diff --git a/.dagger/modules/e2e/util.dang b/.dagger/modules/e2e/util.dang
index af705b5..64585e9 100644
--- a/.dagger/modules/e2e/util.dang
+++ b/.dagger/modules/e2e/util.dang
@@ -152,6 +152,16 @@ type Fixtures {
   that depends on the runtime, deno.json instead of package.json + tsconfig.
   """
   let denoModule: String! = root + "/generate-deno/app"
+
+  """
+  The runtime execution fixtures, managed so `dagger generate` keeps them
+  current, and registered by the engine when the runtimes module loads them.
+  """
+  let runtimeFixtures: [String!]! = [
+    ".dagger/modules/runtimes/fixtures/bun",
+    ".dagger/modules/runtimes/fixtures/deno",
+    ".dagger/modules/runtimes/fixtures/node",
+  ]
   let configBareModule: String! = root + "/config/bare"
 
   # A client binds to client/app (which depends on client/dep) and is generated
@@ -193,5 +203,5 @@ type Fixtures {
     depLibModule,
     denoModule,
     parentSourceModule,
-  ]
+  ] + runtimeFixtures
 }
diff --git a/.dagger/modules/runtimes/dagger.json b/.dagger/modules/runtimes/dagger.json
new file mode 100644
index 0000000..1962b85
--- /dev/null
+++ b/.dagger/modules/runtimes/dagger.json
@@ -0,0 +1,17 @@
+{
+  "name": "runtimes",
+  "engineVersion": "v1.0.0-0",
+  "sdk": {
+    "source": "dang"
+  },
+  "dependencies": [
+    {
+      "name": "typescript-sdk",
+      "source": "../../../"
+    },
+    {
+      "name": "sdk-sdk",
+      "source": "github.com/dagger/sdk-sdk"
+    }
+  ]
+}
diff --git a/.dagger/modules/runtimes/fixtures/bun/.gitignore b/.dagger/modules/runtimes/fixtures/bun/.gitignore
new file mode 100644
index 0000000..5b4e8f0
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/bun/.gitignore
@@ -0,0 +1,5 @@
+/sdk
+/__dagger.entrypoint.ts
+/tsconfig.json
+/**/node_modules/**
+/.env
diff --git a/.dagger/modules/runtimes/fixtures/bun/bun.lock b/.dagger/modules/runtimes/fixtures/bun/bun.lock
new file mode 100644
index 0000000..e69de29
diff --git a/.dagger/modules/runtimes/fixtures/bun/dagger-module.toml b/.dagger/modules/runtimes/fixtures/bun/dagger-module.toml
new file mode 100644
index 0000000..6448a29
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/bun/dagger-module.toml
@@ -0,0 +1,5 @@
+name = "runtime-bun"
+engineVersion = "v1.0.0-beta.9"
+
+[runtime]
+  source = "typescript"
diff --git a/.dagger/modules/runtimes/fixtures/bun/package.json b/.dagger/modules/runtimes/fixtures/bun/package.json
new file mode 100644
index 0000000..3dbc1ca
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/bun/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/.dagger/modules/runtimes/fixtures/bun/src/index.ts b/.dagger/modules/runtimes/fixtures/bun/src/index.ts
new file mode 100644
index 0000000..e3e7fc4
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/bun/src/index.ts
@@ -0,0 +1,9 @@
+import { object, func } from "@dagger.io/dagger"
+
+@object()
+export class RuntimeBun {
+  @func()
+  greet(name: string): string {
+    return "hello " + name + " from bun"
+  }
+}
diff --git a/.dagger/modules/runtimes/fixtures/deno/.gitignore b/.dagger/modules/runtimes/fixtures/deno/.gitignore
new file mode 100644
index 0000000..5b4e8f0
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/deno/.gitignore
@@ -0,0 +1,5 @@
+/sdk
+/__dagger.entrypoint.ts
+/tsconfig.json
+/**/node_modules/**
+/.env
diff --git a/.dagger/modules/runtimes/fixtures/deno/dagger-module.toml b/.dagger/modules/runtimes/fixtures/deno/dagger-module.toml
new file mode 100644
index 0000000..66e89a1
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/deno/dagger-module.toml
@@ -0,0 +1,5 @@
+name = "runtime-deno"
+engineVersion = "v1.0.0-beta.9"
+
+[runtime]
+  source = "typescript"
diff --git a/.dagger/modules/runtimes/fixtures/deno/deno.json b/.dagger/modules/runtimes/fixtures/deno/deno.json
