Context

PR #389 bumps 9 major npm dependencies in /web. Beyond just compatibility, these upgrades bring significant new features and improvements worth evaluating and adopting.

Packages to investigate

1. ECharts 5 → 6

• New theme: Updated default visual style (colors, legend position at bottom, axis anti-overflow). Review chart appearance and decide whether to keep the new theme or restore v5 theme via import 'echarts/theme/v5'
• New chart types: chord series, matrix coordinate system — potential for analytics dashboards
• Dynamic themes: Support for registering and switching themes at runtime
• Scatter jittering: Useful for data visualization
• Axis breaks: Visual axis breaks for discontinuous data
• Performance: Memory leak fix in tooltip, various rendering fixes

2. Vue-ECharts 7 → 8

• Smart update strategy: More efficient chart updates — evaluate if this simplifies our SpendingChart.vue and SpendingSummary.vue
• Tooltip/data view slots: Render Vue components inside ECharts tooltips
• CSS border-radius: Works out-of-the-box now

3. Vite 6 → 8 (via 7)

• Rolldown replaces Rollup + esbuild: Significant build performance improvements
• Browser console forwarding: Dev server shows browser console logs/errors
• Integrated devtools: Built-in Vite devtools
• Build performance: Rolldown is faster than Rollup
• Note: We skip Vite 7 entirely (short-lived transitional version)

4. Vitest 3 → 4

• aroundEach/aroundAll hooks: Wrap test lifecycle for setup/teardown patterns
• Tags: Tag tests for selective execution
• mockThrow/mockThrowOnce: Cleaner error mocking
• --detect-async-leaks: Find async resource leaks in tests
• coverage.changed: Report coverage only for changed files — useful for dev workflow
• Chai-style assertions: Alternative assertion syntax
• Static test collection: vitest list can collect tests without running files

5. ESLint 9 → 10

• 3 new recommended rules: no-unassigned-vars, no-useless-assignment, preserve-caught-error — evaluate adding these to our config
• JSX reference tracking: Better scope analysis (relevant if we add JSX)
• Security fixes: Updated ajv and minimatch for vulnerabilities

6. eslint-plugin-vue 9 → 10

• vue/block-order added to essential config (replaces deprecated vue/component-tags-order)
• New essential rules: vue/no-deprecated-delete-set, vue/no-deprecated-model-definition, vue/valid-define-options
• vue/no-required-prop-with-default in recommended — evaluate adopting
• Performance: vue-eslint-parser v10 has TypeScript parsing improvements

7. vue-tsc 2 → 3

• Hybrid Mode always on: Better IDE/CLI type-check alignment
• Stricter checking options: strictSlotChildren, strictVModel, strictCssModules — evaluate enabling
• resolveStyleImports: Type-safe CSS module imports

8. jsdom 26 → 28

• Review changelog for any test environment improvements or new Web API support

Acceptance criteria

• Visual review of ECharts 6 theme on budget charts (SpendingChart, SpendingSummary)
• Evaluate smart update strategy in vue-echarts 8
• Evaluate new ESLint/vue rules for adoption
• Evaluate vue-tsc 3 strict options
• Evaluate Vitest 4 coverage.changed and --detect-async-leaks for CI/dev workflow
• Document any adopted improvements