diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2d55356..5f8c97b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,6 +46,31 @@ jobs:
           uv run ruff check src/ tests/ scripts/
           uv run ruff format --check src/ tests/ scripts/
 
+  coverage:
+    name: Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Install Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@1c37ad07a6a961277cf70c0d37d6f313000f5884 # v10.3.0
+        with:
+          version: ${{ env.UV_VERSION }}
+          enable-cache: true
+
+      - name: Install the complete locked test environment
+        run: uv sync --locked --all-extras --all-groups
+
+      - name: Enforce package coverage
+        run: uv run pytest tests/ -q -ra --cov=ml4t.data --cov-report=term-missing
+
   dependency-audit:
     name: Dependency Audit
     runs-on: ubuntu-latest
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index d8a03b8..a9fca8c 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -102,7 +102,7 @@ jobs:
           uv run ruff check src/ tests/ scripts/
           uv run ruff format --check src/ tests/ scripts/
           uv run ty check
-          uv run pytest tests/ -q -ra
+          uv run pytest tests/ -q -ra --cov=ml4t.data --cov-report=term-missing
           uv run pytest tests/ -q -ra -W error::ResourceWarning
       - name: Audit locked dependencies
         run: |
diff --git a/AGENTS.md b/AGENTS.md
index 74644a7..0a07fcf 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -60,7 +60,7 @@ Run focused tests while editing, then run the repository gates:
 uv run ruff check src tests scripts
 uv run ruff format --check src tests scripts
 uv run ty check
-uv run pytest tests -q -ra
+uv run pytest tests -q -ra --cov=ml4t.data --cov-report=term-missing
 uv run pytest tests -q -ra -W error::ResourceWarning
 uv run mkdocs build --strict
 uv build
diff --git a/README.md b/README.md
index 78fbe5d..8055c60 100644
--- a/README.md
+++ b/README.md
@@ -70,7 +70,7 @@ uv run pre-commit install
 uv run ruff check src/ tests/
 uv run ruff format --check src/ tests/
 uv run ty check
-uv run pytest tests/ -q
+uv run pytest tests/ -q -ra --cov=ml4t.data --cov-report=term-missing
 uv run mkdocs build --strict
 uv build
 ```
diff --git a/docs/contributing/testing.md b/docs/contributing/testing.md
index a56bad7..f8b7446 100644
--- a/docs/contributing/testing.md
+++ b/docs/contributing/testing.md
@@ -14,11 +14,11 @@ uv sync --locked --all-extras --all-groups
 ## Run the default lane
 
 ```bash
-uv run pytest tests -q -ra
+uv run pytest tests -q -ra --cov=ml4t.data --cov-report=term-missing
 ```
 
 `pyproject.toml` excludes `slow`, `paid_tier`, `integration`, and `requires_api_key` tests from this
-command. It also enables strict marker validation, so an undeclared marker fails collection.
+command. It also enables strict marker validation and fails if package coverage falls below 85%.
 
 Run the separate resource-leak lane before submitting a change that opens files, HTTP clients, or
 other managed resources:
@@ -82,11 +82,8 @@ Import-time behavior must not require unrelated extras or credentials.
 
 ## Coverage and failure diagnosis
 
-Generate a local report with the package import path:
-
-```bash
-uv run pytest tests -q --cov=ml4t.data --cov-report=term-missing
-```
+The default lane reports missing lines for the `ml4t.data` package and enforces the same 85%
+threshold as CI and the release workflow.
 
 When a test fails only in the full suite, rerun it sequentially and preserve the order-dependent
 reproduction. Do not remove the resource-warning lane, weaken markers, or replace a live contract
diff --git a/pyproject.toml b/pyproject.toml
index 004cb6e..687b8c5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -301,6 +301,8 @@ omit = [
 ]
 
 [tool.coverage.report]
+fail_under = 85
+show_missing = true
 exclude_lines = [
     "pragma: no cover",
     "def __repr__",