feat(#1129): tell test builds of one version apart by commit

Test builds share a version and build number, so the sponsor window would
show only for the first of them. A build passed --dart-define=GIT_SHA=<sha>
is now known as 1.8.0+69@<sha>; a build without it (CI releases, whose
build number always changes) stays 1.8.0+69.

Tests: two commits of one version each show it once; the gate test passes
with and without GIT_SHA defined, and failed with the old fixed expectation
when it was defined. Full suite 2076 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/widgets/sponsor_prompt.dart

@@ -18,9 +18,20 @@ class SponsorPrompt {
   static const String offKey = 'sponsor_prompt_off';
   static final Uri sponsorUri = Uri.parse('https://offband.org/donate');
 
-  /// Shows the window unless it has already shown for [version], the user
-  /// turned it off, or this is iOS (hidden there like About's Donate, #1051).
-  /// The version is saved before the window opens, so a crash can't loop it.
+  /// The commit a test build was made from, passed with
+  /// `--dart-define=GIT_SHA=<sha>`. Test builds share one version and build
+  /// number, so this is what tells them apart. Release builds leave it empty:
+  /// their build number already changes every time.
+  static const String buildSha = String.fromEnvironment('GIT_SHA');
+
+  /// What one installed build is known by: `1.8.0+69`, or `1.8.0+69@<sha>`.
+  static String buildId(String version, {String sha = buildSha}) =>
+      sha.isEmpty ? version : '$version@$sha';
+
+  /// Shows the window unless it has already shown for this build ([version] is
+  /// its [buildId]), the user turned it off, or this is iOS (hidden there like
+  /// About's Donate, #1051). The build is saved before the window opens, so a
+  /// crash can't loop it.
   static Future<void> maybeShow(
     BuildContext context, {
     String? version,
@@ -68,7 +79,7 @@ class SponsorPrompt {
   static Future<String?> _installedVersion() async {
     try {
       final info = await PackageInfo.fromPlatform();
-      return '${info.version}+${info.buildNumber}';
+      return buildId('${info.version}+${info.buildNumber}');
     } catch (e) {
       appLogger.error('Sponsor prompt: no app version: $e', tag: 'Sponsor');
       return null;

test/widgets/sponsor_prompt_test.dart

@@ -131,9 +131,10 @@ void main() {
     );
     await tester.pumpAndSettle();
     expect(_title, findsOneWidget);
+    // Carries the commit when the test run passes --dart-define=GIT_SHA.
     expect(
       PrefsManager.instance.getString(SponsorPrompt.shownForKey),
-      '1.8.0+69',
+      SponsorPrompt.buildId('1.8.0+69'),
     );
   });
 
@@ -179,6 +180,32 @@ void main() {
     });
   }
 
+  test('a test build is known by its commit, a release by its version', () {
+    expect(SponsorPrompt.buildId('1.8.0+69', sha: ''), '1.8.0+69');
+    expect(
+      SponsorPrompt.buildId('1.8.0+69', sha: 'abc1234'),
+      '1.8.0+69@abc1234',
+    );
+  });
+
+  testWidgets('two test builds of one version each show it once', (
+    tester,
+  ) async {
+    final prefs = await _prefs();
+    final first = SponsorPrompt.buildId('1.8.0+69', sha: 'abc1234');
+    final second = SponsorPrompt.buildId('1.8.0+69', sha: 'def5678');
+    await _launch(tester, prefs, version: first);
+    expect(_title, findsOneWidget);
+    await tester.tap(find.text('Not now'));
+    await tester.pumpAndSettle();
+
+    await _launch(tester, prefs, version: first);
+    expect(_title, findsNothing);
+
+    await _launch(tester, prefs, version: second);
+    expect(_title, findsOneWidget);
+  });
+
   test('Sponsor opens the donate page the About screen uses', () {
     expect(SponsorPrompt.sponsorUri.toString(), 'https://offband.org/donate');
   });