plugin upgrade or degrade plugin file is not exists

[fatelei]

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Versions

1. dify-plugin-daemon Version
2. dify-api Version

Describe the bug

When a user triggers a plugin downgrade (e.g., from langgenius/openai:0.4.0 to langgenius/openai:0.3.8) through the Dify UI, the upgrade_plugin_with_marketplace method in plugin_service.py fails due to an inconsistency between two database tables in the daemon:

1. fetch_plugin_manifest(0.3.8) is called on the daemon
   → The daemon looks up the plugin_declarations table and finds the record (this table is NOT cleaned up during upgrades)
   → Returns success ✅
2. Since the manifest exists, the code assumes the package is already available locally
   → Skips the download_plugin_pkg + upload_pkg steps ❌
3. upgrade_plugin(0.4.0 → 0.3.8) is called on the daemon directly
   → The daemon queries the plugins table (this record WAS deleted during the previous upgrade when refers dropped to 0)
   → Falls through to the slow path, calls manager.Install()
   → Tries to read the package file from packageBucket → file not found → ERROR ❌

Root cause: The Dify API server uses fetch_plugin_manifest to determine whether a plugin package is already available in the daemon's local storage. However, the plugin_declarations record persists even after the corresponding plugins record and the actual packageBucket file have been removed. These two checks are inconsistent, causing the API server to skip the download-and-upload step for downgrade scenarios.

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