diff --git a/.planning/phases/04-tickets-restyle/04-03-SUMMARY.md b/.planning/phases/04-tickets-restyle/04-03-SUMMARY.md
new file mode 100644
index 0000000..b449e27
--- /dev/null
+++ b/.planning/phases/04-tickets-restyle/04-03-SUMMARY.md
@@ -0,0 +1,110 @@
+---
+phase: 04
+plan: 03
+subsystem: mobile-tickets-detail
+tags: [mobile, tickets, header, navigation, accessibility]
+dependency_graph:
+  requires: []
+  provides: [ticket-detail-header-D18]
+  affects: [app/mobile/tickets/[id]/page.tsx]
+tech_stack:
+  added: []
+  patterns: [three-slot-header, external-link-with-noopener]
+key_files:
+  modified:
+    - app/mobile/tickets/[id]/page.tsx
+decisions:
+  - Desktop URL chosen as /analyzer/ticket/{id} (in-app, stays in auth boundary; UI-SPEC permits either Autotask direct URL or analyzer URL)
+  - rel="noopener noreferrer" added per T-04-11 threat mitigation (reverse tabnabbing defense-in-depth, even on same-origin)
+  - -mx-4 px-4 technique extends header band to parent div's edges so border-b runs full-width under the new header bar
+metrics:
+  duration_minutes: 5
+  completed_date: "2026-05-03"
+  tasks_completed: 1
+  files_changed: 1
+---
+
+# Phase 4 Plan 3: Detail Page In-Page Header Reskin Summary
+
+**One-liner:** Three-slot in-page header on `/mobile/tickets/[id]` — back chevron + breadcrumb + external-link icon — replacing the legacy `Back` button per D-18.
+
+---
+
+## What Changed
+
+### Exact Lines Modified in `app/mobile/tickets/[id]/page.tsx`
+
+**Import line (line 7):** Added `ExternalLink` to the named lucide-react import, alphabetically between `Eye` and `Mail`. All existing imports retained.
+
+**Header bar (lines ~240-264, replacing ~240-242):** The legacy single-line back button:
+
+```tsx
+<button onClick={() => router.back()} className="flex items-center gap-1 text-sm text-muted-foreground mb-3 hover:text-foreground">
+  <ArrowLeft className="w-4 h-4" /> Back
+</button>
+```
+
+Was replaced with the D-18 three-slot header bar (25 lines). The replacement lives inside the existing `<div className="px-4 pt-4 pb-3 border-b">` parent — that wrapper was NOT changed. The new inner `div` uses `-mx-4 px-4` to extend to the parent's edges so its `border-b` runs full-width as a visual separator between the new header and the body below.
+
+---
+
+## Desktop URL Choice
+
+`/analyzer/ticket/{id}` was used as the desktop link target.
+
+**Rationale:** The analyzer ticket view (`/analyzer/ticket/{id}`) is the canonical in-app desktop view of a ticket in this codebase. It stays within the auth boundary (same domain, same session cookie), so the user lands on a fully functional desktop page rather than being redirected to an external system. The UI-SPEC permits either the Autotask direct URL or the analyzer URL — the analyzer URL is preferred per the plan's spec note.
+
+---
+
+## D-19 Body Untouched — Confirmation
+
+The following sections were preserved verbatim (not modified):
+
+| Section | Preserved |
+|---------|-----------|
+| Badges row (`flex items-start gap-2 mb-2` — priority + ticket# + status pills) | Yes |
+| `<h1 className="text-base font-bold leading-snug">` ticket title | Yes |
+| Metadata icons row (Briefcase / User / Clock) | Yes |
+| 3-card stats grid (Notes / Time entries / Hours logged) | Yes |
+| Description Collapsible block (`AlignLeft` icon, raw/formatted toggle) | Yes |
+| Timeline section (filter toggles, `TimelineCard` list) | Yes |
+| `TimelineCard` component definition | Yes |
+| `loading` and `error` states | Yes |
+| Helper functions: `fmtDate`, `fmtHours`, `renderContent`, `relTime` | Yes (note: `relTime` is not in this file — lives in the list page; all helpers in this file preserved) |
+| Constant maps: `STATUS_LABEL`, `PRIORITY_LABEL`, `PRIORITY_COLOR` | Yes |
+
+---
+
+## Parallel Execution
+
+This plan (04-03) ran in parallel with 04-01 and 04-02 in wave 1. There is no shared file conflict — 04-03 only touches `app/mobile/tickets/[id]/page.tsx`, while 04-01 touches `app/api/mobile/tickets/route.ts` and 04-02 touches `app/mobile/tickets/page.tsx`. No merge conflicts expected.
