diff --git a/packages/cli/script/build.ts b/packages/cli/script/build.ts
index f0197be59d1e..7f22183e5dcf 100755
--- a/packages/cli/script/build.ts
+++ b/packages/cli/script/build.ts
@@ -7,6 +7,7 @@ import { Script } from "@opencode/script"
 import { createSolidTransformPlugin } from "@opentui/solid/bun-plugin"
 import type { BunPlugin } from "bun"
 import pkg from "../package.json"
+import { discoverPluginRuntimeSpecifiers, pluginRuntimeLoaderCode } from "@opencode/plugin/runtime-modules"
 import { buildAppArchive } from "./app-assets"
 import { verifyArtifact, verifySimulationGraph } from "./verify-artifact"
 import { resolveOpencodePty } from "./opencode-pty"
@@ -82,6 +83,30 @@ export default () => readFileSync(archive)`,
     }))
   },
 }
+const pluginRuntimeEntries = discoverPluginRuntimeSpecifiers()
+const pluginRuntimeModulesSource = [
+  "export const resolveHostPackageRoots = () => []",
+  "const modules = {",
+  ...[...pluginRuntimeEntries.keys()].map(
+    (specifier) => `  ${JSON.stringify(specifier)}: ${pluginRuntimeLoaderCode(specifier, pluginRuntimeEntries)},`,
+  ),
+  "}",
+  "export const loadRuntimeModules = () => modules",
+].join("\n")
+const pluginRuntimePlugin: BunPlugin = {
+  name: "opencode-plugin-runtime",
+  setup(build) {
+    build.onLoad({ filter: /plugin[/\\]src[/\\]runtime-modules\.ts$/ }, () => ({
+      contents: pluginRuntimeModulesSource,
+      loader: "ts",
+    }))
+    build.onLoad({ filter: /[/\\]internal[/\\]httpApi(?:Scalar|Swagger)\.js$/ }, () => ({
+      contents:
+        'export const css = ""; export const javascript = \'document.body.textContent = "Scalar/Swagger UI assets are not bundled in OpenCode"\'',
+      loader: "js",
+    }))
+  },
+}
 
 for (const item of targets) {
   const opencodePty = await resolveOpencodePty({
@@ -128,7 +153,14 @@ export default { path: file, version: ${JSON.stringify(opencodePty.version)}, sh
   const result = await Bun.build({
     entrypoints: ["./src/index.ts"],
     tsconfig: "./tsconfig.json",
-    plugins: [appAssetsPlugin, solidPlugin, parcelWatcherPlugin, opencodePtyPlugin, simulationGraphPlugin],
+    plugins: [
+      appAssetsPlugin,
+      solidPlugin,
+      parcelWatcherPlugin,
+      opencodePtyPlugin,
+      pluginRuntimePlugin,
+      simulationGraphPlugin,
+    ],
     external: ["node-gyp"],
     format: "esm",
     minify: true,
diff --git a/packages/cli/src/index.ts b/packages/cli/src/index.ts
index f396062c2fb2..0ae8c1f12fc7 100755
--- a/packages/cli/src/index.ts
+++ b/packages/cli/src/index.ts
@@ -1,5 +1,6 @@
 #!/usr/bin/env bun
 
+import { ensurePluginRuntime } from "@opencode/plugin/runtime"
 import { NodeRuntime, NodeServices } from "@effect/platform-node"
 import { Cause, Effect } from "effect"
 import { getErrorReported } from "effect/Runtime"
@@ -17,6 +18,8 @@ import { EffectFlock } from "@opencode/util/effect-flock"
 import { Heap } from "./heap"
 import { CpuProfile } from "./cpu-profile"
 
+ensurePluginRuntime()
+
 if (process.env.OPENCODE_SSH_ASKPASS_PORT) {
   const { askpass } = await import("./ssh-askpass")
   process.exit(await Effect.runPromise(askpass.pipe(Effect.provide(NodeServices.layer))))
diff --git a/packages/core/test/plugin/module.test.ts b/packages/core/test/plugin/module.test.ts
index 1b4c2087c686..f19d8e398123 100644
--- a/packages/core/test/plugin/module.test.ts
+++ b/packages/core/test/plugin/module.test.ts
@@ -1,21 +1,32 @@
 import { expect } from "bun:test"
+import { cp } from "node:fs/promises"
 import path from "node:path"
-import { Deferred, Effect, Exit, Fiber, Layer, Schedule, Scope, Stream } from "effect"
+import { Brand, Cause, Deferred, Effect, Exit, Fiber, Layer, Option, Schedule, Schema, Scope, Stream } from "effect"
+import { Agent } from "@opencode/schema/agent"
+import { Session } from "@opencode/schema/session"
+import { SessionMessage } from "@opencode/schema/session-message"
 import { AppNodeBuilder } from "@opencode/core/effect/app-node-builder"
 import { Watcher } from "@opencode/core/filesystem/watcher"
-import { Config } from "@opencode/core/config"
+import { Plugin } from "@opencode/core/plugin"
 import { ManagedPolicy } from "@opencode/core/managed-policy"
 import { PluginModule } from "@opencode/core/plugin/module"
+import { Rpc } from "@opencode/core/rpc"
+import { Tool } from "@opencode/core/tool"
+import { execute } from "@opencode/core/tool/runtime"
 import { Global } from "@opencode/util/global"
 import { Npm } from "@opencode/util/npm"
+import { createForeignPackageFilter, ensurePluginRuntime } from "@opencode/plugin/runtime"
+import { createLoader, discoverPluginRuntimeSpecifiers, pluginRuntimeLoaderCode } from "@opencode/plugin/runtime-modules"
 import { tempGlobalLayer } from "../fixture/global"
 import { tmpdirScoped } from "../fixture/tmpdir"
 import { testEffect } from "../lib/effect"
+import { PluginTestLayer } from "./fixture"
+
+ensurePluginRuntime()
 
 const it = testEffect(
   Layer.mergeAll(
-    Config.testLayer(),
-    ManagedPolicy.layer,
+    PluginTestLayer,
     AppNodeBuilder.build(Npm.node, [Global.node.replace(tempGlobalLayer)]),
     Watcher.layer().pipe(Layer.provide(Watcher.nativeLayer)),
   ),
@@ -95,6 +106,297 @@ it.live("interrupts pending watcher setup when the loader scope closes during mo
   }),
 )
 
+it.live("loads plugins and their transitive dependencies against the host's Effect and @opencode/plugin instances", () =>
+  Effect.gen(function* () {
