fix: unblock command also clears merge_failure field

Previously unblock only checked for blocked=true. Stories stuck in
merge with a merge_failure field were not considered "blocked" and
unblock refused to act. Now it clears both blocked and merge_failure,
and reports which fields were cleared.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/chat/commands/unblock.rs

@@ -98,15 +98,27 @@ pub(crate) fn unblock_by_path(path: &Path, story_id: &str) -> String {
 
     let story_name = meta.name.as_deref().unwrap_or(story_id).to_string();
 
-    if meta.blocked != Some(true) {
+    let has_blocked = meta.blocked == Some(true);
+    let has_merge_failure = meta.merge_failure.is_some();
+
+    if !has_blocked && !has_merge_failure {
         return format!(
             "**{story_name}** ({story_id}) is not blocked. Nothing to unblock."
         );
     }
 
-    // Clear the blocked flag (reads + writes the file).
-    if let Err(e) = clear_front_matter_field(path, "blocked") {
-        return format!("Failed to clear blocked flag on **{story_id}**: {e}");
+    // Clear the blocked flag if present.
+    if has_blocked {
+        if let Err(e) = clear_front_matter_field(path, "blocked") {
+            return format!("Failed to clear blocked flag on **{story_id}**: {e}");
+        }
+    }
+
+    // Clear merge_failure if present.
+    if has_merge_failure {
+        if let Err(e) = clear_front_matter_field(path, "merge_failure") {
+            return format!("Failed to clear merge_failure on **{story_id}**: {e}");
+        }
     }
 
     // Reset retry_count to 0 (re-read the updated file, modify, write).
@@ -119,7 +131,10 @@ pub(crate) fn unblock_by_path(path: &Path, story_id: &str) -> String {
         return format!("Failed to reset retry_count on **{story_id}**: {e}");
     }
 
-    format!("Unblocked **{story_name}** ({story_id}). Retry count reset to 0.")
+    let mut cleared = Vec::new();
+    if has_blocked { cleared.push("blocked"); }
+    if has_merge_failure { cleared.push("merge_failure"); }
+    format!("Unblocked **{story_name}** ({story_id}). Cleared: {}. Retry count reset to 0.", cleared.join(", "))
 }
 
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