chore(release): v0.21.0

CHANGELOG.md

@@ -7,6 +7,39 @@ change type. Preview the next one with `ludic dev release --dry-run`.
 A released section may carry a hand-written summary paragraph above its groups
 (v0.2.0 has one); the generated bullets below it are not edited by hand.
 
+## v0.21.0 — 2026-09-17
+
+### Features
+
+- **A launcher's runtime** — start a program, step aside while it runs, and download large
+  files with a progress bar.
+
+  - **`Process.*`** — `Process.spawn(path, args)` starts a program directly (no shell) with this
+    process's environment and working directory and returns at once; `Process.poll(h)` is `-1`
+    while it runs, then its exit code (`128 + signal` for a signal death, `137` after
+    `Process.kill`); `Process.free` lets a handle go. `posix_spawn` on macOS
+    (`runtime/native/process.ll`); `CreateProcessW` on Windows (`process_win.ll`), with each
+    argument quoted by the MSVC rules and no console window. Linked only into a program that
+    uses `Process.*`.
+  - **`Http.save_to(h, path)`** — before `Http.send`, streams the response body straight into a
+    file (written at `path` itself, created on send) instead of memory; `Http.text` of such a
+    request is empty and `Http.body_len` is the bytes written. **`Http.received(h)`** and
+    **`Http.expected(h)`** (the `Content-Length`, or `-1`) are live while it is pending. macOS
+    streams through an `NSURLSession` with a delegate built at run time, Windows through the
+    WinHTTP read loop. Freeing a pending request now cancels it and parks its slot until the
+    worker has let go, rather than freeing what the worker is still writing.
+  - **`App.window_hide()` / `App.window_show()`** — take the game's window off the screen and
+    bring it back without closing it or its GL / Vulkan surface; the run goes on while it is
+    hidden. No-ops headless and before there is a window.
+
+### Fixes
+
+- A game's window takes the title it asks for. The runtime opens a game's window before `main`,
+  titled with the `program` name, and `Gl.open` / render3d's `gl_open` and `gvk_open` attached
+  to it without passing their title on, so a `program Valley` that opened "Maroon Lake" showed
+  "Valley". `win_set_title` (cocoa.ll `setTitle:`, win32.ll `SetWindowTextW`, UTF-8 to UTF-16)
+  now retitles it, and a second `win_open` on macOS retitles the open window instead of making
+  another, as it already did on Windows.
 ## v0.20.0 — 2026-09-17
 
 ### Features