fix(firestore): keep thought parts out of FirestoreMemoryService - #7831

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Link to Issue or Description of Change

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

• Closes: FirestoreMemoryService indexes, stores and returns the model's thought parts #7830

Problem:
FirestoreMemoryService built search keywords from every part of an event, including the model's thought parts. It stored those parts in the memory content, and search_memory returned them. Words that only appeared in the model's hidden reasoning made a memory match a query, load_memory / PreloadMemoryTool handed that reasoning back to the model, and a thought-only event still got a memory document.

Solution:

• Ingest: keep only non-thought parts. They are the source of the keywords and of the stored content, and an event with no visible text is skipped as before.
• Search: drop thought parts from returned content, so memories written before this change come back clean too (as fix(memory): exclude thought parts from SQLite search results #7691 did for SQLite).

This matches the in-memory and Vertex RAG memory services (#7473) and SQLite (#7691). Parts with thought=False or None are unchanged.

Testing Plan

Unit Tests:

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

Added to tests/unittests/integrations/firestore/test_firestore_memory_service.py:

• test_add_session_to_memory_keeps_thoughts_out: keywords and stored content come from the visible part only.
• test_add_session_to_memory_skips_thought_only_events: no document is written.
• test_search_memory_drops_stored_thought_parts: a document that already holds a thought part is returned without it.

# On main (before the fix)
AssertionError: assert {'brown', 'es...', 'weighing'} == {'brown', 'fox', 'quick'}
AssertionError: Expected 'set' to not have been called. Called 1 times.
AssertionError: assert ['weighing th...ck brown fox'] == ['quick brown fox']

# With the fix
$ pytest tests/unittests/integrations/firestore tests/unittests/memory
256 passed

pre-commit run passes on the changed files, and mypy reports no issues in firestore_memory_service.py.

Manual End-to-End (E2E) Tests:

I don't have a Firestore instance or emulator. The tests drive the service through the mocked Firestore client the existing tests use, and assert on what batch.set writes and what search_memory returns.

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.

Additional context

None.