feat: aggregations, multiple lines in line chart and dashboard tools refactoring - #591

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/mosaic/src/chart-types/line-chart/schema.ts`:
- Around line 24-26: The schema currently uses
AggregateFunction.optional().default('sum') so Zod 4 treats undefined as
optional and the default never runs; update the line in the line-chart schema to
remove .optional() (i.e., use AggregateFunction.default('sum') and keep
.describe(...)) so the default is applied by Zod at runtime, and then remove or
reconsider the defensive fallback (const aggregate = fieldConfig.aggregate ||
'sum') in definition.ts since the schema will now guarantee a value.

---

Outside diff comments:
In `@packages/mosaic/src/dashboard/MosaicDashboardSlice.ts`:
- Around line 742-758: The eviction check in shouldEvictPanelRuntimeForPatch is
using a nonexistent patch.config.vgplot property so chart config updates never
trigger eviction; update the MOSAIC_DASHBOARD_VGPLOT_PANEL_TYPE branch to
inspect actual VgPlotChartConfig fields (e.g., check whether patch.config has
ownProperty 'chartType' or 'settings' or 'settingsOpen') and return true when
any of those are present, or if you prefer, remove the specialized vgplot branch
and always return true for any config patch on VGPLOT panels to ensure
evictPanelRuntime is called on chart-settings updates.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/mosaic/src/chart-types/bubble-chart/schema.ts`:
- Around line 4-9: The optional string fields x, y and size in the Zod schema
currently allow empty strings; update their schema definitions to normalize
empty-string values to undefined so consumers never see '' (e.g., use a
preprocess/transform that maps '' to undefined before validating). Locate the
symbols x, y, and size in the schema.ts Zod object and replace the current
z.string().optional() chains with a z.preprocess or
z.string().optional().transform that returns undefined for '' and preserves
other strings/undefined.

In `@packages/mosaic/src/chart-types/count-plot/schema.ts`:
- Around line 4-7: The count-plot schema declares field as a categorical column
but tool.ts currently validates against QUANTITATIVE_COLUMN_TYPES
(numeric/temporal), which is backwards; fix by changing the validation in
tool.ts for the count-plot to accept categorical columns instead of quantitative
ones—either add a new CATEGORICAL_COLUMN_TYPES constant (e.g., include
nominal/ordinal/string/category types used elsewhere) and validate field against
that, or invert the existing check to ensure the chosen field's type is NOT in
QUANTITATIVE_COLUMN_TYPES; update the validation logic that references
QUANTITATIVE_COLUMN_TYPES so the count-plot only allows categorical columns,
keeping the schema.field (z.string()) unchanged.

---

Outside diff comments:
In `@packages/mosaic/__tests__/ChartSettings.test.tsx`:
- Line 119: Update the test fixture for the 'line-chart' entry so its settings
follow the new multiple-Y-fields schema: replace the single y property with
yFields being an array of YFieldConfig objects (e.g., change settings from {x:
'id', y: 'amount'} to {x: 'id', yFields: [{field: 'amount'}]}), ensuring the
'line-chart' fixture in ChartSettings.test.tsx matches the schema defined for
the line-chart type and exercises multiple Y fields support.
- Around line 16-22: The test fixture for "line-chart" uses the old shape {x:
'id', y: 'amount'}; update it to the new schema by replacing the old y property
with the new yFields array of YFieldConfig objects (e.g., yFields: [{ field:
'amount' }] while keeping the x/xField as appropriate) and ensure the fixture
matches the actual ChartSettings schema; also remove or narrow the settings: any
usage in the test and either import/apply the proper type for settings or use a
type assertion to the chart settings type so the mismatch is caught at compile
time (update references to settings and the "line-chart" fixture and ensure
YFieldConfig is used).

---

Nitpick comments:
In `@apps/sqlrooms-cli-ui/src/createChartToolDeps.ts`:
- Around line 23-26: The guard `if (!table?.columns) return null` is redundant
because getTablesWithColumns() already filters out empty columns; update the
check to only return when the table itself is not found (e.g., replace or remove
the columns null-check so you only handle `!table`) in the code around the
`getTablesWithColumns(state).find(...)` call in createChartToolDeps.ts; ensure
subsequent code uses `table.columns` without additional null guards.

In `@packages/mosaic/__tests__/ChartSettings.test.tsx`:
- Around line 113-116: The chartTypes test fixture declares each item with
settings: any which bypasses compile-time schema checks; update the chartTypes
definition so settings is typed as VgPlotChartConfig['settings'] (or replace the
array with a discriminated-union type keyed by chartType to match per-chart
schemas), e.g. change the array element type to { type:
VgPlotChartConfig['chartType']; settings: VgPlotChartConfig['settings'] } (or
the appropriate union) so TypeScript will error when a fixture's settings no
longer match the chart's schema; update any iteration or assertions that consume
chartTypes accordingly to preserve behavior.

In `@packages/mosaic/src/chart-types/box-plot/tool.ts`:
- Around line 9-33: The schema and title logic disagree: BoxPlotChartSettings
was made required (via BoxPlotToolParameters) so params.settings.x is always
present, yet createBoxPlotAiTool treats x as optional and never validates it;
either make x optional in the schema or validate x when present. Fix by updating
BoxPlotToolParameters to not force x (use a settings schema where x is optional)
if grouping should be optional, or keep the schema required and call
validateColumnExists(params.settings.x, NUMERIC_OR_CATEGORICAL_COLUMN_TYPES,
columns, 'x') before building the title; also adjust the title construction in
createBoxPlotAiTool to reflect the chosen optional/required semantics (use
conditional title only when x is truly optional).