Summary

Referencing a resource (e.g. an image) whose source is missing previously produced a plain, code-less error from OutputSinkError::Copy, flattened to QuartoError::other(String) and printed via the legacy single-line path:

error: <doc>: failed to copy <src> -> <dest>: No such file or directory (os error 2)

No error code, no explanation, no source span. This PR routes it (and its sibling I/O faults) through quarto-error-reporting as structured diagnostics, splitting the two failure modes:

• Q-5-6 "Referenced resource not found" — a warning, located on the offending ![](…) reference. Detected via runtime.is_file(src) before the copy is attempted; the render continues without the file (matching Quarto 1's tolerant behavior).
• Q-5-7 "Resource copy failed" — a hard error for a genuine flush-time fault (permission denied, disk full). Span-less; the underlying io::ErrorKind is surfaced as advisory detail. Reaches the pretty reporting path via QuartoError::Parse.

Implementation

• ResourceCopyIntent { src, dest, origin: SourceInfo } replaces the bare (PathBuf, PathBuf) copy-intent tuple, carrying the reference's span (img.target_source.url, falling back to img.source_info). Threaded through the render context, stage context, collector, and both drain sites.
• New resource_copy_diagnostics module with the two converters plus shared enqueue_resource_copies (existence-check + enqueue) and copy_failure_error helpers, mirroring the existing resource_error_to_parse_error precedent. Both the native (render_document_to_file) and WASM/preview (pass2_renderer::flush_resource_copies) drains use them.
• Only OutputSinkError::Copy routes to Q-5-7; HTML-write / dir-create faults keep their existing path.

Tests

• Catalog presence test for Q-5-6/Q-5-7.
• Converter unit tests: missing → Q-5-6 located warning; permission-denied → Q-5-7 with advisory; disk-full surfaces the raw OS message.
• Integration regression tests (single-doc + website) asserting a missing image yields a Q-5-6 warning and the render still succeeds.

Docs

docs/errors/project/Q-5-6.qmd, docs/errors/project/Q-5-7.qmd.

Verification

• cargo nextest run --workspace — 10,284 passed.
• cargo xtask verify (Rust + WASM + hub-client builds and tests) — all steps passed.
• End-to-end through the binary: q2 render of a doc with a missing image prints the pretty [Q-5-6] diagnostic underlining the reference, exit 0, HTML produced. q2 render docs/ turns the former hard copy error into Q-5-6 warnings (168/168 files rendered).

The one remaining error in a full docs/ render (duplicate crossref identifier fig-charts) is a pre-existing, unrelated docs-content bug, tracked separately in bd-rr6qzcvu.

Plan: claude-notes/plans/2026-06-19-resource-copy-error-diagnostic.md

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