diff --git a/lib/mix/tasks/appdeps.update.ex b/lib/mix/tasks/appdeps.update.ex
index c3d920f..cf68f43 100644
--- a/lib/mix/tasks/appdeps.update.ex
+++ b/lib/mix/tasks/appdeps.update.ex
@@ -6,7 +6,8 @@ defmodule Mix.Tasks.Appdeps.Update do
 
       mix appdeps.update DEP [DEP ...]
 
-  Runs `mix deps.update` for the named dependencies from the `app/` project.
+  Checks that CI uses mise's pinned toolchain, runs `mix deps.update` for the
+  named dependencies from the `app/` project, then runs the full `mix ci` gate.
   """
 
   use Mix.Task
@@ -24,7 +25,9 @@ defmodule Mix.Tasks.Appdeps.Update do
   end
 
   def run(dependencies, shell) do
+    Mix.Tasks.Toolchain.Check.run([])
     shell.("mix", ["deps.update" | dependencies], cd: "app")
+    Mix.Tasks.Ci.run([], shell)
     :ok
   end
 end
diff --git a/lib/mix/tasks/ci.ex b/lib/mix/tasks/ci.ex
index 75f0cf8..4129d7e 100644
--- a/lib/mix/tasks/ci.ex
+++ b/lib/mix/tasks/ci.ex
@@ -54,6 +54,7 @@ defmodule Mix.Tasks.Ci do
 
   @doc false
   def run([], shell) do
+    Mix.Tasks.Toolchain.Check.run([])
     shell.("mix", ["deps.get"], cd: "app")
     shell.("./ci/validate_pull_request_title.sh", [], [])
     shell.("./ci/validate_commit_range.sh", [], [])
diff --git a/lib/mix/tasks/toolchain.check.ex b/lib/mix/tasks/toolchain.check.ex
new file mode 100644
index 0000000..f5b6fee
--- /dev/null
+++ b/lib/mix/tasks/toolchain.check.ex
@@ -0,0 +1,70 @@
+defmodule Mix.Tasks.Toolchain.Check do
+  @shortdoc "Checks that CI and mise use the same OTP and Elixir versions"
+
+  @moduledoc """
+  #{@shortdoc}.
+
+      mix toolchain.check
+
+  `mise.toml` is the local toolchain source of truth. This task rejects a
+  workflow that configures erlef/setup-beam with different OTP or Elixir pins.
+  """
+
+  use Mix.Task
+
+  @impl Mix.Task
+  def run([]) do
+    workflows =
+      ".github/workflows/*.yaml"
+      |> Path.wildcard()
+      |> Enum.map(&{&1, File.read!(&1)})
+
+    case validate(File.read!("mise.toml"), workflows) do
+      :ok -> :ok
+      {:error, message} -> Mix.raise(message)
+    end
+  end
+
+  def run(_argv), do: Mix.raise("Usage: mix toolchain.check")
+
+  @doc false
+  def validate(mise_toml, workflows) do
+    expected = %{otp: pin!(mise_toml, "erlang"), elixir: pin!(mise_toml, "elixir")}
+
+    mismatches =
+      Enum.flat_map(workflows, fn {path, workflow} ->
+        Enum.flat_map(setup_beam_steps(workflow), fn step ->
+          Enum.flat_map(expected, fn {name, expected_pin} ->
+            case Map.get(workflow_pins(step), name) do
+              ^expected_pin -> []
+              nil -> ["#{path}: #{name} missing (expected #{expected_pin})"]
+              pin -> ["#{path}: #{name} #{pin} (expected #{expected_pin})"]
+            end
+          end)
+        end)
+      end)
+
+    case mismatches do
+      [] -> :ok
+      _ -> {:error, "Toolchain pins differ from mise.toml:\n  #{Enum.join(mismatches, "\n  ")}"}
+    end
+  end
+
+  defp pin!(contents, name) do
+    case Regex.run(~r/^#{name}\s*=\s*"([^"]+)"$/m, contents) do
+      [_, pin] -> pin
+      nil -> Mix.raise("mise.toml does not pin #{name}")
+    end
+  end
+
+  defp workflow_pins(workflow) do
+    Regex.scan(~r/^\s*(otp|elixir)-version:\s*"([^"]+)"$/m, workflow)
+    |> Map.new(fn [_, name, pin] -> {if(name == "otp", do: :otp, else: :elixir), pin} end)
+  end
+
+  defp setup_beam_steps(workflow) do
+    workflow
+    |> String.split(~r/\n(?=\s*-\s*$)/m)
+    |> Enum.filter(&String.contains?(&1, "uses: erlef/setup-beam@v1"))
+  end
+end
diff --git a/mise.toml b/mise.toml
index b29c54e..5dedb63 100644
--- a/mise.toml
+++ b/mise.toml
@@ -18,6 +18,14 @@ python = "3.14.1"
 #CLAUDE_CODE_ATTRIBUTION_HEADER = 0
 #CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC = 1
 
