Prevent updating if proposal is too close to voting period start

.forge-snapshots/ProposeSigComp.snap

@@ -1 +1 @@
-171010
+171002

.forge-snapshots/VoteSigComp.snap

@@ -1 +1 @@
-51977
+51969

.forge-snapshots/VoteSigCompMetadata.snap

@@ -1 +1 @@
-53663
+53655

.forge-snapshots/VoteTxComp.snap

@@ -1 +1 @@
-45218
+45210

.forge-snapshots/VoteTxCompMetadata.snap

@@ -1 +1 @@
-46809
+46801

src/Space.sol

@@ -42,6 +42,9 @@ contract Space is ISpace, Initializable, IERC4824, UUPSUpgradeable, OwnableUpgra
     /// @dev Evaluates to: `0xf2cda9b1`.
     uint32 private constant NO_UPDATE_UINT32 = uint32(bytes4(keccak256(abi.encodePacked("No update"))));
 
+    /// @dev Buffer between when the voting period starts and when the proposal can be updated for the last time.
+    uint32 private PROPOSAL_MODIFICATION_BUFFER = 15 * 60;
+
     /// @inheritdoc IERC4824
     string public daoURI;
     /// @inheritdoc ISpaceState
@@ -335,7 +338,7 @@ contract Space is ISpace, Initializable, IERC4824, UUPSUpgradeable, OwnableUpgra
     ) external override onlyAuthenticator {
         Proposal storage proposal = proposals[proposalId];
         if (author != proposal.author) revert InvalidCaller();
-        if (block.timestamp >= proposal.startTimestamp) revert VotingDelayHasPassed();
+        if (block.timestamp >= proposal.startTimestamp - PROPOSAL_MODIFICATION_BUFFER) revert TooLateToUpdateProposal();
 
         proposal.executionPayloadHash = keccak256(executionStrategy.params);
         proposal.executionStrategy = IExecutionStrategy(executionStrategy.addr);

src/interfaces/space/ISpaceErrors.sol

@@ -50,8 +50,9 @@ interface ISpaceErrors {
     /// @notice Thrown if a user attempts to finalize (execute or cancel) a proposal that has already been finalized.
     error ProposalFinalized();
 
-    /// @notice Thrown if an author attempts to update their proposal after the voting delay has passed.
-    error VotingDelayHasPassed();
+    /// @notice Thrown if an author attempts to update their proposal after the voting delay has passed (or if
+    ///         if too close to when the voting starts).
+    error TooLateToUpdateProposal();
 
     /// @notice Thrown if a new proposal did not pass the proposal validation strategy for the space.
     error FailedToPassProposalValidation();

test/UpdateProposalMetadata.t.sol

@@ -67,7 +67,7 @@ contract UpdateProposalTest is SpaceTest {
         uint256 proposalId = _createProposal(author, proposalMetadataURI, executionStrategy, new bytes(0));
         vm.warp(block.timestamp + votingDelay);
 
-        vm.expectRevert(VotingDelayHasPassed.selector);
+        vm.expectRevert(TooLateToUpdateProposal.selector);
         // Try to update metadata. Should fail.
         _updateProposal(author, proposalId, newStrategy, newMetadataURI);
     }