fix(xlsx): seat category labels using native font metrics

[developer0hye]

Summary

Place explicitly sized worksheet line/area category labels using the measured font ascent, descent, and leading, the actual plot bottom, and the available chart height. The old automatic label band placed the budget workbook's month labels too high and did not follow shorter manual plots. Native one-factor font-size, font-family, plot-height, and fractional-frame-height probes distinguish the natural baseline from its bottom cap and the order of rounding.

The calibrated Calibri/Avenir metrics retain their source line gap when a runner uses a substitute font.

Related: #1568. The shared chart-origin offset remains tracked in #1542.

Testing

• Failing native-observation regressions captured before each correction: plot/size seating, fractional remaining-space rounding, and Arial leading quantization. Portable Calibri and numeric Arial cases cover line/area charts and short/default plots; host, flowed-chart, and implicit-size controls preserve their existing behavior.
• Initial candidate workspace tests: 3,473 passed. Linux CI then exposed a source/substitute metric mismatch for Calibri 24pt on a short plot. The follow-up keeps the calibrated source ascent, descent, and zero line gap together; both existing worksheet-baseline regressions and current workspace clippy pass without changing their expectations. Exact-head CI validates the follow-up across platforms.
• Native probe matrix on the initial candidate: 61 conversions passed; maximum origin-corrected baseline residual 0.000189 pt (0.01 pt gate). Five font families and multiple sizes, plot heights, and fractional frame heights; every native suite has a layout-identical no-patch control.
• The follow-up locked rebuild has a complete two-page MuPDF trace identical to the reviewed initial candidate (excluding the PDF filename).
• Same source fixture, Cargo.lock, and Excel DFonts before/after. The 13 month/year labels move from y=347.31837pt to 347.67213pt (native 347.88pt). The remaining -0.20787pt agrees with the independent chart text-origin offset in XLSX charts: fitted drawing foreground keeps the physical page origin #1542. January's x=185.98150pt is unchanged.
• Page 1 is pixel-identical at 150 DPI. At 300 DPI, page 2 changes 7,544 pixels, all within the category labels. All 831 canonical page-2 drawing primitives retain geometry and paint.
• All 55 page-1 and 480 page-2 material clusters have reviewed explicit dispositions. Normalized native/before/after text matches on both pages (486 and 2,120 non-whitespace characters).

Baseline: f0071d9ea88b71d33f4e5ba8fc2fc30ad206c099, including the separate axis-font and boundary-space fixes. Fixture SHA-256: 2b4a2d8dceda58758593c88409875efbda05780559154c02bd13fef4f7a1c65b; Cargo.lock SHA-256: 750f50c507b281f84b945b09573333ffa02dc45cddd566481af8535ae101e612.

Reproduce conversion with cargo run --locked -p office2pdf-cli -- tests/fixtures/xlsx/issue_1181_fit_to_height.xlsx -o output.pdf --font-path '/Applications/Microsoft Excel.app/Contents/Resources/DFonts'. Compare both pages using scripts/compare_layout.py GT.pdf output.pdf --audit --fine-shift 0.5 --json, and scripts/compare_render.py GT.pdf output.pdf --page P --dpi DPI --fine-shift 0.5 --cluster-report PATH --cluster-dispositions PATH --strict-clusters (150 DPI page 1, 300 DPI page 2).

