## Summary
Adds a pattern mining feature to the CLI, accessible via `Shift+P`. This mirrors the web app's Pattern Table functionality but runs entirely in TypeScript — no Pyodide/Python WASM needed.
**Linear:** https://linear.app/hyperdx/issue/HDX-3964
## What changed
### 1. Drain library in common-utils (`packages/common-utils/src/drain/`)
Ported the [browser-drain](https://github.com/DeploySentinel/browser-drain) TypeScript library into `@hyperdx/common-utils`. This is a pure TypeScript implementation of the Drain3 log template mining algorithm, including:
- `TemplateMiner` / `TemplateMinerConfig` — main API
- `Drain` — core algorithm with prefix tree and LRU cluster cache
- `LogMasker` — regex-based token masking (IPs, numbers, etc.)
- `LruCache` — custom LRU cache matching Python Drain3's eviction semantics
- 11 Jest tests ported from the original `node:test` suite
### 2. CLI pattern view (`packages/cli/src/components/EventViewer/`)
**Keybinding:** `Shift+P` toggles pattern view (pauses follow mode, restores on exit)
**Data flow (mirrors web app's `useGroupedPatterns`):**
- Issues `SELECT ... ORDER BY rand() LIMIT 100000` to randomly sample up to 100K events
- Issues parallel `SELECT count()` to get true total event count
- Feeds sampled log bodies through the TypeScript `TemplateMiner`
- Estimates pattern counts via `sampleMultiplier = totalCount / sampledRowCount`
- Computes time-bucketed trend data per pattern
**UI:**
- Pattern list with columns: Est. Count (with `~` prefix), Pattern
- `l`/`Enter` expands a pattern to show its sample events (full table columns)
- `h`/`Esc` returns to pattern list
- `j/k/G/g/Ctrl+D/Ctrl+U` navigation throughout
- Loading spinner while sampling query runs
**Alias fix:** Pattern and count queries compute `WITH` clauses from the source's `defaultTableSelectExpression` so Lucene searches using aliases (e.g. `level:error` where `level` is an alias for `SeverityText`) resolve correctly.
### New files
- `packages/common-utils/src/drain/` — 7 source files + barrel index
- `packages/common-utils/src/__tests__/drain.test.ts`
- `packages/cli/src/components/EventViewer/usePatternData.ts`
- `packages/cli/src/components/EventViewer/PatternView.tsx`
- `packages/cli/src/components/EventViewer/PatternSamplesView.tsx`
### Modified files
- `packages/cli/src/api/eventQuery.ts` — added `buildPatternSampleQuery`, `buildTotalCountQuery`, `buildAliasWithClauses`
- `packages/cli/src/components/EventViewer/EventViewer.tsx` — wired in pattern state + rendering
- `packages/cli/src/components/EventViewer/useKeybindings.ts` — added P, l, h keybindings + pattern/sample navigation
- `packages/cli/src/components/EventViewer/SubComponents.tsx` — added P to help screen
### Demo
https://github.com/user-attachments/assets/50a2edfc-8891-43ae-ab86-b96fca778c66
