Fix command modified keys. Add plan for splitscreen

Downterm/CommandNotch.xcodeproj/xcshareddata/xcschemes/CommandNotch.xcscheme

@@ -1,11 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "2620"
+   LastUpgradeVersion = "1600"
    version = "1.7">
    <BuildAction
       parallelizeBuildables = "YES"
       buildImplicitDependencies = "YES"
-      buildArchitectures = "Automatic">
+      runPostActionsOnFailure = "NO">
       <BuildActionEntries>
          <BuildActionEntry
             buildForTesting = "YES"
@@ -15,7 +15,7 @@
             buildForAnalyzing = "YES">
             <BuildableReference
                BuildableIdentifier = "primary"
-               BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+               BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
                BuildableName = "CommandNotch.app"
                BlueprintName = "CommandNotch"
                ReferencedContainer = "container:CommandNotch.xcodeproj">
@@ -28,7 +28,42 @@
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES"
-      shouldAutocreateTestPlan = "YES">
+      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
+            BuildableName = "CommandNotch.app"
+            BlueprintName = "CommandNotch"
+            ReferencedContainer = "container:CommandNotch.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <Testables>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "036FDAECD12C0A679DA1F5D6"
+               BuildableName = "CommandNotchTests.xctest"
+               BlueprintName = "CommandNotchTests"
+               ReferencedContainer = "container:CommandNotch.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "1C8D00CBB29219BD347E9CC4"
+               BuildableName = "CommandNotchUITests.xctest"
+               BlueprintName = "CommandNotchUITests"
+               ReferencedContainer = "container:CommandNotch.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </TestAction>
    <LaunchAction
       buildConfiguration = "Debug"
@@ -44,12 +79,14 @@
          runnableDebuggingMode = "0">
          <BuildableReference
             BuildableIdentifier = "primary"
-            BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
             BuildableName = "CommandNotch.app"
             BlueprintName = "CommandNotch"
             ReferencedContainer = "container:CommandNotch.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"
@@ -61,12 +98,14 @@
          runnableDebuggingMode = "0">
          <BuildableReference
             BuildableIdentifier = "primary"
-            BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
             BuildableName = "CommandNotch.app"
             BlueprintName = "CommandNotch"
             ReferencedContainer = "container:CommandNotch.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </ProfileAction>
    <AnalyzeAction
       buildConfiguration = "Debug">

Downterm/CommandNotch.xcodeproj/xcshareddata/xcschemes/Release-CommandNotch.xcscheme

@@ -1,11 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "2620"
+   LastUpgradeVersion = "1600"
    version = "1.7">
    <BuildAction
       parallelizeBuildables = "YES"
       buildImplicitDependencies = "YES"
-      buildArchitectures = "Automatic">
+      runPostActionsOnFailure = "NO">
       <BuildActionEntries>
          <BuildActionEntry
             buildForTesting = "YES"
@@ -15,7 +15,7 @@
             buildForAnalyzing = "YES">
             <BuildableReference
                BuildableIdentifier = "primary"
-               BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+               BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
                BuildableName = "CommandNotch.app"
                BlueprintName = "CommandNotch"
                ReferencedContainer = "container:CommandNotch.xcodeproj">
@@ -28,13 +28,48 @@
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES"
-      shouldAutocreateTestPlan = "YES">
+      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
+            BuildableName = "CommandNotch.app"
+            BlueprintName = "CommandNotch"
+            ReferencedContainer = "container:CommandNotch.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <Testables>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "036FDAECD12C0A679DA1F5D6"
+               BuildableName = "CommandNotchTests.xctest"
+               BlueprintName = "CommandNotchTests"
+               ReferencedContainer = "container:CommandNotch.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "1C8D00CBB29219BD347E9CC4"
+               BuildableName = "CommandNotchUITests.xctest"
+               BlueprintName = "CommandNotchUITests"
+               ReferencedContainer = "container:CommandNotch.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </TestAction>
    <LaunchAction
       buildConfiguration = "Release"
-      selectedDebuggerIdentifier = ""
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
-      selectedLauncherIdentifier = "Xcode.IDEFoundation.Launcher.PosixSpawn"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      launchStyle = "1"
+      launchStyle = "0"
       useCustomWorkingDirectory = "NO"
       ignoresPersistentStateOnLaunch = "NO"
       debugDocumentVersioning = "YES"
@@ -44,12 +79,14 @@
          runnableDebuggingMode = "0">
          <BuildableReference
             BuildableIdentifier = "primary"
-            BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
             BuildableName = "CommandNotch.app"
             BlueprintName = "CommandNotch"
             ReferencedContainer = "container:CommandNotch.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"
@@ -61,12 +98,14 @@
          runnableDebuggingMode = "0">
          <BuildableReference
             BuildableIdentifier = "primary"
-            BlueprintIdentifier = "1485207FA11756EC2DF4F08B"
+            BlueprintIdentifier = "D5585E5732CD067DF6EF0C69"
             BuildableName = "CommandNotch.app"
             BlueprintName = "CommandNotch"
             ReferencedContainer = "container:CommandNotch.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <CommandLineArguments>
+      </CommandLineArguments>
    </ProfileAction>
    <AnalyzeAction
       buildConfiguration = "Debug">

