Fix 412 race condition in tag delete command

Add retry logic (up to 3 attempts) for PreConditionFailedError in the
delete_tags CLI command. The Zotero API uses optimistic concurrency
control, and the library version can change between the version check
and the DELETE request, causing spurious 412 errors.

Also fix the temp_tag_in_library test fixture to re-fetch items before
deletion to avoid stale version errors in cleanup.

Fixes #35

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

Author: chriscarrollsmith

pyzotero_cli/tag_cmds.py

@@ -1,6 +1,8 @@
+import time
 import click
 import json
 from pyzotero import zotero
+from pyzotero import zotero_errors
 from .utils import common_options, format_data_for_output, handle_zotero_exceptions_and_exit, create_click_exception, initialize_zotero_client
 
 @click.group(name='tags')
@@ -67,8 +69,20 @@ def delete_tags(ctx, tag_names, force):
             click.echo("Operation cancelled.")
             return
 
-    try:
-        result = zot.delete_tags(*tag_names)
-        click.echo(f"Successfully deleted tags: {', '.join(tag_names)}")
-    except Exception as e:
-        handle_zotero_exceptions_and_exit(ctx, e)
+    max_retries = 3
+    for attempt in range(max_retries):
+        try:
+            result = zot.delete_tags(*tag_names)
+            click.echo(f"Successfully deleted tags: {', '.join(tag_names)}")
+            return
+        except zotero_errors.PreConditionFailedError:
+            if attempt < max_retries - 1:
+                time.sleep(1)
+                continue
+            else:
+                handle_zotero_exceptions_and_exit(ctx, zotero_errors.PreConditionFailedError(
+                    "Library version conflict persisted after retries. "
+                    "Another process may be modifying the library."
+                ))
+        except Exception as e:
+            handle_zotero_exceptions_and_exit(ctx, e)

tests/test_tag_cmds.py

@@ -28,10 +28,11 @@ def temp_tag_in_library(zot_instance):
 
     yield tag_name # Yield the tag name to the test
 
-    # Cleanup
+    # Cleanup - re-fetch item to get latest version before deleting
     try:
-        if created_item and item_key:
-            zot_api_client.delete_item(created_item) # Delete the temporary item
+        if item_key:
+            fresh_item = zot_api_client.item(item_key)
+            zot_api_client.delete_item(fresh_item)
     except Exception as e:
         print(f"Error during tag fixture cleanup (deleting item {item_key}): {e}")