ci: run the orphaned tests/test_indexer.py in the test job

[CGFixIT]

Summary

ci.yml runs an explicit, hand-maintained list of test files. tests/test_indexer.py was added to the suite but never added to that list, so its 7 tests never run in CI:

• TestChunkDocument — 4 tests for chunk_document edge cases (empty text, single window, overlap stride, exact partitioning)
• TestBuildIndexValidation — 3 tests for the build_index fail-fast guards that reject chunk_size < 1 and chunk_overlap >= chunk_size before a corrupt index is written

Net effect: the indexer's chunking math and config-validation guards had zero enforced regression coverage, even though the tests already exist and pass.

The change

One line — add the file to the existing list:

             tests/test_hybrid_search.py \
+            tests/test_indexer.py \
             tests/test_graph.py \

The tests are fully hermetic (validation cases raise before any embedding/Chroma work; chunking cases are pure Python), so they need no live services and fit the existing hermetic CI env.

Note on coverage

I intentionally did not add --cov=retrieval.indexer. The validation tests exit early and would only partially cover the module; adding it to the coverage denominator could push the run under the fail_under = 80 gate. The goal of this PR is simply to execute the existing tests.

Verification

tests/test_indexer.py .......  7 passed
python -c "import yaml; yaml.safe_load(open('.github/workflows/ci.yml'))"  # valid YAML

Note: the explicit-list pattern is inherently easy to drift out of sync (this is how the gap arose). A follow-up could switch to directory-based collection, but that's a larger change with coverage-scoping implications, so it's kept out of this focused PR.

🤖 Generated with Claude Code

https://claude.ai/code/session_01LvLWMML8cpBq2q81kL1ByJ

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