Downterm/CommandNotch/Components/TerminalCommandArrowBehavior.swift

@@ -0,0 +1,31 @@
+import AppKit
+import Carbon.HIToolbox
+import SwiftTerm
+
+enum TerminalCommandArrowBehavior {
+    private static let relevantModifiers: NSEvent.ModifierFlags = [.command, .control, .option, .shift]
+    private static let lineKill: [UInt8] = [0x15]
+    private static let clearScreen: [UInt8] = [0x0c]
+
+    static func sequence(
+        for modifierFlags: NSEvent.ModifierFlags,
+        keyCode: UInt16,
+        applicationCursor: Bool
+    ) -> [UInt8]? {
+        let flags = modifierFlags.intersection(relevantModifiers)
+        guard flags == [.command] else { return nil }
+
+        switch Int(keyCode) {
+        case kVK_LeftArrow:
+            return applicationCursor ? EscapeSequences.moveHomeApp : EscapeSequences.moveHomeNormal
+        case kVK_RightArrow:
+            return applicationCursor ? EscapeSequences.moveEndApp : EscapeSequences.moveEndNormal
+        case kVK_Delete:
+            return lineKill
+        case kVK_ANSI_L:
+            return clearScreen
+        default:
+            return nil
+        }
+    }
+}

Downterm/CommandNotch/Models/TerminalSession.swift

@@ -9,6 +9,7 @@ class TerminalSession: NSObject, ObservableObject, LocalProcessDelegate, @precon
     let id = UUID()
     let terminalView: TerminalView
     private var process: LocalProcess?
+    private var keyEventMonitor: Any?
     private let backgroundColor = NSColor.black
     private let configuredShellPath: String
 
@@ -26,10 +27,17 @@ class TerminalSession: NSObject, ObservableObject, LocalProcessDelegate, @precon
         let font = NSFont.monospacedSystemFont(ofSize: fontSize, weight: .regular)
         terminalView.font = font
         applyTheme(theme)
+        installCommandArrowMonitor()
 
         startShell()
     }
 
+    deinit {
+        if let keyEventMonitor {
+            NSEvent.removeMonitor(keyEventMonitor)
+        }
+    }
+
     // MARK: - Shell management
 
     private func startShell() {
@@ -58,6 +66,26 @@ class TerminalSession: NSObject, ObservableObject, LocalProcessDelegate, @precon
         return ProcessInfo.processInfo.environment["SHELL"] ?? "/bin/zsh"
     }
 
+    private func installCommandArrowMonitor() {
+        keyEventMonitor = NSEvent.addLocalMonitorForEvents(matching: .keyDown) { [weak self] event in
+            guard let self else { return event }
+            guard let window = self.terminalView.window else { return event }
+            guard event.window === window else { return event }
+            guard window.firstResponder === self.terminalView else { return event }
+
+            guard let sequence = TerminalCommandArrowBehavior.sequence(
+                for: event.modifierFlags,
+                keyCode: event.keyCode,
+                applicationCursor: self.terminalView.getTerminal().applicationCursor
+            ) else {
+                return event
+            }
+
+            self.terminalView.send(data: sequence[...])
+            return nil
+        }
+    }
+
     func updateFontSize(_ size: CGFloat) {
         terminalView.font = NSFont.monospacedSystemFont(ofSize: size, weight: .regular)
     }

