Implement multi-source workspace with enhanced UI and file handling

.cspell.yaml

@@ -11,6 +11,7 @@
 version: '0.2'
 language: en
 words:
+  - APFS
   - Argb
   - axaml
   - BGRA
@@ -21,12 +22,15 @@ words:
   - Dema
   - doctitle
   - docversion
+  - Dedupe
+  - dedupe
   - Dockable
   - Dockables
   - fileassert
   - Hmmssfff
   - LOCALAPPDATA
   - Mvvm
+  - ordinally
   - Pandoc
   - pagetitle
   - pasteable
@@ -46,8 +50,19 @@ words:
   - sonar
   - sonarmark
   - Stdlib
+  - Subfolders
+  - subfolders
   - sysml
   - timeslice
+  - TOCTOU
+  - uncontended
+  - unioned
+  - Unwatch
+  - unwatch
+  - Unwatches
+  - unwatches
+  - Unwatching
+  - unwatching
   - versionmark
   - Weasyprint
   - xunit

.reviewmark.yaml

@@ -118,6 +118,20 @@ reviews:
       - docs/verification/sysml2-workbench/workspace-subsystem/diagnostics-aggregator.md
       - src/**/WorkspaceSubsystem/DiagnosticsAggregator.cs
       - test/**/WorkspaceSubsystem/DiagnosticsAggregatorTests.cs
+  - id: SysML2Workbench-WorkspaceSubsystem-WorkspaceSourceSet
+    title: Review that SysML2Workbench WorkspaceSubsystem WorkspaceSourceSet Implementation
+      is Correct
+    context:
+      - docs/design/sysml2-workbench.md
+      - docs/reqstream/sysml2-workbench.yaml
+      - docs/design/sysml2-workbench/workspace-subsystem.md
+      - docs/reqstream/sysml2-workbench/workspace-subsystem.yaml
+    paths:
+      - docs/reqstream/sysml2-workbench/workspace-subsystem/workspace-source-set.yaml
+      - docs/design/sysml2-workbench/workspace-subsystem/workspace-source-set.md
+      - docs/verification/sysml2-workbench/workspace-subsystem/workspace-source-set.md
+      - src/**/WorkspaceSubsystem/WorkspaceSourceSet.cs
+      - test/**/WorkspaceSubsystem/WorkspaceSourceSetTests.cs
   - id: SysML2Workbench-ViewCatalogSubsystem
     title: Review that SysML2Workbench ViewCatalogSubsystem Satisfies Subsystem Requirements
     context:
@@ -292,6 +306,22 @@ reviews:
       - docs/verification/sysml2-workbench/app-shell-subsystem/main-window-shell.md
       - src/**/AppShellSubsystem/MainWindowShell.cs
       - test/**/AppShellSubsystem/MainWindowShellTests.cs
+  - id: SysML2Workbench-AppShellSubsystem-WorkspacePanel
+    title: Review that SysML2Workbench AppShellSubsystem WorkspacePanel Implementation
+      is Correct
+    context:
+      - docs/design/sysml2-workbench.md
+      - docs/reqstream/sysml2-workbench.yaml
+      - docs/design/sysml2-workbench/app-shell-subsystem.md
+      - docs/reqstream/sysml2-workbench/app-shell-subsystem.yaml
+    paths:
+      - docs/reqstream/sysml2-workbench/app-shell-subsystem/workspace-panel.yaml
+      - docs/design/sysml2-workbench/app-shell-subsystem/workspace-panel.md
+      - docs/verification/sysml2-workbench/app-shell-subsystem/workspace-panel.md
+      - src/**/AppShellSubsystem/WorkspacePanelToolViewModel.cs
+      - src/**/AppShellSubsystem/WorkspacePanelToolView.axaml
+      - src/**/AppShellSubsystem/WorkspacePanelToolView.axaml.cs
+      - test/**/AppShellSubsystem/WorkspacePanelToolViewModelTests.cs
   - id: OTS-DemaConsultingSysML2Tools
     title: Review that DemaConsulting.SysML2Tools Provides Required Functionality
     paths:

docs/design/sysml2-workbench/app-shell-subsystem.md

@@ -6,9 +6,10 @@
 
 AppShellSubsystem is the composition root for the desktop application. It owns
 the main window, navigation flow, and tabbed viewing experience that tie the
-other subsystems into one coherent user workflow. Its only documented unit is
-MainWindowShell. The thin desktop platform head remains outside the documented
-unit set because it is only a bootstrap and lifetime host.
+other subsystems into one coherent user workflow. Its documented units are
+MainWindowShell and WorkspacePanel. The thin desktop platform head remains
+outside the documented unit set because it is only a bootstrap and lifetime
+host.
 
