fix(query): align error display with existdb-openapi#71 envelope

[joewiz]

[This PR was prompted by Joe, drafted by Claude Code, and reviewed by Joe.]

Summary

Brings eXide's query-error display to parity with eXist-db/existdb-openapi#71's error envelope — the QueryError schema { code, message, line, column, raw } (HTTP 400): a concise human message, with the verbose W3C/Java boilerplate moved to raw and user-relative line/column. eXide's Run path consumes existdb-openapi's /api/query directly (runQueryCursor → ../existdb-openapi/api/query), so it sees this envelope. The change makes eXide prefer the concise message, keep raw available on hover, and fall back gracefully to the generic { error } shape that current existdb-openapi releases (≤ v0.9.7) still return.

eXide handles exactly these two shapes — QueryError (incoming, eXist-db/existdb-openapi#71) and generic { error } (current release). The intermediate { code, description, module, value } shape that some pre- eXist-db/existdb-openapi#71 dev builds emit was never tagged and won't be (releases go { error } → QueryError), so it isn't carried.

Changes

• runQueryCursor (src/eXide.js): factor a single queryErrorMessage() helper used by both the !response.ok branch and the 200-body guard (eXide#828). It prefers message (QueryError), then error (generic), then raw — so the pill shows the clean cause on either shape.
• src/error-status-ui.js: the detail panel and the hover-dump render message and expose raw on hover, and fall back to the plain-text formatter for the generic { error } so the panel is never blank. The pure formatters move to module scope (out of init()) so they can be unit-tested; the DOM bootstrap is guarded for that.

Tests

• test/error-status-ui-test.js (5 tests, node --test): pins the message/raw split and the generic-{ error } fallback against the real envelope samples captured from existdb-openapi. Mutation-verified — reverting the message preference fails the panel test, dropping the raw line fails the dump test, and removing the { error } fallback fails the generic test.
• query_error_structured_spec.cy.js: a version-robust live case (any envelope surfaces an error pill with the cause), plus a cy.intercept case that stubs the fix(query): user-relative line/column + clean message in /api/query error envelope existdb-openapi#71 envelope to exercise the full client path (queryErrorMessage → evalError → structured panel) deterministically, independent of the bed's existdb-openapi version.

Verification note

The node unit tests run green and are mutation-verified. The Cypress specs are written but I was not able to run them against a live bed in this pass: validating the eXist-db/existdb-openapi#71 envelope end-to-end needs a bed carrying both this eXide build and a post- eXist-db/existdb-openapi#71 (whose newer langservice dependency the local pkg bed doesn't satisfy). They will run in CI / against a matching bed.

Background

The eXist-db/existdb-openapi#71 heads-up originally pointed at eXide's own query:execute catch, but that endpoint is unused (the editor calls existdb-openapi directly) and is retired separately. The live error display is the existdb-openapi response path addressed here.