+    const directory = yield* tmpdirScoped()
+    const pluginDir = path.join(directory.path, "plugin")
+    const pluginEffectDir = path.join(pluginDir, "node_modules/effect")
+    const hostEffectDir = path.dirname(Bun.resolveSync("effect/package.json", import.meta.dir))
+
+    yield* Effect.promise(async () => {
+      await cp(path.join(hostEffectDir, "dist"), path.join(pluginEffectDir, "dist"), {
+        recursive: true,
+        filter: (src) => !src.endsWith(".d.ts") && !src.endsWith(".map") && !/httpApi(?:Scalar|Swagger)\.js$/.test(src),
+      })
+      const pkg = { ...(await Bun.file(path.join(hostEffectDir, "package.json")).json()), version: "4.0.0-rc.111" }
+
+      // Sabotage the plugin's own Effect copy with the version-skew failure modes so loading it would crash:
+      // 1. Effect.log reading an incompatible fiber log-level property (crashing host logger with logLevel.toUpperCase)
+      // 2. Effect.runPromise calling fiber.succeedWith on a host fiber
+      // 3. Schema.withDecodingDefault / Schema.Int / Schema.isPattern / Schema.Trim using foreign parser sentinels
+      const internalEffectPath = path.join(pluginEffectDir, "dist/internal/effect.js")
+      const originalInternalEffect = await Bun.file(internalEffectPath).text()
+      const logPattern =
+        /const logLevel = level \?\? fiber\.(?:currentLogLevel|cache\.logLevel);\r?\n\s*if \(isLogLevelGreaterThan\(fiber\.(?:minimumLogLevel|cache\.minimumLogLevel), logLevel\)\) \{/
+      const runPromisePattern = /const runPromiseExit = runPromiseExitWith\(context\);/
+      expect(logPattern.test(originalInternalEffect)).toBe(true)
+      expect(runPromisePattern.test(originalInternalEffect)).toBe(true)
+
+      await writeFiles(pluginDir, {
+        "node_modules/effect/package.json": JSON.stringify(pkg),
+        "node_modules/effect/dist/internal/effect.js": originalInternalEffect
+          .replace(
+            logPattern,
+            "const logLevel = level ?? fiber.foreignSkew?.logLevel;\n    if (isLogLevelGreaterThan(fiber.foreignSkew?.minimumLogLevel, logLevel)) {",
+          )
+          .replace(
+            runPromisePattern,
+            "if (true) return (effect) => Promise.resolve().then(() => { const fiber = {}; return fiber.succeedWith(effect); });\n  const runPromiseExit = runPromiseExitWith(context);",
+          ),
+        "node_modules/transitive-dep/package.json":
+          '{"name":"transitive-dep","type":"module","exports":{".":"./index.js"}}',
+        "node_modules/transitive-dep/index.js": `import { Effect, Schema } from "effect"
+import { some } from "effect/Option"
+export const depToolInput = Schema.Struct({
+  mode: Schema.String.pipe(Schema.withDecodingDefault(Effect.succeed("from-dep"))),
+  count: Schema.Int,
+  code: Schema.Trim.check(Schema.isPattern(/^v[0-9]+$/)),
+})
+export const depCaptured = { Effect, Schema, some }`,
+        "node_modules/@opencode/plugin/package.json":
+          '{"name":"@opencode/plugin","type":"module","exports":{"./effect":"./effect.js","./rpc":"./rpc.js"}}',
+        "node_modules/@opencode/plugin/effect.js": "export const Plugin = { define: (p) => p }",
+        "node_modules/@opencode/plugin/rpc.js": "export const Rpc = { define: (d) => d }",
+        "index.ts": `import { Plugin } from "@opencode/plugin/effect"
+import { Rpc } from "@opencode/plugin/rpc"
+import { Effect, Schema } from "effect"
+import { some } from "effect/Option"
+import { nominal } from "effect/Brand"
+import { depCaptured, depToolInput } from "transitive-dep"
+
+export const captured = {
+  plugin: { Effect, Schema, some, nominal },
+  dep: depCaptured,
+  pluginCount: -1,
+}
+
+const Contract = Rpc.define({
+  id: "host-effect-rpc",
+  methods: {
+    check: {
+      input: Schema.Struct({
+        count: Schema.Int.pipe(Schema.withDecodingDefault(Effect.succeed(5))),
+        tag: Schema.Trim.check(Schema.isPattern(/^v[0-9]+$/)),
+      }),
+      output: Schema.Struct({ value: Schema.String }),
+    },
+  },
+  events: {},
+})
+
+export default Plugin.define({
+  id: "host-effect-fixture",
+  effect: (ctx) =>
+    Effect.gen(function* () {
+      yield* Effect.log("setup log from plugin")
+      const listed = yield* Effect.promise(() =>
+        Effect.runPromise(ctx.plugin.list().pipe(Effect.orDie)),
+      )
+      captured.pluginCount = listed.data.length
+
+      yield* ctx.tool.transform((editor) => {
+        editor.add({
+          name: "check_tool",
+          description: "Tool with decoding default from transitive dependency and Int/Trim/isPattern checks",
+          input: depToolInput,
+          output: Schema.Struct({ formatted: Schema.String }),
+          execute: ({ mode, count, code }) =>
+            Effect.log("executing check_tool").pipe(
+              Effect.as({
+                output: { formatted: \`\${mode}:\${code}:\${count}\` },
+                content: \`\${mode}:\${code}:\${count}\`,
+              }),
+            ),
+        })
+      })
+
+      yield* ctx.rpc.register(Contract, {
+        check: ({ count, tag }) =>
+          Effect.log("executing rpc check").pipe(
+            Effect.as({ value: \`\${tag}#\${count}\` }),
+          ),
+      }).pipe(Effect.orDie)
+    }),
+})`,
+      })
+    })
+
+    const modules = yield* PluginModule.make()
+    const plugins = yield* Plugin.Service
+    const tools = yield* Tool.Service
+    const rpc = yield* Rpc.Service
+
+    const definition = yield* modules.load({ type: "add", target: pluginDir, options: {} })
