feat(frontend): Phase 6 Locale + Date/Time Discipline — close I18N-H1 + I18N-H2 + I18N-H3 + I18N-M2

Closes the Phase 6 batch from cowork/frontend-design-audit.html: makes
every timestamp in the dashboard byte-identical to its server-audit-log
equivalent under UTC, makes every number format browser-locale-aware,
and builds the i18n-ready boundary without shipping a full i18n
framework (deferred to Phase 10).

═════════════════════════ AUDIT VERIFICATION ═════════════════════════

  • Q1 utils.ts hardcoded 'en-US' at lines 3 + 8 — confirmed
  • Q2 raw new Date(x).toLocaleString() sites — verified 8 sites
    across 6 pages (audit said "7+"):
      SessionsPage:178, SessionsPage:181        (last_seen, abs_expires)
      BreakglassPage:236, BreakglassPage:248    (last_pw_change, locked_until)
      GroupMappingsPage:206                     (created_at)
      OIDCProvidersPage:434                     (created_at)
      ApprovalsPage:379                         (created_at)
      ObservabilityPage:71                      (server_started)
  • Q3 no i18n framework — confirmed (no i18next/react-intl/@formatjs/
    date-fns in web/package.json)
  • Q4 zero Intl.NumberFormat usage — confirmed (audit-accurate)
  • Q5 Tooltip API — `<Tooltip content={…}>{singleChild}</Tooltip>`,
    Floating-UI-backed, aria-describedby wired
  • Q6 toFixed sites — 1 site in dashboard/charts.tsx (Recharts tooltip
    rate formatter); audit was vague but actual is minimal

═════════════════════════════ CLOSURES ═══════════════════════════════

I18N-H1 — drop hardcoded en-US in utils.ts
  • formatDate / formatDateTime now pass `undefined` for the locale
    arg, meaning the runtime uses navigator.language. Output SHAPE
    stable (month: 'short' etc.); LANGUAGE follows the browser.
  • New formatDateUTC / formatDateTimeUTC siblings force timeZone:
    'UTC' for byte-equivalent display vs server audit log + journalctl.
  • New formatDateTimeInZone(iso, ianaTz) backs the Custom-TZ branch
    in operator settings; falls back to UTC on invalid IANA name
    (Intl throws RangeError; we catch + degrade gracefully).
  • Existing tests in utils.test.ts already used locale-tolerant
    assertions (.toContain('Jun')) so no test update needed.

I18N-H3 — UTC display + operator-local hover + preference toggle
  • web/src/components/Timestamp.tsx — wraps a UTC-default string in
    the Phase 1 Tooltip showing the operator-local equivalent. Three
    modes:
      utc    — display UTC (default; screen ≡ logs).
      local  — display browser-local, hover shows UTC.
      custom — display configured IANA tz, hover shows UTC.
  • web/src/api/timestampPref.ts — typed localStorage helper with
    `certctl:timestamp-pref-changed` CustomEvent so live <Timestamp>
    components re-render without a page reload when the operator
    flips the toggle.
  • New "Timestamp display" card on AuthSettingsPage with radio
    selector + IANA-tz input that appears only when mode='custom'.

I18N-H2 — migrate raw toLocaleString sites + CI guard
  • 8/8 raw `new Date(x).toLocaleString()` / `.toLocaleDateString()`
    sites migrated:
      SessionsPage    — Timestamp (×2, last_seen + abs_expires)
      BreakglassPage  — Timestamp (×2, last_password_change + locked_until)
      ApprovalsPage   — Timestamp (created_at)
      ObservabilityPage — Timestamp (server_started)
      GroupMappingsPage — formatDate (date-only column)
      OIDCProvidersPage — formatDate (date-only column)
  • scripts/ci-guards/no-raw-toLocaleString.sh fails CI on any new
    raw new Date(x).toLocaleString[Date]Date call outside the
    canonical utils.ts impls. Tests + utils.ts itself are excluded.

I18N-M2 — Intl.NumberFormat helpers
  • New web/src/api/format.ts exports formatNumber / formatCompact /
    formatPercent / formatBytes — all backed by Intl.NumberFormat
    constructed once at module load (NumberFormat construction is
    the expensive part; .format() is cheap).
  • Locale-tolerant test fixtures assert format SHAPE (e.g.
    "5[ .,]?432") not exact strings — so the CI runner's locale
    doesn't break assertions.
  • formatBytes uses SI-decimal scaling (1KB=1000B); manual fallback
    for old Safari that doesn't support `style: 'unit'`.

═══════════════════════════ AUDIT-ACCURACY CALLOUTS ════════════════════

  (1) Audit said "7+ pages with raw .toLocaleString" — verified 8 raw
      SITES across 6 PAGES. Direction was right; counts were vague.
  (2) Audit said "no i18n framework + no Intl.NumberFormat" — both
      verified accurate (zero matches in production tsx).
  (3) Audit suggested SessionsPage / BreakglassPage / GroupMappings /
      OIDCProviders / Approvals / Observability "and others" — all six
      named confirmed; no "others" found. List was complete.

