fix(py): properly handle mutliple runtimes in the reflection api

[pavelgj]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Summary of Changes

Hello @pavelgj, 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 a robust mechanism to properly handle multiple Genkit runtime instances, particularly within the reflection API. By assigning a unique identifier to each runtime and integrating this ID into the health check process, the changes ensure that interactions with the reflection API are correctly routed to the intended runtime instance. This enhancement improves the stability and reliability of the system when operating with several concurrent Genkit environments.

Highlights

• Unique Runtime Identification: Each Genkit runtime instance is now assigned a unique identifier, composed of the process ID and an instance counter, to differentiate it from other runtimes that might be active within the same process.
• ID Propagation to Reflection API: This newly generated unique ID is consistently passed to the reflection server creation and the runtime file initialization processes, ensuring all related components are aware of the specific instance.
• Enhanced Health Check Validation: The reflection API's __health endpoint now includes logic to validate an optional id query parameter. If provided, the health check will only succeed if the requested ID matches the server's own ID, preventing misdirected health checks when multiple runtimes are present.

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[gemini-code-assist]

Code Review

This pull request introduces a mechanism to handle multiple Genkit runtimes within the same process by assigning a unique ID to each GenkitBase instance. This ID is then used in the reflection API, particularly in the health check endpoint, to distinguish between different runtimes. The changes look good overall, but I have a couple of suggestions.

First, the method for generating unique instance IDs is not thread-safe, which could lead to race conditions. I've suggested using a threading.Lock to resolve this.

Second, the health check endpoint returns a 500 status code with an 'OK' message on an ID mismatch, which is unconventional. I've recommended a change to make the error response clearer.