fix(rag): scope lazy-load catches so model failures aren't mislabeled 'not installed' (#118)

[daviddgonzalez]

Closes #118.

Problem

loadPipeline in packages/rag/src/embedding-providers/transformers-embedding-provider.ts wrapped both the dynamic import('@xenova/transformers') and the model download/inference in a single try/catch that always rethrew a fixed @xenova/transformers is not installed message. Any failure in step B (model download, network error, onnxruntime-node native backend, OOM, …) was reported as "not installed" even when the package was installed and importable — and the real error was swallowed, not even attached as cause.

This actively misled debugging: a Windows CI failure was initially diagnosed as a missing/optional dependency when the package was in fact installed; the real failure was the model download / native backend. PR #119 fixed the test-reliability symptom by skipping those tests on Windows, but the misleading error remained.

Fix

transformers-embedding-provider.ts — split the two failure modes so each surfaces an accurate message:

• Import failure → keeps the actionable @xenova/transformers is not installed hint, now with the original error attached as cause (previously dropped entirely).
• Model/inference failure → throws Failed to load transformers model '<model>' preserving the original error as cause.

A type-only import of pipeline types the holder variable across the two try blocks without an import() type annotation (lint) or any runtime dependency on the optional package.

onnx-embedding-provider.ts (the issue's "audit siblings" note) — its install-hint catch (loadOnnxRuntime) was already correctly scoped to the import alone, so it was left unchanged. But loadModel's model download (ensureModelFiles) and session creation (InferenceSession.create) previously bubbled raw errors with no provider/model context, so they now throw Failed to download ONNX model '<model>' / Failed to load ONNX model '<model>' with cause preserved.

Tests

No new tests. This is a pure error-message refinement adding no new branches that aren't already exercised by the existing integration paths; the happy path stays covered by the integration tests. Full bun run validate (lint, typecheck, unit + integration + system tests, duplication) passes.

Changelog

Added an entry under ### Fixed in the [Unreleased] section.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.69%. Comparing base (5d6f2ff) to head (a17a423).

Files with missing lines	Patch %	Lines
...src/embedding-providers/onnx-embedding-provider.ts	0.00%	18 Missing ⚠️
...dding-providers/transformers-embedding-provider.ts	0.00%	13 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
- Coverage   81.78%   81.69%   -0.10%     
==========================================
  Files         223      223              
  Lines       17135    17155      +20     
  Branches     3326     3326              
==========================================
  Hits        14014    14014              
- Misses       3121     3141      +20     

Files with missing lines	Coverage Δ
...dding-providers/transformers-embedding-provider.ts	1.92% <0.00%> (-0.35%)	⬇️
...src/embedding-providers/onnx-embedding-provider.ts	20.86% <0.00%> (-1.98%)	⬇️

Files with missing lines	Coverage Δ
...dding-providers/transformers-embedding-provider.ts	1.92% <0.00%> (-0.35%)	⬇️
...src/embedding-providers/onnx-embedding-provider.ts	20.86% <0.00%> (-1.98%)	⬇️

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[daviddgonzalez]

This is just to do with I/O which will be tested in integration tests. Putting it in unit tests is redundant/might confuse other claudes that looks at the test suite

[jdutton]

@daviddgonzalez you can merge this whenever you are ready