lib.feature-flags

@lssm-tech/lib.feature-flags

Website: https://contractspec.io

Feature flags and experiments module for ContractSpec applications.

What It Provides

• Layer: lib.
• Consumers: bundles, apps.
• src/contracts/ contains contract specs, operations, entities, and registry exports.
• src/docs/ contains docblocks and documentation-facing exports.
• src/contracts/ contains contract specs, operations, entities, and registry exports.
• src/docs/ contains docblocks and documentation-facing exports.

Installation

npm install @lssm-tech/lib.feature-flags

or

bun add @lssm-tech/lib.feature-flags

Usage

Import the root entrypoint from @lssm-tech/lib.feature-flags, or choose a documented subpath when you only need one part of the package surface.

The root entry point exports vendor-neutral FeatureFlagPort and ExperimentPort contracts. ResilientFeatureFlagClient provides deterministic provider → cache → bootstrap → typed-default fallback and records exposures only when explicitly requested. Experiment allocation is deterministic and guardrail evaluation fails closed on missing observations.

Structured provider and bootstrap values must be cycle-free, recursively plain JSON without dangerous prototype keys, and are validated against the typed default before use. Unknown-consent evaluation is fail-closed unless non-personal use is explicitly enabled; even then, subject keys are pseudonymized, targeting attributes require a normalized ASCII allowlist, and Unicode compatibility, separator, case, or camel variants of personal and secret attribute names remain redacted.

Provider capabilities declare registry scope independently. Railway Signals are project- or workspace-scoped feature-flag registries (project scope writable, workspace scope read-only); they are never modeled as environment variables.

Architecture

• src/contracts/ contains contract specs, operations, entities, and registry exports.
• src/docs/ contains docblocks and documentation-facing exports.
• src/entities/ contains domain entities and value objects.
• src/evaluation is part of the package's public or composition surface.
• src/events.ts is package-level event definitions.
• src/feature-flags.capability.ts defines a capability surface.
• src/feature-flags.feature.ts defines a feature entrypoint.

Public Entry Points

• Export . resolves through ./src/index.ts.
• Export ./contracts resolves through ./src/contracts/index.ts.
• Export ./docs resolves through ./src/docs/index.ts.
• Export ./docs/feature-flags.docblock resolves through ./src/docs/feature-flags.docblock.ts.
• Export ./entities resolves through ./src/entities/index.ts.
• Export ./evaluation resolves through ./src/evaluation/index.ts.
• Export ./events resolves through ./src/events.ts.
• Export ./feature-flags.capability resolves through ./src/feature-flags.capability.ts.
• Export ./feature-flags.feature resolves through ./src/feature-flags.feature.ts.

Local Commands

• bun run dev — contractspec-bun-build dev
• bun run build — contractspec-bun-build build
• bun run lint — bun lint:fix
• bun run lint:check — biome check .
• bun run lint:fix — biome check --write --unsafe --only=nursery/useSortedClasses . && biome check --write .
• bun run typecheck — tsgo --noEmit
• bun run publish:pkg — bun publish --tolerate-republish --ignore-scripts --verbose
• bun run publish:pkg:canary — bun publish:pkg --tag canary
• bun run clean — rimraf dist .turbo
• bun run build:bundle — contractspec-bun-build transpile
• bun run build:types — contractspec-bun-build types
• bun run prebuild — contractspec-bun-build prebuild

Recent Updates

• Replace eslint+prettier by biomejs to optimize speed.

Notes

• Flag evaluation logic must be deterministic — same input always produces same output.
• Capability and feature contracts are public API; changes are breaking.
• Follow the PostHog naming conventions defined in workspace rules for new flag names.

Repository location and type configuration

The existing owner lives at packages/platform/delivery/feature-flags; its package name, twelve supported exports and implementation remain unchanged. The local typecheck script uses a source root that contains the package and its explicit ContractsSpec/Schema source aliases. Canonical declaration builds use ToolBun's entry-derived src root, preserving the existing source-relative dist paths. Clean producers, strict consumers and resulting-tree acceptance remain pending.