test: lock in the field-specific startup error with static, mutation and deterministic probes (E00-S04-T02)

- tests/config-startup-error.test.mjs: static assertions on the committed
  startup-error module, the package boundary, the server wiring (validation
  before bind), the compose secret and the Dockerfile shipping, each backed
  by mutation probes; the deterministic probes execute the issue's test plan
  ("start with a missing required field and confirm the error names it") —
  the compiled boundary throws MissingRequiredSettingError naming
  sessionSecret, and booting the committed server without EPPP_SESSION_SECRET
  exits non-zero naming the field while a valid secret boots to /health 200
- health-endpoint/app-readiness boot probes: provide a valid
  EPPP_SESSION_SECRET (the required setting is validated at startup)
- ci.yml: new config-startup-error job (builds config + database-postgres,
  runs the suite); app-readiness job now builds the config package too
- .gitignore: transient .config-startup-probe-*.mjs files

.gitea/workflows/ci.yml

@@ -145,10 +145,11 @@ jobs:
   # migration run is blocked behind a held ACCESS EXCLUSIVE lock on the
   # migration ledger, /health stays not-ready, then flips ready once the lock
   # releases) runs where a Docker daemon is available and skips cleanly
-  # otherwise. The job installs the frozen workspace and builds the
+  # otherwise. The job installs the frozen workspace and builds the config
-  # database-postgres package because the probes boot the committed server
+  # and database-postgres packages because the probes boot the committed
-  # from the host (it imports @personal-blog/database-postgres through the
+  # server from the host (it imports @personal-blog/config and
-  # package's own links).
+  # @personal-blog/database-postgres through the packages' own links; the
+  # required EPPP_SESSION_SECRET is provided by the probe's boot env).
   app-readiness:
     name: App readiness after migrations (E00-S03-T06)
     runs-on: ubuntu-latest
@@ -162,11 +163,40 @@ jobs:
         run: corepack enable
       - name: Install dependencies (frozen lockfile)
         run: pnpm install --frozen-lockfile
-      - name: Build the database-postgres package (the probes boot the committed server which imports it)
+      - name: Build the config and database-postgres packages (the probes boot the committed server which imports them)
-        run: pnpm --filter @personal-blog/database-postgres build
+        run: pnpm --filter @personal-blog/config build && pnpm --filter @personal-blog/database-postgres build
       - name: Run app readiness test suite
         run: node --test tests/app-readiness.test.mjs
 
+  # E00-S04-T02: the static assertions of tests/config-startup-error.test.mjs
+  # gate every PR — the suite locks in the field-specific startup error (a
+  # missing required setting fails startup with an error naming the missing
+  # field: packages/config's MissingRequiredSettingError/assertValidConfig,
+  # wired into the committed server before it binds) with mutation probes, and
+  # the deterministic probes execute the issue's test plan ("start with a
+  # missing required field and confirm the error names it"): booting the
+  # committed server without EPPP_SESSION_SECRET exits non-zero naming
+  # sessionSecret, while a valid secret boots to GET /health 200. The job
+  # installs the frozen workspace and builds the config and database-postgres
+  # packages because the probes boot the committed server which imports them.
+  config-startup-error:
+    name: Field-specific startup errors (E00-S04-T02)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Node.js 24
+        uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+      - name: Enable pnpm (corepack, pinned to 11.23.0 via packageManager)
+        run: corepack enable
+      - name: Install dependencies (frozen lockfile)
+        run: pnpm install --frozen-lockfile
+      - name: Build the config and database-postgres packages (the probes boot the committed server which imports them)
+        run: pnpm --filter @personal-blog/config build && pnpm --filter @personal-blog/database-postgres build
+      - name: Run config startup error test suite
+        run: node --test tests/config-startup-error.test.mjs
+
   # E00-S04-T01: the static assertions of tests/config-schema.test.mjs gate
   # every PR — the suite locks in the TypeBox/Ajv configuration schema
   # (packages/config, golden-tuple pins @sinclair/typebox@0.34.52 +

.gitignore

@@ -23,5 +23,9 @@ coverage/
 # the package (removed in its finally block)
 .config-schema-probe-*.mjs
 
+# Transient host-side probe file written by the config-startup-error test
+# suite into the package (removed in its finally block)
+.config-startup-probe-*.mjs
+
 # OS / editor
 .DS_Store

tests/app-readiness.test.mjs

@@ -246,7 +246,11 @@ function reservePort() {
 /**
  * Boots the committed server source on `port` with the given env overrides
  * (merged over `process.env`; `DATABASE_URL` is stripped unless explicitly
- * provided). Returns `{ child, stderr, stdout }`; the child writes its
+ * provided, and a valid `EPPP_SESSION_SECRET` is provided unless explicitly
+ * overridden — since E00-S04-T02 the required admin-session secret is
+ * validated at startup, and a missing secret is the field-specific
+ * startup-error path locked in by tests/config-startup-error.test.mjs).
