity, even when operators perform migrate their ndoes
 at slightly different times.
 
+### Testnet 70 -> 71
+
+For the first chain upgrade performed on a Penumbra testnet, use this value for genesis time: `{{ #include ../upgrade_genesis_time_70_71.md }}`.
+See an example below for how to supply this value when performing the migration.
+
 ## Performing a chain upgrade
 
 The following steps assume that `pd` is using the default home directory of `~/.penumbra/testnet_data/node0/pd`.
@@ -58,8 +62,8 @@ An example log message emitted by `pd migrate` without providing `--genesis-star
 The value after `now=` is what should be copied. In practice, for testnets, Penumbra Labs will advise on a genesis time
 and provide that value in the documentation. Or should we just pick a genesis start ahead of time, and use that for all?
 -->
-5. Apply the migration: `pd migrate --genesis-start "GENESIS_TIME" --target-directory ~/.penumbra/testnet_net/node0/pd-exported-state/ --migrate-archive ~/.penumbra/testnet_data/node0/pd-migrated-state-{{ #include ../penumbra_version.md }}.tar.gz`.
-   Replace `GENESIS_TIME` with the exact string: `XXXXX`.
+5. Apply the migration: `pd migrate --genesis-start "{{ #include ../upgrade_genesis_time_70_71.md }}" --target-directory ~/.penumbra/testnet_net/node0/pd-exported-state/ --migrate-archive ~/.penumbra/testnet_data/node0/pd-migrated-state-{{ #include ../penumbra_version.md }}.tar.gz`.
+   You must use that precise genesis time, otherwise your node will not be able to reach consensus with the rest of the network.
 6. Move the migrated state into place: `mkdir ~/.penumbra/testnet_data/node0/pd && mv ~/.penumbra/testnet_data/node0/pd-exported-state/rocksdb ~/.penumbra/testnet_data/node0/pd/`
 7. Move the upgrade cometbft state into place: `cp ~/.penumbra/testnet_data/node0/pd-exported-state/genesis.json ~/.penumbra/testnet_data/node0/cometbft/config/genesis.json
    && cp ~/.penumbra/testnet_data/pd-exported-state/priv_validator_state.json ~/.penumbra/testnet_data/node0/cometbft/data/priv_validator_state.json`

docs/guide/src/pd/join-testnet.md

@@ -37,27 +37,27 @@ The following section describes how to join a testnet chain *which has never upg
 Once a chain upgrade occurs, a new-joining node must have access to an archive
 of historical, migrated state. When we upgrade the chain, we should update these
 docs to switch to the archive-url version:
+-->
 
 ```shell
 pd testnet join --external-address IP_ADDRESS:26656 --moniker MY_NODE_NAME \
-    --archive-url "https://snapshots.penumbra.zone/testnet/pd-archived-stated-xxxxx.tar.gz
+    --archive-url "https://snapshots.penumbra.zone/testnet/pd-migrated-state-70-71.tar.gz"
 ```
 
 where `IP_ADDRESS` (like `1.2.3.4`) is the public IP address of the node you're running,
 and `MY_NODE_NAME` is a moniker identifying your node. Other peers will try to connect
 to your node over port `26656/TCP`. Finally, the `--archive-url` flag will fetch
 a tarball of historical blocks, so that your newly joining node can understand transactions
 that occurred prior to the most recent chain upgrade.
--->
 
+<!--
 ```shell
 pd testnet join --external-address IP_ADDRESS:26656 --moniker MY_NODE_NAME
 ```
 
 where `IP_ADDRESS` (like `1.2.3.4`) is the public IP address of the node you're running,
 and `MY_NODE_NAME` is a moniker identifying your node. Other peers will try to connect
 to your node over port `26656/TCP`.
-<!--
 ### End join customization
 -->
 

docs/guide/src/upgrade_genesis_time_70_71.md

@@ -0,0 +1 @@
+2024-03-28T19:18:38.745760868Z