docs: add v0.4.0 release narrative

Author: pallyoung

docs/promotion/releases/README.md

@@ -18,5 +18,6 @@ Add a release narrative when a version is published to GitHub and npm, especiall
 
 ## Current releases
 
+- [v0.4.0](v0.4.0.md)
 - [v0.3.6](v0.3.6.md)
 - [v0.3.5](v0.3.5.md)

docs/promotion/releases/v0.4.0.md

@@ -0,0 +1,39 @@
+# Coder Studio v0.4.0
+
+## Why this release matters
+
+`v0.4.0` is a substantial workflow and platform update. It gives Coder Studio more control over how language-server support runs, removes the remaining SQLite-era runtime persistence path in favor of the newer file-backed model, and tightens supervisor restore and editing flows across desktop and mobile.
+
+In practice, this release means:
+
+- language-server runtime behavior is now configurable, including managed installation flows for supported runtimes
+- workspace, terminal, auth, settings, provider config, and supervisor persistence no longer depend on the retired SQLite compatibility layer
+- supervisor sessions restore more reliably after reconnects or restarts, with clearer edit and recovery flows
+- UI foundations for overlays, spacing, typography, and session-state visibility are more consistent across desktop and mobile
+
+## Included in v0.4.0
+
+- add configurable LSP runtime behavior and managed language-server installation support
+- remove the remaining SQLite runtime compatibility chain and move persistence onto the newer file-backed repositories
+- improve supervisor restore, edit, decomposition, and details-first workflows across desktop and mobile
+- tighten running-session visibility and session-state feedback in the workspace shell
+- unify overlay, drawer, and modal foundations so shared surfaces behave more consistently
+- ship a broad pass of web polish and regression fixes around diagnostics, settings, mobile session flows, and supervisor layout
+
+## Who benefits most
+
+- users relying on Monaco + LSP support inside the browser workspace
+- developers reopening long-lived workspaces and expecting supervisor state to restore cleanly
+- teams evaluating Coder Studio for steadier day-to-day use beyond early prototype flows
+- contributors who need the runtime and persistence model to be easier to reason about and maintain
+
+## Install or upgrade
+
+```bash
+npm install -g @spencer-kit/coder-studio
+coder-studio open
+```
+
+## Full changelog
+
+- [Compare `v0.3.11...v0.4.0`](https://github.com/spencerkit/coder-studio/compare/v0.3.11...v0.4.0)