chore(release): bump assembly version to 1.9.0

The whole v1.9.0 cycle ran without a version bump, so the plugin still reported
1.8.8 in-game. For a tester beta that is untenable: bug reports would name a
version that does not identify the code they ran.

Download links stay pinned to v1.5.6 on purpose. There is no v1.9.0 release, and
pointing at an artifact that does not exist is worse than the visible mismatch
between assembly version and download target. Public stays on v1.5.6 until
v2.0.0.

docs/CHANGELOG.md

@@ -11,6 +11,40 @@ releases as an overview and links to the release pages for details.
 
 ---
 
+## [1.9.0] — unreleased (local only)
+
+Polish, tester-beta preparation and a concurrency hardening pass. **Not published** — the public
+release stays at v1.5.6, so the download links in `repo.json` deliberately still point there while
+the assembly version reads 1.9.0.
+
+### Fixed
+
+- Incoming messages could be dropped without a trace. The worker walked the tab list while another
+  thread rewrote it, the resulting exception was swallowed by the surrounding error handler, and the
+  message ended up nowhere: no tab entry, no notification sound, no tell routing.
+- Clicking a tab could open a different one, or crash the render loop, when tabs appeared or were
+  evicted in the same frame. The window now renders from one consistent snapshot per frame.
+- An open tab context menu could silently re-bind to a different tab. Widget identity is derived
+  from the tab itself now, not from its position in the list.
+- `Tab.Clone()` dropped the tab icon and legacy channel data.
+
+### Changed
+
+- Settings sliders write the configuration once, on release, instead of on every frame while
+  dragging. Renaming a tab writes once when you finish, including when the context menu is
+  dismissed by clicking elsewhere.
+- Tell history loads through a dedicated `(Receiver, Date)` index (schema 5). Opening a tell tab no
+  longer sorts the entire conversation history first.
+- Pinning, unpinning and promoting tabs no longer write to disk while holding the tab lock.
+
+### Internal
+
+- New `ConfigMapsLock` guards the config maps the settings UI edits while a background save may be
+  serialising them.
+- Removed `DeferredSaveFrames`: the debounce was fully wired but never armed.
+- Test suite 812 → 829, including migration and query-plan coverage.
+
+
 ## Hellion Chat 1.5.6 — Settings Overhaul + Filter & Notification Polish (2026-05-23)
 
 - Settings window reorganised: ten tabs down to seven (General, Appearance, Chat, Window, Channels, Data & Privacy, About). Each tab now uses collapsible sections grouped by control type. Sections start collapsed every time you open a tab — less noise, easier to find what you need.