Downterm/CommandNotchTests/TerminalCommandArrowBehaviorTests.swift

@@ -0,0 +1,57 @@
+import AppKit
+import Carbon.HIToolbox
+import XCTest
+import SwiftTerm
+@testable import CommandNotch
+
+final class TerminalCommandArrowBehaviorTests: XCTestCase {
+    func testCommandLeftUsesHomeSequence() {
+        let sequence = TerminalCommandArrowBehavior.sequence(
+            for: [.command],
+            keyCode: UInt16(kVK_LeftArrow),
+            applicationCursor: false
+        )
+
+        XCTAssertEqual(sequence, EscapeSequences.moveHomeNormal)
+    }
+
+    func testCommandRightUsesApplicationEndSequence() {
+        let sequence = TerminalCommandArrowBehavior.sequence(
+            for: [.command],
+            keyCode: UInt16(kVK_RightArrow),
+            applicationCursor: true
+        )
+
+        XCTAssertEqual(sequence, EscapeSequences.moveEndApp)
+    }
+
+    func testOptionLeftKeepsSwiftTermWordNavigationPath() {
+        let sequence = TerminalCommandArrowBehavior.sequence(
+            for: [.option],
+            keyCode: UInt16(kVK_LeftArrow),
+            applicationCursor: false
+        )
+
+        XCTAssertNil(sequence)
+    }
+
+    func testCommandDeleteUsesLineKillSequence() {
+        let sequence = TerminalCommandArrowBehavior.sequence(
+            for: [.command],
+            keyCode: UInt16(kVK_Delete),
+            applicationCursor: false
+        )
+
+        XCTAssertEqual(sequence, [0x15])
+    }
+
+    func testCommandLUsesClearScreenSequence() {
+        let sequence = TerminalCommandArrowBehavior.sequence(
+            for: [.command],
+            keyCode: UInt16(kVK_ANSI_L),
+            applicationCursor: false
+        )
+
+        XCTAssertEqual(sequence, [0x0c])
+    }
+}

Downterm/project.yml

@@ -14,6 +14,45 @@ packages:
   SwiftTerm:
     url: https://github.com/migueldeicaza/SwiftTerm.git
     from: "1.2.0"
+schemes:
+  CommandNotch:
+    build:
+      targets:
+        CommandNotch: all
+    test:
+      config: Debug
+      targets:
+        - CommandNotchTests
+        - CommandNotchUITests
+    run:
+      config: Debug
+    profile:
+      config: Release
+    analyze:
+      config: Debug
+    archive:
+      config: Release
+    management:
+      shared: true
+  Release-CommandNotch:
+    build:
+      targets:
+        CommandNotch: all
+    test:
+      config: Debug
+      targets:
+        - CommandNotchTests
+        - CommandNotchUITests
+    run:
+      config: Release
+    profile:
+      config: Release
+    analyze:
+      config: Debug
+    archive:
+      config: Release
+    management:
+      shared: true
 targets:
   CommandNotch:
     type: application
@@ -29,9 +68,9 @@ targets:
       properties:
         CFBundleName: CommandNotch
         CFBundleDisplayName: CommandNotch
-        CFBundleIdentifier: com.commandnotch.app
+        CFBundleIdentifier: "$(PRODUCT_BUNDLE_IDENTIFIER)"
         CFBundleVersion: "1"
-        CFBundleShortVersionString: "0.2.0"
+        CFBundleShortVersionString: "0.0.3"
         CFBundlePackageType: APPL
         CFBundleExecutable: CommandNotch
         LSMinimumSystemVersion: "14.0"

