provide Ditto 3.9.2 release notes

Author: thjaeckle

documentation/src/main/resources/_data/sidebars/ditto_sidebar.yml

@@ -699,6 +699,9 @@ entries:
       - title: Release Notes
         output: web
         folderitems:
+          - title: 3.9.2
+            url: /release_notes_392.html
+            output: web
           - title: 3.9.1
             url: /release_notes_391.html
             output: web

documentation/src/main/resources/pages/ditto/release_notes_392.md

@@ -0,0 +1,65 @@
+---
+title: Release notes 3.9.2
+tags: [release_notes]
+published: true
+keywords: release notes, announcements, changelog
+summary: "Version 3.9.2 of Eclipse Ditto, released on 12.06.2026"
+permalink: release_notes_392.html
+---
+
+This is a bugfix release, no new features since [3.9.1](release_notes_391.html) were added.
+
+## Changelog
+
+Compared to the latest release [3.9.1](release_notes_391.html), the following changes and bugfixes were added.
+
+### Changes
+
+This is a complete list of the
+[merged pull requests](https://github.com/eclipse-ditto/ditto/pulls?q=is%3Apr+milestone%3A3.9.2).
+
+#### Defer CBOR/string pre-encoding in `SoftReferencedFieldMap` until needed
+
+PR [#2461](https://github.com/eclipse-ditto/ditto/pull/2461) eliminates eager CBOR (or string fallback) serialization
+in the `ImmutableJsonObject` constructor chain. JFR profiling of production `things-service` pods on 3.9.1 showed the
+combined `SoftReferencedFieldMap.<init>` / `createCborRepresentation` / `JacksonSerializationContext` allocation and
+flush samples accounting for ~6–10% of CPU. Intermediate `JsonObject` instances produced by transformation and
+projection pipelines paid this cost without ever benefiting, because the cached bytes were discarded along with the
+object.
+
+Encoding is now deferred to the first call that actually needs it (`toString` / `writeValue` /
+`upperBoundForStringSize`), and the field-map reference is only softened once a recoverable representation exists.
+JMH benchmarks show 2.6×–2.9× speedups on build-without-serialize paths and a 1.5× speedup on build-then-access
+paths, with no public API change and no behavior change in the size-validation contract.
+
+#### Remove regex from `ImmutableJsonPointer` escape/parse hot path
+
+PR [#2460](https://github.com/eclipse-ditto/ditto/pull/2460) replaces `Pattern`/`Matcher` usage in
+`ImmutableJsonPointer.escapeTilde`, `decodeTilde`, and the consecutive-slash check with manual single-pass
+character scans that fast-return the input string unchanged when no tilde is present — the dominant production case.
+
+JFR profiling of production `things-service` pods on 3.9.1 had identified `escapeTilde` as the single hottest Ditto
+method at ~3.8% of CPU. JMH benchmarks show 1.19×–2.57× speedups across realistic scenarios, with behavior that is
+character-for-character identical to the prior implementation.
+
+### Bugfixes
+
+#### Fix partial-access filter stripping `thingId` and audit fields from SSE/WebSocket events
+
+PR [#2465](https://github.com/eclipse-ditto/ditto/pull/2465) fixes a regression introduced with the 3.9.0
+partial-events feature where the emitted Thing JSON was filtered by exact path match against the subscriber's policy
+grants. Top-level entity fields that were not a listed grant were stripped, including `thingId`. A subscriber with
+READ on `thing:/attributes` therefore received SSE events without any way to identify which Thing the change applied
+to — a behavior regression versus 3.8.x. The same code path also stripped identity and audit fields from WebSocket
+payloads of full-Thing events (`ThingCreated` / `ThingModified` / `ThingMerged`) and from user-requested
+`extraFields`.
+
+The fix preserves `thingId`, `_namespace`, `_revision`, `_modified`, and `_created` whenever the subscriber holds at
+least partial READ access on the Thing, applied consistently across the SSE filter, the adaptable payload and extras
+filters, and the `RetrieveThing` response allowlist. `policyId` and `_metadata` are intentionally excluded from the
+allowlist and remain per-path policy-enforced.
+
+
+## Migration notes
+
+No known migration steps are required for this release.