Policy - add an explanation for automatic capabilities for transactions and transaction comments

Summary: Ref T7094. I am not sure when this text is legitimately exposed to users - they should be getting an error about not being able to see the object before they get an error about not being able to see a given transaction... That said, I think this text is logically correct at least.

Test Plan: read the text

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7094

Differential Revision: https://secure.phabricator.com/D11632

src/applications/transactions/storage/PhabricatorApplicationTransaction.php

@@ -1140,8 +1140,10 @@ abstract class PhabricatorApplicationTransaction
   }
 
   public function describeAutomaticCapability($capability) {
-    // TODO: (T603) Exact policies are unclear here.
-    return null;
+    return pht(
+      'Transactions are visible to users that can see the object which was '.
+      'acted upon. Some transactions - in particular, comments - are '.
+      'editable by the transaction author.');
   }
 
 

src/applications/transactions/storage/PhabricatorApplicationTransactionComment.php

@@ -143,8 +143,9 @@ abstract class PhabricatorApplicationTransactionComment
   }
 
   public function describeAutomaticCapability($capability) {
-    // TODO: (T603) Policies are murky.
-    return null;
+    return pht(
+      'Comments are visible to users who can see the object which was '.
+      'commented on. Comments can be edited by their authors.');
   }