docs: add hashed workspace persistence story

docs/ROADMAP.md

@@ -121,6 +121,31 @@ A prioritized roadmap for the Vault Dashboard Lombard loan hedging platform.
 
 **Dependencies:** PORT-001
 
+### PORT-004: Hashed Workspace Persistence [P0, L] **[depends: PORT-001]**
+**As a** user, **I want** my dashboard settings and scenarios to live inside a shareable hashed workspace URL **so that** I can return on a new device or share the exact workspace with someone else.
+
+**Acceptance Criteria:**
+- First visit with no known workspace creates a new workspace id (UUID/hash-like token) and redirects to `/{workspace_id}`
+- App stores the workspace id in a browser cookie for return visits
+- Visiting an existing `/{workspace_id}` loads that workspace without requiring the cookie
+- Workspace URL is copyable/shareable and restores the same settings on another device/browser
+- Settings persistence is scoped by workspace id rather than one global local file
+- Existing pages (`/settings`, `/overview`, `/hedge`, `/backtests`, `/event-comparison`) read/write the active workspace state
+- Invalid or unknown workspace ids show a clear recovery path instead of a server error
+- Browser test verifies:
+  - first visit creates/redirects to a workspace route
+  - cookie-backed revisit returns to the same workspace
+  - visiting the same workspace URL in a fresh context restores the same settings
+
+**Technical Notes:**
+- Introduce a workspace model/repository keyed by generated id
+- Prefer server-side persistence keyed by workspace id; cookie stores only the id, not the full state
+- Keep workspace ids opaque and non-sequential
+- Consider root route `/` as a bootstrap that resolves/creates the active workspace and redirects to `/{workspace_id}` plus nested page routes as needed
+- Ensure routing design stays compatible with existing NiceGUI pages before implementation
+
+**Dependencies:** PORT-001
+
 ---
 
 ## Phase 3: Strategy Execution (Advanced Features)
@@ -469,11 +494,12 @@ DATA-001 (Price Feed)
 
 ## Implementation Priority Queue
 
-1. **BT-001B** - Prefill backtest UIs from canonical saved portfolio settings
-2. **BT-003B** - Add event-comparison drilldown and explanation of ranking outcomes
-3. **PORT-003** - Historical LTV visibility and export groundwork
-4. **BT-002** - Upgrade backtests to real daily options snapshots
-5. **BT-001C** - Consolidate deterministic historical fixture/demo provider logic
-6. **EXEC-001** - Core user workflow
-7. **EXEC-002** - Execution capability
-8. Remaining features
+1. **PORT-004** - Introduce hashed workspace persistence as the new state foundation
+2. **BT-001B** - Prefill backtest UIs from canonical saved portfolio settings
+3. **BT-003B** - Add event-comparison drilldown and explanation of ranking outcomes
+4. **PORT-003** - Historical LTV visibility and export groundwork
+5. **BT-002** - Upgrade backtests to real daily options snapshots
+6. **BT-001C** - Consolidate deterministic historical fixture/demo provider logic
+7. **EXEC-001** - Core user workflow
+8. **EXEC-002** - Execution capability
+9. Remaining features