+ * Returns `{ child, stderr, stdout }`; the child writes its
  * stdout/stderr into closures for diagnostics.
  */
 function bootServer(port, envOverrides = {}) {
@@ -254,7 +258,12 @@ function bootServer(port, envOverrides = {}) {
     tsExecMode() === 'strip-types-flag'
       ? ['--experimental-strip-types', SERVER_SRC]
       : [SERVER_SRC];
-  const env = { ...process.env, PORT: String(port), ...envOverrides };
+  // Strip an inherited DATABASE_URL unless the caller explicitly provides one
+  // (the no-database path must be deterministic), and provide the required
+  // admin-session secret (E00-S04-T02) unless the caller overrides it.
+  const env = { ...process.env, PORT: String(port) };
+  delete env.DATABASE_URL;
+  Object.assign(env, { EPPP_SESSION_SECRET: 's'.repeat(32) }, envOverrides);
   const child = spawn(process.execPath, args, {
     cwd: REPO_ROOT,
     env,

tests/config-startup-error.test.mjs

@@ -0,0 +1,634 @@
+/**
+ * Config startup error test — locks in the [E00-S04-T02] guarantee that a
+ * missing required setting gives a field-specific startup error.
+ *
+ * Acceptance criteria covered (each test fails without the committed state):
+ *   - "missing required setting gives a field-specific startup error" → the
+ *     `packages/config` package exposes the startup validation entry point
+ *     (`assertValidConfig`, building on the E00-S04-T01 TypeBox/Ajv schema)
+ *     and the committed `apps/server/src/index.ts` calls it before the server
+ *     binds, so a deployment missing a required setting (the admin-session
+ *     secret `EPPP_SESSION_SECRET` — the schema's required field,
+ *     Security-and-Operations §32/§26) fails fast at startup instead of
+ *     booting with an invalid configuration. Locked in statically (mutation
+ *     probes prove non-vacuity: dropping the startup validation call,
+ *     moving it after the bind, or dropping the compose/Dockerfile support
+ *     all fail) and behaviorally by the deterministic probes (the issue's
+ *     test plan: "start with a missing required field and confirm the error
+ *     names it" — booting the committed server without `EPPP_SESSION_SECRET`
+ *     exits non-zero with the error naming the missing field).
+ *   - "the error names the missing field" → a missing required setting throws
+ *     `MissingRequiredSettingError` whose message and `missingField` name the
+ *     missing field (e.g. `"missing required setting: sessionSecret"`); other
+ *     schema violations throw `ConfigStartupError` whose message names the
+ *     violating field too. Locked in statically and by the deterministic
+ *     probes (boundary + booted server).
+ *   - the compose stack and the server image stay runnable with the required
+ *     secret: `compose.yaml` provides `EPPP_SESSION_SECRET` for the `app`
+ *     service (dev-only default, ≥ 32 chars — override via .env / shell) and
+ *     the `apps/server/Dockerfile` ships the compiled `packages/config` next
+ *     to the other workspace deps, so the app container boots (the
+ *     deterministic probe boots with a valid secret and `GET /health` answers
+ *     200 — a valid startup still works).
+ *
+ * Run: `node --test tests/config-startup-error.test.mjs`
+ * (node:test — built into Node >= 18; no dependencies, lockfile untouched.
+ * The deterministic probes boot the committed server, which imports
+ * `@personal-blog/config` and `@personal-blog/database-postgres` — build those
+ * packages first, exactly as the CI job does.)
+ */
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync, existsSync, writeFileSync, rmSync } from 'node:fs';
+import { spawn, spawnSync } from 'node:child_process';
+import { once } from 'node:events';
+import { createServer as createNetServer } from 'node:net';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const REPO_ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+
+const read = (relPath) => readFileSync(path.join(REPO_ROOT, relPath), 'utf8');
+
+/** The committed config package and server entrypoint under test. */
+const CONFIG_DIR = 'packages/config';
+const STARTUP_SRC = `${CONFIG_DIR}/src/startup.ts`;
+const INDEX_SRC = `${CONFIG_DIR}/src/index.ts`;
+const SERVER_SRC = 'apps/server/src/index.ts';
+const COMPOSE_PATH = 'compose.yaml';
+const DOCKERFILE_PATH = 'apps/server/Dockerfile';
+
+/** The root test glob (root `scripts.test`, E00-S01-T12) that runs every suite. */
+const ROOT_TEST_GLOB = 'tests/**/*.test.mjs';
+
+/** The CI job that gates the startup-error criterion on every PR. */
+const CI_JOB = 'config-startup-error';
+
+const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
+
+// ---------------------------------------------------------------------------
+// Static assertions on the committed sources
+// ---------------------------------------------------------------------------
+
+/**
+ * Asserts the config package exposes the field-specific startup error: the
+ * startup module compiles the TypeBox `configSchema` with Ajv and exports
+ * `assertValidConfig` plus the field-specific errors — `ConfigStartupError`
+ * for any schema violation, and `MissingRequiredSettingError` (whose message
+ * and `missingField` name the missing field, e.g.