+    if ("pending" in definition || "blocked" in definition) return yield* Effect.die(new Error("Local plugin was not loaded"))
+    yield* plugins.activate([definition])
+    yield* plugins.awaitActivation
+
+    expect(yield* plugins.list()).toMatchObject([{ id: "host-effect-fixture", state: { status: "active" } }])
+
+    const imported = yield* Effect.promise(() => import(path.join(pluginDir, "index.ts")))
+    expect(imported.captured.plugin.Effect).toBe(Effect)
+    expect(imported.captured.plugin.Schema).toBe(Schema)
+    expect(imported.captured.plugin.some).toBe(Option.some)
+    expect(imported.captured.plugin.nominal).toBe(Brand.nominal)
+    expect(imported.captured.dep.Effect).toBe(Effect)
+    expect(imported.captured.dep.Schema).toBe(Schema)
+    expect(imported.captured.dep.some).toBe(Option.some)
+    expect(imported.captured.pluginCount).toBe(0)
+
+    const checkTool = (yield* tools.list()).find((tool) => tool.id === "check_tool")
+    expect(checkTool).toBeDefined()
+    if (!checkTool) return
+
+    const context = {
+      sessionID: Session.ID.make("ses_host_effect"),
+      agent: Agent.ID.make("build"),
+      messageID: SessionMessage.ID.make("msg_host_effect"),
+      id: Tool.CallID.make("call_host_effect"),
+      progress: () => Effect.void,
+    }
+
+    expect(yield* execute(checkTool, { count: 3, code: "  v42  " }, context)).toEqual({
+      output: { formatted: "from-dep:v42:3" },
+      content: [{ type: "text", text: "from-dep:v42:3" }],
+    })
+    expect(yield* rpc.call("host-effect-rpc", "check", { tag: " v9 " })).toEqual({ value: "v9#5" })
+  }),
+)
+
+it.live("redirects plugin dependencies with a nested Effect 3 installation to the host, allows effect/package.json, and fails loudly on unprovided subpaths", () =>
+  Effect.gen(function* () {
+    const directory = yield* tmpdirScoped()
+    const pluginDir = path.join(directory.path, "v3-dep-plugin")
+    const badDir = path.join(directory.path, "removed-subpath-plugin")
+    const v3DepDir = path.join(pluginDir, "node_modules/v3-dep")
+
+    yield* Effect.promise(() =>
+      writeFiles(directory.path, {
+        "v3-dep-plugin/node_modules/effect/package.json":
+          '{"name":"effect","version":"4.0.0-rc.111","type":"module","exports":{"./package.json":"./package.json"}}',
+        "v3-dep-plugin/node_modules/v3-dep/node_modules/effect/package.json":
+          '{"name":"effect","version":"3.19.19","type":"module","exports":{".":"./index.js","./Option":"./Option.js","./ReadonlyArray":"./ReadonlyArray.js"}}',
+        "v3-dep-plugin/node_modules/v3-dep/node_modules/effect/index.js":
+          "export const Effect = { major: 3 }; export const Schema = { major: 3 }",
+        "v3-dep-plugin/node_modules/v3-dep/node_modules/effect/Option.js": "export const some = () => ({ major: 3 })",
+        "v3-dep-plugin/node_modules/v3-dep/node_modules/effect/ReadonlyArray.js": "export const fromIterable = () => []",
+        "v3-dep-plugin/node_modules/v3-dep/package.json":
+          '{"name":"v3-dep","type":"module","exports":{".":"./index.js","./v3-only":"./v3-only.js"}}',
+        "v3-dep-plugin/node_modules/v3-dep/index.js":
+          'import { Effect, Schema } from "effect"; import { some } from "effect/Option"; export const v3DepCaptured = { Effect, Schema, some }',
+        "v3-dep-plugin/node_modules/v3-dep/v3-only.js":
+          'import { fromIterable } from "effect/ReadonlyArray"; export { fromIterable }',
+        "v3-dep-plugin/index.ts":
+          'import pkg from "effect/package.json" with { type: "json" }; import { v3DepCaptured } from "v3-dep"; export const effectPkgName = pkg.name; export { v3DepCaptured }; export default { id: "v3-dep-plugin", async setup() {} }',
+        "removed-subpath-plugin/node_modules/effect/package.json":
+          '{"name":"effect","type":"module","exports":{"./RemovedLegacySubpath":"./RemovedLegacySubpath.js"}}',
+        "removed-subpath-plugin/node_modules/effect/RemovedLegacySubpath.js": "export const legacy = true",
+        "removed-subpath-plugin/index.ts":
+          'import { legacy } from "effect/RemovedLegacySubpath"; export default { id: "removed-subpath", async setup() { void legacy } }',
+      }),
+    )
+
+    const modules = yield* PluginModule.make()
+    expect(yield* modules.load({ type: "add", target: pluginDir, options: {} })).toMatchObject({ id: "v3-dep-plugin" })
+
+    const imported = yield* Effect.promise(() => import(path.join(pluginDir, "index.ts")))
+    expect(imported.effectPkgName).toBe("effect")
+    expect(imported.v3DepCaptured.Effect).toBe(Effect)
+    expect(imported.v3DepCaptured.Schema).toBe(Schema)
+    expect(imported.v3DepCaptured.some).toBe(Option.some)
+    yield* Effect.promise(async () => {
+      await expect(import(path.join(v3DepDir, "v3-only.js"))).rejects.toThrow("effect/ReadonlyArray.js")
+    })
+
+    const exit = yield* modules.load({ type: "add", target: badDir, options: {} }).pipe(Effect.exit)
+    expect(Exit.isFailure(exit)).toBe(true)
+    if (Exit.isFailure(exit)) {
+      expect(String(Cause.squash(exit.cause))).toContain("effect/RemovedLegacySubpath.js")
+    }
+  }),
+)
+
+it.live("discovers exported specifiers from the resolved tree even when dist/ exists, and validates barrel loader routing, async loader dedup, and Windows foreign filters", () =>
+  Effect.gen(function* () {
+    const directory = yield* tmpdirScoped()