+
+---
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+---
+
+## Known Stubs
+
+None. The header bar is fully wired: `router.back()` for navigation, `ticket.ticket_number` for breadcrumb text, `ticket.id` for the external link href. No placeholder values.
+
+---
+
+## Threat Flags
+
+No new threat surface beyond what was declared in the plan's threat model (T-04-11, T-04-12). T-04-11 mitigation (`rel="noopener noreferrer"`) is implemented.
+
+---
+
+## Self-Check
+
+Checking created file and commit:
+
+- `app/mobile/tickets/[id]/page.tsx` — FOUND
+- Commit `b1ff866` — FOUND
+- `04-03-SUMMARY.md` — FOUND
+
+## Self-Check: PASSED
diff --git a/app/mobile/tickets/[id]/page.tsx b/app/mobile/tickets/[id]/page.tsx
index 7de406f..e85b2da 100644
--- a/app/mobile/tickets/[id]/page.tsx
+++ b/app/mobile/tickets/[id]/page.tsx
@@ -4,7 +4,7 @@ import { useEffect, useState, use } from 'react';
 import { useRouter } from 'next/navigation';
 import {
   ArrowLeft, RefreshCw, Clock, FileText, Timer, CheckCircle2,
-  ChevronDown, ChevronRight, User, Briefcase, AlertCircle, EyeOff, Eye, Mail, AlignLeft, Code2,
+  ChevronDown, ChevronRight, User, Briefcase, AlertCircle, EyeOff, Eye, ExternalLink, Mail, AlignLeft, Code2,
 } from 'lucide-react';
 
 const PRIORITY_LABEL: Record<number, string> = {
@@ -237,9 +237,31 @@ export default function TicketTimeline({ params }: { params: Promise<{ id: strin
     <div>
       {/* Ticket header */}
       <div className="px-4 pt-4 pb-3 border-b">
-        <button onClick={() => router.back()} className="flex items-center gap-1 text-sm text-muted-foreground mb-3 hover:text-foreground">
-          <ArrowLeft className="w-4 h-4" /> Back
-        </button>
+        <div className="flex items-center justify-between -mx-4 px-4 py-3 border-b mb-3">
+          <button
+            type="button"
+            onClick={() => router.back()}
+            aria-label="Back to Tickets"
+            className="flex items-center gap-1 text-sm text-muted-foreground hover:text-foreground transition-colors"
+          >
+            <ArrowLeft className="w-4 h-4" aria-hidden="true" />
+            <span>Tickets</span>
+          </button>
+
+          <p className="text-sm font-semibold truncate mx-2 flex-1 text-center">
+            Tickets / #{ticket.ticket_number}
+          </p>
+
+          <a
+            href={`/analyzer/ticket/${ticket.id}`}
+            target="_blank"
+            rel="noopener noreferrer"
+            aria-label="Open ticket on desktop"
+            className="text-muted-foreground hover:text-foreground transition-colors shrink-0"
+          >
+            <ExternalLink className="w-4 h-4" aria-hidden="true" />
+          </a>
+        </div>
         <div className="flex items-start gap-2 mb-2">
           <span className={`shrink-0 text-xs font-medium px-2 py-0.5 rounded-full border ${priClass}`}>
             {PRIORITY_LABEL[ticket.priority] ?? `P${ticket.priority}`}