fix: log persistence storage location for @persist decorator

[devin-ai-integration]

Summary

When using @persist on a flow, users had no way to discover where their flow state was being stored. The default SQLiteFlowPersistence resolves its path via appdirs.user_data_dir(), which is platform-specific and was never surfaced to the user. This addresses #5372.

Changes:

• SQLiteFlowPersistence._setup() now logs the resolved db_path at INFO level on initialization
• PersistenceDecorator.persist_state() now logs the storage location (the db_path for SQLite, or the class name for custom backends) at INFO level after each state save
• When verbose=True, the storage location is also printed to the console via PRINTER
• Adds 5 new tests covering path discoverability (init logging, save logging, verbose output, class-level decorator)

Behavioral note: The old save_state log message was renamed from "Saving flow state to memory for ID: {}" to "Saving flow state for ID: {}". The storage location is now logged unconditionally at INFO level on every save (previously, no log was emitted with verbose=False).

Review & Testing Checklist for Human

• Verify the INFO-level log on every save is acceptable noise. The storage location is logged at INFO on every persist_state() call, not just the first. For flows with many persisted steps, this could be chatty. Consider whether this should be DEBUG instead, or only logged once per persistence instance.
• Check the removed QuietFlow test was intentional. The old test asserted that verbose=False produced no "Saving flow state" logs. This assertion is no longer valid because storage location is now always logged at INFO. The test was removed rather than updated — confirm this behavioral change is desired.
• Verify getattr fallback for custom persistence backends. For non-SQLite backends without a db_path attribute, the log falls back to type(persistence_instance).__name__. Confirm this is useful enough for custom implementations.

Notes

• To manually verify: run any flow with @persist() and check that the log output includes the SQLite database path. Enable Python INFO logging (e.g., logging.basicConfig(level=logging.INFO)) or use verbose=True on the decorator.

Link to Devin session: https://app.devin.ai/sessions/0bf4c592e402444eb5656a8159404869

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Note

Low Risk
Low risk behavior change limited to additional INFO-level logging during persistence initialization and every state save; main concern is potential log noise or tests that assume quiet default logging.

Overview
Makes persisted flow state discoverable by logging where it is stored.

@persist now logs an INFO message after each save that includes the flow ID and the persistence storage location (uses db_path when available, otherwise the backend class name), and prints the same message to the console when verbose=True. SQLiteFlowPersistence also logs its resolved db_path on initialization.

Updates and expands tests to cover the new logging behavior (including default path logging, save-time storage logging, verbose output, and class-level @persist).

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