docs/workspace-split-pane-plan.md

@@ -0,0 +1,351 @@
+# Workspace Split Pane Plan
+
+## Purpose
+
+Capture the agreed design for workspace-owned split terminals so the feature can be implemented later without redoing scope and architecture decisions.
+
+## Agreed Scope
+
+- Split layouts belong to the workspace, not the screen.
+- A workspace may only be actively presented on one screen at a time.
+- Split layouts should be visible the same way when that workspace is opened on another monitor.
+- Nested splits are supported.
+- Any two tabs may be joined into a split.
+- Closing a pane causes its sibling to expand.
+- Split layout must survive relaunch.
+
+## Non-Goals
+
+- Simultaneous live rendering of the same workspace on multiple screens.
+- Full multi-user or collaborative state sync.
+- Arbitrary freeform pane layout. The model is tree-based binary splits.
+- Solving all interaction polish in the first pass.
+
+## Current Constraint
+
+The current workspace model is flat:
+
+- `WorkspaceController` owns `[TerminalSession]`
+- one tab is active at a time
+- `ContentView` renders exactly one active `SwiftTermView`
+
+This means split panes are not an additive UI feature. They require a workspace model refactor.
+
+## Recommended Model
+
+Do not model splits as "adjacent tabs with special behavior" internally.
+
+Instead:
+
+1. A workspace owns ordered top-level tabs.
+2. Each top-level tab owns a pane tree.
+3. Pane tree leaves own `TerminalSession` instances.
+4. Pane tree internal nodes represent binary splits.
+5. The tab bar can visually present grouped/joined tabs based on the active tab's pane composition.
+
+This keeps the domain model clean while still allowing the desired visual metaphor.
+
+## Proposed Domain Types
+
+```swift
+typealias WorkspaceTabID = UUID
+typealias PaneID = UUID
+
+struct WorkspaceTab: Identifiable, Equatable, Codable {
+    var id: WorkspaceTabID
+    var rootPane: PaneNode
+    var selectedPaneID: PaneID?
+    var titleMode: WorkspaceTabTitleMode
+}
+
+enum PaneNode: Equatable, Codable, Identifiable {
+    case leaf(PaneLeaf)
+    case split(PaneSplit)
+
+    var id: PaneID { ... }
+}
+
+struct PaneLeaf: Equatable, Codable, Identifiable {
+    var id: PaneID
+    var sessionID: UUID
+}
+
+struct PaneSplit: Equatable, Codable, Identifiable {
+    var id: PaneID
+    var axis: SplitAxis
+    var ratio: Double
+    var first: PaneNode
+    var second: PaneNode
+}
+
+enum SplitAxis: String, Codable {
+    case horizontal
+    case vertical
+}
+```
+
+Notes:
+
+- `ratio` should be persisted so user-adjusted divider positions survive relaunch.
+- `selectedPaneID` allows focus-based commands such as split active pane, close active pane, and move focus.
+- The persisted model should store session identity separately from runtime AppKit/SwiftTerm objects.
+
+## Runtime Ownership
+
+Global:
+
+- workspace summaries
+- workspace ordering
+- workspace-to-screen assignment
+- hotkeys
+
+Workspace:
+
+- ordered top-level tabs
+- active top-level tab
+- per-tab pane tree
+- active/selected pane
+- terminal sessions for pane leaves
+
+Screen:
+
+- which workspace is assigned
+- notch open/close state
+- geometry and transitions
+
+This remains aligned with the existing workspace architecture.
+
+## Persistence Strategy
+
+Split layout must survive relaunch, so workspace persistence needs to grow beyond summary metadata.
+
+Recommended approach:
+
+1. Keep `WorkspaceSummary` for list metadata only.
+2. Introduce a persisted `WorkspaceDocument` or `WorkspaceSnapshot` per workspace.
+3. Persist:
+   - top-level tabs
+   - pane tree
+   - active tab ID
+   - selected pane ID
+   - divider ratios
+4. Do not attempt to persist shell process contents.
+5. On relaunch, recreate sessions for pane leaves and restore layout structure only.
+
+Important distinction:
+
+- layout persistence is required
+- terminal process continuity is not
+
+## UI Model
+
+### Main Content
+
+The active top-level tab renders as a recursive split tree.
+
+- leaf node -> one `SwiftTermView`
+- split node -> `HSplitView`/`VSplitView` equivalent SwiftUI container with draggable divider
+
+### Tab Bar
+
+Top-level tabs remain the primary navigation unit.
+
+Visual behavior:
+
+- a normal unsplit tab looks like today
+- a joined/split tab should look grouped
+- grouped tabs should expose child pane titles visually inside the tab item
+
+Recommended first-pass appearance:
+
+- one outer tab pill per top-level tab
+- inside that pill, show compact child title chips for each leaf pane
+- highlight the selected pane's chip
+
+This gives the "tabs are joined" feel without making pane leaves first-class top-level tabs in the data model.
+
+## Command Model
+
+New actions likely needed:
+
+- split active pane horizontally
+- split active pane vertically
+- focus next pane
+- focus previous pane
+- close active pane
