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

.cursor/skills/strategic-compact/suggest-compact.js

@@ -0,0 +1,74 @@
+#!/usr/bin/env node
+/**
+ * Strategic Compact Suggester
+ *
+ * Cross-platform (Windows, macOS, Linux)
+ *
+ * Runs on PreToolUse or periodically to suggest manual compaction at logical intervals
+ *
+ * Why manual over auto-compact:
+ * - Auto-compact happens at arbitrary points, often mid-task
+ * - Strategic compacting preserves context through logical phases
+ * - Compact after exploration, before execution
+ * - Compact after completing a milestone, before starting next
+ */
+
+const fs = require('fs');
+const path = require('path');
+const {
+  getTempDir,
+  writeFile,
+  log
+} = require('../lib/utils');
+
+async function main() {
+  // Track tool call count (increment in a temp file)
+  // Use a session-specific counter file based on session ID from environment
+  // or parent PID as fallback
+  const sessionId = process.env.CLAUDE_SESSION_ID || String(process.ppid) || 'default';
+  const counterFile = path.join(getTempDir(), `claude-tool-count-${sessionId}`);
+  const rawThreshold = parseInt(process.env.COMPACT_THRESHOLD || '50', 10);
+  const threshold = Number.isFinite(rawThreshold) ? rawThreshold : 50;
+
+  let count = 1;
+
+  // Read existing count or start at 1
+  // Use fd-based read+write to reduce (but not eliminate) race window
+  // between concurrent hook invocations
+  try {
+    const fd = fs.openSync(counterFile, 'a+');
+    try {
+      const buf = Buffer.alloc(64);
+      const bytesRead = fs.readSync(fd, buf, 0, 64, 0);
+      if (bytesRead > 0) {
+        const parsed = parseInt(buf.toString('utf8', 0, bytesRead).trim(), 10);
+        count = Number.isFinite(parsed) ? parsed + 1 : 1;
+      }
+      // Truncate and write new value
+      fs.ftruncateSync(fd, 0);
+      fs.writeSync(fd, String(count), 0);
+    } finally {
+      fs.closeSync(fd);
+    }
+  } catch {
+    // Fallback: just use writeFile if fd operations fail
+    writeFile(counterFile, String(count));
+  }
+
+  // Suggest compact after threshold tool calls
+  if (count === threshold) {
+    log(`[StrategicCompact] ${threshold} tool calls reached - consider /compact if transitioning phases`);
+  }
+
+  // Suggest at regular intervals after threshold
+  if (count > threshold && count % 25 === 0) {
+    log(`[StrategicCompact] ${count} tool calls - good checkpoint for /compact if context is stale`);
+  }
+
+  process.exit(0);
+}
+
+main().catch(err => {
+  console.error('[StrategicCompact] Error:', err.message);
+  process.exit(0);
+});