diff --git a/.github/workflows/code-quality.yml b/.github/workflows/code-quality.yml
index 6079a4a..69c52ee 100644
--- a/.github/workflows/code-quality.yml
+++ b/.github/workflows/code-quality.yml
@@ -59,3 +59,49 @@ jobs:
 
       - name: Validate docs (AGENTS.md/README commands + links)
         run: pnpm validate-docs
+
+  build:
+    runs-on: ubuntu-latest
+    env:
+      # Public, non-secret placeholders so the production build is deterministic
+      # and does not depend on repository secrets (the app reads Supabase at runtime).
+      NEXT_PUBLIC_SUPABASE_URL: http://127.0.0.1:54321
+      NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY: build-placeholder-key
+      NEXT_PUBLIC_SITE_URL: http://localhost:3000
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 11.5.0
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Restore Next.js build cache
+        id: next-cache
+        uses: actions/cache@v4
+        with:
+          path: .next/cache
+          # Cache the Next.js compiler/incremental cache so rebuilds reuse work.
+          key: ${{ runner.os }}-nextjs-${{ hashFiles('pnpm-lock.yaml') }}-${{ hashFiles('src/**/*.[jt]s', 'src/**/*.[jt]sx', '*.ts', '*.mjs') }}
+          restore-keys: |
+            ${{ runner.os }}-nextjs-${{ hashFiles('pnpm-lock.yaml') }}-
+
+      - name: Build with metrics (incremental via restored .next/cache)
+        env:
+          NEXT_BUILD_CACHE_HIT: ${{ steps.next-cache.outputs.cache-hit }}
+        run: pnpm build:metrics
+
+      - name: Upload build metrics (duration + cache hit)
+        if: ${{ !cancelled() }}
+        uses: actions/upload-artifact@v4
+        with:
+          name: build-metrics
+          path: reports/build-metrics.json
+          if-no-files-found: warn
diff --git a/AGENTS.md b/AGENTS.md
index 6fa6630..a2acf7b 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -19,6 +19,7 @@ Requires Node 22+, pnpm 11.5.0, the Supabase CLI, and Docker.
 | --------------- | ---------------------------------------------------- |
 | Dev server      | `pnpm dev`                                           |
 | Build           | `pnpm build`                                         |
+| Build + metrics | `pnpm build:metrics`                                 |
 | Lint            | `pnpm lint`                                          |
 | Type-check      | `pnpm typecheck`                                     |
 | Format          | `pnpm format` (write) / `pnpm format:check` (verify) |
@@ -33,6 +34,8 @@ Requires Node 22+, pnpm 11.5.0, the Supabase CLI, and Docker.
 
 **Before committing or finishing a task, run:** `pnpm lint && pnpm typecheck && pnpm test`. The Husky `pre-commit` hook enforces `lint-staged` (Prettier check + ESLint with `--max-warnings=0`), `pnpm typecheck`, and `pnpm tech-debt`, so commits fail on any lint warning, format drift, type error, or untracked TODO marker. The `Code Quality` GitHub Actions workflow (`.github/workflows/code-quality.yml`) additionally runs `knip`, `jscpd`, and the tech-debt scan on every push and PR.
 
+**Build performance:** the same workflow has a separate `build` job that restores the Next.js incremental cache (`.next/cache`, keyed on the lockfile and source hash via `actions/cache`) so rebuilds reuse compiler work, then runs `pnpm build:metrics`. `scripts/build-metrics.mjs` times the production build, writes `reports/build-metrics.json` (duration, `cacheRestored` flag, Next/Node versions, commit), appends a summary to the GitHub job page, and uploads the JSON as a `build-metrics` artifact so build-duration regressions are visible across runs.
+
 ## Conventions
 
 - **Language:** TypeScript in strict mode. Do not introduce `any`; prefer precise types. JS files are not allowed (`allowJs: false`).
diff --git a/package.json b/package.json
index 29c191d..a143287 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
   "scripts": {
     "dev": "next dev",
     "build": "next build",
+    "build:metrics": "node scripts/build-metrics.mjs",
     "start": "next start",
     "lint": "eslint .",
     "format": "prettier . --write",
diff --git a/scripts/build-metrics.mjs b/scripts/build-metrics.mjs
new file mode 100644
index 0000000..e2340fa
--- /dev/null
+++ b/scripts/build-metrics.mjs
@@ -0,0 +1,79 @@
+#!/usr/bin/env node
+// Runs the production build, measures wall-clock duration, and exports a
+// machine-readable build-metrics report. Used in CI to track build performance
+// over time and surface regressions; appends a summary to the GitHub job page
+// when GITHUB_STEP_SUMMARY is available. Forwards the build's exit code.
+import { spawn } from "node:child_process";
+import { mkdirSync, readFileSync, appendFileSync, writeFileSync } from "node:fs";
+import { resolve, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const reportPath = resolve(repoRoot, "reports", "build-metrics.json");
+
+function readNextVersion() {
+  try {
+    const pkg = JSON.parse(readFileSync(resolve(repoRoot, "package.json"), "utf8"));
+    return pkg.dependencies?.next ?? pkg.devDependencies?.next ?? "unknown";
+  } catch {
+    return "unknown";
+  }
+}
+
+function runBuild() {
+  return new Promise((resolveRun) => {
+    const start = process.hrtime.bigint();
+    const child = spawn("pnpm", ["build"], { stdio: "inherit", cwd: repoRoot, env: process.env });
+
+    let settled = false;
+    const settle = (code) => {
+      if (settled) return;
+      settled = true;
+      const durationMs = Number((process.hrtime.bigint() - start) / 1_000_000n);
+      resolveRun({ code: code ?? 1, durationMs });
+    };
+
+    child.on("error", (err) => {
+      console.error("Failed to run pnpm build", err);
+      settle(1);
+    });
+    child.on("close", (code) => settle(code));
+  });
+}
+
+const { code, durationMs } = await runBuild();
+const durationSec = Math.round(durationMs / 100) / 10;
+
+const metrics = {
+  status: code === 0 ? "success" : "failure",
+  durationMs,
+  durationSec,
+  timestamp: new Date().toISOString(),
+  nodeVersion: process.version,
+  nextVersion: readNextVersion(),
+  cacheRestored: process.env.NEXT_BUILD_CACHE_HIT === "true",
+  commit: process.env.GITHUB_SHA ?? null
+};
+
+mkdirSync(dirname(reportPath), { recursive: true });
+writeFileSync(reportPath, `${JSON.stringify(metrics, null, 2)}\n`);
+
+const summary =
+  `### Build metrics\n\n` +
+  `- Status: ${metrics.status}\n` +
+  `- Duration: ${durationSec}s\n` +
+  `- Cache restored: ${metrics.cacheRestored}\n` +
+  `- Next.js: ${metrics.nextVersion}\n` +
+  `- Node: ${metrics.nodeVersion}\n`;
+
+console.log(`\nBuild ${metrics.status} in ${durationSec}s (metrics -> ${resolve("reports/build-metrics.json")})`);
+
+if (process.env.GITHUB_STEP_SUMMARY) {
+  try {
+    appendFileSync(process.env.GITHUB_STEP_SUMMARY, `${summary}\n`);
+  } catch {
+    // Non-fatal: summary is best-effort.
+  }
+}
+
+process.exit(code);