engineering

name	engineering
description	Engineering deep-dive for poku covering performance, code, and security patterns, TypeScript config, build pipeline, developer experience, and CI/CD. Use when implementing or optimizing code, writing performance-sensitive logic, touching the build, or applying code-style and security rules.

Engineering patterns, performance, security, and build/CI. Read the actual source and config to confirm details, since implementations change over time.

1. Performance Patterns

Look in src/services/ and src/polyfills/:

• Each test file runs in its own process via spawn with shell: false. stdout/stderr are piped. A plugin can request an extra IPC channel via plugin.ipc
• The runner uses a concurrency-bounded promise queue. The default limit is availableParallelism(). Sequential mode or isolation: none forces a limit of 1
• availableParallelism is polyfilled by feature-detecting the native function at runtime and falling back to the CPU count

Authoring rules to respect when writing performance-sensitive code:

• NEVER let extra or uncommon features compromise or pollute the default path. Keep them behind a user-triggered conditional so the code stays unreached ("dead code") until the flag activates it
• ALWAYS early-return to the extreme. The moment a path is decided, leave it with return, break, or continue before doing any further work, so the common path runs the least code
• Declare each variable ONLY after the guards that could exit, in the narrowest scope that uses it. NEVER allocate on a path that never reaches it
• ALWAYS cache repeated state checks in the GLOBAL singleton instead of recomputing them

Performance priority order when trade-offs arise:

1. Long-term maintainability and readable code
2. V8 and JIT optimizations, including minimal memory allocation
3. Algorithmic complexity (Big O)

Performance and maintainability must stay in balance with each other.

2. Code Patterns

• Functional composition: Object.assign(coreFn, { todo, skip, only }) exposes modifiers on it and describe
• Fluent formatter: the Formatter class implements [Symbol.toPrimitive]() for implicit string coercion
• Promise coordination: a captured resolve callback, no external queue dependency
• GLOBAL singleton: a single object holds runtime config and shared state
• Parent→Child: POKU_* env vars carry context to child processes
• Timing: hrtime() (the [seconds, nanoseconds] tuple form) for high-precision durations
• Naming: NEVER use abbreviated variable names, including basic loop counters. Use index instead of i, element instead of el. Names MUST be fully spelled out and descriptive
• Comments: AVOID them. Clear code, organization, logic, and naming MUST make them unnecessary. The only exception is a public API exposed directly to the end user, which MAY carry objective inline docs

3. Security Patterns

• shell: false in spawn() prevents shell injection
• escapeRegExp() sanitizes user-supplied filter and pattern input before it becomes a RegExp
• Config auto-discovery only loads an allowlisted set of filenames (an explicit --config= path bypasses the list)
• Windows path safety: the config loader loads from a file:// URL on Windows, and the in-process test loader uses pathToFileURL()
• Process kill uses kill -9 on Unix and taskkill /F /T /PID on Windows

4. TypeScript Configuration

tsconfig.json is the source of truth. The constraint that drives it: output must run on the oldest supported Node, so prefer compatibility over newer language/output targets when changing it.

5. Build Pipeline

scripts/build.sh (wired to the build script in package.json) is the source of truth. It compiles source and tests, then runs post-build fixups. Read it before changing build behavior rather than relying on a description here.

6. Developer Experience (DX)

ALWAYS preserve or improve the developer experience. Read the assertion builder in src/builders/, the formatter and reporters in src/services/, and the runner/output/options parsers in src/parsers/. Key principles:

• Assertion failures must be actionable: file path, code line, operator, and full actual/expected diff (red/green). Non-comparison assertions (throws, rejects) pass hideDiff: true to keep the output focused
• Visual hierarchy: status icons, colors, and dynamic indentation that tracks describe/it nesting depth encode test state. Read the reporter and the formatter for the current icon and color mapping
• Output filtering: in non-debug mode only ANSI-colored lines pass through, hiding noisy library output. Debug mode (or a failed file) passes everything through
• Zero friction: TypeScript is auto-detected by file extension (the runner injects --import=tsx for .ts/.mts/.cts), config files are auto-discovered, and defineConfig() enables IDE autocomplete
• Config auto-discovery order: poku.config.js, then .pokurc.json, then .pokurc.jsonc, then built-in defaults
• Formatter usage: ALWAYS build output with the fluent format('text').bold().success() chain, NEVER raw ANSI codes

7. CI/CD

Read .github/workflows/ for the current pipeline. What constrains the work:

• Lint must pass (Biome + Prettier, see biome.jsonc)
• Coverage has a minimum threshold (checkCoverage in .nycrc, the source of truth)
• Cross-runtime and multi-version compatibility is enforced. See the workflows and test/__docker__/node/ for the current runtimes and versions