[RAG Retrieval] Add deterministic semantic and hybrid retrieval

[rica-v3]

Summary

• add bounded semantic retrieval and deterministic rank-only hybrid fusion over caller-owned collaborators
• extract and publish the unchanged v1 projection integrity algorithms for shared current-state validation
• filter stale revisions, deduplicate exact identities, map branch failures truthfully, and keep results score-free
• document the complete independent host flow for authorization, source revalidation, citations, users, and agents
• preserve an empty package-root facade and a dependency-free/provider-neutral seven-module distribution

Verification

• 139 unit tests on Python 3.11 and 3.14
• Ruff lint and format checks
• strict mypy on both interpreters
• compileall on both interpreters
• wheel/sdist artifact verification, clean installs, isolated imports, and sdist rebuild
• 7/7 module-index parity, exact 12-edge acyclic graph, no private crossings
• executable documentation example and local Markdown link/anchor checks
• final main-agent 139-test run and git diff --check

Closes #4

[Copilot]

Pull request overview

This PR adds a new, dependency-free retrieval layer to generic-rag, implementing bounded semantic retrieval and deterministic rank-only hybrid fusion over caller-owned collaborators, while also extracting shared deterministic projection integrity algorithms into a dedicated module.

Changes:

• Introduces generic_rag.retrieval with retrieve_semantic and retrieve_hybrid, including strict contract validation, stale/current filtering, deduplication, deterministic tie-breaking, and score-free hybrid fusion (RRF with offset 60).
• Extracts projection integrity derivation/validation into generic_rag.projection_integrity and wires projection/retrieval to use it.
• Updates public docs, module index, packaging boundary tests, and adds comprehensive behavioral + golden tests for retrieval and integrity.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_retrieval.py	New end-to-end behavioral matrix for semantic + hybrid retrieval, determinism, validation, dedup, truncation, and failure/stale precedence.
tests/test_retrieval_contracts.py	Extends contract tests to cover the new RetrievalLimits type and invariants.
tests/test_projection_integrity.py	New golden/validation tests for extracted v1 integrity algorithms and workflow parity with projection.
tests/test_package_boundaries.py	Updates module inventory, dependency graph, and export assertions for the new modules.
tests/support/verify_artifacts.py	Ensures built artifacts include the two new production modules.
src/generic_rag/retrieval.py	Implements bounded semantic retrieval and deterministic hybrid fusion with strict validation and content-free failure mapping.
src/generic_rag/projection.py	Replaces inlined integrity logic with calls to generic_rag.projection_integrity.
src/generic_rag/projection_integrity.py	New shared module owning deterministic v1 digest/ID/token derivation and checkpoint validation.
src/generic_rag/contracts.py	Adds RetrievalLimits contract type and exports it via __all__.
README.md	Updates package overview and guidance to include retrieval and links to the retrieval guide.
PYTHON_MODULE_INDEX.md	Expands indexed production units to 7 and documents responsibilities/dependencies for new modules.
docs/security-and-privacy.md	Documents retrieval-specific trust boundary, caller obligations, and collaborator data exposure.
docs/retrieval.md	New retrieval guide with an independent-consumer example and full host flow requirements.
docs/projection.md	Links projection lifecycle to retrieval usage and documents the extracted integrity helpers.
docs/lifecycle.md	Updates lifecycle guidance to include retrieval call scope and host operational ownership.
docs/api.md	Updates public API reference to include retrieval workflows and projection integrity helpers.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.