Report YAML syntax errors as located Q-1-1 (quarto-yaml 0.4.0)

[cscheid]

Fixes bd-x30aq7ae: a malformed YAML front-matter block was reported as Q-0-99 with an internal source path in the title ((at crates/pampa/src/utils/diagnostic_collector.rs:45)) and a span over the whole block. It now reports as Q-1-1 "YAML Syntax Error", located at the character where parsing failed.

Error: [Q-1-1] YAML Syntax Error
   ╭─[ bad-frontmatter.qmd:4:7 ]
 4 │ format: html
   │       ┬
   │       ╰── illegal placement of ':' indicator
ℹ The YAML front matter at the top of this document could not be parsed

The precise position comes from quarto-yaml 0.4.0 (posit-dev/quarto-yaml#21, upstream strand qy-scan-error-location-f9r4yvxq). Scan errors now carry location, and the message no longer embeds position text. Plan: claude-notes/plans/2026-10-08-frontmatter-yaml-error-code.md.

What changed

• Dependency: quarto-yaml 0.3.0 → 0.4.0.
• New pampa::utils::yaml_syntax_error: shared helpers that turn a quarto_yaml::Error into either a Q-1-1 diagnostic builder or prose ending in (line L, column C). It also contains the end-of-input clamp described below.
• Frontmatter (pampa/src/pandoc/meta.rs): emits a located Q-1-1 diagnostic with a hint naming the front matter.
• The bump regressed every site that stringified the error, so this PR fixes them all. Before 0.4.0, the message for parse_file callers ended in … at byte N line L column C, and that line number was file-relative and correct. After the bump, these sites would have printed no position at all:
  • Located Q-1-1 via QuartoError::Parse, with the file content registered under quarto-yaml's FileId (config_sources::yaml_parse_error): _quarto.yml, profile overlays and _quarto.yml.local, _metadata.yml.
  • Prose via describe_yaml_error: extension manifests (shown inside a Q-16-1 warning), the _variables.yml warning, language term files (×2), and the quarto use config loader.
  • No change needed: the Jupyter cell-option paths already used CellOptionsError::location(). They gain precise spans automatically.
• End-of-input clamp. The scanner reports a missing closer ([a, b with no ]) at end of input, which is past the trailing newline. That put the caret on the closing --- of front matter, or on a code cell's first code line. Such locations are now pulled back to the end of the YAML's last content: title: [unclosed points at 2:17.

Regression report: changed tests

Every existing test whose assertions changed:

Test	Before	After	Why
quarto::preview_static_e2e::a_failing_rerender_reports_diagnostics_and_does_not_reload	asserted SSE text and stderr contain Q-0-99	asserts Q-1-1 (2 asserts)	It pinned the bug: broken front matter was Q-0-99.
quarto::preview_static_e2e::boot_with_a_failing_page_still_serves_the_rest	stderr contains Q-0-99	stderr contains Q-1-1	Same fixture, same reason.
quarto render_once_tests::page_error_is_reported_not_fatal	diagnostics text contains Q-0-99	contains Q-1-1	Same.
quarto-core::pandoc_request_books::a_chapter_with_broken_front_matter_fails_before_any_chapter_renders	out.error.to_lowercase().contains("front")	out.error == "YAML Syntax Error", and the chapter's Q-1-1 diagnostic has a hint containing "front matter"	Worth a look. PandocRequestOutcome.error is the title of the first error. The old title was "Failed to parse YAML frontmatter: …"; the new one is the catalog title, so the one-line summary no longer says "front matter". The context moved into the diagnostic's hint, which this test now asserts. This was a design decision (catalog title + hint); if hub-client surfaces only error, a custom title may be preferable.
quarto-core project::…::test_directory_metadata_invalid_yaml_fails	to_string() contains "metadata"/"parse"/"yaml"	is QuartoError::Parse with one Q-1-1 diagnostic, and the render contains _metadata.yml:1:	Tightened to the new structured shape.
quarto-core::project_profile_overlays::overlay_yaml_parse_error_aborts_discovery	result.is_err()	also asserts a Q-1-1 located in _quarto-prod.yml with that file's content registered	Strengthened; the input is unchanged.

Unchanged on purpose: ipynb_content_processor::cell_option_yaml_error_lands_in_owning_cell failed after the bump alone. The caret had moved to row 1 (print(1)), off the #| error: [unclosed option line. The end-of-input clamp fixes this, and the test passes unmodified. pampa::test_warnings still pins Q-0-99 for the caption-without-table fallback, which is out of scope (see follow-ups).

New tests

• pampa::test_frontmatter_yaml_syntax_error: Q-1-1 with no internal path, the exact offending byte, non-ASCII text before the error, and an end-of-input error staying in bounds.
• pampa utils::yaml_syntax_error::tests: location and fallback, describe_yaml_error, the end-of-input clamp, and line_column on char boundaries.
• project_profile_overlays::base_config_yaml_syntax_error_is_located_q_1_1: _quarto.yml:3:6.
• One position test per prose site: extension manifest, term file, _variables.yml warning, and quarto use.

Not covered by a test

• The "before" strings for the config sites above come from reading quarto-yaml 0.3.0's Display (Parse error: {ScanError}, which ends in at byte N line L column C). They were not captured from a pre-change binary. The front-matter "before" was captured: claude-notes/plans/frontmatter-yaml-error-code-investigation/.

Verification

• cargo xtask verify --skip-css-lint:
  • Rust tests: 16,007 / 16,008 pass. The one failure is smoke_all, whose failing cases all fail for local engine reasons: R/knitr "R process failed", and great_tables/pandas missing for Jupyter. The same documents fail on unmodified main in this environment.
  • Steps 6–14, including the hub-client WASM build and test:wasm: all pass.
• --skip-css-lint is needed because main is red on lint:css. npm run lint:css -w hub-client also selects the nested hub-client/vscode-sync-experiment workspace. This is unrelated to this PR and tracked in bd-verify-css-lint-nested-ws-r0dd5vdk.

Follow-ups filed

• bd-caption-warning-q099-5krqlz6w: "Caption found without a preceding table" fallback is still Q-0-99 with a path in the title.
• bd-depth-limit-q099-f1q9vqjw: "too deeply nested" is Q-0-99 with no location.
• bd-metadata-yml-error-swallowed-b8sjkxek: a malformed _metadata.yml is silently ignored (metadata_merge.rs calls .unwrap_or_default()). This predates this PR. The error is now structured, but it still never reaches the user.

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