+ * `"missing required setting: sessionSecret"`) for a missing required
+ * setting. Fails fast on a deviation; the mutation probes below prove the
+ * assertions are non-vacuous.
+ */
+function assertStartupErrorSource(src) {
+  // Built on the E00-S04-T01 schema boundary: the module compiles the
+  // TypeBox configSchema with Ajv (same golden-tuple validator as
+  // validate.ts) and derives the missing-field names from the Ajv `required`
+  // keyword errors.
+  assert.match(
+    src,
+    /import \{ Ajv, type ErrorObject \} from 'ajv'/,
+    'the startup module must import Ajv (the golden-tuple validator) and the ErrorObject type',
+  );
+  assert.match(
+    src,
+    /import \{ configSchema, type Config \} from '\.\/schema\.js'/,
+    'the startup module must build on the committed configSchema (import from ./schema.js)',
+  );
+  assert.match(
+    src,
+    /new Ajv\(\{ allErrors: true \}\)/,
+    'the startup module must create the Ajv instance with allErrors (report every violation)',
+  );
+  assert.match(
+    src,
+    /\.compile\(configSchema\)/,
+    'the startup module must compile the TypeBox configSchema with Ajv',
+  );
+
+  // The field-specific errors.
+  assert.match(
+    src,
+    /export class ConfigStartupError extends Error/,
+    'the startup module must export ConfigStartupError (any invalid configuration is a field-specific startup error)',
+  );
+  assert.match(
+    src,
+    /export class MissingRequiredSettingError extends ConfigStartupError/,
+    'the startup module must export MissingRequiredSettingError (a missing required setting is the field-specific startup error)',
+  );
+  assert.match(
+    src,
+    /missing required setting: \$\{missingField\}/,
+    'the MissingRequiredSettingError message must name the missing field ("missing required setting: <field>")',
+  );
+  assert.match(
+    src,
+    /readonly missingField: string/,
+    'MissingRequiredSettingError must carry the missing field name (missingField)',
+  );
+
+  // The startup entry point: validates and throws the field-specific error
+  // for a missing required setting (Ajv `required` keyword -> missingProperty).
+  assert.match(
+    src,
+    /export function assertValidConfig\(value: unknown\): Config/,
+    'the startup module must export assertValidConfig (the startup validation entry point)',
+  );
+  assert.match(
+    src,
+    /error\.keyword === 'required'/,
+    'assertValidConfig must detect missing required settings from the Ajv "required" keyword errors',
+  );
+  assert.match(
+    src,
+    /throw new MissingRequiredSettingError\(missingFields\.join\(', '\)\)/,
+    'assertValidConfig must throw MissingRequiredSettingError naming the missing field(s)',
+  );
+}
+
+/**
+ * Asserts the committed server validates the required settings at startup:
+ * it imports `assertValidConfig` from `@personal-blog/config` and calls it
+ * with the parsed startup configuration (including the required
+ * `EPPP_SESSION_SECRET`) BEFORE the server binds — so a missing required
+ * setting is a startup error, never a silently-booted invalid configuration.
+ */
+function assertServerStartupValidation(src) {
+  assert.match(
+    src,
+    /import \{ assertValidConfig \} from '@personal-blog\/config'/,
+    'the server must import the startup validation entry point from the config package',
+  );
+  assert.match(
+    src,
+    /assertValidConfig\(\{/,
+    'the server must call assertValidConfig with its startup configuration',
+  );
+  assert.match(
+    src,
+    /sessionSecret: process\.env\.EPPP_SESSION_SECRET/,
+    'the server must feed the required admin-session secret (EPPP_SESSION_SECRET) into the startup validation',
+  );
+  const callIndex = src.indexOf('assertValidConfig({');
+  const listenIndex = src.indexOf('server.listen(');
+  assert.ok(
+    callIndex !== -1 && listenIndex !== -1 && callIndex < listenIndex,
+    'the startup validation must run before the server binds (server.listen) so a missing required setting is a startup error',
+  );
+}
+
+/**
+ * Asserts the compose app service provides the required admin-session secret
+ * (`EPPP_SESSION_SECRET`) with a dev-only default of at least 32 characters
+ * (the schema's required field, Security-and-Operations §32/§26), so
+ * `docker compose up -d` keeps working from a clean clone while the app's
+ * startup validation has the secret it requires.
