fix(releases): don't drop the prerelease marker when comparing versions

A MinVer dev build on main computes a prerelease of its own guessed next
version (e.g. 2.9.1-alpha.0.14 after tag v2.9.0), which already sorts
above the last tag by numeric core, so the update banner correctly
stays quiet there. But the reduction to a bare numeric core meant a
genuine new release landing at exactly that guessed version (v2.9.1
real) compared equal to the still-running prerelease and the banner
never fired. A prerelease now only loses to a real release of the same
core, not to another prerelease of the same core.

Verified against the live repo: latest published tag is v2.9.0; a
Release build of this worktree (14 commits ahead) reports
AssemblyInformationalVersion 2.9.1-alpha.0.14+<sha>.

src/ClaudeDo.App/Program.cs

@@ -111,7 +111,9 @@ sealed class Program
             var releases = sp.GetRequiredService<IReleaseClient>();
             var informational = Assembly.GetEntryAssembly()?
                 .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion;
-            // Strip MinVer build metadata ("+sha") and any prerelease suffix for the update-compare.
+            // Strip MinVer build metadata ("+sha") only — keep the prerelease suffix
+            // (e.g. "-alpha.0.14"), VersionComparer needs it to tell a dev build on
+            // main apart from a tagged release of the same numeric core.
             var version = (informational ?? "0.0.0").Split('+')[0];
             return new UpdateCheckService(releases, version);
         });

src/ClaudeDo.Releases/VersionComparer.cs

@@ -10,7 +10,17 @@ public static class VersionComparer
                         | !Version.TryParse(CoreVersion(current), out var cv);
 
         if (unparseable) return new VersionCompareResult(false, true);
-        return new VersionCompareResult(lv > cv, false);
+        if (lv != cv) return new VersionCompareResult(lv > cv, false);
+
+        // Same numeric core: a MinVer dev build sitting on main between two tags
+        // reports a prerelease of its own guessed *next* version (e.g. after tag
+        // v1.4.0, main computes "1.4.1-alpha.0.12" — already ahead of the tag by
+        // core, handled above). But when a real release is tagged at exactly that
+        // guessed version, the tag itself has no prerelease suffix while a still-
+        // running dev build does — that dev build must still count as older, or a
+        // genuine new release would be silently missed.
+        var isNewer = HasPrerelease(current) && !HasPrerelease(latest);
+        return new VersionCompareResult(isNewer, false);
     }
 
     // Reduce a tag/version to its numeric core: drop a leading "v", MinVer build
@@ -18,4 +28,7 @@ public static class VersionComparer
     // which System.Version can parse. So "v1.0.2-alpha+abc" -> "1.0.2".
     private static string CoreVersion(string value)
         => (value ?? "").TrimStart('v', 'V').Split('+')[0].Split('-')[0];
+
+    private static bool HasPrerelease(string value)
+        => (value ?? "").TrimStart('v', 'V').Split('+')[0].Contains('-');
 }

tests/ClaudeDo.Releases.Tests/VersionComparerTests.cs

@@ -17,6 +17,15 @@ public class VersionComparerTests
     [InlineData("v1.0.2-alpha+1c764dae", "1.0.0", true, false)]             // v-prefix + prerelease + build metadata combined
     [InlineData("1.0.2-alpha+abc", "1.0.2-alpha", false, false)]           // same core -> not newer
     [InlineData("1.2.0-rc1", "1.2.0", false, false)]                       // prerelease of an already-installed release
+    // A dev build sitting on main computes a MinVer prerelease of its own guessed next
+    // version, ahead of the last tag by core -> no banner (real-world repro: latest
+    // published tag v2.9.0, worktree 14 commits ahead builds "2.9.1-alpha.0.14+sha").
+    [InlineData("2.9.0", "2.9.1-alpha.0.14", false, false)]
+    // A genuine new release lands at exactly the version a running dev build had
+    // already guessed -> the release must still win over the still-running prerelease.
+    [InlineData("1.4.1", "1.4.1-alpha.0.12", true, false)]
+    // An installed real release exactly matching the latest tag stays "up to date".
+    [InlineData("1.4.1", "1.4.1", false, false)]
     public void Compare_ParseableVersions(string latest, string current, bool expectedNewer, bool expectedUnparseable)
     {
         var result = VersionComparer.Compare(latest, current);