fix(memory): keep turns a rewind took back out of long-term memory - #7571

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: After Runner.rewind_async, add_session_to_memory still stores the rewound turns in long-term memory #7570

2. Or, if no issue exists, describe the change:

Problem:
Runner.rewind_async keeps every event and appends a rewind event, and _apply_rewinds decides which events are still live; prompt building and compaction both use it. add_session_to_memory in all five memory services read session.events directly, so the turns a rewind took back were ingested into long-term memory, and load_memory / preload_memory handed them back to the model in later sessions. The rewind documentation says the rewound requests are ignored when the next model requests are prepared.

Solution:
add_session_to_memory in InMemoryMemoryService, SqliteMemoryService, VertexAiMemoryBankService, VertexAiRagMemoryService and FirestoreMemoryService passes _apply_rewinds(session.events) instead of session.events, the same filter the prompt and compaction paths use.

• InMemoryMemoryService replaces a session's events on each call, so adding the session again after a rewind also drops turns stored before the rewind.
• Not changed, to keep this to one concern: add_events_to_memory, where the caller chooses the events, and memories a remote service (Memory Bank, RAG, Firestore) already ingested before the rewind; the rewind documentation leaves external systems to the caller.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

New tests, one per service, each with a kept turn, a rewound turn and the rewind event:

• test_in_memory_memory_service.py::test_add_session_to_memory_skips_rewound_events: search no longer finds the rewound turn, also when the session was added once before the rewind.
• test_sqlite_memory_service.py::test_add_session_to_memory_skips_rewound_events (FTS on and off).
• test_vertex_ai_memory_bank_service.py::test_add_session_to_memory_skips_rewound_events: only the kept event is sent to ingest_events.
• test_vertex_ai_rag_memory_service.py::test_add_session_to_memory_skips_rewound_events: the uploaded file has the kept turn and not the rewound one.
• test_firestore_memory_service.py::test_add_session_to_memory_skips_rewound_events: only the kept turn's keywords are written.

All 6 cases fail with the src/ change reverted and pass with it:

$ pytest tests/unittests/memory tests/unittests/integrations/firestore/test_firestore_memory_service.py
195 passed

The full tests/unittests run has no new failures: 6 more tests pass than on main, and the tests that fail locally (Windows shell, symlink and path tests) fail on main too.

Manual End-to-End (E2E) Tests:

The script in #7570 (no model or credentials needed) rewinds a two-turn session and adds it to InMemoryMemoryService and SqliteMemoryService.

Before:

events the model sees after the rewind: ['I am planning a trip to Paris.', 'Paris sounds great.']
InMemoryMemoryService recalls the undone turn: ['Actually my new address is 42 Baker Street.', 'Noted, 42 Baker Street.']
SqliteMemoryService recalls the undone turn: ['Noted, 42 Baker Street.', 'Actually my new address is 42 Baker Street.']

After:

events the model sees after the rewind: ['I am planning a trip to Paris.', 'Paris sounds great.']
InMemoryMemoryService recalls the undone turn: []
SqliteMemoryService recalls the undone turn: []

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.