Fix runaway Convex demo dashboard reads

[bryanlin850]

Summary

• Replace the reactive demo-status scans across ten tables with two settings reads, persisting seeded counts when demo data changes.
• Load dashboard metrics as an explicit refreshable snapshot instead of keeping a live subscription open.
• Stop memory-record scans as soon as enough matching rows are found, with bounded scan work and normalized fractional limits.
• Preserve safe UI behavior for legacy deployments that do not have a persisted demo summary yet.

Why

The debug dashboard's reactive demo-status query repeatedly scanned operational tables after writes. On an active development deployment, this caused excessive Convex function calls and database reads even when the dashboard only needed a small status summary.

Validation

• npm run typecheck
• npm test — 16 test files, 73 tests
• npm run build:debug

Scope

Two commits and six files, all specific to the Convex demo/dashboard read-amplification fix. No fork-only application changes are included.

[greptile-apps]

Greptile Summary

Replace reactive, scan-heavy dashboard queries with persisted demo summaries and explicitly refreshed snapshots.

• Persist demo row counts whenever demo mode is reseeded or cleared.
• Bound memory-record scans and normalize fractional or invalid limits.
• Add dashboard snapshot refresh, loading, error, and last-updated states.
• Preserve legacy demo-status behavior when persisted counts are unavailable.

Confidence Score: 5/5

The PR appears safe to merge with no concrete correctness or security failures identified.

The persisted demo summary is maintained by the sole demo seed and teardown mutation, existing memory-list callers retain equivalent behavior, and dashboard snapshot races and failures are handled with request guards and explicit retry controls.

Important Files Changed

Filename	Overview
convex/demo.ts	Replaces repeated operational-table status scans with an atomically maintained settings-backed demo summary and a legacy-safe fallback.
convex/memoryRecordLimits.ts	Adds deterministic normalization and clamping for optional memory-list limits.
convex/memoryRecords.ts	Stops ordered memory scans after collecting the requested matches or reaching the existing scan bound.
debug/src/components/DashboardPanel.tsx	Replaces the live metrics subscription with a guarded, manually refreshable snapshot and explicit loading/error states.
debug/src/components/SettingsPanel.tsx	Handles unavailable legacy demo counts without presenting them as zero.
test/memory-record-limits.test.ts	Covers fractional, default, negative, infinite, and NaN limit normalization.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[Demo mode mutation] --> B[Delete existing demo rows]
    B --> C{Enable demo mode?}
    C -->|Yes| D[Seed demo rows]
    C -->|No| E[Use zero counts]
    D --> F[Persist demo count summary]
    E --> F
    F --> G[Persist enabled setting]
    G --> H[Status reads two settings rows]
    I[Dashboard mounts or user refreshes] --> J[Run one-shot metrics query]
    J --> K[Render snapshot and timestamp]

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_{Reviews (1): Last reviewed commit: "fix: normalize memory dashboard limits" | Re-trigger Greptile}