+    const consumerDir = path.join(directory.path, "consumer")
+    const jitFixtureDir = path.join(directory.path, "jit-fixture")
+    const asyncModPath = path.join(directory.path, "async-mod.ts")
+
+    yield* Effect.promise(() =>
+      writeFiles(directory.path, {
+        "consumer/node_modules/@opencode/plugin/package.json": JSON.stringify({
+          name: "@opencode/plugin",
+          type: "module",
+          exports: {
+            ".": "./src/promise/index.ts",
+            "./effect": "./src/effect/index.ts",
+            "./effect/*": "./src/effect/*.ts",
+          },
+        }),
+        "consumer/node_modules/@opencode/plugin/src/promise/index.ts": "export const root = 'src'",
+        "consumer/node_modules/@opencode/plugin/src/effect/index.ts": "export * as plugin from './plugin.ts'",
+        "consumer/node_modules/@opencode/plugin/src/effect/plugin.ts": "export const leaf = 'src'",
+        "consumer/node_modules/@opencode/plugin/src/unexported.ts": "export const secret = true",
+        "consumer/node_modules/@opencode/plugin/dist/promise/index.js": "export const root = 'dist'",
+        "consumer/node_modules/@opencode/plugin/dist/effect/index.js": "export const index = 'dist'",
+        "consumer/node_modules/@opencode/plugin/dist/effect/plugin.js": "export const leaf = 'dist'",
+        "jit-fixture/SchemaJITCompiler.js": "export const enable = () => 'fn'",
+        "jit-fixture/enable.js": "export {}",
+        "async-mod.ts": "await new Promise((r) => setTimeout(r, 20)); export const nonce = Math.random()",
+      }),
+    )
+
+    const discovered = discoverPluginRuntimeSpecifiers(consumerDir, ["@opencode/plugin"])
+    expect(discovered.get("@opencode/plugin")?.replaceAll("\\", "/")).toEndWith("src/promise/index.ts")
+    expect(discovered.get("@opencode/plugin/effect")?.replaceAll("\\", "/")).toEndWith("src/effect/index.ts")
+    expect(discovered.get("@opencode/plugin/effect/plugin")?.replaceAll("\\", "/")).toEndWith("src/effect/plugin.ts")
+    expect(discovered.has("@opencode/plugin/unexported")).toBe(false)
+
+    const hostDiscovered = new Map(discoverPluginRuntimeSpecifiers())
+    hostDiscovered.set("effect/schema/SchemaJITCompiler", path.join(jitFixtureDir, "SchemaJITCompiler.js"))
+    hostDiscovered.set("effect/schema/SchemaJITCompiler/enable", path.join(jitFixtureDir, "enable.js"))
+    expect(pluginRuntimeLoaderCode("effect/Option", hostDiscovered)).toBe('() => require("effect")["Option"]')
+    expect(pluginRuntimeLoaderCode("effect/testing", hostDiscovered)).toBe('() => require("effect/testing")')
+    expect(pluginRuntimeLoaderCode("effect/unstable/http/MultipartParser/HeadersParser", hostDiscovered)).toBe(
+      '() => require("effect/unstable/http/MultipartParser/HeadersParser")',
+    )
+    expect(pluginRuntimeLoaderCode("effect/schema/SchemaJITCompiler/enable", hostDiscovered)).toBe(
+      '() => require("effect/schema/SchemaJITCompiler/enable")',
+    )
+
+    const loadAsync = createLoader(asyncModPath)
+    const first = loadAsync()
+    const second = loadAsync()
+    expect(first).toBeInstanceOf(Promise)
+    expect(first).toBe(second)
+    const [res1, res2] = yield* Effect.promise(() => Promise.all([first, second]))
+    expect(res1).toBe(res2)
+
+    const winFilter = createForeignPackageFilter([
+      "C:\\runner\\_work\\opencode\\node_modules\\.bun\\effect@4.0.0-rc.112\\node_modules\\effect",
+    ])
+    expect(
+      winFilter.test(
+        "C:\\runner\\_work\\opencode\\node_modules\\.bun\\effect@4.0.0-rc.112\\node_modules\\effect\\dist\\index.js",
+      ),
+    ).toBe(false)
+    expect(
+      winFilter.test(
+        "C:/runner/_work/opencode/node_modules/.bun/effect@4.0.0-rc.112/node_modules/effect/dist/index.js",
+      ),
+    ).toBe(false)
+    expect(winFilter.test("C:\\Users\\plugin\\node_modules\\effect\\dist\\index.js")).toBe(true)
+    expect(winFilter.test("C:/Users/plugin/node_modules/effect/dist/index.js")).toBe(true)
+    expect(winFilter.test("C:\\Users\\user\\.bun\\install\\cache\\effect@4.0.1@@@1\\dist\\index.js")).toBe(true)
+    expect(winFilter.test("C:/Users/user/.bun/install/cache/effect@4.0.1@@@1/dist/index.js")).toBe(true)
+  }),
+)
+
+async function writeFiles(root: string, files: Record<string, string>) {
+  await Promise.all(Object.entries(files).map(([file, text]) => Bun.write(path.join(root, file), text)))
+}
+
 it.live("blocks a local plugin before module initialization and honors replacement policies", () =>
   Effect.gen(function* () {
     const directory = yield* tmpdirScoped()
diff --git a/packages/plugin/README.md b/packages/plugin/README.md
new file mode 100644
index 000000000000..72b7b56ee922
--- /dev/null
+++ b/packages/plugin/README.md
@@ -0,0 +1,18 @@
+# `@opencode/plugin`
+
+Authoring interfaces and runtime loader support for OpenCode V2 plugins:
+
+- `@opencode/plugin` — [Promise plugin API](./src/README.md)
+- `@opencode/plugin/effect` — [Effect plugin API](./src/effect/README.md)
+- `@opencode/plugin/rpc` — portable RPC contract definitions
+- `@opencode/plugin/tui` — terminal UI plugin API
+
+## Packaging And Runtime `effect`
+
+When the OpenCode CLI loads server or TUI plugins, it resolves imports of `effect`, exported `effect/*` subpaths, and `@opencode/plugin` entrypoints (including imports from dependencies inside a plugin's `node_modules`) to the host's runtime module instances so fibers, loggers, and `Schema` parsers share one copy.
