perf(editor): optimize code-lens entity lookup and cache popover fetches

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Summary

Follow-up to #10161 that optimizes editor_code_lens hot paths and adds regression coverage.

• getLensEntities: Precompute datasource/bucket entity kinds once per store update via Jotai derived atoms (lensEntityKindsAtom, lensEntitiesByCellAtom), turning per-cell O(C × T) rescans into O(T) grouping plus O(1) per-cell lookups.
• findCacheSites: Bail out early on syntax errors (same as findDeclarationSites), avoiding regex scans on unparsable cells mid-edit.
• Cache popover: Throttle notebook-wide getCacheInfo fetches across repeated hovers (5s interval); reset throttle on failure so the next hover can retry immediately.

Tests

• perf.test.ts — wall-time regression guards for large notebooks (generous 200ms budgets)
• entities.test.ts — shared entity map is built once, not per getLensEntities call
• popover.test.ts — fetch throttling and failure retry behavior
• analyzer.test.ts — syntax-error short-circuit for findCacheSites

Test plan

• pnpm test src/core/codemirror/code-lens
• Manual: hover a cache code lens repeatedly and confirm only one getCacheInfo request fires within 5s
• Manual: open a large notebook with many datasources and confirm code lenses still feel responsive

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview	Jul 31, 2026 11:45am

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Coverage Report for ./frontend

Status	Category	Percentage	Covered / Total
🔵	Lines	77.37%	78924 / 102001
🔵	Statements	77.37%	78924 / 102001
🔵	Functions	72.02%	672 / 933
🔵	Branches	79.06%	4687 / 5928

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
frontend/src/core/codemirror/code-lens/analyzer.ts	100%	80%	100%	100%
frontend/src/core/codemirror/code-lens/entities.ts	100%	100%	100%	100%
frontend/src/core/codemirror/code-lens/popover.tsx	78.88%	29.41%	100%	78.88%	55, 57, 59, 68, 175, 196-213, 216-232

Generated in workflow #20144 for commit 3ed5e4f by the Vitest Coverage Report Action

[cubic-dev-ai]

No issues found across 8 files

Architecture diagram

sequenceDiagram
    participant UI as Editor UI
    participant Lens as Code Lens Extension
    participant Entities as getLensEntities
    participant Store as Jotai Store
    participant Analyzer as findCacheSites
    participant Popover as Cache Popover
    participant API as getCacheInfo API

    Note over UI,API: Code Lens Entity Lookup (per cell render)

    UI->>Lens: Render code lenses for cell
    Lens->>Entities: getLensEntities(cellId)
    Entities->>Store: get(lensEntitiesByCellAtom)
    Store->>Store: CHANGED: Precompute lensEntityKindsAtom (scans datasets, connections, storage)
    Store->>Store: CHANGED: Group by declaring cell in lensEntitiesByCellAtom -> O(T) total
    Store-->>Entities: { byCell, pending }
    Entities-->>Lens: Map<string, CodeLensKind> (O(1) per-cell lookup)
    Lens-->>UI: Render lens decorations

    Note over UI,Analyzer: Cache Site Detection (syntax error fast-path)

    UI->>Lens: Parse cell code for cache sites
    Lens->>Analyzer: findCacheSites(state)
    Analyzer->>Analyzer: Parse syntax tree
    alt Syntax errors present
        Analyzer->>Analyzer: CHANGED: Return empty array immediately
        Analyzer-->>Lens: [] (no regex scan)
    else Valid syntax
        Analyzer->>Analyzer: Apply CACHE_PATTERN regex
        Analyzer-->>Lens: CacheSite[]
    end

    Note over UI,API: Cache Popover Throttling (repeated hovers)

    UI->>Popover: Hover over cache lens (mountLensPopover)
    Popover->>Popover: Check hasLocalStats (per-cache boundName)
    alt Has per-cache stats
        Popover->>Popover: Show local hit/miss stats
    else No per-cache stats
        Popover->>Popover: CHANGED: Check lastCacheInfoFetchAt throttle
        alt Within 5s throttle window
            Popover->>Popover: Skip fetch (reuse cached data)
        else Throttle expired or first fetch
            Popover->>Popover: CHANGED: Set lastCacheInfoFetchAt = now
            Popover->>API: getCacheInfo()
            alt Success
                API-->>Popover: Cache info data
                Popover->>Popover: Display fallback stats
            else Failure
                API-->>Popover: Error
                Popover->>Popover: CHANGED: Reset lastCacheInfoFetchAt = null (allow immediate retry)
            end
        end
    end
    Popover-->>UI: Render popover content

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