fix(desktop): keep Close and + on a lone workspace even when tabs are hidden

A lone workspace pane is stranded without its strip: Close still empties it
to a draft and + still opens a tab, so a chromeless workspace is a dead zone
for both handles. Treat any lone main pane as stranded, workspace included,
which also makes the auto-only lone-main clause unnecessary.

Approach from #107444 by @abundantbeing.

Co-authored-by: abundantbeing <beingsabundant@gmail.com>

apps/desktop/src/components/pane-shell/tree/renderer/strip-visibility.test.ts

@@ -44,11 +44,16 @@ describe('no dead zone', () => {
     expect(resolveTabStripVisible({ mode: 'never', shown: [toolPanel()] })).toBe(true)
   })
 
+  it('keeps the strip for a lone workspace even when the zone says never', () => {
+    // Workspace cannot leave the tree, but Close still empties it to a draft
+    // and + still opens a tab. Chromeless is a dead zone for those handles.
+    expect(resolveTabStripVisible({ mode: 'never', shown: [workspace()] })).toBe(true)
+  })
+
   it('still hides a zone that cannot strand anything', () => {
-    // The workspace is uncloseable, a stack is reachable by tab cycling, and
-    // hide-only chrome (sessions / Bots) keeps its panes + ⌘⌥T — the invariant
-    // protects handles, it does not veto hiding as such.
-    expect(resolveTabStripVisible({ mode: 'never', shown: [workspace()] })).toBe(false)
+    // A stack is reachable by tab cycling, and hide-only chrome (sessions /
+    // Bots) keeps its panes + ⌘⌥T — the invariant protects handles, it does
+    // not veto hiding as such.
     expect(resolveTabStripVisible({ mode: 'never', shown: [toolPanel(), toolPanel()] })).toBe(false)
     expect(resolveTabStripVisible({ mode: 'never', shown: [sideChrome()] })).toBe(false)
     expect(resolveTabStripVisible({ mode: 'never', shown: [sideChrome(), sideChrome()] })).toBe(false)
@@ -86,15 +91,13 @@ describe('a full-page view', () => {
 })
 
 // Every launch and client update lands on a lone workspace. Chromeless, that
-// layout had no session switcher and no "+" until the app-wide default was
-// flipped to always — the "tab header disappeared" reports (#89350).
+// layout had no session switcher, no Close and no "+" (#89350).
 describe('a lone workspace', () => {
-  it('keeps its strip on auto, and only on auto', () => {
+  it('keeps its strip whatever the zone says', () => {
     expect(resolveTabStripVisible({ shown: [workspace()] })).toBe(true)
+    expect(resolveTabStripVisible({ mode: 'never', shown: [workspace()] })).toBe(true)
     // Standing side chrome never joins the tabbed workflow.
     expect(resolveTabStripVisible({ shown: [sideChrome()] })).toBe(false)
-    // Hide tabs (menu row / ⌘⌥T) still wins — the workspace strands nothing.
-    expect(resolveTabStripVisible({ mode: 'never', shown: [workspace()] })).toBe(false)
   })
 })
 
@@ -127,7 +130,7 @@ describe('tabStripVisibleForZone', () => {
 
   it('reads placement, uncloseable and collapse off the contributions', () => {
     expect(visible(['workspace'])).toBe(true)
-    expect(visible(['workspace'], 'never')).toBe(false)
+    expect(visible(['workspace'], 'never')).toBe(true)
     expect(visible(['tile:a'], 'never')).toBe(true)
     expect(visible(['terminal'], 'never')).toBe(true)
   })
@@ -137,15 +140,15 @@ describe('tabStripVisibleForZone', () => {
     expect(visible(['workspace'])).toBe(true)
 
     setTabStripDefault('never')
-    expect(visible(['workspace'])).toBe(false)
+    expect(visible(['workspace'])).toBe(true)
     expect(visible(['workspace', 'terminal'])).toBe(false)
   })
 
   it("lets a zone's own choice beat the app default", () => {
     setTabStripDefault('never')
-    expect(visible(['workspace'], 'always')).toBe(true)
+    expect(visible(['workspace', 'terminal'], 'always')).toBe(true)
 
     setTabStripDefault('always')
-    expect(visible(['workspace'], 'never')).toBe(false)
+    expect(visible(['workspace', 'terminal'], 'never')).toBe(false)
   })
 })

apps/desktop/src/components/pane-shell/tree/renderer/strip-visibility.ts

@@ -38,12 +38,13 @@ export interface StripZone {
 
 /**
  * A pane is STRANDED without a strip when the strip is the only thing carrying
- * its handle: a lone closeable tile needs its ✕, a lone tool panel needs a chip
- * to grab. The uncloseable workspace is not strandable — it cannot be closed
- * or lost, so an explicit `never` may hide its strip. Hide-only chrome (sessions
- * / Bots) is the same: the panes stay, Show/Hide is a separate verb, and a
- * hidden strip comes back via ⌘⌥T. Treating it as stranded at any count made
- * Hide tabs a silent no-op on the sessions sidebar.
+ * its handle: a lone main tile needs its ✕ and +, a lone tool panel needs a
+ * chip to grab. The workspace cannot leave the tree, but Close still empties
+ * it to a draft and + still opens a tab — chromeless is a dead zone for those
+ * handles. Hide-only chrome (sessions / Bots) is different: the panes stay,
+ * Show/Hide is a separate verb, and a hidden strip comes back via ⌘⌥T.
+ * Treating side chrome as stranded at any count made Hide tabs a silent no-op
+ * on the sessions sidebar.
  *
  * This outranks an explicit `never` on purpose. "Hide the strip" is a request
  * about chrome, never a request to make a surface unreachable, and a zone that
@@ -64,7 +65,7 @@ function stranded(shown: readonly StripPane[]): boolean {
 
   const [only] = shown
 
-  return only.collapsePane || (!only.uncloseable && only.placement === 'main')
+  return only.collapsePane || only.placement === 'main'
 }
 
 export function resolveTabStripVisible(zone: StripZone): boolean {
@@ -87,17 +88,10 @@ export function resolveTabStripVisible(zone: StripZone): boolean {
     return zone.mode === 'always'
   }
 
-  // Auto: two or more panes need a strip to switch between them.
-  if (zone.shown.length > 1) {
-    return true
-  }
-
-  // A lone MAIN tile keeps its strip too. The strip is the session switcher:
-  // its tab names the chat and its "+" opens the next one, so a chromeless
-  // lone workspace — the layout every launch and update lands on — read as
-  // "my tabs disappeared". Standing side chrome still goes without; hiding
-  // the workspace's strip remains an explicit choice (`never`, ⌘⌥T).
-  return zone.shown.some(pane => pane.placement === 'main')
+  // Auto: two or more panes need a strip to switch between them. A lone main
+  // tile never reaches here (it is stranded above), so what is left alone is
+  // standing side chrome, which goes without.
+  return zone.shown.length > 1
 }
 
 /**