+ */
+function assertComposeSecret(composeText) {
+  // The app service block runs from the top-level "  app:" key to the
+  // top-level "volumes:" map (the db service has its own nested "volumes:"
+  // key earlier, so slice to the root-level one).
+  const appBlock = composeText.slice(composeText.indexOf('  app:'), composeText.indexOf('\nvolumes:'));
+  assert.match(
+    appBlock,
+    /EPPP_SESSION_SECRET: \$\{EPPP_SESSION_SECRET:-[^}]{32,}\}/,
+    'the app service must provide EPPP_SESSION_SECRET with a >= 32 char dev-only default (${EPPP_SESSION_SECRET:-...}), so the app boots with the required secret from a clean clone',
+  );
+}
+
+/**
+ * Asserts the server image ships the config package: the build stage copies
+ * `packages/config` source (the server's build compiles it) and the runtime
+ * stage copies the compiled `packages/config/dist` + manifest next to the
+ * other workspace deps the server imports.
+ */
+function assertDockerfileConfig(dockerfile) {
+  assert.match(
+    dockerfile,
+    /COPY packages\/config packages\/config/,
+    'the build stage must copy the config package source (the server build compiles its workspace dependency)',
+  );
+  assert.match(
+    dockerfile,
+    /COPY --from=build \/app\/packages\/config\/dist \.\/packages\/config\/dist/,
+    'the runtime stage must ship the compiled config package (packages/config/dist) so the server import resolves in the image',
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Criterion tests
+// ---------------------------------------------------------------------------
+
+test('the config package exposes the field-specific startup error (MissingRequiredSettingError + assertValidConfig)', () => {
+  assert.ok(existsSync(path.join(REPO_ROOT, STARTUP_SRC)), `committed ${STARTUP_SRC} must exist`);
+  assertStartupErrorSource(read(STARTUP_SRC));
+});
+
+test('the package boundary re-exports the startup validation entry point and its errors', () => {
+  const src = read(INDEX_SRC);
+  assert.match(
+    src,
+    /export \{ assertValidConfig, ConfigStartupError, MissingRequiredSettingError \} from '\.\/startup\.js'/,
+    'the boundary must re-export assertValidConfig and the field-specific startup errors',
+  );
+});
+
+test('the server validates the required settings at startup, before it binds', () => {
+  assert.ok(existsSync(path.join(REPO_ROOT, SERVER_SRC)), `committed ${SERVER_SRC} must exist`);
+  assertServerStartupValidation(read(SERVER_SRC));
+});
+
+test('the compose app service provides the required admin-session secret (EPPP_SESSION_SECRET)', () => {
+  assertComposeSecret(read(COMPOSE_PATH));
+});
+
+test('the server image ships the config package (build source + runtime dist)', () => {
+  assertDockerfileConfig(read(DOCKERFILE_PATH));
+});
+
+test('the config-startup-error criterion is enforced in CI', () => {
+  // Picked up by the root test command (root `scripts.test` glob).
+  const scripts = JSON.parse(read('package.json')).scripts ?? {};
+  assert.equal(
+    scripts.test,
+    `node --test "${ROOT_TEST_GLOB}"`,
+    `root scripts.test must run the "${ROOT_TEST_GLOB}" glob so this suite runs with the rest`,
+  );
+  // And a dedicated CI job gates it on every PR.
