Semantic layer: install hint names the wrong venv, [semantic] lacks onnxruntime, doctor reports a missing runtime as info

[NetDevAutomate]

Found while fixing semantic: failed (0.0s) on the web header (studyloop tool venv missing the semantic runtime; fixed by the installer change on fix/tool-env-semantic-deps). Three defects in the same class remain. Each makes a missing runtime harder to see or to fix.

1. The install hint points at the wrong venv. embedding_store.INSTALL_HINT is uv tool install 'agent-session-tools[semantic]'. It reaches the learner through the warm's failure detail, which is the chip's tooltip, and through doctor. That command installs into agent-session-tools' own tool venv, not the studyloop venv that runs studyloop web, so following it changes nothing the learner sees.
2. [semantic] does not declare onnxruntime. The default backend (auto) resolves to ONNX for bge-small-en-v1.5, and onnx_encoder.py imports onnxruntime, tokenizers, huggingface_hub and numpy directly. A dry run shows agent-session-tools[semantic] resolves no onnxruntime. It arrives only through kokoro-onnx in [tts], so [all] works by coupling and [semantic] alone fails at onnxruntime is not installed.
3. doctor reports a missing runtime as info. check_query_encoder_artefact returns info: semantic layer not installed; ... does not apply when sentence_transformers is absent, even when a surface resolves to hybrid. That is the silent lexical-only degradation the check exists to report. The probe (sentence_transformers) is also not what the ONNX path imports.

Definition of done

• [semantic] declares every module the ONNX encoder and vector store import directly. A contract test pins this: onnxruntime, tokenizers, huggingface-hub, numpy, sqlite-vec.
• The missing-runtime hint names a command that fixes the venv that raised it (for a source install, ./scripts/install.sh --tools-only).
• doctor warns, not infos, when any surface resolves to hybrid and the ONNX path's modules are not importable in the running venv. The fix hint is the one above.
• One RED per item before its GREEN.