fix: renameAlias data corruption, empty sessionId match, NaN threshold

- Fix renameAlias() leaving orphaned newAlias key on save failure,
  causing in-memory data corruption with both old and new keys present
- Add sessionPath validation to setAlias() to reject empty/null paths
- Guard getSessionById() against empty string matching all sessions
  (startsWith('') is always true in JavaScript)
- Fix suggest-compact.js NaN comparison when COMPACT_THRESHOLD env var
  is set to a non-numeric value — falls back to 50 instead of silently
  disabling the threshold check
- Sync suggest-compact.js to .cursor/ copy

scripts/lib/session-aliases.js

@@ -189,6 +189,11 @@ function setAlias(alias, sessionPath, title = null) {
     return { success: false, error: 'Alias name cannot be empty' };
   }
 
+  // Validate session path
+  if (!sessionPath || typeof sessionPath !== 'string' || sessionPath.trim().length === 0) {
+    return { success: false, error: 'Session path cannot be empty' };
+  }
+
   if (!/^[a-zA-Z0-9_-]+$/.test(alias)) {
     return { success: false, error: 'Alias name must contain only letters, numbers, dashes, and underscores' };
   }
@@ -325,8 +330,9 @@ function renameAlias(oldAlias, newAlias) {
     };
   }
 
-  // Restore old alias on failure
+  // Restore old alias and remove new alias on failure
   data.aliases[oldAlias] = aliasData;
+  delete data.aliases[newAlias];
   return { success: false, error: 'Failed to rename alias' };
 }
 

scripts/lib/session-manager.js

@@ -271,7 +271,7 @@ function getSessionById(sessionId, includeContent = false) {
     if (!metadata) continue;
 
     // Check if session ID matches (short ID or full filename without .tmp)
-    const shortIdMatch = metadata.shortId !== 'no-id' && metadata.shortId.startsWith(sessionId);
+    const shortIdMatch = sessionId.length > 0 && metadata.shortId !== 'no-id' && metadata.shortId.startsWith(sessionId);
     const filenameMatch = filename === sessionId || filename === `${sessionId}.tmp`;
     const noIdMatch = metadata.shortId === 'no-id' && filename === `${sessionId}-session.tmp`;