Visual impact

• Rendered PDF change or visual evidence added

Visual audit

• Issue: Charts: Cambria line-chart category baselines sit 0.56pt above Excel #1568
• Fixture: tests/fixtures/xlsx/issue_1181_fit_to_height.xlsx (SHA-256 2b4a2d8dceda58758593c88409875efbda05780559154c02bd13fef4f7a1c65b)
• Page(s): 1, 2
• Renderer and DPI: pdftoppm at 150 DPI for page 1 and 300 DPI for page 2; MuPDF trace geometry
• Evidence mode: fix
• Layout audit report: assets/bugfixes/issue-1568/layout-audit.json
• Render cluster reports: assets/bugfixes/issue-1568/render-clusters-page-1.json, assets/bugfixes/issue-1568/render-clusters-page-2.json
• Reference exporter differences: None
• Fine-detail threshold: 0.5pt
• Layout audit page count: Pass
• Layout audit text flow: XLSX: fitted fixed-row cell baselines sit up to 2.16pt above Excel on the budget sheet #1545, XLSX: wrapped Trebuchet MS 10pt lines advance 11.89pt instead of Excel’s 13pt #1551
• Layout audit visible fills: Pass
• Layout audit rectangle geometry: XLSX: an anchored chart's frame sits 12.4pt right of the native export's and 1.9% narrow #1272, XLSX: the Arial 18pt auto title row prints 28pt instead of Excel’s 24pt #1550
• Layout audit large shifts: Pass
• Layout audit fine shifts: XLSX: an anchored chart's frame sits 12.4pt right of the native export's and 1.9% narrow #1272, XLSX charts: fitted drawing foreground keeps the physical page origin #1542, XLSX: fitted fixed-row cell baselines sit up to 2.16pt above Excel on the budget sheet #1545, XLSX: the Arial 18pt auto title row prints 28pt instead of Excel’s 24pt #1550, XLSX: wrapped Trebuchet MS 10pt lines advance 11.89pt instead of Excel’s 13pt #1551, XLSX: a mixed-size Aptos footer remains 0.78pt above its native baseline #1552
• New follow-up issues found in this audit: None
• Model vision findings: Inspected both full GT/output pages and diffs, all 64 matched fine-shift crops at full resolution, the final JPEG, and the exact before/after change mask. The 13 month/year labels move down 0.35376pt to y=347.67213pt against native y=347.88pt; the remaining -0.20787pt matches the shared text-origin offset in XLSX charts: fitted drawing foreground keeps the physical page origin #1542. Their horizontal position, source boundary spaces, Cambria face, size, and color remain unchanged. All 831 canonical page-2 drawing primitives retain geometry and paint. Only 7,544 pixels change, confined to these labels; page 1 is identical. All 535 material clusters retain reviewed exact-ID dispositions. Gray hairlines, double rules, teal totals and brown rules retain their paths, with known thickness/placement differences XLSX: fitted worksheet rules remain centered 1pt strokes instead of 0.78pt boundary bands #1564; the omitted chart separators remain XLSX: anchored worksheet line shapes between budget charts are omitted #1566. Existing marker, frame, fixed-row, and first-page layout defects remain tracked below.
• GT: assets/bugfixes/issue-1568/gt.jpg
• Before: assets/bugfixes/issue-1568/before.jpg
• After: assets/bugfixes/issue-1568/after.jpg
• Native: None
• Compare: None

Visual comparison

Native Excel 16.112.3 exports, verified Excel/Quartz PDF provenance. Page 2 at 300 DPI:

GT	Before	After

The unchanged page-1 native comparison is attached to #1550, #1551, and #1552.

Required inspection

• Rendered all evidence at 150 DPI or higher
• Stored progressive JPEG quality 86 assets with metadata stripped
• Used Codex/Claude vision to inspect the full GT/output pages, diff, and matched crops
• Inspected matched region crops at full resolution
• Ran compare_layout.py --audit --fine-shift PT and dispositioned every fine/large text-instance shift, rectangle geometry deviation, painted-text visibility mismatch, and visible-fill occlusion
• Ran compare_render.py --cluster-report PATH --strict-clusters and dispositioned every material 5% fuzz diff cluster by explicit ID
• Inventoried hairlines and border dash styles
• Inventoried font weight, italic, and underline emphasis

Deviation audit

Check	Result
Page count/order	Matches GT: two printable sheets retain their native order.
Element presence	Remaining: #1185 marker rendering and #1566 omitted worksheet separator lines. Existing axes and chart grid paths are retained.
Position/size	Remaining: #1272 chart frame, #1542 fitted drawings, #1545 fixed-row text, #1550 title-row height, #1552 footer position. Fixed: the category baseline follows the native face metrics and available chart height.
Rotation/flip	No deviation observed: no transform changes.
Fill	Matches GT: intended series, header, and table fills are unchanged.
Stroke/border	Remaining: #1566 omitted worksheet separator lines; #1564 fitted worksheet rule thickness/placement. Declared chart-line opacity remains 25% and 50%, matching native. Gray table hairlines, teal total rules, and brown category rules retain their paths; no dashed or dotted source rules are lost.
Shape outline geometry	Remaining: #1185 marker, #1272 chart frame, and #1550 title-band height. All 831 canonical primitives retain geometry and paint.
Text content	Matches GT after whitespace normalization of pdftotext -layout; all label/value characters are preserved; the source month categories also retain their significant trailing space.
Font family/weight/style	Matches GT: the existing Cambria major-theme category font is preserved. Bold Cambria section headings, bold Trebuchet expense headings, Arial bold instruction title, and Aptos footer retain their emphasis. No italic or underlined runs are changed.
Text color	Matches GT: chart labels and worksheet text retain their colors.
Alignment	Remaining: #1542 drawing labels, #1545 row text, #1550 first-page content, #1552 footer baselines. Fixed: month/year labels now use the native baseline seat relative to the chart origin.
Line/paragraph spacing	Remaining: #1545 fixed-row seating and #1551 wrapped note line pitch.
Clipping/overflow	No deviation observed: no new clipping or overflow; native and output both display ##### in the narrow annual-total cells.