diff --git a/build-logic/convention/DESIGN_NOTES.md b/build-logic/convention/DESIGN_NOTES.md
new file mode 100644
index 0000000..4a3bdaf
--- /dev/null
+++ b/build-logic/convention/DESIGN_NOTES.md
@@ -0,0 +1,36 @@
+# DESIGN_NOTES — 约定插件
+
+## 为什么存在
+
+多模块项目里，`compileSdk`/`minSdk`/Java target、Compose、Hilt、Room、Lint、Spotless 等配置若在每个模块重复手写，必然漂移。约定插件把这些配置**集中编码**，模块只声明"我是什么类型"（`mcl.*` 插件），不关心"怎么配"。
+
+这也是 harness-engineering 的"严谨性转移"：把约束写进确定性规则，而不是依赖记忆。
+
+## 插件映射
+
+| 插件 id | 实现类 | 作用 |
+|---------|--------|------|
+| `mcl.kotlin.library` | `JvmLibraryConventionPlugin` | 纯 JVM（kotlin-jvm + jvmTarget 11 + spotless + junit） |
+| `mcl.android.library` | `AndroidLibraryConventionPlugin` | Android 库（application/library 插件的库版 + lint + spotless + compileSdk/minSdk） |
+| `mcl.android.library.compose` | `AndroidLibraryComposeConventionPlugin` | = library + Compose |
+| `mcl.android.application.compose` | `AndroidApplicationComposeConventionPlugin` | = application + Compose |
+| `mcl.android.feature` | `AndroidFeatureConventionPlugin` | = library.compose + hilt + 导航/lifecycle/共享模块依赖 |
+| `mcl.android.hilt` | `AndroidHiltConventionPlugin` | KSP + Hilt（hilt-android + hilt-compiler） |
+| `mcl.android.room` | `AndroidRoomConventionPlugin` | KSP + Room（runtime/ktx/compiler + schema 目录） |
+| `mcl.android.lint` | `AndroidLintConventionPlugin` | lint 配置（checkDependencies、disable GradleDependency） |
+| `mcl.root` | `RootPlugin` | 注册 `verifyArchitecture` |
+
+## 关键实现要点
+
+- **内置 Kotlin**：AGP 9 内置 Kotlin，因此**不**显式应用 `org.jetbrains.kotlin.android`；Kotlin 编译选项通过 `KotlinAndroidProjectExtension` 的 `compilerOptions` 配置（见 `KotlinAndroid.kt`）。
+- **compose 插件自包含**：`*.compose` 插件先 `apply(mcl.android.library/application)` 再叠加 Compose，所以模块只需声明 compose 插件一个。
+- **helper 函数**：`KotlinAndroid.kt`（SDK/Java/Kotlin）、`AndroidCompose.kt`（compose feature + BOM + tooling + material3）、`Spotless.kt`（ktlint，无 license header）拆成独立函数，插件只做编排。
+- **`libs` 访问器**：`ProjectExtensions.kt` 里的 `val Project.libs` 让插件能引用版本目录（`libs.findLibrary/findVersion`）。
+
+## 如何新增
+
+1. **新模块**：建 `build.gradle.kts`（选对插件 + namespace）+ 空 `AndroidManifest.xml`（Android 模块），在 `settings.gradle.kts` include，在 `RootPlugin.kt` 的 allow-list 加一行。
+2. **新插件**：在 `convention/build.gradle.kts` 的 `gradlePlugin { plugins { register(...) } }` 注册，并在 `gradle/libs.versions.toml` 的 `[plugins]` 里加一个 `mcl-*` 条目（无 version）。
+3. **改配置**：优先改 helper 函数，让所有适用模块一并生效。
+
+> 注意：`mcl-android-application` 与 `mcl-android-library` 因有 `-compose` 变体（叶子也是前缀），在 `convention/build.gradle.kts` 里引用它们的 plugin id 时要用 `.asProvider().get().pluginId`，其余用 `.get().pluginId`。
diff --git a/build-logic/convention/build.gradle.kts b/build-logic/convention/build.gradle.kts
new file mode 100644
index 0000000..92c699e
--- /dev/null
+++ b/build-logic/convention/build.gradle.kts
@@ -0,0 +1,79 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    `kotlin-dsl`
+}
+
+group = "com.mingyuan.androidclient.buildlogic"
+
+// build-logic targets the JDK used to run Gradle (17), unrelated to the device/runtime JDK.