new file mode 100644
index 0000000..256151a
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/deno/deno.json
@@ -0,0 +1,20 @@
+{
+  "tasks": {
+    "dev": "deno run main.ts"
+  },
+  "imports": {
+    "typescript": "npm:typescript@5.9.3",
+    "@dagger.io/dagger": "./sdk/index.ts",
+    "@dagger.io/dagger/telemetry": "./sdk/telemetry.ts"
+  },
+  "nodeModulesDir": "auto",
+  "unstable": [
+    "bare-node-builtins",
+    "sloppy-imports",
+    "node-globals",
+    "byonm"
+  ],
+  "compilerOptions": {
+    "experimentalDecorators": true
+  }
+}
diff --git a/.dagger/modules/runtimes/fixtures/deno/src/index.ts b/.dagger/modules/runtimes/fixtures/deno/src/index.ts
new file mode 100644
index 0000000..64c3e92
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/deno/src/index.ts
@@ -0,0 +1,9 @@
+import { object, func } from "@dagger.io/dagger"
+
+@object()
+export class RuntimeDeno {
+  @func()
+  greet(name: string): string {
+    return "hello " + name + " from deno"
+  }
+}
diff --git a/.dagger/modules/runtimes/fixtures/node/.gitignore b/.dagger/modules/runtimes/fixtures/node/.gitignore
new file mode 100644
index 0000000..5b4e8f0
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/node/.gitignore
@@ -0,0 +1,5 @@
+/sdk
+/__dagger.entrypoint.ts
+/tsconfig.json
+/**/node_modules/**
+/.env
diff --git a/.dagger/modules/runtimes/fixtures/node/dagger-module.toml b/.dagger/modules/runtimes/fixtures/node/dagger-module.toml
new file mode 100644
index 0000000..ab4c158
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/node/dagger-module.toml
@@ -0,0 +1,5 @@
+name = "runtime-node"
+engineVersion = "v1.0.0-beta.9"
+
+[runtime]
+  source = "typescript"
diff --git a/.dagger/modules/runtimes/fixtures/node/package.json b/.dagger/modules/runtimes/fixtures/node/package.json
new file mode 100644
index 0000000..3dbc1ca
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/node/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/.dagger/modules/runtimes/fixtures/node/src/index.ts b/.dagger/modules/runtimes/fixtures/node/src/index.ts
new file mode 100644
index 0000000..37fcba5
--- /dev/null
+++ b/.dagger/modules/runtimes/fixtures/node/src/index.ts
@@ -0,0 +1,9 @@
+import { object, func } from "@dagger.io/dagger"
+
+@object()
+export class RuntimeNode {
+  @func()
+  greet(name: string): string {
+    return "hello " + name + " from node"
+  }
+}
diff --git a/.dagger/modules/runtimes/main.dang b/.dagger/modules/runtimes/main.dang
new file mode 100644
index 0000000..df7c929
--- /dev/null
+++ b/.dagger/modules/runtimes/main.dang
@@ -0,0 +1,103 @@
+"""
+Execution checks: does a module this SDK generates actually run?
+
+Every other check in this repo inspects what generation *writes*. These load
+the result, which for a dagger-module.toml module means the engine builds the
+runtime container and executes the generated entrypoint to discover its types —
+there is no codegen at call time to paper over a bad tree.
+
+That makes them the only checks covering the contract the whole move rests on:
+sdk/ resolving as @dagger.io/dagger, the bundle it holds being loadable, the
+entrypoint importing the user's classes and registering them. A break here is a
+module that generates cleanly and then fails at `dagger call`.
+
+One fixture per TypeScript runtime, because this is where they stop being
+interchangeable: generation differs only in which config file it writes, but
+node, bun and deno each run the entrypoint in a different container, with a
+different interpreter, resolving @dagger.io/dagger a different way.
+"""
+type Runtimes {
+  let fixtures: String! = ".dagger/modules/runtimes/fixtures"
+
+  """
+  A node module should generate and run.