+  const workflow = read('.gitea/workflows/ci.yml');
+  assert.ok(
+    workflow.includes(`node --test tests/config-startup-error.test.mjs`),
+    `CI must run the config-startup-error suite (job "${CI_JOB}") on every PR`,
+  );
+  assert.ok(
+    workflow.includes(
+      'pnpm --filter @personal-blog/config build && pnpm --filter @personal-blog/database-postgres build',
+    ),
+    'the CI job must build the config and database-postgres packages (the probes boot the committed server which imports them)',
+  );
+});
+
+// ---------------------------------------------------------------------------
+// Mutation probes — the static assertions are non-vacuous
+// ---------------------------------------------------------------------------
+
+test('dropping the startup validation call fails the server wiring assertion (mutation probe)', () => {
+  const src = read(SERVER_SRC);
+  const withoutCall = src.replace('assertValidConfig({\n', 'assertValidConfigx({\n');
+  assert.notEqual(withoutCall, src, 'the mutation must actually replace the assertValidConfig call');
+  assert.throws(() => assertServerStartupValidation(withoutCall), /must call assertValidConfig/);
+});
+
+test('moving the startup validation after the server binds fails the order assertion (mutation probe)', () => {
+  const src = read(SERVER_SRC);
+  const moved = src
+    .replace(/assertValidConfig\(\{\n  host: '0\.0\.0\.0',\n  port: PORT,\n  databaseUrl: process\.env\.DATABASE_URL,\n  sessionSecret: process\.env\.EPPP_SESSION_SECRET,\n\}\);\n/, '')
+    .replace(
+      'server.listen(PORT, () => {',
+      'server.listen(PORT, () => {\n  assertValidConfig({ sessionSecret: process.env.EPPP_SESSION_SECRET });',
+    );
+  assert.notEqual(moved, src, 'the mutation must actually move the validation call after the bind');
+  assert.throws(() => assertServerStartupValidation(moved), /before the server binds/);
+});
+
+test('an error message that does not name the missing field fails the naming assertion (mutation probe)', () => {
+  const src = read(STARTUP_SRC);
+  const noField = src.replace(/missing required setting: \$\{missingField\}/g, 'missing required setting');
+  assert.notEqual(noField, src, 'the mutation must actually drop the field name from the message');
+  assert.throws(() => assertStartupErrorSource(noField), /must name the missing field/);
+});
+
+test('dropping MissingRequiredSettingError fails the field-specific error assertion (mutation probe)', () => {
+  const src = read(STARTUP_SRC);
+  const noError = src.replace('export class MissingRequiredSettingError extends ConfigStartupError', 'export class MissingRequiredSettingErrorX extends ConfigStartupError');
+  assert.notEqual(noError, src, 'the mutation must actually rename the error class');
+  assert.throws(() => assertStartupErrorSource(noError), /must export MissingRequiredSettingError/);
+});
+
+test('dropping the missing-field detection fails the required-setting assertion (mutation probe)', () => {
+  const src = read(STARTUP_SRC);
+  const noDetection = src.replace("error.keyword === 'required'", "error.keyword === 'minLength'");
+  assert.notEqual(noDetection, src, 'the mutation must actually change the missing-field detection');
+  assert.throws(() => assertStartupErrorSource(noDetection), /"required" keyword/);
+});
+
+test('removing EPPP_SESSION_SECRET from the compose app service fails the compose assertion (mutation probe)', () => {
+  const composeText = read(COMPOSE_PATH);
+  const withoutSecret = composeText.replace(
+    /      EPPP_SESSION_SECRET: \$\{EPPP_SESSION_SECRET:-[^}]*\}\n/,
+    '',
+  );
+  assert.notEqual(withoutSecret, composeText, 'the mutation must actually remove the secret env entry');
+  assert.throws(() => assertComposeSecret(withoutSecret), /EPPP_SESSION_SECRET/);
+});
+
+test('dropping the config package from the image fails the Dockerfile assertion (mutation probe)', () => {
+  const dockerfile = read(DOCKERFILE_PATH);
+  const withoutDist = dockerfile.replace(
+    'COPY --from=build /app/packages/config/dist ./packages/config/dist\n',
+    '',
+  );
+  assert.notEqual(withoutDist, dockerfile, 'the mutation must actually drop the runtime dist copy');
+  assert.throws(() => assertDockerfileConfig(withoutDist), /runtime stage must ship the compiled config package/);
+});
+
+// ---------------------------------------------------------------------------
+// Deterministic behavioral probe — the issue's test plan: "start with a
+// missing required field and confirm the error names it"
+// ---------------------------------------------------------------------------
+
+/**
+ * How the current Node executes TypeScript sources: `default` (>= 23.6, type
+ * stripping on by default), `strip-types-flag` (>= 22.6 via
+ * `--experimental-strip-types`) or `null` (cannot run .ts at all). The
+ * workspace pins engines.node to 24.x, where type stripping is stable.
+ */
+function tsExecMode() {
+  const [major, minor] = process.versions.node.split('.').map(Number);
+  if (major > 23 || (major === 23 && minor >= 6)) return 'default';
+  if (major === 22 && minor >= 6) return 'strip-types-flag';
+  return null;
+}
+
+/** True when this Node can execute the committed `.ts` server source (>= 22.6, type stripping). */
+const TS_STRIPPING = tsExecMode() !== null;
+
+/** The compiled config package boundary the probes import (built by the CI job first). */
+const CONFIG_DIST = existsSync(path.join(REPO_ROOT, CONFIG_DIR, 'dist', 'index.js'));
+/** The compiled database-postgres package the booted server also imports. */
+const DATABASE_POSTGRES_DIST = existsSync(
+  path.join(REPO_ROOT, 'packages/database-postgres', 'dist', 'index.js'),
+);
+
+/** Why the boot probes may be skipped on a clean clone without a build step. */
+const BUILD_HINT =
+  'build the config and database-postgres packages first (pnpm --filter @personal-blog/config build && pnpm --filter @personal-blog/database-postgres build)';
+
+/**
+ * The boundary probe source: exercises the compiled `@personal-blog/config`
+ * startup boundary (`assertValidConfig` + the field-specific errors) exactly
+ * as the server consumes it — a valid configuration passes (including the
+ * no-database local path), a missing required setting throws
+ * `MissingRequiredSettingError` naming the field, and other violations throw
+ * `ConfigStartupError` naming the violating field. Written to a temp file
+ * inside `packages/config/` so `ajv`/`@sinclair/typebox` resolve through the
+ * package's own dependency links, then removed.