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JvmTarget.JVM_17
+    }
+}
+
+dependencies {
+    compileOnly(libs.android.gradlePlugin)
+    compileOnly(libs.kotlin.gradlePlugin)
+    compileOnly(libs.ksp.gradlePlugin)
+    compileOnly(libs.room.gradlePlugin)
+    compileOnly(libs.spotless.gradlePlugin)
+}
+
+tasks {
+    validatePlugins {
+        enableStricterValidation = true
+        failOnWarning = true
+    }
+}
+
+gradlePlugin {
+    plugins {
+        register("androidApplication") {
+            id = libs.plugins.mcl.android.application.asProvider().get().pluginId
+            implementationClass = "AndroidApplicationConventionPlugin"
+        }
+        register("androidApplicationCompose") {
+            id = libs.plugins.mcl.android.application.compose.get().pluginId
+            implementationClass = "AndroidApplicationComposeConventionPlugin"
+        }
+        register("androidLibrary") {
+            id = libs.plugins.mcl.android.library.asProvider().get().pluginId
+            implementationClass = "AndroidLibraryConventionPlugin"
+        }
+        register("androidLibraryCompose") {
+            id = libs.plugins.mcl.android.library.compose.get().pluginId
+            implementationClass = "AndroidLibraryComposeConventionPlugin"
+        }
+        register("androidFeature") {
+            id = libs.plugins.mcl.android.feature.get().pluginId
+            implementationClass = "AndroidFeatureConventionPlugin"
+        }
+        register("androidHilt") {
+            id = libs.plugins.mcl.android.hilt.get().pluginId
+            implementationClass = "AndroidHiltConventionPlugin"
+        }
+        register("androidRoom") {
+            id = libs.plugins.mcl.android.room.get().pluginId
+            implementationClass = "AndroidRoomConventionPlugin"
+        }
+        register("androidLint") {
+            id = libs.plugins.mcl.android.lint.get().pluginId
+            implementationClass = "AndroidLintConventionPlugin"
+        }
+        register("kotlinLibrary") {
+            id = libs.plugins.mcl.kotlin.library.get().pluginId
+            implementationClass = "JvmLibraryConventionPlugin"
+        }
+        register("root") {
+            id = libs.plugins.mcl.root.get().pluginId
+            implementationClass = "RootPlugin"
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidApplicationComposeConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidApplicationComposeConventionPlugin.kt
new file mode 100644
index 0000000..e2fcb00
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidApplicationComposeConventionPlugin.kt
@@ -0,0 +1,21 @@
+import com.android.build.api.dsl.ApplicationExtension
+import com.mingyuan.androidclient.buildlogic.configureAndroidCompose
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.getByType
+
+/**
+ * Compose for the application module. Applies [AndroidApplicationConventionPlugin] (compileSdk,
+ * lint, formatting) and then adds Compose. Apply this single plugin for the app module.
+ */
+class AndroidApplicationComposeConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "mcl.android.application")
+            apply(plugin = "org.jetbrains.kotlin.plugin.compose")
+
+            configureAndroidCompose(extensions.getByType<ApplicationExtension>())
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidApplicationConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidApplicationConventionPlugin.kt
new file mode 100644
index 0000000..ad40f84
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidApplicationConventionPlugin.kt
@@ -0,0 +1,30 @@
+import com.android.build.api.dsl.ApplicationExtension
+import com.mingyuan.androidclient.buildlogic.configureKotlinAndroid
+import com.mingyuan.androidclient.buildlogic.configureSpotless
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.configure
+
+/**
+ * Base convention for the application module. Applies the Android application plugin, Kotlin +
+ * Android SDK defaults, lint, and deterministic formatting. Compose is added by
+ * [AndroidApplicationComposeConventionPlugin].
+ */
+class AndroidApplicationConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "com.android.application")
+            apply(plugin = "mcl.android.lint")
+
+            extensions.configure<ApplicationExtension> {
+                configureKotlinAndroid(this)
+                defaultConfig.targetSdk = 37
+                defaultConfig.testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+                testOptions.animationsDisabled = true
+            }
+
+            configureSpotless()
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidFeatureConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidFeatureConventionPlugin.kt
new file mode 100644
index 0000000..95e4240
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidFeatureConventionPlugin.kt
@@ -0,0 +1,30 @@
+import com.mingyuan.androidclient.buildlogic.libs
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Convention for a feature module: Compose + Hilt, plus the shared dependencies every feature
+ * needs (shared UI, design system, domain models, and Navigation). Feature modules should apply
+ * only this plugin (plus any feature-specific additions).
