Navigation stack: Ctrl+− / Ctrl+Shift+− back and forward through tab history

[JoshuaRowePhantom]

Summary

Maintain a linear navigation history of tabs and top-level views visited. Ctrl+−
navigates backward and Ctrl+Shift+− (Ctrl+_) navigates forward, analogous to
browser back/forward or Visual Studio Ctrl+−/Ctrl+Shift+−.

Design

See docs/design/navigation-stack.md.

Scope

INavigationHistoryService

• Linear list with current-position pointer (max 200 entries)
• Push(NavigationEntry) — called by every tab/view activation
• GoBack / GoForward — move the pointer, activate the entry
• Deduplication: skip push if entry is identical to the one immediately before current
• No persistence — stack is in-memory only

NavigationEntry / TabDescriptor

• Each entry stores: workspace id, tab id, and a TabDescriptor for reopening closed tabs
• TabDescriptor subclasses per tab kind: entity, agent-session, browser, entity-browser
• Closed tab reopen: call TabDescriptor.OpenAsync; skip and try next on failure

Push sources

• MainWindowViewModel.OpenTabAsync
• MainWindowViewModel top-level view selection
• Notification click / F7/F8 navigation
• (AI tool integration tracked separately)

Guard against double-push

• _navigatingViaHistory bool in MainWindowViewModel suppresses push during GoBack/GoForward activations

Key bindings

• Ctrl+OemMinus → NavigateBackCommand
• Ctrl+Shift+OemMinus → NavigateForwardCommand
• Added to MainWindow.axaml

Acceptance

• Ctrl+− navigates to the previously active tab/view
• Ctrl+Shift+− navigates forward after going back
• Navigating to a new tab while mid-history truncates forward history
• Navigating to a closed tab reopens it; deleted entities are skipped

[JoshuaRowePhantom]

Verification failed

Checked: Commit 94354f0 (Fix #52) on the features branch — files Phantom.Workspaces/Services/Navigation/INavigationHistoryService.cs, NavigationHistoryService.cs, NavigationEntry.cs, MainWindowViewModel.cs, MainWindow.axaml, and test file Phantom.Workspaces.Tests/NavigationStackTests.cs. Also checked the full features branch tree for any subsequent commits adding the missing pieces.

Found:

• INavigationHistoryService with Push, GoBack, GoForward, CanGoBack, CanGoForward
• NavigationHistoryService: linear list, max 200 entries, deduplication, truncation on new push
• _navigatingViaHistory guard in MainWindowViewModel
• Key bindings Ctrl+OemMinus / Ctrl+Shift+OemMinus wired in MainWindow.axaml
• Push calls from OpenTabAsync, top-level view selection, and F7/F8 notification navigation
• Tests for basic Push, GoBack, GoForward, ClearsForwardHistory behaviour

Missing: behaviour not implemented + tests missing

1. TabDescriptor abstract base class — Phantom.Workspaces/Services/Navigation/TabDescriptor.cs with virtual OpenAsync(mainWindowViewModel) is absent. No EntityTabDescriptor, AgentSessionTabDescriptor, or BrowserTabDescriptor subclasses exist in the Navigation folder.
2. NavigationEntry.TabDescriptor? field — the current record is sealed record NavigationEntry(string TabId, string? WorkspacePaneId) with no TabDescriptor? for closed-tab reopening.
3. Closed-tab reopen in ActivateTabById — when a tab is not found in any pane, ActivateTabById silently returns without calling TabDescriptor.OpenAsync. The acceptance criterion "Navigating to a closed tab reopens it; deleted entities are skipped" is not satisfied.
4. Tests for closed-tab reopen — NavigationStackTests.cs has no test for the reopen-on-closed-tab or skip-deleted-entity paths.