+ */
+const PROBE_SOURCE = `
+import { assertValidConfig, ConfigStartupError, MissingRequiredSettingError } from './dist/index.js';
+
+const capture = (fn) => {
+  try {
+    return { threw: false, value: fn() };
+  } catch (error) {
+    return {
+      threw: true,
+      name: error && typeof error === 'object' ? error.name : String(error),
+      message: error instanceof Error ? error.message : String(error),
+      missingField: error && typeof error === 'object' ? error.missingField : undefined,
+      isMissingRequired: error instanceof MissingRequiredSettingError,
+      isConfigStartup: error instanceof ConfigStartupError,
+    };
+  }
+};
+
+const result = {
+  // A valid configuration passes and is returned — including the local
+  // non-container path with no databaseUrl (host/port/databaseUrl optional).
+  validReturnsConfig: capture(() => assertValidConfig({ sessionSecret: 's'.repeat(32) })).threw === false,
+  fullValid: capture(() => assertValidConfig({ host: '0.0.0.0', port: 3000, databaseUrl: 'postgres://eppp:eppp@db:5432/eppp', sessionSecret: 's'.repeat(32) })).threw === false,
+  // The issue's test plan: start with a missing required field — the error
+  // must be MissingRequiredSettingError and name the missing field.
+  missingSecret: capture(() => assertValidConfig({ host: '0.0.0.0', port: 3000 })),
+  // Other violations are field-specific too (the message names the field).
+  shortSecret: capture(() => assertValidConfig({ sessionSecret: 'short' })),
+  unknownProperty: capture(() => assertValidConfig({ sessionSecret: 's'.repeat(32), extra: true })),
+};
+
+console.log('CONFIG_STARTUP_PROBE_RESULT ' + JSON.stringify(result));
+`;
+
+test('the compiled startup boundary throws a field-specific error naming the missing required setting (deterministic probe)', { skip: !CONFIG_DIST ? BUILD_HINT : false }, () => {
+  const probeFile = path.join(REPO_ROOT, CONFIG_DIR, `.config-startup-probe-${process.pid}.mjs`);
+  try {
+    writeFileSync(probeFile, PROBE_SOURCE);
+    const run = spawnSync(process.execPath, [path.basename(probeFile)], {
+      cwd: path.join(REPO_ROOT, CONFIG_DIR),
+      encoding: 'utf8',
+      timeout: 60_000,
+    });
+    assert.equal(
+      run.status,
+      0,
+      `the probe must exit 0 (status ${run.status}):\n${(run.stderr || run.stdout || '').trim()}`,
+    );
+    const match = run.stdout.match(/CONFIG_STARTUP_PROBE_RESULT (\{.*\})/);
+    assert.ok(match, `the probe must print CONFIG_STARTUP_PROBE_RESULT:\n${run.stdout.trim()}`);
+    const result = JSON.parse(match[1]);
+
+    // A valid configuration passes (including the no-database local path).
+    assert.equal(result.validReturnsConfig, true, 'a valid config (only the required secret) must pass assertValidConfig');
+    assert.equal(result.fullValid, true, 'a full valid config must pass assertValidConfig');
+
+    // Missing required setting: field-specific startup error naming the field.
+    assert.equal(result.missingSecret.threw, true, 'a config missing the required secret must throw');
+    assert.equal(result.missingSecret.isMissingRequired, true, 'a missing required setting must throw MissingRequiredSettingError');
+    assert.equal(result.missingSecret.isConfigStartup, true, 'MissingRequiredSettingError must be a ConfigStartupError');
+    assert.equal(
+      result.missingSecret.missingField,
+      'sessionSecret',
+      `MissingRequiredSettingError must carry the missing field name (got: ${JSON.stringify(result.missingSecret)})`,
+    );
+    assert.match(
+      result.missingSecret.message,
+      /missing required setting: sessionSecret/,
+      `the startup error must name the missing field (got: ${JSON.stringify(result.missingSecret)})`,
+    );
+
+    // Other violations are field-specific too.
