Scott/combo chart fix

[sagrimson]

Overview

Fixes combo (comparison) chart generation when multiple variables are selected for the same place, adds LLM-driven chart style changes and compare/combine intent detection, and stabilizes the Y-axis width across all chart types.

Previously, selecting cards like "Female Life Expectancy in Japan" and "Male Life Expectancy in Japan" would overwrite each other since they shared the same entity key, resulting in only one series appearing in the combined chart. Additionally, changing chart styles and triggering combine/compare flows relied on fragile client-side regex matching — both are now delegated to the LLM via the query parsing step.

Changes Made

LLM-driven chart style changes

• chartStyleIntent in query parsing — the LLM can now detect when a user wants to change chart appearance (e.g. "make these horizontal", "switch to a line chart") and returns a chartStyleIntent with a targetStyle value (bar-vertical | bar-horizontal | line). Unsupported chart types (pie, scatter, etc.) produce a follow-up with supported options instead (parse_query.md, parse_query.ts)
• chartStyleChange stream event — new stream event type lets the server signal a style change; the client applies it to all selected chart shapes and persists it in the store (types.ts, route.ts, query_provider.tsx)
• Persisted chartStyle on cards — ChartStyle type promoted from the local menu component to server/types.ts; stored on CardEntry, the tldraw shape props, and AtlasContent so it survives across export/import and re-renders (types.ts, store.ts, helpers.ts, shapes/card.tsx, chart.tsx, menu_chart_options.tsx)
• cardSetChartStyle store action — new zustand action to update a card's persisted chart style (store.ts)

LLM-driven combine/compare intent

• combineIntent in query parsing — the LLM detects compare/combine requests (e.g. "combine these", "compare these charts") when multiple chart cards are selected, replacing the client-side isCombineIntent regex. Returns combineIntent: true in the parsed query (parse_query.md, parse_query.ts)
• Server-side combine flow — route.ts handles combineIntent as an early exit: runs the comparison step directly with the selected results sent from the client, removing the separate /api/combine endpoint dependency for this path
• Selection context sent to API — hasChartSelection, chartSelectionCount, and selectedResults are now included in the query request so the LLM and server have full context about what's selected (types.ts, query_provider.tsx, route.ts)

Same-place multi-variable fix

• Same-place, multi-variable combine logic — when combining cards that share the same entity, merge their variables and timeSeries arrays instead of overwriting. Deduplicates by dcid / variableDcid+entityDcid so repeated entries are skipped (query_provider.tsx)
• Comparison chart derivation — deriveComparisonChartContent detects same-place vs. different-place scenarios: when all results share one entity it overlays every variable as a separate series; otherwise it builds one series per place as before (sync_store.ts)
• Per-variable chart content — new deriveChartContentForVariable derives chart content targeting a specific variable DCID (and optionally entity DCID), used by deriveContentForCard when a card has variableDcid set (sync_store.ts)
• Selection deduplication — getResultsForSelectedCards uses a composite entityDcid::variableDcid key so cards with the same place but different variables produce distinct results; narrows each result to only the targeted variable's timeSeries and variables when card.variableDcid is set (store.ts)

Stable Y-axis width

• measureAxisWidth utility — new shared utility uses a cached off-screen <canvas> to measure the widest label in pixels; companion numericAxisLabels generates representative formatted tick strings. Applied to bar-vertical, bar-horizontal, and line charts, replacing Recharts' width="auto" with a pre-measured value that prevents layout jitter on resize (measure_axis_width.ts)

Minor

• Formatting fix in content.tsx

[gemini-code-assist]

Code Review

This pull request introduces a stable Y-axis width calculation for charts by extracting measurement utilities into a shared measure_axis_width.ts file, and updates horizontal/vertical bar and line charts to use it. It also enhances the query provider, store, and comparison chart derivation to correctly support same-place, different-variable comparisons by merging and narrowing results appropriately. The review feedback points out that the helper functions niceNum and numericAxisLabels were duplicated in both data_chart_bar_vertical.tsx and data_chart_line.tsx instead of being imported from the new utility file.