+ */
+class AndroidFeatureConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "mcl.android.library.compose")
+            apply(plugin = "mcl.android.hilt")
+
+            dependencies {
+                "implementation"(project(":core:ui"))
+                "implementation"(project(":core:designsystem"))
+                "implementation"(project(":core:model"))
+                "implementation"(project(":core:domain"))
+                "implementation"(libs.findLibrary("androidx-navigation-compose").get())
+                "implementation"(libs.findLibrary("androidx-lifecycle-runtime-compose").get())
+                "implementation"(libs.findLibrary("androidx-lifecycle-viewmodel-compose").get())
+                "implementation"(libs.findLibrary("androidx-hilt-navigation-compose").get())
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidHiltConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidHiltConventionPlugin.kt
new file mode 100644
index 0000000..f7a7500
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidHiltConventionPlugin.kt
@@ -0,0 +1,22 @@
+import com.mingyuan.androidclient.buildlogic.libs
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Applies Hilt via KSP (not kapt) and wires the Hilt runtime + compiler.
+ */
+class AndroidHiltConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            with(pluginManager) {
+                apply("com.google.devtools.ksp")
+                apply("com.google.dagger.hilt.android")
+            }
+            dependencies {
+                "implementation"(libs.findLibrary("hilt-android").get())
+                "ksp"(libs.findLibrary("hilt-compiler").get())
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidLibraryComposeConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidLibraryComposeConventionPlugin.kt
new file mode 100644
index 0000000..8bc0c31
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidLibraryComposeConventionPlugin.kt
@@ -0,0 +1,21 @@
+import com.android.build.api.dsl.LibraryExtension
+import com.mingyuan.androidclient.buildlogic.configureAndroidCompose
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.getByType
+
+/**
+ * Compose for an Android library module. Applies [AndroidLibraryConventionPlugin] (compileSdk,
+ * lint, formatting) and then adds Compose. Apply this single plugin for Compose-enabled libraries.
+ */
+class AndroidLibraryComposeConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "mcl.android.library")
+            apply(plugin = "org.jetbrains.kotlin.plugin.compose")
+
+            configureAndroidCompose(extensions.getByType<LibraryExtension>())
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidLibraryConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidLibraryConventionPlugin.kt
new file mode 100644
index 0000000..f678bab
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidLibraryConventionPlugin.kt
@@ -0,0 +1,34 @@
+import com.android.build.api.dsl.LibraryExtension
+import com.mingyuan.androidclient.buildlogic.configureKotlinAndroid
+import com.mingyuan.androidclient.buildlogic.configureSpotless
+import com.mingyuan.androidclient.buildlogic.libs
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.configure
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Base convention for Android library modules. Applies the Android library plugin, Kotlin +
+ * Android SDK defaults, lint, formatting, and shared test dependencies. Compose is added by
+ * [AndroidLibraryComposeConventionPlugin].
+ */
+class AndroidLibraryConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "com.android.library")
+            apply(plugin = "mcl.android.lint")
+
+            extensions.configure<LibraryExtension> {
+                configureKotlinAndroid(this)
+                defaultConfig.testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+            }
+
+            configureSpotless()
+
+            dependencies {
+                "testImplementation"(libs.findLibrary("junit").get())
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidLintConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidLintConventionPlugin.kt
new file mode 100644
index 0000000..7aad1f9
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidLintConventionPlugin.kt
@@ -0,0 +1,27 @@
+import com.android.build.api.dsl.ApplicationExtension
+import com.android.build.api.dsl.LibraryExtension
+import com.android.build.api.dsl.Lint
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.configure
+
+/**
+ * Project-wide Android Lint configuration, applied to application and library modules.