+
+- Declare `effect` as a `peerDependency` (and `devDependency` for local type-checking and testing) rather than a bundled runtime dependency.
+- Do not bundle `effect` into published plugin files; if you build with a bundler, keep `effect` and `effect/*` external. Two copies of `effect` do not share fiber, logger, or `Schema` internals.
+- Plugins and their `node_modules` dependencies always receive OpenCode's host `effect` instance. Use `effect` APIs and module paths compatible with the OpenCode release you target; dependencies built on another `effect` major (such as Effect 3) are not supported.
+- Only public `effect` subpaths are provided. A plugin that imports one of Effect's private `internal` modules fails to load with an error naming the path.
+- The compiled OpenCode binary does not include the Scalar and Swagger UI assets used by Effect's HTTP API docs pages; serving those pages from a plugin shows a notice instead.
diff --git a/packages/plugin/package.json b/packages/plugin/package.json
index 94c248f66ce7..442f0a3aa37b 100644
--- a/packages/plugin/package.json
+++ b/packages/plugin/package.json
@@ -13,6 +13,7 @@
     ".": "./src/promise/index.ts",
     "./effect": "./src/effect/index.ts",
     "./host": "./src/host.ts",
+    "./runtime": "./src/runtime.ts",
     "./tui": "./src/tui/index.ts",
     "./*": "./src/*.ts"
   },
diff --git a/packages/plugin/src/runtime-modules.ts b/packages/plugin/src/runtime-modules.ts
new file mode 100644
index 000000000000..bbbc1034f241
--- /dev/null
+++ b/packages/plugin/src/runtime-modules.ts
@@ -0,0 +1,113 @@
+import { existsSync, realpathSync } from "node:fs"
+import path from "node:path"
+import { pathToFileURL } from "node:url"
+
+export type RuntimeModuleLoader = () => Record<string, unknown> | Promise<Record<string, unknown>>
+
+const runtimePackages = ["effect", "@opencode/plugin"] as const
+
+export function resolveHostPackageRoots(from = import.meta.dir, packages: readonly string[] = runtimePackages) {
+  return packages.flatMap((pkgName) => {
+    const dir = path.dirname(Bun.resolveSync(`${pkgName}/package.json`, from))
+    return [dir, findNodeModulesDir(pkgName, from, dir)]
+  })
+}
+
+export function loadRuntimeModules(): Readonly<Record<string, RuntimeModuleLoader>> {
+  const entries = discoverPluginRuntimeSpecifiers()
+  const effectEntry = entries.get("effect")
+  if (effectEntry) require(effectEntry)
+  return Object.fromEntries(
+    [...entries.entries()].map(([specifier, resolved]) => [specifier, createLoader(resolved)]),
+  )
+}
+
+export function discoverPluginRuntimeSpecifiers(
+  from = import.meta.dir,
+  packages: readonly string[] = runtimePackages,
+): ReadonlyMap<string, string> {
+  const entries = new Map<string, string>()
+  for (const pkgName of packages) {
+    const realDir = path.dirname(Bun.resolveSync(`${pkgName}/package.json`, from))
+    // Resolve workspace @opencode/plugin paths via node_modules so OpenTUI does not wrap host files in async rewrite loaders.
