Misc fixes 2025-06-30 (#731)

* Change link to vector docs

* Unify release notes between 3.12 and 3.13

Author: Simran-B

site/content/3.12/release-notes/version-3.12/api-changes-in-3-12.md

@@ -441,7 +441,7 @@ curl "http://localhost:8529/_api/index?collection=myCollection&withHidden=true"
 <small>Introduced in: v3.12.4</small>
 
 A new `vector` index type has been added as an experimental feature.
-See this [blog post](https://arangodb.com/2024/11/vector-search-in-arangodb-practical-insights-and-hands-on-examples/)
+See [HTTP interface for vector indexes](../../develop/http-api/indexes/vector.md)
 for details.
 
 #### Optimizer rule descriptions

site/content/3.13/release-notes/version-3.12/api-changes-in-3-12.md

@@ -441,7 +441,7 @@ curl "http://localhost:8529/_api/index?collection=myCollection&withHidden=true"
 <small>Introduced in: v3.12.4</small>
 
 A new `vector` index type has been added as an experimental feature.
-See this [blog post](https://arangodb.com/2024/11/vector-search-in-arangodb-practical-insights-and-hands-on-examples/)
+See [HTTP interface for vector indexes](../../develop/http-api/indexes/vector.md)
 for details.
 
 #### Optimizer rule descriptions

site/content/3.13/release-notes/version-3.12/whats-new-in-3-12.md

@@ -1688,6 +1688,18 @@ The following startup options for cluster deployments have been added:
   The delay (in seconds) before shutting down a Coordinator if no heartbeat can
   be sent. Set to `0` to deactivate this shutdown.
 
+### Limit for shard synchronization actions
+
+<small>Introduced in: v3.11.14, v3.12.5</small>
+
+The number of `SynchronizeShard` actions that can be scheduled internally by the
+cluster maintenance has been restricted to prevent these actions from blocking
+`TakeoverShardLeadership` actions with a higher priority, which could lead to
+service interruption during upgrades and after failovers.
+
+The new `--server.maximal-number-sync-shard-actions` startup option controls
+how many `SynchronizeShard` actions can be queued at any given time.
+
 ## Miscellaneous changes
 
 ### V8 and ICU library upgrades