docs(discern): add repository README and contributor setup

CONTRIBUTING.md

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+# Contributing to discern
+
+This guide outlines prerequisites, repository setup, and conventions for developing in the systemfsoftware/discern monorepo.
+
+## Prerequisites
+
+Development requires the repository's Nix flake and dev shell. The dev shell provides:
+
+- Node.js 24
+- pnpm 12 (the repository pins `pnpm@12.9.0`)
+
+## Source Setup
+
+Core dependencies are pinned by `flake.nix` and consumed as local tarballs rather than fetched from a registry. The repository's `pnpm-workspace.yaml` maps these dependencies to `file:.sfs-deps/*.tgz` overrides.
+
+To build the local dependency tarballs and install workspace packages, run:
+
+```sh
+mkdir -p .sfs-deps && cp -L --no-preserve=mode "$(nix build --no-link --print-out-paths .#sfs-deps)"/*.tgz .sfs-deps/
+pnpm install
+```
+
+## Running Package Commands
+
+Execute package scripts from the repository root using pnpm workspace filters:
+
+```text
+pnpm --filter <pkg> <cmd>
+```
+
+Do not change directories (`cd`) into individual package folders to run commands, and do not use `npx`.
+
+## Commit Conventions
+
+Commit messages must adhere to conventional commit syntax:
+
+```text
+type(scope): subject
+```
+
+## Testing Boundaries
+
+Mutation testing is executed exclusively in continuous integration (CI) environments. Do not run mutation testing locally.

README.md

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+# discern
+
+discern provides uncertainty-aware semantic pattern matching and control flow for Effect. It allows developers to evaluate inputs against classification, rating, probability, and deterministic criteria, compose them using logical operators, and explicitly branch on whether an outcome matches, misses, or remains uncertain.
+
+The repository is a TypeScript and ESM monorepo forked under systemfsoftware from [doeixd/discern](https://github.com/doeixd/discern).
+
+## Repository Package Map
+
+This repository manages the following package:
+
+- [`packages/discern`](packages/discern): Contains the source code for `@systemfsoftware/discern` (current source version: 1.1.3). For API reference, procedure routing, recording and replay, caching, budgets, and evaluation workflows, see [`packages/discern/README.md`](packages/discern/README.md).
+
+## Installation
+
+The published consumer artifact is version 1.0.0. You can install it alongside Effect v4:
+
+```sh
+npm install @systemfsoftware/discern@1.0.0 'effect@^4'
+```
+
+## Quick Start
+
+The following example demonstrates a review policy evaluated against a stand-in Effect DecisionModel provider. This allows you to run the flow locally without configuring external model credentials:
+
+```js
+import { Discern } from '@systemfsoftware/discern'
+import { Effect, Schema } from 'effect'
+
+const standIn = (answer) =>
+  Discern.Model.provider((request) =>
+    Effect.succeed({
+      answers: Object.fromEntries(Object.entries(request.decisions).map(([key, decision]) => [key, answer(decision)])),
+      usage: { inputTokens: undefined, outputTokens: undefined },
+    })
+  )
+const Change = Discern.on(Schema.String)
+const impact = Change.classify({
+  id: 'impact',
+  instructions: 'How does this change affect callers of the API?',
+  criteria: {
+    none: 'Internal only',
+    additive: 'New surface, nothing existing changes',
+    breaking: 'Existing callers change',
+  },
+})
+const risk = Change.probability({ id: 'risk', instructions: 'Is this change likely to cause a regression?' })
+const review = Discern.type(Schema.String).pipe(
+  Discern.when(Discern.and(impact.is('breaking'), risk.above(0.8)), (change) => `block: ${change}`),
+  Discern.when(impact.is('breaking'), (change) => `migration guide: ${change}`),
+  Discern.orElse((change) => `ship: ${change}`),
+)
+const cautious = standIn((decision) =>
+  decision._tag === 'Classify'
+    ? { _tag: 'Classify', label: 'breaking', probabilities: { none: 0.02, additive: 0.08, breaking: 0.9 } }
+    : { _tag: 'Probability', probability: 0.93 }
+)
+const verdict = await Effect.runPromise(
+  review('rename User.id to User.key').pipe(Effect.provide(Discern.Model.layer(cautious))),
+)
+console.log(verdict)
+```
+
+Expected output:
+
+```text
+block: rename User.id to User.key
+```
+
+## Pattern Matching and Uncertainty
+
+Policies compose classification, rating, probability, and deterministic conditions using combinators such as `and`, `or`, and `when`. In the quick start example, the classification and probability criteria are evaluated in a single model-provider request.
+
+Pattern evaluations resolve to one of three states:
+
+- `Match`: The condition was met.
+- `Miss`: The condition was not met.
+- `Uncertain`: The model or heuristic evaluation cannot definitively resolve the condition.
+
+Rather than coercing uncertainty silently into a match or miss, discern exposes uncertainty directly in control flow.
+
+## Contributing and Issues
+
+For local development setup, environment prerequisites, and repository conventions, consult [CONTRIBUTING.md](CONTRIBUTING.md).
+
+For bug reports, feature requests, and support, open an [issue](https://github.com/systemfsoftware/discern/issues).
+
+## License
+
+This project is licensed under the Apache-2.0 License. See [`packages/discern/LICENSE`](packages/discern/LICENSE) for the full license text.
+
+Forked from [doeixd/discern](https://github.com/doeixd/discern).