+    assert.equal(result.shortSecret.threw, true, 'a too-short secret must throw');
+    assert.equal(result.shortSecret.isMissingRequired, false, 'a too-short secret is not a missing required setting');
+    assert.equal(result.shortSecret.isConfigStartup, true, 'a too-short secret must throw ConfigStartupError');
+    assert.match(
+      result.shortSecret.message,
+      /sessionSecret/,
+      `the startup error must name the violating field (got: ${JSON.stringify(result.shortSecret)})`,
+    );
+    assert.equal(result.unknownProperty.threw, true, 'an unknown property must throw');
+    assert.match(
+      result.unknownProperty.message,
+      /extra/,
+      `the startup error must name the unexpected field (got: ${JSON.stringify(result.unknownProperty)})`,
+    );
+  } finally {
+    rmSync(probeFile, { force: true });
+  }
+});
+
+// ---------------------------------------------------------------------------
+// Server-boot probes — the issue's test plan executed against the real
+// committed startup: "start with a missing required field and confirm the
+// error names it"
+// ---------------------------------------------------------------------------
+
+/** Reserves an ephemeral TCP port, then releases it for the child to bind. */
+function reservePort() {
+  return new Promise((resolve, reject) => {
+    const probe = createNetServer();
+    probe.once('error', reject);
+    probe.listen(0, '127.0.0.1', () => {
+      const address = probe.address();
+      const port = typeof address === 'object' && address !== null ? address.port : 0;
+      probe.close(() => resolve(port));
+    });
+  });
+}
+
+/**
+ * Boots the committed server source on `port` with the given env overrides.
+ * An inherited `DATABASE_URL` (the no-database path must be deterministic)
+ * and `EPPP_SESSION_SECRET` (the missing-secret case must be deterministic)
+ * are stripped unless explicitly provided. Returns `{ child, stdout, stderr }`
+ * with closures for diagnostics.
+ */
+function bootServer(port, envOverrides = {}) {
+  const args =
+    tsExecMode() === 'strip-types-flag'
+      ? ['--experimental-strip-types', SERVER_SRC]
+      : [SERVER_SRC];
+  const env = { ...process.env, PORT: String(port) };
+  delete env.DATABASE_URL;
+  delete env.EPPP_SESSION_SECRET;
+  Object.assign(env, envOverrides);
+  const child = spawn(process.execPath, args, {
+    cwd: REPO_ROOT,
+    env,
+    stdio: ['ignore', 'pipe', 'pipe'],
+  });
+  let stdout = '';
+  let stderr = '';
+  child.stdout.on('data', (chunk) => {
+    stdout += String(chunk);
+  });
+  child.stderr.on('data', (chunk) => {
+    stderr += String(chunk);
+  });
+  return { child, stdout: () => stdout, stderr: () => stderr };
+}
+
+/** Waits for the child to exit (it fails fast on a startup error). */
+function waitForExit(child, deadlineMs = 10_000) {
+  return new Promise((resolve, reject) => {
+    if (child.exitCode !== null || child.signalCode !== null) {
+      resolve({ code: child.exitCode, signal: child.signalCode });
+      return;
+    }
+    const timer = setTimeout(
+      () => reject(new Error('the server did not exit within the deadline (expected a startup error)')),
+      deadlineMs,
+    );
+    child.once('exit', (code, signal) => {
+      clearTimeout(timer);
+      resolve({ code, signal });
+    });
+  });
+}
+
+/**
+ * Polls `GET /health` until the server answers with ANY status, the child
+ * exits, or the deadline passes. Returns the fetch Response.
+ */
+async function waitForAnswer(port, child, stderr, deadlineMs = 10_000) {
+  const deadline = Date.now() + deadlineMs;
+  let lastError = '';
+  while (Date.now() < deadline) {
+    if (child.exitCode !== null) {
+      throw new Error(
+        `the server exited before answering GET /health (code ${child.exitCode}): ${stderr().trim()}`,
+      );
+    }
+    try {
+      return await fetch(`http://127.0.0.1:${port}/health`, {
+        signal: AbortSignal.timeout(1_000),
+      });
+    } catch (err) {
+      lastError = err instanceof Error ? err.message : String(err);
+      await delay(100);
+    }
+  }
+  throw new Error(
+    `GET /health did not answer within ${deadlineMs}ms (last error: ${lastError}; server stderr: ${stderr().trim()})`,
+  );
+}
+
+/** Kills a booted child (SIGTERM, then SIGKILL if needed) and waits for exit. */
+async function stopChild(child) {
+  if (child.exitCode !== null || child.signalCode !== null) return;
+  child.kill('SIGTERM');
+  await Promise.race([once(child, 'exit'), delay(2_000)]);
+  if (child.exitCode === null && child.signalCode === null) child.kill('SIGKILL');
+}
+
+test('starting without the required setting exits non-zero naming the missing field (server boot probe)', { skip: !TS_STRIPPING || !CONFIG_DIST || !DATABASE_POSTGRES_DIST ? BUILD_HINT : false }, async () => {
+  // The issue's test plan: "start with a missing required field and confirm
+  // the error names it". The committed server validates its required settings
+  // at startup, so booting it without EPPP_SESSION_SECRET must fail fast —
+  // the process exits non-zero and the error names the missing field.