+ */
+class AndroidLintConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            when {
+                pluginManager.hasPlugin("com.android.application") ->
+                    configure<ApplicationExtension> { lint(Lint::configure) }
+                pluginManager.hasPlugin("com.android.library") ->
+                    configure<LibraryExtension> { lint(Lint::configure) }
+            }
+        }
+    }
+}
+
+private fun Lint.configure() {
+    checkDependencies = true
+    disable += "GradleDependency"
+}
diff --git a/build-logic/convention/src/main/kotlin/AndroidRoomConventionPlugin.kt b/build-logic/convention/src/main/kotlin/AndroidRoomConventionPlugin.kt
new file mode 100644
index 0000000..4540e14
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/AndroidRoomConventionPlugin.kt
@@ -0,0 +1,35 @@
+import androidx.room.gradle.RoomExtension
+import com.google.devtools.ksp.gradle.KspExtension
+import com.mingyuan.androidclient.buildlogic.libs
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.configure
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Applies Room (via KSP) and wires runtime/ktx/compiler, generating Kotlin code and storing
+ * database schemas for future auto-migrations.
+ */
+class AndroidRoomConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "androidx.room")
+            apply(plugin = "com.google.devtools.ksp")
+
+            extensions.configure<KspExtension> {
+                arg("room.generateKotlin", "true")
+            }
+
+            extensions.configure<RoomExtension> {
+                schemaDirectory("$projectDir/schemas")
+            }
+
+            dependencies {
+                "implementation"(libs.findLibrary("androidx-room-runtime").get())
+                "implementation"(libs.findLibrary("androidx-room-ktx").get())
+                "ksp"(libs.findLibrary("androidx-room-compiler").get())
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/JvmLibraryConventionPlugin.kt b/build-logic/convention/src/main/kotlin/JvmLibraryConventionPlugin.kt
new file mode 100644
index 0000000..a0da895
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/JvmLibraryConventionPlugin.kt
@@ -0,0 +1,25 @@
+import com.mingyuan.androidclient.buildlogic.configureKotlinJvm
+import com.mingyuan.androidclient.buildlogic.configureSpotless
+import com.mingyuan.androidclient.buildlogic.libs
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Convention for pure Kotlin/JVM modules (no Android dependency) such as :core:model and
+ * :core:domain. Keeping these modules Android-free keeps them fast to test and forces domain
+ * logic to stay framework-agnostic.
+ */
+class JvmLibraryConventionPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            apply(plugin = "org.jetbrains.kotlin.jvm")
+            configureKotlinJvm()
+            configureSpotless()
+            dependencies {
+                "testImplementation"(libs.findLibrary("junit").get())
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/RootPlugin.kt b/build-logic/convention/src/main/kotlin/RootPlugin.kt
new file mode 100644
index 0000000..8ecc872
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/RootPlugin.kt
@@ -0,0 +1,89 @@
+import org.gradle.api.GradleException
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.register
+import java.io.File
+
+/**
+ * Root convention plugin. Registers the `verifyArchitecture` task, which enforces the module
+ * dependency direction declared in `docs/architecture.md`.
+ *
+ * The allow-list lives in ONE place here; adding a module means adding a line to [allowList]
+ * (and mirroring it in the architecture doc). The check reads each module's `build.gradle.kts`
+ * as a file (config-cache safe) and rejects any `project(":...")` reference that is not allowed.
+ */
+class RootPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        val featureAllowed = setOf(
+            ":core:ui",
+            ":core:designsystem",
+            ":core:domain",
+            ":core:model",
+        )
+
+        val allowList = mapOf(
+            ":app" to setOf(
+                ":core:common", ":core:model", ":core:domain", ":core:designsystem",
+                ":core:ui", ":core:data", ":core:network", ":core:database", ":core:datastore",
+                ":feature:auth", ":feature:checkin", ":feature:plan", ":feature:course",
+                ":feature:survey", ":feature:feedback", ":feature:profile",
+            ),
+            ":core:common" to emptySet(),
+            ":core:model" to emptySet(),
+            ":core:domain" to setOf(":core:common", ":core:model"),
+            ":core:designsystem" to setOf(":core:common"),
+            ":core:ui" to setOf(":core:designsystem", ":core:model"),
+            ":core:network" to setOf(":core:common", ":core:model"),
+            ":core:database" to setOf(":core:model"),
+            ":core:datastore" to setOf(":core:model"),
+            ":core:data" to setOf(
+                ":core:domain", ":core:model", ":core:network", ":core:database", ":core:datastore",
+            ),
+            ":feature:auth" to featureAllowed,
+            ":feature:checkin" to featureAllowed,
+            ":feature:plan" to featureAllowed,
