🎨 Palette: Improve HTML report table accessibility with row headers

.jules/palette.md

@@ -19,3 +19,7 @@
 ## 2024-07-13 - CLI Debugging Stack Traces
 **Learning:** Adding a `FAST_MLSIRM_DEBUG` bypass to user-friendly `try/except` blocks is crucial for DX. Otherwise, unexpected runtime errors during development will be swallowed into generic stderr messages, hiding the stack trace needed to actually fix the bug.
 **Action:** When adding `try-except` blocks to Python CLI subcommands to improve Developer Experience (DX) by preventing raw tracebacks for users, include a debug bypass (e.g., `if os.environ.get("FAST_MLSIRM_DEBUG"): raise`) in *all* catch blocks (including `RuntimeError` and `Exception`) to ensure tracebacks aren't swallowed during local development and debugging.
+
+## 2026-07-28 - Table Row Header Accessibility
+**Learning:** When generating HTML data tables for reports, using `<th scope="row">` for the first identifying column improves screen reader accessibility by clearly associating the row header with its corresponding data cells. Additionally, applying `font-variant-numeric: tabular-nums;` ensures numbers align properly in columns for better visual tracking.
+**Action:** Always use `<th scope="row">` for the primary identifying cell in a table row, update base CSS selectors (like `thead th, tbody th, td`) to include the new tags to prevent visual regressions, and apply tabular-nums for numeric alignment in data-heavy tables.

python/fast_mlsirm/report.py

@@ -317,11 +317,14 @@ def _table(rows: list[dict[str, Any]], *, label: str, limit: int = 12) -> str:
     columns = _columns(rows)
     body_rows = []
     for row in rows[:limit]:
-        cells = "".join(
-            f"<td>{escape(_format_value(row.get(column, '')))}</td>"
-            for column in columns
-        )
-        body_rows.append(f"<tr>{cells}</tr>")
+        cells = []
+        for index, column in enumerate(columns):
+            val = escape(_format_value(row.get(column, "")))
+            if index == 0:
+                cells.append(f'<th scope="row">{val}</th>')
+            else:
+                cells.append(f"<td>{val}</td>")
+        body_rows.append(f"<tr>{''.join(cells)}</tr>")
 
     note = ""
     described_by = ""
@@ -679,21 +682,28 @@ def _css() -> str:
   border: 0;
 }
 
-th,
+thead th,
+tbody th,
 td {
   padding: 10px 12px;
   text-align: left;
   border-bottom: 1px solid var(--line);
   white-space: nowrap;
+  font-variant-numeric: tabular-nums;
 }
 
-th {
+thead th {
   background: #f1f4ef;
   color: #2f3437;
   font-size: 0.8rem;
 }
 
-tr:last-child td {
+tbody th {
+  font-weight: normal;
+}
+
+tr:last-child td,
+tr:last-child th {
   border-bottom: 0;
 }