diff --git a/.forgejo/workflows/ci.yml b/.forgejo/workflows/ci.yml
index 9bf7ac0..4f2108d 100644
--- a/.forgejo/workflows/ci.yml
+++ b/.forgejo/workflows/ci.yml
@@ -126,20 +126,25 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ~/.cache/uv
-          key: uv-${{ hashFiles('pyproject.toml') }}
+          # Keyed on the LOCK, not pyproject: the lock is what determines the
+          # installed set now, and a pyproject edit that doesn't change
+          # resolution shouldn't throw the cache away.
+          key: uv-${{ hashFiles('uv.lock') }}
           restore-keys: uv-
 
-      - name: Create virtual environment
-        run: uv venv /opt/venv
-
-      - name: Install package with dev deps
-        run: |
-          # http-ece doesn't declare setuptools as a build dep, and uv
-          # creates bare venvs without it. Install setuptools first so
-          # --no-build-isolation can find it.
-          uv pip install --python /opt/venv/bin/python setuptools wheel
-          uv pip install --python /opt/venv/bin/python --no-build-isolation http-ece
-          uv pip install --python /opt/venv/bin/python -e ".[dev]"
+      # Installs exactly what uv.lock pins. `--locked` additionally FAILS if the
+      # lock is stale against pyproject, so a dependency change has to go through
+      # a deliberate `uv lock` — it can't drift in silently.
+      #
+      # This replaced `uv pip install -e ".[dev]"`, which resolved from the
+      # pyproject constraints and ignored the lock entirely. Every dependency
+      # floated: on 2026-07-28 mcp 2.0.0 shipped mid-session and turned `main`
+      # red with no repo change (issue #2194). Green CI has to mean "these exact
+      # versions passed", or it isn't evidence of anything.
+      - name: Install locked dependencies
+        env:
+          UV_PROJECT_ENVIRONMENT: /opt/venv
+        run: uv sync --locked --extra dev
 
       - name: Run tests
         # Integration tests (real Postgres) run in the `integration` job below.
@@ -179,13 +184,12 @@ jobs:
           --health-retries 10
     steps:
       - uses: actions/checkout@v6
-      - name: Create virtual environment
-        run: uv venv /opt/venv
-      - name: Install package with dev deps
-        run: |
-          uv pip install --python /opt/venv/bin/python setuptools wheel
-          uv pip install --python /opt/venv/bin/python --no-build-isolation http-ece
-          uv pip install --python /opt/venv/bin/python -e ".[dev]"
+      # Same locked install as the unit lane — the two must agree on versions,
+      # or "unit green, integration red" stops being a signal about the code.
+      - name: Install locked dependencies
+        env:
+          UV_PROJECT_ENVIRONMENT: /opt/venv
+        run: uv sync --locked --extra dev
       - name: Integration suite (resolve service IP, migrate, test)
         run: |
           set -eux
diff --git a/uv.lock b/uv.lock
index 8cd7f5c..fdcb59c 100644
--- a/uv.lock
+++ b/uv.lock
@@ -393,7 +393,7 @@ requires-dist = [
     { name = "httpx", specifier = ">=0.27" },
     { name = "hypercorn", specifier = ">=0.17" },
     { name = "icalendar", specifier = ">=5.0" },
-    { name = "mcp", extras = ["cli"], specifier = ">=1.0" },
+    { name = "mcp", extras = ["cli"], specifier = ">=1.0,<2" },
     { name = "pytest", marker = "extra == 'dev'", specifier = ">=8.0" },
     { name = "pytest-asyncio", marker = "extra == 'dev'", specifier = ">=0.23" },
     { name = "quart", specifier = ">=0.19" },