+    const loadDir = findNodeModulesDir(pkgName, from, realDir)
+    const toLoadPath = (resolved: string) =>
+      loadDir === realDir ? resolved : path.join(loadDir, path.relative(realDir, resolved))
+    const rootEntry = Bun.resolveSync(pkgName, from)
+    const relParts = path.relative(realDir, rootEntry).replaceAll("\\", "/").split("/")
+    const scanDir = relParts.length > 1 ? path.join(realDir, relParts[0]) : realDir
+    const ext = path.extname(rootEntry) || ".js"
+    entries.set(pkgName, toLoadPath(rootEntry))
+    for (const file of new Bun.Glob(`**/*${ext}`).scanSync({ cwd: scanDir })) {
+      const normalized = file.replaceAll("\\", "/")
+      if (
+        normalized.startsWith("internal/") ||
+        normalized.includes("/internal/") ||
+        normalized.startsWith("source.") ||
+        normalized.startsWith("runtime")
+      ) {
+        continue
+      }
+      const base = normalized.slice(0, -ext.length)
+      if (base === "index") continue
+      const candidates = base.endsWith("/index")
+        ? [`${pkgName}/${base.slice(0, -"/index".length)}`, `${pkgName}/${base}`]
+        : [`${pkgName}/${base}`]
+      for (const specifier of candidates) {
+        if (entries.has(specifier)) continue
+        try {
+          entries.set(specifier, toLoadPath(Bun.resolveSync(specifier, from)))
+        } catch {}
+      }
+    }
+  }
+  return entries
+}
+
+export function pluginRuntimeLoaderCode(specifier: string, entries: ReadonlyMap<string, string>) {
+  if (specifier.startsWith("effect/")) {
+    const slash = specifier.lastIndexOf("/")
+    const parent = specifier.slice(0, slash)
+    const member = specifier.slice(slash + 1)
+    const parentResolved = entries.get(parent)
+    const resolved = entries.get(specifier)
+    if (
+      member !== "index" &&
+      parentResolved &&
+      resolved &&
+      (require(parentResolved) as Record<string, unknown>)[member] === require(resolved)
+    ) {
+      return `() => require(${JSON.stringify(parent)})[${JSON.stringify(member)}]`
+    }
+  }
+  return `() => require(${JSON.stringify(specifier)})`
+}
+
+export function createLoader(resolved: string): RuntimeModuleLoader {
+  let cached: Record<string, unknown> | undefined
+  let pending: Promise<Record<string, unknown>> | undefined
+  return () => {
+    if (cached) return cached
+    if (pending) return pending
+    try {
+      return (cached = require(resolved) as Record<string, unknown>)
+    } catch {
+      return (pending = import(pathToFileURL(resolved).href).then(
+        (mod: Record<string, unknown>) => (cached = mod),
+        (error) => {
+          pending = undefined
+          throw error
+        },
+      ))
+    }
+  }
+}
+
+function findNodeModulesDir(pkgName: string, from: string, realDir: string) {
+  if (/[/\\]node_modules[/\\]/.test(realDir)) return realDir
+  for (let dir = path.resolve(from); ; dir = path.dirname(dir)) {
+    const candidate = path.join(dir, "node_modules", pkgName)
+    if (existsSync(candidate) && realpathSync(candidate) === realDir) return candidate
+    if (path.dirname(dir) === dir) return realDir
+  }
+}
diff --git a/packages/plugin/src/runtime.ts b/packages/plugin/src/runtime.ts
new file mode 100644
index 000000000000..d7df51df2ae1
--- /dev/null
+++ b/packages/plugin/src/runtime.ts
@@ -0,0 +1,52 @@
+import { loadRuntimeModules, resolveHostPackageRoots, type RuntimeModuleLoader } from "./runtime-modules.js"
+
+const foreignPkgSuffix = String.raw`(?:node_modules[/\\](@opencode[/\\]plugin|effect)|(@opencode[/\\]plugin|effect)@[^/\\]+@@@\d+)`
+const foreignPkgPattern = new RegExp(String.raw`^(.*[/\\]${foreignPkgSuffix})[/\\](.+)$`)
+
+let installed: Readonly<Record<string, RuntimeModuleLoader>> | undefined
+
+export function provides(specifier: string) {
+  return installed !== undefined && Object.hasOwn(installed, specifier)
+}
+
+export function ensurePluginRuntime() {
+  if (typeof Bun === "undefined") return {}
+  if (installed) return installed
+  const modules = loadRuntimeModules()
+  installed = modules
+  Bun.plugin({
+    name: "opencode-plugin-runtime",
+    setup(build) {
+      for (const [specifier, load] of Object.entries(modules)) {
+        build.module(specifier, () => {
+          const exports = load()
+          return exports instanceof Promise
+            ? exports.then((value) => ({ exports: value, loader: "object" as const }))
+            : { exports, loader: "object" as const }
+        })
+      }
+      build.onLoad({ filter: createForeignPackageFilter() }, (args) => {
+        const match = args.path.match(foreignPkgPattern)
+        const target = match ? `${match[2] ?? match[3]}/${match[4]}`.replaceAll("\\", "/") : args.path
+        throw new Error(
+          `Cannot load "${target}" from plugin node_modules: "${target}" is not provided by OpenCode; plugins must use the host's "effect" and "@opencode/plugin" modules.`,
+        )
+      })
+    },
+  })
+  return modules
+}
+
+export function createForeignPackageFilter(rootsInput: Iterable<string> = resolveHostPackageRoots()) {
+  const suffix = String.raw`[/\\]${foreignPkgSuffix}[/\\].*\.[cm]?[jt]sx?(?:[?#].*)?$`
+  const roots = [...new Set(rootsInput)]
+  if (roots.length === 0) return new RegExp(suffix)
+  const escaped = roots
+    .map((value) =>
+      value
+        .replace(/[.*+?^${}()|[\]\\]/g, "\\$&")
+        .replace(/(?:\\\/|\\\\|\/)+/g, "[/\\\\]"),
+    )
+    .join("|")
+  return new RegExp(`^(?!(?:${escaped})[/\\\\]).*${suffix}`)
+}
diff --git a/packages/plugin/src/source.bun.ts b/packages/plugin/src/source.bun.ts
index 618f51556b92..7a2d6fd54e4d 100644
--- a/packages/plugin/src/source.bun.ts
+++ b/packages/plugin/src/source.bun.ts
@@ -3,6 +3,7 @@ import { readFileSync } from "node:fs"
 import path from "node:path"
 import { fileURLToPath, pathToFileURL } from "node:url"
 import { Host } from "./host.js"
+import { provides } from "./runtime.js"