+            ":feature:course" to featureAllowed,
+            ":feature:survey" to featureAllowed,
+            ":feature:feedback" to featureAllowed,
+            ":feature:profile" to featureAllowed,
+        )
+
+        val rootDir = target.rootDir
+
+        target.tasks.register("verifyArchitecture") {
+            group = "verification"
+            description = "Enforce module dependency direction (see docs/architecture.md)"
+
+            doLast {
+                val projectDependency = Regex("""project\("(:[^"]+)"\)""")
+                val violations = mutableListOf<String>()
+
+                for ((modulePath, allowed) in allowList) {
+                    val buildFile = File(
+                        rootDir,
+                        "${modulePath.removePrefix(":").replace(":", "/")}/build.gradle.kts",
+                    )
+                    if (!buildFile.exists()) {
+                        violations += "$modulePath: missing build.gradle.kts"
+                        continue
+                    }
+                    val declared = projectDependency
+                        .findAll(buildFile.readText())
+                        .map { it.groupValues[1] }
+                        .toSet()
+                    for (dep in declared) {
+                        if (dep !in allowed) violations += "$modulePath -> $dep"
+                    }
+                }
+
+                if (violations.isNotEmpty()) {
+                    throw GradleException(
+                        "Architecture violations (see docs/architecture.md):\n" +
+                            violations.joinToString("\n") { "  - $it" },
+                    )
+                }
+                logger.lifecycle("Architecture check passed: no forbidden module dependencies.")
+            }
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/AndroidCompose.kt b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/AndroidCompose.kt
new file mode 100644
index 0000000..ebed3a0
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/AndroidCompose.kt
@@ -0,0 +1,29 @@
+package com.mingyuan.androidclient.buildlogic
+
+import com.android.build.api.dsl.CommonExtension
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.dependencies
+
+/**
+ * Configure Compose-specific options for an Android module: enable the Compose build feature,
+ * add the Compose BOM so all Compose artifacts share one version, and wire the preview/tooling
+ * dependencies used by Android Studio.
+ */
+internal fun Project.configureAndroidCompose(commonExtension: CommonExtension) {
+    commonExtension.apply {
+        buildFeatures.apply {
+            compose = true
+        }
+
+        dependencies {
+            val bom = libs.findLibrary("androidx-compose-bom").get()
+            "implementation"(platform(bom))
+            "androidTestImplementation"(platform(bom))
+            "implementation"(libs.findLibrary("androidx-compose-ui").get())
+            "implementation"(libs.findLibrary("androidx-compose-ui-graphics").get())
+            "implementation"(libs.findLibrary("androidx-compose-material3").get())
+            "implementation"(libs.findLibrary("androidx-compose-ui-tooling-preview").get())
+            "debugImplementation"(libs.findLibrary("androidx-compose-ui-tooling").get())
+        }
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/KotlinAndroid.kt b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/KotlinAndroid.kt
new file mode 100644
index 0000000..954a74a
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/KotlinAndroid.kt
@@ -0,0 +1,66 @@
+package com.mingyuan.androidclient.buildlogic
+
+import com.android.build.api.dsl.CommonExtension
+import org.gradle.api.JavaVersion
+import org.gradle.api.Project
+import org.gradle.api.plugins.JavaPluginExtension
+import org.gradle.kotlin.dsl.assign
+import org.gradle.kotlin.dsl.configure
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension
+import org.jetbrains.kotlin.gradle.dsl.KotlinBaseExtension
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension
+
+/**
+ * Configure base Kotlin + Android options shared by every Android module.
+ *
+ * compileSdk / minSdk are the project-wide contract (see docs/architecture.md); Java/Kotlin
+ * target stays at 11 so library modules and the app agree on bytecode level.
+ */
+internal fun Project.configureKotlinAndroid(commonExtension: CommonExtension) {
+    commonExtension.apply {
+        compileSdk = 37
+
+        defaultConfig.apply {
+            minSdk = 28
+        }
+
+        compileOptions.apply {
+            sourceCompatibility = JavaVersion.VERSION_11
+            targetCompatibility = JavaVersion.VERSION_11
+        }
+    }
+
+    configureKotlin<KotlinAndroidProjectExtension>()
+}
+
+/**
+ * Configure base Kotlin options for pure JVM (non-Android) modules such as :core:model.
+ */
+internal fun Project.configureKotlinJvm() {
+    extensions.configure<JavaPluginExtension> {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+
+    configureKotlin<KotlinJvmProjectExtension>()
+}
+
+private inline fun <reified T : KotlinBaseExtension> Project.configureKotlin() = configure<T> {
+    // Treat Kotlin warnings as errors only when the `warningsAsErrors` Gradle property is set.
