Add similarity scores and threshold filtering to Redis semantic search

[thepatrickchin]

Description

Add similarity_score field to MemoryItem and implement threshold-based filtering in Redis search method with similarity_threshold kwarg

Closes #1433

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Summary by CodeRabbit

• New Features

  • Added similarity-based filtering for search results via a configurable similarity threshold.
  • Search results now surface per-item similarity scores as part of returned memory items.

• Tests

  • Added tests verifying similarity_score is recorded and that threshold-based filtering excludes appropriate results.

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[coderabbitai]

Walkthrough

Adds similarity score handling to Redis semantic search: a similarity_threshold search kwarg is accepted and used to filter results by doc.score; each returned MemoryItem now carries an optional similarity_score field.

Changes

Cohort / File(s)	Summary
Redis Editor Implementation packages/nvidia_nat_redis/src/nat/plugins/redis/redis_editor.py	Adds similarity_threshold to search kwargs and logs it. Extracts similarity_score from doc.score, skips items failing the threshold, passes similarity_score into _create_memory_item(), and updates logging to report processed vs filtered counts. Updated _create_memory_item() signature to accept `similarity_score: float
Redis Editor Tests packages/nvidia_nat_redis/tests/test_redis_editor.py	Adds assertion that similarity_score is set for first search result. New test test_search_with_similarity_threshold_filters_results mocks docs with scores [0.2, 0.6, 0.4] and verifies threshold filtering yields only the expected subset; adjusts mocked JSON fetches accordingly.
Data Model src/nat/memory/models.py	Adds `similarity_score: float

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant RedisEditor as Editor
  participant EmbeddingService as Embeddings
  participant Redis
  participant Storage as JSONStore

  Client->>Editor: search(query, top_k, similarity_threshold?)
  Editor->>Embeddings: embed(query)
  Embeddings-->>Editor: vector
  Editor->>Redis: semantic search(vector, top_k)
  Redis-->>Editor: docs with doc.score
  Editor->>Editor: filter docs by similarity_threshold (doc.score <= threshold)
  Editor->>JSONStore: fetch JSON for kept docs
  JSONStore-->>Editor: doc JSONs
  Editor->>Client: [MemoryItem{..., similarity_score}] list

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main changes: adding similarity scores and threshold filtering to Redis semantic search, matching the PR's core objectives.
Linked Issues check	✅ Passed	The PR fully implements both requirements from issue #1433: adds similarity_score field to MemoryItem and implements similarity_threshold parameter for filtering in Redis search.
Out of Scope Changes check	✅ Passed	All changes are within scope: MemoryItem model extended with similarity_score, Redis editor implements threshold filtering and score propagation, and tests validate both features.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

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[willkill07]

/ok to test c6f419d

[willkill07]

Documentation build appears to have failed.

The runner failure is a known transient issue -- working on a fix for that separately.

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@packages/nvidia_nat_redis/src/nat/plugins/redis/redis_editor.py`:
- Around line 126-129: Validate and coerce similarity_threshold from kwargs
(e.g., in the block where similarity_threshold = kwargs.get(...)) by checking
isinstance/try-converting to float and setting a safe default or None on
failure; then when iterating search results (references to doc.score in the
vector search loop), ensure doc.score is not None and is numeric before
converting to float or comparing—skip or treat non-numeric scores as
below-threshold. Update the comparison logic to only compare when both floats
are valid and use a defined fallback behavior (e.g., treat invalid threshold as
no threshold or treat invalid score as failing the threshold check).

[willkill07]

/ok to test bf1292d

[willkill07]

/merge