Update changelogs from fern repo (#4432)

Co-authored-by: patrickthornton <70873350+patrickthornton@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/java/changelog/2026-03-20.mdx

@@ -0,0 +1,27 @@
+## 4.0.3
+**`(fix):`** Fix WebSocket `handleIncomingMessage()` using Fern-internal message IDs
+(e.g. `AgentV1Welcome`, `ListenV1Results`) instead of the wire discriminant
+values from the spec (e.g. `Welcome`, `Results`). This caused all incoming
+message handlers to never fire, falling through to the unknown type handler.
+
+The generator now extracts wire discriminant values from each message body's
+`type` property — resolving literal values (e.g. `literal<"Welcome">`) and
+enum values (e.g. `enum[Flushed, Cleared]`) — and dispatches via a `switch`
+statement on those values. This aligns with the approach used by the Python
+generator.
+
+
+**`(fix):`** WebSocket handler registration methods and field names now use
+wire discriminant values instead of Fern-internal prefixed names. For example,
+`onAgentV1Welcome(handler)` is now `onWelcome(handler)`, and
+`onAgentV1PromptUpdated(handler)` is now `onPromptUpdated(handler)`. Methods
+that were already backed by a custom `x-fern-sdk-method-name` (e.g.
+`onFunctionCallResponse`) are unchanged.
+
+
+**`(chore):`** Improve generated WebSocket client code quality: use a string literal for
+static URL paths instead of `StringBuilder`, remove dead if/else branches in
+async `sendMessage()`, consolidate redundant catch blocks in message dispatch,
+and correct Javadoc articles ("a" vs "an") for type names starting with vowels.
+
+