+  """
+  nodeRunsCheck(ws: Workspace!): Void @check {
+    assertRuns(ws, "node", "RuntimeNode")
+  }
+
+  """
+  A bun module should generate and run.
+
+  The engine picks bun over node by finding a lockfile next to package.json, so
+  the generated tree is byte-identical to the node one — only the container it
+  is executed in differs. Nothing else in this repo has ever run bun.
+  """
+  bunRunsCheck(ws: Workspace!): Void @check {
+    assertRuns(ws, "bun", "RuntimeBun")
+  }
+
+  """
+  A deno module should generate and run.
+
+  Deno has no node_modules to fall back on: if generation writes the wrong
+  config, the runtime cannot resolve @dagger.io/dagger at all.
+  """
+  denoRunsCheck(ws: Workspace!): Void @check {
+    assertRuns(ws, "deno", "RuntimeDeno")
+  }
+
+  """
+  A scaffolded module should answer a function call.
+
+  Loading a module proves the entrypoint registers its types; this proves the
+  other half of the dispatcher — that a call reaches the user's code and its
+  return value comes back. It goes through sdk-sdk's harness, which builds a
+  scratch workspace and drives a release CLI the way a user would: `sdk
+  install`, `module init`, `generate`, then the call.
+
+  The function is the default template's `baseImageAddress`, whose value is set
+  by the module's constructor, so a passing call also means the constructor ran
+  and its default was applied.
+  """
+  invokesFunctionCheck(ws: Workspace!): Void @check {
+    let target = sdkSdk.target(ws.directory("/"), ".")
+    let run = target.run(["call", target.moduleName, "base-image-address"])
+
+    run.assertSuccess
+
+    if (run.stdout.contains("alpine") == false) {
+      raise "calling a scaffolded module returned unexpected output: " + run.stdout
+    }
+
+    null
+  }
+
+  """
+  Generate a fixture, stage the result, and load the module from it.
+
+  Staging through withChanges rather than writing to disk keeps the generated
+  tree out of the fixture entirely — which also sidesteps the trap that a
+  module whose .gitignore covers sdk/ hides its own generated files from the
+  engine's module context.
+
+  Reading the module's objects is what forces execution: the TypeScript SDK has
+  no ModuleTypes function, so type discovery goes through the runtime and the
+  committed entrypoint's register().
+  """
+  let assertRuns(ws: Workspace!, runtime: String!, objectName: String!): Void {
+    let path = fixtures + "/" + runtime
+    let staged = ws.withChanges(typescriptSdk.mod(ws, path: path).generate(ws))
+
+    let objects = staged.moduleSource("/" + path).asModule.objects
+      .{{ asObject.{{ name }} }}
+      .map { o => o.asObject.name }
+
+    if (objects.filter { name => name == objectName }.length == 0) {
+      raise runtime + " module did not load: expected object " + objectName +
+        ", got [" + objects.join(", ") + "]"
+    }
+
+    null
+  }
+}
diff --git a/dagger.toml b/dagger.toml
index 7924f2a..1a39d26 100644
--- a/dagger.toml
+++ b/dagger.toml
@@ -12,6 +12,9 @@ source = ".dagger/modules/e2e"
 [modules.packager]
 source = ".dagger/modules/packager"
 
+[modules.runtimes]
+source = ".dagger/modules/runtimes"
+
 [modules.typescript-sdk]
 source = "."
 check.skip = ["*"]
@@ -51,6 +54,15 @@ path = ".dagger/modules/e2e/fixtures/generate-deps/dep"
 [[modules.typescript-sdk.as-sdk.modules]]
 path = ".dagger/modules/e2e/fixtures/parent-source/.dagger/modules/app"
 
+[[modules.typescript-sdk.as-sdk.modules]]
+path = ".dagger/modules/runtimes/fixtures/bun"
+
+[[modules.typescript-sdk.as-sdk.modules]]
+path = ".dagger/modules/runtimes/fixtures/deno"
+
+[[modules.typescript-sdk.as-sdk.modules]]
+path = ".dagger/modules/runtimes/fixtures/node"
+
 [[modules.typescript-sdk.as-sdk.clients]]
 path = ".dagger/modules/e2e/fixtures/client/out"
 module = ".dagger/modules/e2e/fixtures/client/app"