 ### Interfaces
 
@@ -51,18 +52,28 @@ environment.
    user workflow without pushing UI-specific code into those subsystems.
 5. The desktop platform head initializes the shell and application lifetime but
    remains a bootstrap concern rather than a separately documented unit.
-6. The Avalonia UI layer presents MainWindowShell's panels (predefined
-   views, custom view builder, diagnostics, and diagram) as a resizable,
-   floatable Dock layout, composed by a Dock factory from thin panel views
-   and view models that hold no logic beyond forwarding to MainWindowShell
-   and binding its state. The three Tool panels (predefined views, custom
-   view builder, diagnostics) are closable and restorable via a View menu,
-   which reuses the same long-lived panel view model instance so its
-   in-progress state survives the close/restore cycle. The diagram area
-   hosts zero or more independently closable diagram Documents - one per
-   open `WorkbenchTab`, each bound to its own `SvgCanvasHost` - and the
-   Dock `DocumentDock` container itself remains visibly present even when
-   no diagram tab is open, so an empty diagram area is a normal, supported
-   state rather than a dead end. MainWindowShell itself has no dependency
-   on Avalonia or Dock and is unaware of how its panels are arranged on
-   screen.
+6. The Avalonia UI layer presents MainWindowShell's panels (workspace,
+   predefined views, custom view builder, diagnostics, and diagram) as a
+   resizable, floatable Dock layout, composed by a Dock factory from thin
+   panel views and view models that hold no logic beyond forwarding to
+   MainWindowShell and binding its state. The four Tool panels (workspace,
+   predefined views, custom view builder, diagnostics) are closable and
+   restorable via a View menu, which reuses the same long-lived panel view
+   model instance so its in-progress state survives the close/restore
+   cycle. The diagram area hosts zero or more independently closable diagram
+   Documents - one per open `WorkbenchTab`, each bound to its own
+   `SvgCanvasHost` - and the Dock `DocumentDock` container itself remains
+   visibly present even when no diagram tab is open, so an empty diagram
+   area is a normal, supported state rather than a dead end. MainWindowShell
+   itself has no dependency on Avalonia or Dock and is unaware of how its
+   panels are arranged on screen.
+7. A workspace with zero sources open is a first-class, non-error state, not
+   a precondition failure: `MainWindowShell.CurrentWorkspace` is never null
+   and starts as a valid empty snapshot at construction. Every panel that
+   depends on workspace content - the workspace panel, predefined views,
+   custom view builder, and diagnostics - presents a distinct, friendly
+   empty-state message when `Sources.Count == 0` rather than rendering
+   against an empty `SysmlWorkspace` or leaving a blank pane; the diagnostics
+   panel in particular distinguishes "no diagnostics because the workspace is
+   empty" from "no diagnostics because everything is clean," since those are
+   different facts the user needs to tell apart.

docs/design/sysml2-workbench/app-shell-subsystem/main-window-shell.md

@@ -10,8 +10,11 @@ snippet export within a single windowed user experience.
 
 #### Data Model
 
-**CurrentWorkspace**: `WorkspaceSnapshot?` — currently loaded workspace and its
-revision metadata.
+**CurrentWorkspace**: `WorkspaceSnapshot` — currently loaded workspace and its
+revision metadata. Never `null`: initialized at construction to a valid empty
+snapshot (zero sources, zero files, stdlib-only) rather than left unset until
+the first source is added, so every consumer can safely read
+`CurrentWorkspace.Sources` without a null guard.
 
 **ActivePredefinedView**: `ViewDescriptor?` — selected catalog view, if the
 user is in predefined-view mode.
@@ -29,27 +32,55 @@ active/focused, or `null` when no diagram tab is open. Updated both by shell
 operations that open or focus a tab, and by the UI layer forwarding Dock's
 own focus-change signal via `NotifyActiveDiagramTab`.
 
-#### Key Methods
+**CurrentSourceIdToFiles**: `IReadOnlyDictionary<string, IReadOnlyList<string>>`
+— per-source file lists from the most recent workspace resolution, used by
+WorkspacePanel to build its tree without owning its own `WorkspaceSourceSet`
+instance.
 
