session: add ErrSessionNotFound and standardize not-exists handling (Fixes #85)

[casey-quinn]

Summary

• add exported session.ErrSessionNotFound sentinel for missing sessions
• standardize in-memory and database providers to wrap not-found cases with the sentinel
• update provider tests to assert errors.Is(..., session.ErrSessionNotFound)

Fixes #85

Testing

• go test ./...

References

• Branch: https://github.com/agyn-sandbox/adk-go/tree/feature/issue-85-errsessionnotfound
• Commit: agyn-sandbox@981277c

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[gemini-code-assist]

Summary of Changes

Hello @casey-quinn, 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 refines error handling for missing sessions by introducing a dedicated sentinel error, session.ErrSessionNotFound. This change standardizes how both in-memory and database session services report when a session cannot be found, allowing consuming code to reliably identify and react to this specific condition. The update ensures consistency across different storage mechanisms and improves the clarity of error messages.

Highlights

• New Sentinel Error: Introduced session.ErrSessionNotFound, an exported sentinel error for cases where a requested session does not exist. This allows for consistent error checking using errors.Is.
• Standardized Error Handling: The in-memory and database session providers now consistently wrap 'session not found' cases with session.ErrSessionNotFound in their Get, Delete, and AppendEvent methods.
• Updated Tests: Provider tests have been updated to assert errors using errors.Is(err, session.ErrSessionNotFound), ensuring the new error handling is correctly implemented and verifiable.

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[casey-quinn]

Local verification:

• go vet ./... (pass)
• go test ./... (pass, all packages)

[gemini-code-assist]

Code Review

This pull request effectively standardizes the session not-found error handling by introducing ErrSessionNotFound and applying it across both the database and in-memory session providers. The changes are well-implemented and the tests are updated accordingly. I've added a couple of minor suggestions to improve consistency in error messages and to correct some copy-paste errors in the test files, which will enhance maintainability.

[noa-lucent]

Thanks for the thorough update! I verified that session.ErrSessionNotFound is exported with clear GoDoc and is used consistently across both the database and in-memory service implementations for Get/Delete/AppendEvent missing-session paths. The new error wrapping avoids false positives and the provider tests now assert errors.Is against the sentinel for each operation. Everything looks solid to me.