Adding a devcontainer for local testing

.devcontainer/Dockerfile

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+# Linux dev environment matching the CI runner (ubuntu, bash 5, Node 22, Go 1.26).
+# Keep the versions in step with .github/workflows/deploy.yml (node-version, GO_VERSION).
+FROM mcr.microsoft.com/devcontainers/base:ubuntu-24.04
+
+# sqlite3 CLI + fuser (psmisc): used when seeding the E2E fixture DB and freeing the test port.
+RUN apt-get update && apt-get install -y --no-install-recommends sqlite3 psmisc \
+    && rm -rf /var/lib/apt/lists/*
+
+ARG NODE_MAJOR=22
+ARG GO_VERSION=1.26.0
+
+RUN curl -fsSL https://deb.nodesource.com/setup_${NODE_MAJOR}.x | bash - \
+    && apt-get install -y --no-install-recommends nodejs \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN ARCH="$(dpkg --print-architecture)" \
+    && curl -fsSL "https://go.dev/dl/go${GO_VERSION}.linux-${ARCH}.tar.gz" | tar -C /usr/local -xz
+ENV PATH="/usr/local/go/bin:${PATH}"

.devcontainer/devcontainer.json

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+{
+  "name": "CoreScope (CI parity)",
+  "build": {
+    "dockerfile": "Dockerfile"
+  },
+  "postCreateCommand": "npm ci --production=false && npx playwright install --with-deps chromium",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "dbaeumer.vscode-eslint",
+        "golang.go"
+      ]
+    }
+  },
+  "remoteEnv": {
+    "CI": "true"
+  }
+}

scripts/e2e-local.sh

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+#!/usr/bin/env bash
+# usage: bash scripts/e2e-local.sh tests/e2e/<test>.js [more tests...]
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+PORT="${E2E_PORT:-13581}"
+WORK="$(mktemp -d)"
+DB="$WORK/e2e-fixture.db"
+SERVER_PID=""
+cleanup() { [ -n "$SERVER_PID" ] && kill "$SERVER_PID" 2>/dev/null || true; rm -rf "$WORK"; }
+trap cleanup EXIT
+
+[ "$#" -ge 1 ] || { echo "usage: $0 tests/e2e/<test>.js [more tests...]" >&2; exit 2; }
+for t in "$@"; do [ -f "$t" ] || { echo "no such test: $t" >&2; exit 2; }; done
+command -v sqlite3 >/dev/null || { echo "sqlite3 CLI is required" >&2; exit 2; }
+
+go build -o "$WORK/corescope-server" ./cmd/server
+go build -o "$WORK/corescope-migrate" ./cmd/migrate
+
+cp test-fixtures/e2e-fixture.db "$DB"
+bash tools/freshen-fixture.sh "$DB"
+"$WORK/corescope-migrate" -db "$DB" -baseline-stamp-migrate
+
+WF=.github/workflows/deploy.yml
+grep -E "sqlite3 test-fixtures/e2e-fixture.db \"UPDATE observers" "$WF" \
+  | sed -E 's/^ *run: *//; s#test-fixtures/e2e-fixture.db#'"$DB"'#' | bash
+awk '/sqlite3 test-fixtures\/e2e-fixture.db <<.SQL.$/{f=1;next} /^ *SQL$/{f=0} f' "$WF" | sqlite3 "$DB"
+
+fuser -k "$PORT"/tcp 2>/dev/null || true
+"$WORK/corescope-server" -port "$PORT" -db "$DB" -public public >"$WORK/server.log" 2>&1 &
+SERVER_PID=$!
+for i in $(seq 1 120); do
+  if curl -sf "http://localhost:$PORT/api/healthz" 2>/dev/null | grep -q '"ready":true'; then echo "server ready after ${i}s"; break; fi
+  kill -0 "$SERVER_PID" 2>/dev/null || { echo "server exited:"; tail -50 "$WORK/server.log"; exit 1; }
+  [ "$i" -eq 120 ] && { echo "server not ready after 120s:"; tail -50 "$WORK/server.log"; exit 1; }
+  sleep 1
+done
+
+rc=0
+for t in "$@"; do
+  echo "== $t"
+  CHROMIUM_REQUIRE=1 BASE_URL="http://localhost:$PORT" node "$t" || rc=1
+done
+[ "$rc" -eq 0 ] || { echo "== server log tail"; tail -30 "$WORK/server.log"; }
+exit "$rc"