+[tasks.setup]
+description = "Set up the repository"
+run = "mix setup"
+
+[tasks.deps]
+description = "Fetch CLI dependencies"
+run = "cd app && mix deps.get"
+
 [hooks]
 # Keep a freshly cloned checkout protected without rerunning setup after it is installed.
 enter = '''
diff --git a/test/mix/tasks/appdeps.update_test.exs b/test/mix/tasks/appdeps.update_test.exs
index 217f29b..bccf008 100644
--- a/test/mix/tasks/appdeps.update_test.exs
+++ b/test/mix/tasks/appdeps.update_test.exs
@@ -3,7 +3,7 @@ defmodule Mix.Tasks.Appdeps.UpdateTest do
 
   alias Mix.Tasks.Appdeps.Update
 
-  test "updates the named dependencies from app" do
+  test "updates the named dependencies from app, then runs the CI gate" do
     caller = self()
 
     shell = fn cmd, args, opts ->
@@ -13,6 +13,7 @@ defmodule Mix.Tasks.Appdeps.UpdateTest do
 
     assert :ok = Update.run(["ash", "oban"], shell)
     assert_received {:run, "mix", ["deps.update", "ash", "oban"], [cd: "app"]}
+    assert_received {:run, "mix", ["deps.audit"], [cd: "app"]}
   end
 
   test "requires at least one dependency" do
diff --git a/test/mix/tasks/toolchain.check_test.exs b/test/mix/tasks/toolchain.check_test.exs
new file mode 100644
index 0000000..02e7c94
--- /dev/null
+++ b/test/mix/tasks/toolchain.check_test.exs
@@ -0,0 +1,45 @@
+defmodule Mix.Tasks.Toolchain.CheckTest do
+  use ExUnit.Case, async: true
+
+  alias Mix.Tasks.Toolchain.Check
+
+  @mise """
+  [tools]
+  erlang = "29.1"
+  elixir = "1.20.4"
+  """
+
+  test "accepts matching workflow pins" do
+    assert :ok =
+             Check.validate(@mise, [
+               {".github/workflows/ci.yaml", workflow("29.1", "1.20.4")}
+             ])
+  end
+
+  test "reports every workflow pin that differs from mise" do
+    assert {:error, message} =
+             Check.validate(@mise, [
+               {".github/workflows/ci.yaml", workflow("29.0.3", "1.20.3")}
+             ])
+
+    assert message =~ "ci.yaml: otp 29.0.3 (expected 29.1)"
+    assert message =~ "ci.yaml: elixir 1.20.3 (expected 1.20.4)"
+  end
+
+  test "rejects a setup-beam step without both pins" do
+    assert {:error, message} =
+             Check.validate(@mise, [
+               {".github/workflows/ci.yaml", "uses: erlef/setup-beam@v1\notp-version: \"29.1\""}
+             ])
+
+    assert message =~ "ci.yaml: elixir missing (expected 1.20.4)"
+  end
+
+  defp workflow(otp, elixir) do
+    """
+    uses: erlef/setup-beam@v1
+    otp-version: "#{otp}"
+    elixir-version: "#{elixir}"
+    """
+  end
+end
diff --git a/vendor/stokowski b/vendor/stokowski
index 2a43887..79fa1bb 160000
--- a/vendor/stokowski
+++ b/vendor/stokowski
@@ -1 +1 @@
-Subproject commit 2a43887511e8b3d16559e84c6e8626cef43646de
+Subproject commit 79fa1bb032fdb4517a28a2f6dcf074ff4571829e
diff --git a/workflow.opus.yaml b/workflow.opus.yaml
index dcefed7..1139ddf 100644
--- a/workflow.opus.yaml
+++ b/workflow.opus.yaml
@@ -116,6 +116,7 @@ hooks:
   after_create: |
     git clone --depth 1 --recursive git@github.com:rubyists/linear-cli .
     mix setup
+    cd app && mix deps.get
   before_run: |
     set -eu
     git fetch origin main