 import { localSource } from "./source.js"
 import { missingPackageTarget } from "./source.package.js"
 
@@ -39,6 +40,7 @@ export async function prepareSource(entrypoint: string, track: (file: string, di
           ? new URL(item.path, pathToFileURL(file))
           : localSource(item.path, path.dirname(file))
       if (!local) {
+        if (provides(item.path)) continue
         try {
           Bun.resolveSync(item.path, path.dirname(file))
         } catch {
diff --git a/packages/plugin/test/host.test.ts b/packages/plugin/test/host.test.ts
index 7d90cf702594..707081d180b6 100644
--- a/packages/plugin/test/host.test.ts
+++ b/packages/plugin/test/host.test.ts
@@ -1,5 +1,5 @@
 import assert from "node:assert/strict"
-import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises"
+import { mkdir, mkdtemp, realpath, rm, writeFile } from "node:fs/promises"
 import { tmpdir } from "node:os"
 import path from "node:path"
 import { describe, it } from "node:test"
@@ -11,7 +11,7 @@ const source = 'throw new Error("Plugin code must not run during resolution")'
 const name = "@fixture/plugin"
 
 async function fixture(files: Record<string, string>, installed = false) {
-  const root = await mkdtemp(path.join(tmpdir(), "opencode-host-"))
+  const root = await realpath(await mkdtemp(path.join(tmpdir(), "opencode-host-")))
   const directory = installed ? path.join(root, "node_modules", name) : root
   await Promise.all(
     Object.entries(files).map(async ([file, content]) => {
diff --git a/packages/tui/src/plugin/runtime-plugin-support.bun.ts b/packages/tui/src/plugin/runtime-plugin-support.bun.ts
index e1d7ae2cfa8d..b1ebab022675 100644
--- a/packages/tui/src/plugin/runtime-plugin-support.bun.ts
+++ b/packages/tui/src/plugin/runtime-plugin-support.bun.ts
@@ -1,8 +1,11 @@
+import { ensurePluginRuntime, provides } from "@opencode/plugin/runtime"
 import { Plugin, PluginContextProvider, usePlugin } from "@opencode/plugin/tui"
 import { ensureRuntimePluginSupport } from "@opentui/solid/runtime-plugin-support/configure"
 
+ensurePluginRuntime()
 ensureRuntimePluginSupport({
   additional: {
     "@opencode/plugin/tui": { Plugin, PluginContextProvider, usePlugin },
   },
+  preserve: provides,
 })
diff --git a/packages/tui/test/plugin-source.test.ts b/packages/tui/test/plugin-source.test.ts
index bffbd2807d39..2f4d396a6155 100644
--- a/packages/tui/test/plugin-source.test.ts
+++ b/packages/tui/test/plugin-source.test.ts
@@ -1,4 +1,5 @@
 import { expect, test } from "bun:test"
+import { createRequire } from "node:module"
 import path from "node:path"
 import { mkdir, rename, symlink } from "node:fs/promises"
 import { fileURLToPath, pathToFileURL } from "node:url"
@@ -7,6 +8,7 @@ import "../src/plugin/runtime-plugin-support.bun"
 import { createPluginSources } from "../src/plugin/source"
 import { createSourceWatcher } from "../src/plugin/watch"
 import { createSignal } from "solid-js"
+import { Effect, Option, Schema } from "effect"
 import { Plugin } from "@opencode/plugin/tui"
 import { tmpdir } from "./fixture/fixture"
 
@@ -138,6 +140,104 @@ test("shared runtime and ordinary package identities survive plugin generations"
   }
 })
 
+test("TUI plugins importing @opencode/plugin/tui and solid-js alongside effect resolve effect and effect/* to the host copy without rewriting host Effect or hijacking plugin dependencies", async () => {
+  const effectPlugin = await import("@opencode/plugin/effect")
+  const req = createRequire(import.meta.url)
+  expect(req("effect").Effect).toBe(Effect)
+  expect(req("effect/Option").some).toBe(Option.some)
+  expect(req("@opencode/plugin/effect").Plugin).toBe(effectPlugin.Plugin)
+  expect(JSON.stringify(Schema.Option(Schema.String).ast)).not.toContain("opentui:runtime-module:")
+
+  const standalone = Bun.spawnSync(
+    [
+      process.execPath,
+      "-e",
+      [
+        `import ${JSON.stringify(fileURLToPath(new URL("../src/plugin/runtime-plugin-support.bun.ts", import.meta.url)))}`,
+        'import assert from "node:assert/strict"',
+        'import { createRequire } from "node:module"',
+        "const req = createRequire(import.meta.url)",
+        'const eff = req("effect")',
+        'const opt = req("effect/Option")',
+        'const plug = req("@opencode/plugin/effect")',
+        'const { Effect } = await import("effect")',
+        'const { some } = await import("effect/Option")',
+        'const { Plugin } = await import("@opencode/plugin/effect")',
+        "assert.equal(eff.Effect, Effect)",
+        "assert.equal(opt.some, some)",
+        "assert.equal(plug.Plugin, Plugin)",
+      ].join("\n"),
+    ],
+    { cwd: fileURLToPath(new URL("..", import.meta.url)), stdout: "pipe", stderr: "pipe" },
+  )
+  expect({ stderr: standalone.stderr.toString(), exit: standalone.exitCode }).toEqual({ stderr: "", exit: 0 })
+
+  const watched: string[] = []
+  await using sources = await fixture(async (file) => {
+    watched.push(file)
+  })
+  const entry = new URL("tui.ts", sources.url)
+  const badEntry = new URL("bad-tui.ts", sources.url)
+  await Promise.all(
+    Object.entries({
+      "node_modules/effect/package.json":
+        '{"name":"effect","version":"3.19.19","type":"module","exports":{".":{"import":"./dist/esm/index.js"},"./Option":{"import":"./dist/esm/Option.js"},"./RemovedSubpath":{"import":"./dist/esm/RemovedSubpath.js"},"./package.json":"./package.json"}}',
+      "node_modules/effect/dist/esm/index.js":
+        "export const Effect = { foreign: true }; export const Schema = { foreign: true }",
+      "node_modules/effect/dist/esm/Option.js": "export const some = () => null",
+      "node_modules/effect/dist/esm/RemovedSubpath.js": "export const removed = true",
+      "node_modules/effect-helper/package.json":
+        '{"name":"effect-helper","type":"module","exports":{".":"./index.js"}}',
+      "node_modules/effect-helper/index.js":