-**OpenWorkspace**: Loads a new workspace into the shell.
+#### Key Methods
 
-- *Parameters*: `string rootPath` — user-selected folder.
-- *Returns*: `void` — shell state updates in place.
-- *Preconditions*: `rootPath` exists and is readable.
-- *Postconditions*: WorkspaceSubsystem is initialized, the view catalog is
-  refreshed, diagnostics are displayed, and every open tab is closed
-  (`ActiveTabId` becomes `null`) since a reloaded workspace invalidates every
-  currently-rendered diagram. The file watcher is retargeted to `rootPath` on
-  every call, not only the first: any previously watched root is torn down and
-  its pending change state discarded, so a second or later workspace open
-  never leaves the watcher bound to a stale folder.
+**AddFileSource**: Adds a single file as a new workspace source.
+
+- *Parameters*: `string path` — file to add.
+- *Returns*: `WorkspaceSnapshot` — the reloaded workspace snapshot.
+- *Postconditions*: The path is registered on the shell's owned
+  `WorkspaceSourceSet`, the source set is re-resolved, `WorkspaceModel` is
+  reloaded against the new resolution, the file watcher begins watching the
+  new source (a non-recursive, filtered watcher for a file source), the
+  resulting snapshot is applied (existing tabs are cleared, since a reload
+  invalidates every currently-rendered diagram), and `SourcesChanged` is
+  raised. Idempotent: adding the same path twice does not duplicate the
+  source.
+
+**AddFolderSource**: Adds a folder as a new workspace source.
+
+- *Parameters*: `string path` — folder to add.
+- *Returns*: `WorkspaceSnapshot` — the reloaded workspace snapshot.
+- *Postconditions*: Identical to `AddFileSource`, except the source is a
+  recursively watched folder and its files are discovered via
+  `WorkspaceSourceSet.Resolve()`'s default glob options.
+
+**RemoveSource**: Removes a previously registered source.
+
+- *Parameters*: `string sourceId` — id of the source to remove.
+- *Returns*: `WorkspaceSnapshot` — the reloaded workspace snapshot.
+- *Postconditions*: The source is removed from the source set (a no-op for
+  an unknown id), the set is re-resolved, `WorkspaceModel` is reloaded, the
+  now-unwatched source's watcher is disposed, the resulting snapshot is
+  applied, and `SourcesChanged` is raised. Removing the last remaining source
+  produces a valid empty snapshot (zero sources, zero files) - the same
+  first-class empty state the shell starts in at construction - and still
+  correctly clears every open tab, not only when shrinking to a smaller
+  nonzero file set.
+
+#### Additional Key Methods
 
 **SelectPredefinedView**: Renders a predefined view selected by the user.
 
 - *Parameters*: `string viewId` — identifier from ViewCatalogPresenter.
 - *Returns*: `void` — active diagram state updates in place.
-- *Preconditions*: A workspace is loaded and the view identifier is present in
-  the current catalog.
+- *Preconditions*: `CurrentWorkspace.Sources.Count > 0` and the view
+  identifier is present in the current catalog.
 - *Postconditions*: `ActivePredefinedView` is updated; a tab identified by the
   view's qualified name is opened (or, if already open, reused) and rendered
   into; that tab becomes `ActiveTabId` either way, so selecting an
@@ -61,7 +92,8 @@ own focus-change signal via `NotifyActiveDiagramTab`.
 - *Parameters*: `ViewDefinitionModel definition` — normalized custom-view
   state.
 - *Returns*: `void` — active diagram state updates in place.
-- *Preconditions*: The definition validates against the current workspace.
+- *Preconditions*: `CurrentWorkspace.Sources.Count > 0` and the definition
+  validates against the current workspace.
 - *Postconditions*: `ActiveCustomView` is updated. If the currently active tab
   is itself a custom-view-preview tab, it is re-rendered in place (same tab
   identity and canvas); otherwise a brand-new custom-view-preview tab is
@@ -116,23 +148,33 @@ workspace is reloaded (which clears every tab). The Avalonia-aware UI layer
 add or remove Dock dockables directly. The notification is raised through an
 injected `IUiDispatcher`, so subscribers are guaranteed to observe it on the
 dispatcher's target thread even though methods that trigger it - most notably
-`OpenWorkspace`, which awaits workspace loading with `ConfigureAwait(false)` -
-may themselves resume on a background thread pool thread once the load
-completes.
+`AddFolderSourceAsync`, which awaits workspace loading with
+`ConfigureAwait(false)` - may themselves resume on a background thread pool
+thread once the load completes.
+
+**SourcesChanged**: Raised whenever the set of workspace sources changes - a
+source is added or removed and the resulting resolution has been applied.
+Parallel in structure and marshaling behavior to `TabsChanged`: raised through
+the same injected `IUiDispatcher`. `WorkspacePanelToolViewModel` subscribes to
+this to rebuild its tree, and `CurrentSourceIdToFiles` reflects the change by
+the time subscribers observe the notification.
 
 #### Dependencies
 
 - **WorkspaceSubsystem** — loads and refreshes the workspace state.
+- **WorkspaceSourceSet** — owned by the shell; mutated by
+  `AddFileSourceAsync`/`AddFolderSourceAsync`/`RemoveSourceAsync` and
+  re-resolved before every `WorkspaceModel` load, reload, and watcher diff.
 - **ViewCatalogPresenter** — supplies predefined view choices.
 - **ViewDefinitionModel** — captures custom-view authoring state.
 - **SysmlSnippetGenerator** — exports custom-view definitions as SysML text.
 - **LayoutInvoker** — renders predefined and custom views.
 - **SvgCanvasHost** — displays the active diagram.
 - **DiagnosticsListView** — displays workspace diagnostics.
 - **RollingFileLogger** — records shell-level operational failures.
-- **IUiDispatcher** — marshals `TabsChanged` notifications onto the thread
-  required by UI-facing subscribers; defaults to an immediate, synchronous
-  dispatcher when none is supplied.
+- **IUiDispatcher** — marshals `TabsChanged` and `SourcesChanged`
+  notifications onto the thread required by UI-facing subscribers; defaults
+  to an immediate, synchronous dispatcher when none is supplied.
 - **Avalonia** — provides the window, tab, and application-lifetime framework.
 
 #### Callers