+  const port = await reservePort();
+  const { child, stdout, stderr } = bootServer(port); // EPPP_SESSION_SECRET stripped
+  const { code, signal } = await waitForExit(child);
+  assert.notEqual(
+    code,
+    0,
+    `the server must exit non-zero when a required setting is missing (code ${code}, signal ${signal}); output: ${stdout().trim()} ${stderr().trim()}`,
+  );
+  assert.match(
+    stderr() + stdout(),
+    /missing required setting: sessionSecret/,
+    `the startup error must name the missing field (sessionSecret); got: ${stdout().trim()} ${stderr().trim()}`,
+  );
+});
+
+test('starting with an invalid required secret exits non-zero naming the field (server boot probe)', { skip: !TS_STRIPPING || !CONFIG_DIST || !DATABASE_POSTGRES_DIST ? BUILD_HINT : false }, async () => {
+  // A required setting that violates the schema (a too-short secret, < 32
+  // chars) is also a field-specific startup error naming the field.
+  const port = await reservePort();
+  const { child, stdout, stderr } = bootServer(port, { EPPP_SESSION_SECRET: 'short' });
+  const { code, signal } = await waitForExit(child);
+  assert.notEqual(
+    code,
+    0,
+    `the server must exit non-zero when the required secret is invalid (code ${code}, signal ${signal}); output: ${stdout().trim()} ${stderr().trim()}`,
+  );
+  assert.match(
+    stderr() + stdout(),
+    /sessionSecret/,
+    `the startup error must name the invalid field (sessionSecret); got: ${stdout().trim()} ${stderr().trim()}`,
+  );
+});
+
+test('starting with the required secret present boots to GET /health 200 (server boot probe)', { skip: !TS_STRIPPING || !CONFIG_DIST || !DATABASE_POSTGRES_DIST ? BUILD_HINT : false }, async () => {
+  // The startup validation must not reject a valid configuration: with the
+  // required admin-session secret (and no DATABASE_URL — the local
+  // non-container path) the server reports ready immediately and GET /health
+  // answers 200 {"status":"ok"}.
+  const port = await reservePort();
+  const { child, stdout, stderr } = bootServer(port, { EPPP_SESSION_SECRET: 's'.repeat(32) });
+  try {
+    const response = await waitForAnswer(port, child, stderr);
+    assert.equal(
+      response.status,
+      200,
+      `GET /health with a valid required secret must answer 200 (got ${response.status}); server output: ${stdout().trim()} ${stderr().trim()}`,
+    );
+    assert.deepEqual(
+      await response.json(),
+      { status: 'ok' },
+      'the app must report a healthy application ({"status":"ok"}) when the required settings are valid',
+    );
+  } finally {
+    await stopChild(child);
+  }
+});

tests/health-endpoint.test.mjs

@@ -116,14 +116,22 @@ function reservePort() {
  * env): since E00-S03-T06 the health endpoint is the readiness probe, and the
  * no-DATABASE_URL path is the one with no startup migration run to wait for —
  * the server reports ready immediately, so this smoke test stays deterministic
- * and exercises exactly the committed no-migration readiness path.
+ * and exercises exactly the committed no-migration readiness path. Since
+ * E00-S04-T02 the required admin-session secret (EPPP_SESSION_SECRET, the
+ * schema's required field) is validated at startup, so the boot provides a
+ * valid one — a missing secret is the field-specific startup-error path
+ * locked in by tests/config-startup-error.test.mjs.
  */
 function bootServer(port) {
   const args =
     tsExecMode() === 'strip-types-flag'
       ? ['--experimental-strip-types', SERVER_SRC]
       : [SERVER_SRC];
-  const env = { ...process.env, PORT: String(port) };
+  const env = {
+    ...process.env,
+    PORT: String(port),
+    EPPP_SESSION_SECRET: 's'.repeat(32),
+  };
   delete env.DATABASE_URL;
   const child = spawn(process.execPath, args, {
     cwd: REPO_ROOT,