feat(graph-engine): add command to update variables at runtime

[laipz8200]

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Summary

Adds a new GraphEngine command to update variables at runtime, wiring it through the Redis command channel, manager API, and command handler. Includes unit tests covering command serialization and variable pool updates. Fixes #30562.

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @laipz8200, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the capability to dynamically update variables within a running workflow. By adding a new UpdateVariablesCommand and its corresponding handler, the system can now receive and process requests to modify workflow variables on the fly. This enhancement provides greater flexibility and control over workflow execution, allowing for real-time adjustments to workflow state without requiring a restart. The changes span across command definition, command channel integration, command processing logic, and a public interface for sending these commands, all backed by new unit tests.

Highlights

• New Command Type: Introduced a new UpdateVariablesCommand to allow dynamic modification of variables within a running workflow. This command includes a list of VariableUpdate objects, each specifying a new value for a variable identified by its selector.
• Command Handler Implementation: A dedicated UpdateVariablesCommandHandler has been implemented. This handler processes the UpdateVariablesCommand by iterating through the provided updates and adding or modifying variables in the workflow's VariablePool.
• Redis Channel Integration: The RedisChannel now recognizes and correctly deserializes the new UpdateVariablesCommand when fetching commands from Redis, ensuring that these commands can be transmitted and processed by the graph engine.
• Graph Engine Command Processing: The GraphEngine has been updated to register the UpdateVariablesCommandHandler with its CommandProcessor. This ensures that when an UpdateVariablesCommand is received, it is routed to the appropriate handler for execution.
• Manager Interface for Sending Commands: A new static method, send_update_variables_command, has been added to the GraphEngineManager. This provides a simplified interface for external components to send UpdateVariablesCommands to a specific workflow via the Redis channel.
• Comprehensive Unit Tests: New unit tests have been added to validate the functionality of the UpdateVariablesCommand, covering its deserialization from Redis and its correct processing by the GraphEngine to update the variable pool.

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[gemini-code-assist]

Code Review

This pull request introduces a new update_variables command to the workflow engine, allowing for dynamic variable updates during execution. The implementation is well-structured, touching upon command definition, Redis channel handling, command processing, and engine integration. The changes are accompanied by comprehensive unit and integration tests, ensuring the new functionality is robust. I have one suggestion to simplify the code in the new command handler.