diff --git a/.claude/hooks/session-start.sh b/.claude/hooks/session-start.sh
new file mode 100755
index 0000000..f06736f
--- /dev/null
+++ b/.claude/hooks/session-start.sh
@@ -0,0 +1,36 @@
+#!/bin/bash
+# Install the pinned dev tools so tests and lint run in Claude Code on the web.
+set -euo pipefail
+
+if [ "${CLAUDE_CODE_REMOTE:-}" != "true" ]; then
+  exit 0
+fi
+
+cd "$CLAUDE_PROJECT_DIR"
+
+# The pins live in pyproject.toml's `dev` dependency group; read them from there
+# rather than repeating them, so this hook cannot drift from the gate.
+mapfile -t dev_pins < <(python3 -c '
+import tomllib
+with open("pyproject.toml", "rb") as f:
+    print("\n".join(tomllib.load(f)["dependency-groups"]["dev"]))
+')
+
+# Direct use: `python3 -m pytest`, `ruff check .`.
+python3 -m pip install --quiet --disable-pip-version-check --root-user-action=ignore "${dev_pins[@]}"
+
+# The gate commands in verification.toml run through uv, pinned as in CI.
+python3 -m pip install --quiet --disable-pip-version-check --root-user-action=ignore uv==0.11.29
+
+# The image preinstalls other uv and ruff versions earlier on PATH; put pip's
+# scripts directory first so the pinned ones win for the session.
+scripts_dir=$(python3 -c 'import sysconfig; print(sysconfig.get_path("scripts"))')
+export PATH="$scripts_dir:$PATH"
+if [ -n "${CLAUDE_ENV_FILE:-}" ]; then
+  echo "export PATH=\"$scripts_dir:\$PATH\"" >> "$CLAUDE_ENV_FILE"
+fi
+
+# Warm uv's cache so `uv run --with <pin>` needs no download mid-session.
+with_args=()
+for pin in "${dev_pins[@]}"; do with_args+=(--with "$pin"); done
+uv run --quiet "${with_args[@]}" python -c pass
diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..e06b033
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,14 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/session-start.sh"
+          }
+        ]
+      }
+    ]
+  }
+}