═══════════════════════════ VERIFICATION ════════════════════════════

  • npx tsc --noEmit — exits 0
  • New tests: utils 18/18 (preserved) + format 14/14 + Timestamp 6/6
    = 38 new test assertions
  • Component suite (270/270 across api + Timestamp + Tooltip + sibs)
  • 7 migrated page suites — 62/62 green (Sessions / Approvals /
    Breakglass / GroupMappings / OIDCProviders / AuthSettings /
    Observability)
  • All 34 CI guards pass locally (new no-raw-toLocaleString.sh +
    existing no-unbound-label baseline bumped 132→134 for the 2
    wrap-style implicit-association labels added on AuthSettings
    timestamp preference card; guard's blunt grep can't distinguish
    wrap from sibling labels — documented in the guard header).
  • npx vite build — ✓ in 2.69s
  • grep "'en-US'" web/src/api/utils.ts → 0 matches
  • grep "new Date.*\.toLocaleString\(\)" web/src --include='*.tsx'
    --exclude='*.test.*' → 0 raw sites outside utils.ts

═══════════════════════════ RESIDUAL RISK ════════════════════════════

  • UTC default may surprise non-engineering users who expect their
    local timezone. Mitigation: the AuthSettings toggle gives them
    a one-click out to Local mode. Default UTC is the right safe
    default for an audit-log-paired tool.
  • formatBytes SI vs binary: the helper uses SI-decimal (1KB=1000B)
    by default. If memory/disk numbers in Observability tiles need
    binary scaling (1KiB=1024B), add a formatBytesBinary in a
    follow-up; for now those tiles either don't surface bytes or
    use server-provided pre-formatted strings.
  • i18n framework deferred: no react-i18next, no extraction pass.
    Phase 10 (when first multi-language customer asks) will swap the
    `undefined` locale arg here for a thread-through value; display
    code never touches Date.prototype.toLocaleString directly thanks
    to the no-raw-toLocaleString CI guard.

scripts/ci-guards/no-raw-toLocaleString.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+# Phase 6 closure (I18N-H2 regression gate): fail CI when a new
+# `new Date(x).toLocaleString()` or `.toLocaleDateString()` ships in
+# production tsx outside the canonical web/src/api/utils.ts impls.
+#
+# Pre-Phase-6 the codebase had 8 raw sites across 6 pages, each making
+# its own locale + timezone choice. Phase 6 routed them through the
+# formatDateTime / formatDate / <Timestamp> helpers in utils.ts +
+# components/Timestamp.tsx. This guard prevents new raw sites from
+# landing.
+#
+# Allowlist: web/src/api/utils.ts itself — those raw calls ARE the
+# canonical implementation everyone else routes through.
+#
+# Tests are excluded (web/src/**/*.test.*) so test fixtures + assertions
+# describing the pre-Phase-6 raw pattern don't trip the guard.
+set -euo pipefail
+
+cd "$(dirname "$0")/../../web"
+
+OFFENDERS=$(
+  grep -rnE 'new Date\([^)]*\)\.toLocaleString\(\)|new Date\([^)]*\)\.toLocaleDateString\(\)' \
+    src \
+    --include='*.tsx' \
+    --include='*.ts' \
+    --exclude='*.test.*' \
+    --exclude-dir='node_modules' \
+    --exclude-dir='dist' \
+    2>/dev/null \
+    | grep -v 'src/api/utils.ts:' \
+    || true
+)
+
+if [[ -n "$OFFENDERS" ]]; then
+  echo "::error::I18N-H2 regression: raw new Date(x).toLocaleString() outside web/src/api/utils.ts:"
+  echo "$OFFENDERS"
+  echo ""
+  echo "Migrate to one of:"
+  echo "  • <Timestamp iso={...} />            — for hover-shows-other-zone UX"
+  echo "  • formatDateTime(iso)                 — for local-zone date+time text"
+  echo "  • formatDate(iso) / formatDateUTC(iso) — for date-only text"
+  echo ""
+  echo "All three live in web/src/api/utils.ts / web/src/components/Timestamp.tsx."
+  exit 1
+fi
+
+echo "I18N-H2 no-raw-toLocaleString: clean."

scripts/ci-guards/no-unbound-label-baseline.txt

@@ -1 +1 @@
-132
+134

scripts/ci-guards/no-unbound-label.sh

@@ -16,6 +16,15 @@
 # corresponding line; when the allowlist is empty, this guard becomes
 # strictly enforcing and the allowlist file should be removed.
 #
+# Known false-positive class: wrap-style implicit-association labels —
+# `<label><input/>...</label>`. These ARE a11y-safe (browsers + screen
+# readers pair the wrapped input with the label automatically — no
+# htmlFor needed), but this guard's line-based regex can't tell the
+# wrap pattern apart from a sibling-label-no-htmlFor bug. When such
+# patterns ship, raise the baseline with a one-line explanation in
+# the commit message; they're benign. Phase 6 added 2 (the timestamp-
+# mode radios in AuthSettingsPage), so baseline 132 → 134.
+#
 # Algorithm:
 #   1. Count current unbound labels (labels NOT preceded by htmlFor= on
 #      the same line OR within the wrapping JSX block).