#1261 Attach causes to kb's loader errors and retire its lint deferral

[williamthorsen]

What

Errors kb raises on malformed input now carry the underlying parse error as their cause. Callers constructing one of these errors themselves can attach a cause. When kb reports a thrown error that carries no message, the diagnostic now names the error's class instead of trailing off empty.

Why

kb's loaders folded a caught error's message into a new error and discarded the error itself, leaving a caller that needed the original parse failure to scrape it back out of the message text. The lint rule that catches this saw two of the six sites: the other four throw KbLoaderError, whose constructor took no cause, so the rule had nothing to flag. kb was also one of the last two packages holding its lint rules at warn through a per-package deferral, which kept nine rules advisory across the package.

Details

🎉 Features

• KbLoaderError takes an optional ErrorOptions second argument and forwards it to Error.
• All six sites that fold a caught error into a new error attach it as cause: the registry, alias, config, and taxonomy loaders, and the taxonomy writer.
• Chained messages join their prefix and the underlying message with : , matching the shape of the shared chaining helper. Messages kb composes itself keep the em dash.

🐛 Bug fixes

• A diagnostic naming a thrown error that carries no message reports the error's class rather than ending after the colon.

♻️ Refactoring

• Nine copies of the instanceof Error ? … : String(…) ternary delegate to the shared description helper.
• Rule violations cleared across nine source modules: module-scope sets for repeated-comparison membership, Object.hasOwn for a dynamic in check, Iterator.prototype.toArray() for spreads of a map's keys or values, an awaited cleanup in place of a .catch(() => {}) chain, and a declaration moved past the early exit above it.

🧪 Tests

• The filesystem-fixture suite binds its paths as module-scope constants instead of assigning let declarations from a hook; three suites await a rejection directly rather than threading it through .catch or .then.
• Each of the six sites that gains a cause has an assertion covering it, plus a direct test of the KbLoaderError constructor and one pinning the empty-message rendering.

⚙️ Tooling

• kb's deferred-rule list and package strict-lint config are deleted, along with the eslint.config.ts import and tsconfig.json include that reached them. The nine rules return to the severity the shared preset sets.
• foreman, lifecycle, and run-core drop the same dead .config/**/*.ts tsconfig include, left behind when their own deferrals were retired.

📦 Dependencies

• Adds @williamthorsen/toolbelt.errors 0.2.0, kb's first @williamthorsen/* runtime dependency, for its description and chaining helpers.

Closes #1261

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