+    val warningsAsErrors = providers.gradleProperty("warningsAsErrors").map {
+        it.toBoolean()
+    }.orElse(false)
+    when (this) {
+        is KotlinAndroidProjectExtension -> compilerOptions
+        is KotlinJvmProjectExtension -> compilerOptions
+        else -> TODO("Unsupported project extension $this ${T::class}")
+    }.apply {
+        jvmTarget = JvmTarget.JVM_11
+        allWarningsAsErrors = warningsAsErrors
+        freeCompilerArgs.add(
+            // Enable experimental coroutines APIs, including Flow.
+            "-opt-in=kotlinx.coroutines.ExperimentalCoroutinesApi",
+        )
+    }
+}
diff --git a/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/ProjectExtensions.kt b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/ProjectExtensions.kt
new file mode 100644
index 0000000..c91a620
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/ProjectExtensions.kt
@@ -0,0 +1,16 @@
+package com.mingyuan.androidclient.buildlogic
+
+import org.gradle.api.Project
+import org.gradle.api.artifacts.VersionCatalog
+import org.gradle.api.artifacts.VersionCatalogsExtension
+import org.gradle.kotlin.dsl.getByType
+
+/**
+ * Access to the shared `libs` version catalog from within convention plugins.
+ *
+ * The catalog is declared in `gradle/libs.versions.toml` and wired into the included
+ * build via `build-logic/settings.gradle.kts`, so build-logic and the main build share
+ * one source of truth for versions.
+ */
+val Project.libs
+    get(): VersionCatalog = extensions.getByType<VersionCatalogsExtension>().named("libs")
diff --git a/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/Spotless.kt b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/Spotless.kt
new file mode 100644
index 0000000..b3507c9
--- /dev/null
+++ b/build-logic/convention/src/main/kotlin/com/mingyuan/androidclient/buildlogic/Spotless.kt
@@ -0,0 +1,29 @@
+package com.mingyuan.androidclient.buildlogic
+
+import com.diffplug.gradle.spotless.SpotlessExtension
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.apply
+import org.gradle.kotlin.dsl.configure
+
+/**
+ * Enforce deterministic Kotlin formatting with ktlint (rules driven by `.editorconfig`).
+ *
+ * No license header is applied — this is a private project. Formatting only; run
+ * `./gradlew spotlessCheck` (verify) or `./gradlew spotlessApply` (fix).
+ */
+internal fun Project.configureSpotless() {
+    apply(plugin = "com.diffplug.spotless")
+    extensions.configure<SpotlessExtension> {
+        kotlin {
+            target("src/**/*.kt")
+            ktlint(libs.findVersion("ktlint").get().requiredVersion).editorConfigOverride(
+                mapOf(
+                    "android" to "true",
+                    // 包名 com.mingyuan.android_client 含下划线，刻意保留（见 docs/decisions/0004）。
+                    "ktlint_standard_package-name" to "disabled",
+                ),
+            )
+            endWithNewline()
+        }
+    }
+}
diff --git a/build-logic/gradle.properties b/build-logic/gradle.properties
new file mode 100644
index 0000000..62a516a
--- /dev/null
+++ b/build-logic/gradle.properties
@@ -0,0 +1,5 @@
+# Gradle properties are not passed to included builds https://github.com/gradle/gradle/issues/2534
+org.gradle.parallel=true
+org.gradle.caching=true
+org.gradle.configuration-cache=true
+org.gradle.configuration-cache.parallel=true
diff --git a/build-logic/settings.gradle.kts b/build-logic/settings.gradle.kts
new file mode 100644
index 0000000..0f461ae
--- /dev/null
+++ b/build-logic/settings.gradle.kts
@@ -0,0 +1,27 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        google()
+    }
+}
+
+dependencyResolutionManagement {
+    repositories {
+        google {
+            content {
+                includeGroupByRegex("com\\.android.*")
+                includeGroupByRegex("com\\.google.*")
+                includeGroupByRegex("androidx.*")
+            }
+        }
+        mavenCentral()
+    }
+    versionCatalogs {
+        create("libs") {
+            from(files("../gradle/libs.versions.toml"))
+        }
+    }
+}
+
+rootProject.name = "build-logic"
+include(":convention")