feat: add --watch mode with change diffing

Re-scans every 30 seconds and shows new files, deleted files, and
size changes between scans.

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

luminos_lib/watch.py

@@ -0,0 +1,108 @@
+"""Watch mode — re-scan and show diffs every 30 seconds."""
+
+import json
+import sys
+import time
+import os
+
+
+def _snapshot(classified_files):
+    """Create a snapshot dict: path -> (size, category)."""
+    return {f["path"]: (f["size"], f["category"]) for f in classified_files}
+
+
+def _diff_snapshots(old, new):
+    """Compare two snapshots and return changes."""
+    old_paths = set(old.keys())
+    new_paths = set(new.keys())
+
+    added = new_paths - old_paths
+    removed = old_paths - new_paths
+    common = old_paths & new_paths
+
+    size_changes = []
+    for p in common:
+        old_size = old[p][0]
+        new_size = new[p][0]
+        if old_size != new_size:
+            size_changes.append((p, old_size, new_size))
+
+    return added, removed, size_changes
+
+
+def _human_size(nbytes):
+    for unit in ("B", "KB", "MB", "GB"):
+        if nbytes < 1024:
+            if unit == "B":
+                return f"{nbytes} {unit}"
+            return f"{nbytes:.1f} {unit}"
+        nbytes /= 1024
+    return f"{nbytes:.1f} TB"
+
+
+def watch_loop(target, depth=3, show_hidden=False, json_output=False):
+    """Run scan in a loop, printing diffs between runs."""
+    # Import here to avoid circular import
+    from luminos_lib.filetypes import classify_files
+
+    print(f"[luminos] Watching {target} (Ctrl+C to stop)")
+    print(f"[luminos] Scanning every 30 seconds...")
+    print()
+
+    prev_snapshot = None
+
+    try:
+        while True:
+            classified = classify_files(target, show_hidden=show_hidden)
+            current = _snapshot(classified)
+
+            if prev_snapshot is not None:
+                added, removed, size_changes = _diff_snapshots(
+                    prev_snapshot, current
+                )
+
+                if not added and not removed and not size_changes:
+                    ts = time.strftime("%H:%M:%S")
+                    print(f"[{ts}] No changes detected.")
+                else:
+                    ts = time.strftime("%H:%M:%S")
+                    print(f"[{ts}] Changes detected:")
+
+                    if json_output:
+                        diff = {
+                            "timestamp": ts,
+                            "added": sorted(added),
+                            "removed": sorted(removed),
+                            "size_changes": [
+                                {"path": p, "old_size": o, "new_size": n}
+                                for p, o, n in size_changes
+                            ],
+                        }
+                        print(json.dumps(diff, indent=2))
+                    else:
+                        for p in sorted(added):
+                            name = os.path.basename(p)
+                            print(f"  + NEW  {name}")
+                            print(f"         {p}")
+                        for p in sorted(removed):
+                            name = os.path.basename(p)
+                            print(f"  - DEL  {name}")
+                            print(f"         {p}")
+                        for p, old_s, new_s in size_changes:
+                            name = os.path.basename(p)
+                            delta = new_s - old_s
+                            sign = "+" if delta > 0 else ""
+                            print(f"  ~ SIZE {name}  "
+                                  f"{_human_size(old_s)} -> {_human_size(new_s)} "
+                                  f"({sign}{_human_size(delta)})")
+                    print()
+            else:
+                print(f"[{time.strftime('%H:%M:%S')}] "
+                      f"Initial scan complete: {len(current)} files indexed.")
+                print()
+
+            prev_snapshot = current
+            time.sleep(30)
+
+    except KeyboardInterrupt:
+        print("\n[luminos] Watch stopped.")