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docs/user/develop/basic/config.md

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+# Plugin configuration
+
+English | [中文](config.zh.md)
+
+Accept configuration supplied through `cordis.yml`.
+
+## Define the Config type
+
+Export a `Config` type and a same-named Schemastery schema. Put defaults directly on the schema fields:
+
+```ts
+import type { Context } from 'cordis'
+import Schema from 'schemastery'
+
+export const name = 'my-plugin'
+
+export interface Config {
+  greeting: string
+  maxRetries: number
+  verbose?: boolean
+}
+
+export const Config: Schema<Config> = Schema.object({
+  greeting: Schema.string().default('Hello'),
+  maxRetries: Schema.number().default(3),
+  verbose: Schema.boolean().default(false),
+})
+
+export function apply(ctx: Context, config: Config) {
+  console.log(config.greeting)  // User value or schema default.
+}
+```
+
+Configure it in `cordis.yml`:
+
+```yaml
+- name: './src/my-plugin.ts'
+  config:
+    greeting: 'Hi there'
+    maxRetries: 5
+```
+
+When loading the plugin, Cordis uses the exported schema to validate configuration and fill defaults. Do not export a plain object as `Config`; it does not implement the Standard Schema interface required by Cordis.
+
+## Schema validation
+
+Use Schemastery to express stricter validation:
+
+```ts
+import type { Context } from 'cordis'
+import Schema from 'schemastery'
+
+export const name = 'validated-plugin'
+
+export interface Config {
+  apiKey: string
+  timeout: number
+  mode: 'fast' | 'accurate'
+}
+
+export const Config = Schema.object({
+  apiKey: Schema.string().required(),
+  timeout: Schema.number().default(30000),
+  mode: Schema.union(['fast', 'accurate']).default('fast'),
+})
+
+export function apply(ctx: Context, config: Config) {
+  // config is validated and type-safe.
+}
+```
+
+The schema runs while the plugin loads. Invalid configuration fails the load with an actionable error.
+
+## Design principles
+
+### Do not hardcode tunable values
+
+Harness requires **anything that two deployments may want to set differently to be a configuration field**.
+
+```ts
+// Wrong: hardcoded timeout.
+const TIMEOUT = 30000
+
+// Correct: configurable.
+export interface Config {
+  timeoutMs: number  // Defaults to 30000.
+}
+```
+
+The test is whether `cordis.yml` can change the value without a code edit.
+
+### Fail loudly on invalid configuration
+
+If configuration refers to a missing model or another nonexistent resource, fail early instead of silently skipping it:
+
+```ts ignore-check
+export function apply(ctx: Context, config: Config) {
+  if (!ctx.llm.models().includes(config.model)) {
+    throw new Error(`Model "${config.model}" is not registered by any LLM adapter`)
+  }
+}
+```
+
+## Work with HMR
+
+A configuration edit hot-replaces the plugin: the framework unloads the old instance and loads a new one. Because registrations are effects and clean themselves up, replacement does not retain the old instance's registrations.
+
+## Next steps
+
+- [Plugins and lifecycle](../framework/) — understand the full plugin lifecycle
+- [Services and dependencies](../framework/service.md) — provide a service to other plugins