added permanent artifact links for latest green builds: /branches/<branch-key>/... serves the latest green build's artifacts (green-only, resolved per request), keepLatestGreen retention protection, permanent artifact-index page, and latestGreenUrl links in the branches view

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main/kotlin/de/hoennig/gittally/build/ArtifactKeys.kt

@@ -12,6 +12,13 @@ import java.time.Instant
 object ArtifactKeys {
     fun branchKey(branch: String): String = "${sanitize(branch)}-${sha256Prefix(branch)}"
 
+    /**
+     * The hash-free key of the permanent `/branches/<key>/…` artifact URLs, e.g.
+     * `feature/demo` → `feature_demo`. Unlike [branchKey] it is not necessarily
+     * unique; lookups must reject ambiguous matches.
+     */
+    fun permanentBranchKey(branch: String): String = sanitize(branch)
+
     fun buildKey(
         branch: String,
         startedAt: Instant,

src/main/kotlin/de/hoennig/gittally/build/BuildResultRepository.kt

@@ -17,6 +17,9 @@ interface BuildResultRepository {
 
     fun latestFor(branch: String): BuildResult?
 
+    /** The newest SUCCESS entry of [branch] — the build behind the permanent `/branches/…` links. */
+    fun latestGreenFor(branch: String): BuildResult?
+
     /** The newest entry of each branch, newest first. */
     fun latestPerBranch(): List<BuildResult>
 
@@ -34,10 +37,13 @@ interface BuildResultRepository {
 
     /**
      * Keeps the newest [retentionPerBranch] entries per branch and drops entries of branches
-     * not contained in [originBranches]. Returns the removed entries.
+     * not contained in [originBranches]. With [keepLatestGreen], the newest SUCCESS entry of
+     * each surviving branch is kept even beyond the retention count, so the permanent
+     * `/branches/…` artifact links stay valid while newer builds fail. Returns the removed entries.
      */
     fun prune(
         originBranches: Collection<String>,
         retentionPerBranch: Int,
+        keepLatestGreen: Boolean = false,
     ): List<BuildResult>
 }

src/main/kotlin/de/hoennig/gittally/build/FileBuildResultRepository.kt

@@ -70,6 +70,11 @@ class FileBuildResultRepository(
         return indexOfLatest(results, branch)?.let { results[it] }
     }
 
+    override fun latestGreenFor(branch: String): BuildResult? =
+        load()
+            .filter { it.branch == branch && it.status == BuildStatus.SUCCESS }
+            .maxByOrNull { it.startedAt }
+
     override fun latestPerBranch(): List<BuildResult> =
         load()
             .groupBy { it.branch }
@@ -117,6 +122,7 @@ class FileBuildResultRepository(
     override fun prune(
         originBranches: Collection<String>,
         retentionPerBranch: Int,
+        keepLatestGreen: Boolean,
     ): List<BuildResult> {
         synchronized(lock) {
             val results = load()
@@ -127,9 +133,15 @@ class FileBuildResultRepository(
                     .groupBy { it.branch }
                     .values
                     .flatMap { entries ->
-                        entries
-                            .sortedByDescending { it.startedAt }
-                            .take(retentionPerBranch.coerceAtLeast(0))
+                        val newest =
+                            entries
+                                .sortedByDescending { it.startedAt }
+                                .take(retentionPerBranch.coerceAtLeast(0))
+                        val latestGreen =
+                            entries
+                                .filter { keepLatestGreen && it.status == BuildStatus.SUCCESS }
+                                .maxByOrNull { it.startedAt }
+                        newest + listOfNotNull(latestGreen)
                     }.toSet()
             val removed = results.filterNot { it in kept }
             if (removed.isNotEmpty()) {