+- resize focused split divider
+- join tab A into tab B
+- detach pane into new top-level tab
+
+Semantics:
+
+- joining any two tabs merges one tab's root pane into the other's tree
+- the source top-level tab is removed
+- the destination top-level tab remains
+- sibling expansion on close is standard tree collapse
+
+## Join Semantics
+
+Joining any two tabs should work as:
+
+1. Choose destination tab.
+2. Choose source tab.
+3. Replace destination root with a new split node:
+   - first child = old destination root
+   - second child = source root
+4. Remove source tab from workspace order.
+5. Select a predictable pane, preferably the source pane that was just added.
+
+An explicit split axis should be required for the join action.
+
+## Close Semantics
+
+When closing a pane:
+
+- if the pane has a sibling, the sibling expands into the parent's position
+- if the pane was the only leaf in a top-level tab:
+  - close the whole top-level tab if more than one tab exists
+  - otherwise create a replacement shell pane, matching current single-tab safety behavior
+
+## Focus Semantics
+
+Pane focus must become explicit.
+
+Recommended rules:
+
+- mouse click focuses that pane
+- splitting focuses the new pane
+- joining focuses the moved-in pane
+- closing a pane focuses the surviving sibling
+- top-level tab switch restores the previously selected pane in that tab
+
+## Migration Path
+
+Implement in stages to reduce risk.
+
+### Stage 1: Domain Refactor
+
+- Replace flat workspace tabs with top-level tab objects.
+- Introduce pane tree types.
+- Keep only one leaf per tab initially so behavior is unchanged.
+
+### Stage 2: Runtime Layout Rendering
+
+- Render pane trees recursively in `ContentView`.
+- Add active pane selection.
+- Keep persistence off until runtime behavior is stable.
+
+### Stage 3: Split Actions
+
+- Split active pane horizontally/vertically.
+- Close pane with sibling expansion.
+- Basic focus movement.
+
+### Stage 4: Joined Tab UI
+
+- Update tab bar to show grouped child pane chips.
+- Surface active pane clearly.
+
+### Stage 5: Join / Unjoin Flows
+
+- Join any two tabs with explicit axis choice.
+- Support promoting a pane back to its own top-level tab if needed.
+
+### Stage 6: Persistence
+
+- Persist pane trees and top-level tab state.
+- Recreate sessions on launch.
+
+### Stage 7: Hotkeys and Polish
+
+- Add pane-focused shortcuts.
+- Add divider dragging polish.
+- Improve visual grouped-tab affordances.
+
+## Main Risks
+
+### 1. Model complexity
+
+The current flat `[TerminalSession]` model is simple. Tree-based layout introduces more state, more edge cases, and more focus semantics.
+
+Mitigation:
+
+- refactor the data model before touching complex UI
+- keep top-level tabs and pane leaves distinct
+
+### 2. SwiftTerm view ownership
+
+`TerminalView` cannot be mounted in multiple places safely.
+
+Mitigation:
+
+- preserve current rule: only one active presenting screen per workspace
+- keep one runtime `TerminalSession` per pane leaf
+
+### 3. Persistence mismatch
+
+Persisting layout is easy compared with persisting process state.
+
+Mitigation:
+
+- persist layout and selection only
+- recreate shell sessions on launch
+
+### 4. Joined-tab UX ambiguity
+
+If grouped tabs are also used as pane chips, the interaction model can get confusing.
+
+Mitigation:
+
+- preserve top-level tabs as the real navigation unit
+- use internal chips only as secondary indicators/actions
+
+## Recommended First Implementation Boundary
+
+The first deliverable should include:
+
+- nested binary split trees
+- active pane focus
+- split and close pane actions
+- sibling expansion
+- grouped tab appearance
+- join any two tabs
+- persisted layout across relaunch
+- same workspace layout when moved to another screen
+
+The first deliverable should not include:
+
+- simultaneous same-workspace rendering on multiple screens
+- drag-and-drop tree editing
+- restoring running shell process contents
+
+## Files Likely Impacted
+
+- `Downterm/CommandNotch/Models/WorkspaceController.swift`
+- `Downterm/CommandNotch/Models/WorkspaceRegistry.swift`
+- `Downterm/CommandNotch/Models/WorkspaceStore.swift`
+- `Downterm/CommandNotch/ContentView.swift`
+- `Downterm/CommandNotch/Components/TabBar.swift`
+- `Downterm/CommandNotch/Models/TerminalSession.swift`
+- workspace-related tests
+
+Likely new files:
+
+- pane tree domain types
+- persisted workspace document types
+- split-pane rendering view(s)
+- pane-focused command helpers
+
+## Decision Summary
+
+The feature is feasible.
+
+The correct architecture is:
+
+- workspace-owned split tree
+- top-level tabs remain the primary unit
+- grouped tab visuals are a UI layer over the pane tree
+- one presenting screen per workspace
+- persisted layout, not persisted process contents
+
+That is the implementation direction to use when this work is resumed.