Add ruff BLE001 as a swallowed-exception smell

[LiinaSuoniemi]

What

Adds ruff's BLE001 (blind-except) as a new swallowed-exception smell, with a coaching prompt that tells the agent what to do instead of just reporting the rule.

Why

A broad except that swallows the error is a silent-failure risk. ruff already flags it; this turns the bare "Do not catch blind exception" into actionable guidance, in the habit-hooks style.

Design note

swallowed-exception is the first smell sourced only from ruff, with no TypeScript twin (the existing ruff smells reuse an eslint or knip smell). So Rule.source needed a new value. I added 'ruff' to RuleSource and to config validation, mirroring how knip is a spec-driven source. Happy to take a different approach if you'd prefer.

Severity is suggested, not enforced: blind-except has legitimate top-level uses (request handlers, worker loops), so it coaches rather than failing the run. Easy to flip.

Changes

• src/config/tool-smells.ts (RUFF_SPEC): add BLE001 to --select, produces, and the map.
• src/config/catalogue.ts: new swallowed-exception rule (source: 'ruff').
• src/types.ts and src/config/validate.ts: add the 'ruff' source.
• src/prompts/swallowed-exception.md: the coaching prompt.
• docs/smell-vocabulary.md and docs/DECISIONS.md: catalogue row, ruff mapping row, decision record.
• src/python-acceptance.test.ts: a test that BLE001 fires swallowed-exception and that a specific, named except does not. Gated on ruff like the other Python tests (skipped on CI without the toolchain).

Testing

Full suite green locally with ruff and deptry installed (503 passed). typecheck and lint clean.

[devill]

Cleanly wired: new 'ruff' source is metadata-only (no double-emit), prompt auto-registers via the catalogue, changedFilesOnly/severity consistent with sibling smells. TS swallowed-exception equivalent is a separate, narrower concern (no BLE001 analog in untyped JS catch).