+        'import { Effect, Schema } from "effect"; import { some } from "effect/Option"; export const helper = { Effect, Schema, some }',
+      "node_modules/zod/package.json": '{"name":"zod","type":"module","exports":{".":"./index.js"}}',
+      "node_modules/zod/index.js": "export const fromPluginZod = true",
+      "helper.ts": ['import { fromPluginZod }', 'from "zod"; export { fromPluginZod }'].join(" "),
+      "tui.ts": [
+        "import { createSignal }",
+        'from "solid-js"',
+        "import { Plugin }",
+        'from "@opencode/plugin/tui"',
+        'import { Plugin as HostEffectPlugin } from "@opencode/plugin/effect"',
+        'import { Effect, Schema } from "effect"',
+        'import { some } from "effect/Option"',
+        "import pkg",
+        'from "effect/package.json" with { type: "json" }',
+        'import { helper } from "effect-helper"',
+        'const { fromPluginZod } = await import("./helper.ts")',
+        'const dynOption = await import("effect/Option")',
+        'const dynEffectPlugin = await import("@opencode/plugin/effect")',
+        "export const plugin = { createSignal, Plugin, HostEffectPlugin, Effect, Schema, some, dynSome: dynOption.some, dynEffectPlugin: dynEffectPlugin.Plugin, pkgName: pkg.name, fromPluginZod }",
+        "export { helper }",
+      ].join("\n"),
+      "bad-tui.ts": [
+        "import { Plugin }",
+        'from "@opencode/plugin/tui"; import { removed } from "effect/RemovedSubpath"; export default { Plugin, removed }',
+      ].join(" "),
+    }).map(([file, text]) => Bun.write(new URL(file, sources.url), text)),
+  )
+  const loaded = (await sources.read(entry.href)).module as {
+    plugin: Record<string, unknown>
+    helper: Record<string, unknown>
+  }
+  expect(loaded.plugin.createSignal).toBe(createSignal)
+  expect(loaded.plugin.Plugin).toBe(Plugin)
+  expect(loaded.plugin.HostEffectPlugin).toBe(effectPlugin.Plugin)
+  expect(loaded.plugin.Effect).toBe(Effect)
+  expect(loaded.plugin.Schema).toBe(Schema)
+  expect(loaded.plugin.some).toBe(Option.some)
+  expect(loaded.plugin.dynSome).toBe(Option.some)
+  expect(loaded.plugin.dynEffectPlugin).toBe(effectPlugin.Plugin)
+  expect(loaded.plugin.pkgName).toBe("effect")
+  expect(loaded.plugin.fromPluginZod).toBe(true)
+  expect(loaded.helper.Effect).toBe(Effect)
+  expect(loaded.helper.Schema).toBe(Schema)
+  expect(loaded.helper.some).toBe(Option.some)
+  expect(watched.some((item) => item.replaceAll("\\", "/").endsWith("/node_modules/effect"))).toBe(false)
+  expect(watched.some((item) => item.replaceAll("\\", "/").endsWith("/node_modules/@opencode/plugin"))).toBe(false)
+  await expect(sources.read(badEntry.href)).rejects.toThrow("effect/dist/esm/RemovedSubpath.js")
+})
+
 test("helper import.meta stays anchored to its source, including assets and resolution", async () => {
   await using sources = await fixture()
   const entry = new URL("tui.ts", sources.url)
diff --git a/services/www/src/docs/content/build/plugins/effect.mdx b/services/www/src/docs/content/build/plugins/effect.mdx
index 2e91100bf37a..5f187ad0cd72 100644
--- a/services/www/src/docs/content/build/plugins/effect.mdx
+++ b/services/www/src/docs/content/build/plugins/effect.mdx
@@ -3,11 +3,14 @@ title: "Effect"
 ---
 
 `@opencode/plugin/effect` is the Effect-native version of the OpenCode plugin API. Its context operations return
-Effects or Streams, callbacks return Effects, and plugin lifetime is represented by `Scope`. Install `effect` with the
-plugin package.
+Effects or Streams, callbacks return Effects, and plugin lifetime is represented by `Scope`.
+
+OpenCode provides `effect` (including exported `effect/*` subpaths) and `@opencode/plugin` at runtime when loading
+plugins and their `node_modules` dependencies. Install them as peer/dev dependencies for local type-checking and testing
+rather than bundling them into your plugin.
 
 ```sh
-bun add @opencode/plugin effect
+bun add --peer @opencode/plugin effect
 ```
 
 Export an Effect plugin from `.opencode/plugins/` to load it automatically.
@@ -1500,7 +1503,7 @@ type Transform<Input> = (callback: (input: Input) => void) => Effect.Effect<Regi
 ## Publish
 
 A package plugin uses the same default export as a local Effect plugin. Export the Effect implementation from the main
-entrypoint and declare both runtime dependencies.
+entrypoint and declare `effect` as a `peerDependency`.
 
 ```json title="package.json"
 {
@@ -1511,12 +1514,28 @@ entrypoint and declare both runtime dependencies.
     ".": "./src/index.ts"
   },
   "dependencies": {
-    "@opencode/plugin": "latest",
-    "effect": "4.0.0-rc.111"
+    "@opencode/plugin": "latest"
+  },
+  "peerDependencies": {
+    "effect": ">=4.0.0-rc.112"
   }
 }
 ```
 
+OpenCode redirects imports of `effect`, exported `effect/*` subpaths, and `@opencode/plugin` (including imports from
+dependencies in the plugin's `node_modules`) to the host's runtime instances so fibers, loggers, and `Schema` parsers
+share one runtime copy.
+
+- Do not bundle `effect` into the published plugin artifact. If you build with a bundler, mark `effect` and `effect/*`
+  external.
+- Plugins and their `node_modules` dependencies always execute against the host OpenCode release's `effect` instance.
+  Use `effect` APIs and module paths compatible with the OpenCode release you target; dependencies built on another
+  `effect` major (such as Effect 3) also receive the host's `effect` and are not supported.
+- Only public `effect` subpaths are provided. A plugin that imports one of Effect's private `internal` modules fails to
+  load with an error naming the path.
+- The compiled OpenCode binary does not include the Scalar and Swagger UI assets used by Effect's HTTP API docs pages;
+  serving those pages from a plugin shows a notice instead.
+
 The package entrypoint exports `Plugin.define` with an `effect` function.
 
 ```ts title="src/index.ts"