Nightly builds name themselves on the title screen and in reports

A game built by the nightly workflow (HORIZON_NIGHTLY="<date> <sha>") draws
"Nightly <date> · <sha>" in the title screen's top-left corner, reports it as
its version in crash reports, and logs it as the log's first line, so a bug
report that carries the log names the build. Telemetry gets the version the
launcher installs it as (nightly-<date>-<sha>). Releases and source builds
are unchanged; only the "Horizon <version>" log line is new for them.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client/src/crash.rs

@@ -105,9 +105,13 @@ impl Report {
     }
 }
 
-/// The release this binary is (`v0.2.3`); for a release from before 0.2, its tag and the client's
-/// crate version; for a build from source, that version alone.
+/// The release this binary is (`v0.2.3`); a nightly's label (`Nightly 2026-10-28 · 0c02067`); for a
+/// release from before 0.2, its tag and the client's crate version; for a build from source, that
+/// version alone.
 pub fn version() -> String {
+    if let Some(label) = horizon_core::release::nightly_label() {
+        return label;
+    }
     let version = env!("CARGO_PKG_VERSION");
     match (horizon_core::release::RELEASE, release_tag()) {
         (Some(_), Some(tag)) => tag,
@@ -117,8 +121,12 @@ pub fn version() -> String {
 }
 
 /// The release this binary came with: the version release.yml built in (docs/versioning.md), else
-/// the folder the launcher installed it in, named after the tag (releases from before 0.2).
+/// the folder the launcher installed it in, named after the tag (releases from before 0.2). A
+/// nightly is its version as the launcher installs it (`nightly-2026-10-28-0c02067`).
 pub fn release_tag() -> Option<String> {
+    if let Some(nightly) = horizon_core::release::nightly_version() {
+        return Some(nightly);
+    }
     if let Some(version) = horizon_core::release::RELEASE {
         return Some(format!("v{version}"));
     }
@@ -525,6 +533,11 @@ mod tests {
     #[test]
     fn a_release_reports_its_built_in_version() {
         // release.yml builds with HORIZON_VERSION (docs/versioning.md): `v0.2.3`, wherever it is installed.
+        if let Some(label) = horizon_core::release::nightly_label() {
+            assert_eq!(super::version(), label);
+            assert_eq!(release_tag(), horizon_core::release::nightly_version());
+            return;
+        }
         match horizon_core::release::RELEASE {
             Some(version) => {
                 assert_eq!(release_tag(), Some(format!("v{version}")));

crates/horizon-client/src/main.rs

@@ -23,6 +23,8 @@ fn main() {
     };
     if !help {
         logging::init(&home, thread);
+        // The log's first line names the build, so a bug report that carries the log says which one it was.
+        log::info!("Horizon {}", crash::version());
         crash::install(home.clone(), side);
     }
     if let Err(error) = game::run() {

crates/horizon-client/src/title.rs

@@ -966,6 +966,11 @@ impl Title {
                 }
                 let version = format!("Horizon {} (Rust)", horizon_core::VANILLA_VERSION);
                 batch.text(atlas, &version, 2.0, h - 10.0, u32::MAX, true);
+                // A nightly names its build in the top-left corner, the one spot no button reaches at any GUI
+                // scale, so screenshots and reports say which build they come from.
+                if let Some(nightly) = horizon_core::release::nightly_label() {
+                    batch.text(atlas, &nightly, 2.0, 2.0, u32::MAX, true);
+                }
                 let notice = "Not affiliated with Mojang or Microsoft";
                 let tw = HudBatch::text_width(atlas, notice);
                 batch.text(atlas, notice, w - tw - 2.0, h - 10.0, u32::MAX, true);

crates/horizon-core/src/release.rs

@@ -15,8 +15,43 @@ pub const VERSION: &str = match RELEASE {
     None => env!("CARGO_PKG_VERSION"),
 };
 
+/// A nightly's date and commit (`2026-10-28 0c02067`): nightly-build.yml builds the opt-in Nightly
+/// channel with `HORIZON_NIGHTLY` set (docs/release-flow.md). None for a release or a build from source.
+pub const NIGHTLY: Option<&str> = match option_env!("HORIZON_NIGHTLY") {
+    Some(nightly) if !nightly.is_empty() => Some(nightly),
+    _ => None,
+};
+
+/// How a nightly names itself where players read it, so their reports say which build they come
+/// from: `Nightly 2026-10-28 · 0c02067`. None for any other build.
+pub fn nightly_label() -> Option<String> {
+    NIGHTLY.map(label)
+}
+
+/// A nightly's version as the launcher installs it (`nightly-2026-10-28-0c02067`).
+pub fn nightly_version() -> Option<String> {
+    NIGHTLY.map(|n| format!("nightly-{}", n.replace(' ', "-")))
+}
+
+fn label(nightly: &str) -> String {
+    match nightly.split_once(' ') {
+        Some((date, commit)) => format!("Nightly {date} · {commit}"),
+        None => format!("Nightly {nightly}"),
+    }
+}
+
 #[cfg(test)]
 mod tests {
+    #[test]
+    fn a_nightly_names_its_date_and_commit() {
+        assert_eq!(
+            super::label("2026-10-28 0c02067"),
+            "Nightly 2026-10-28 · 0c02067"
+        );
+        assert_eq!(super::label("2026-10-28"), "Nightly 2026-10-28");
+        assert_eq!(super::nightly_label().is_some(), super::NIGHTLY.is_some());
+    }
+
     #[test]
     fn the_version_is_the_release_or_the_crate() {
         assert_eq!(