update changelogs

Author: dsinghvi

fern/products/cli-api-reference/cli-changelog/2026-05-08.mdx

@@ -1,3 +1,16 @@
+## 5.21.0
+**`(feat):`** Add a new `resumable` sub-property to the `x-fern-streaming` OpenAPI extension
+(and a corresponding `resumable` field on Fern Definition `response-stream`
+blocks). When set on an SSE endpoint, the IR carries `resumable: true` on
+the SSE chunk so generators can emit a client-side reconnect loop using
+standard SSE primitives (`Last-Event-ID`, `retry:`).
+
+The flag is inheritable: setting `x-fern-streaming.resumable: true` at the
+OpenAPI document level applies to every SSE endpoint unless an operation
+overrides it (silent fallback). Defaults to `false`. The IR field is
+optional, so generators that don't read it are unaffected.
+
+
 ## 5.20.1
 **`(fix):`** Pass GitHub Enterprise host to Fiddle for remote generation so that
 self-hosted GHE instances are correctly targeted by the remote pipeline.