Give the terminal back the width and the keyboard the session shell took

Seven things reported from a day's use of v5b's session shell, and they are one
commit because five of them are the same complaint from different angles: the
window spends too much of itself on chrome describing the session, and the parts
that are not chrome do not behave.

◆ THE HOST HEADER IS GONE, and that is a deliberate departure from the design.

Terminal.dc.html and SFTP.dc.html both draw a 60-pixel row above the pane: the
address on the left, a cross-surface button on the right. Both facts are worth
having and the strip they sat in was not — the tab already names the host, and a
full-width bar repeating it was the cheapest 60 pixels in the layout to give
back. The address is now the first line of the sidebar and the button is
stretched across the column under it, so nothing is lost and the pane is taller.

Which word that button carries and which command it runs used to be handed in
from the two usage sites in MainWindow.axaml, because the control was drawn
twice. One sidebar cannot do that, so SessionCrossSurfaceLabel and
OpenOtherSurfaceCommand resolve it in the shell — the same place SessionAddress
already decides which surface's fact to read. The two directions underneath are
untouched: SelectFilesHostAsync for a tab's host, OpenTerminalForFilesHostAsync
for a fresh terminal at whatever SFTP has open.

SessionHeader.axaml is deleted rather than left unused, and LayoutHarness stops
subtracting its 60 pixels from every session screen's budget — the same
treatment the retired window-wide tab strip got, and for the same reason: a
constant for chrome nobody draws is a suite quietly measuring the wrong
rectangle.

◆ AND THE SIDEBAR CLOSES, which the design has no state for at all.

300 pixels of an 1081-pixel minimum is a great deal to spend on a list that is
often two rows long. The column now folds to a 34-pixel rail carrying the
chevron that brings it back — a rail rather than nothing, because a panel that
vanishes leaving no trace is one people report as lost rather than as closed.
Both states live in the one control and swap on IsSessionSidebarOpen, so
MainWindow's own "Auto" column takes whichever width is showing without knowing
the state exists.

Written through to ClientSettings.SessionSidebarOpen rather than held for the
session. It is a decision about how much of the window a terminal gets, and one
that had to be made again on every launch would not really be on offer.

---- THE FOUR SMALLER ONES ----

A SNIP LANDED IN A TERMINAL NOBODY COULD TYPE AT, and looked selected when it
got there. Two causes with nothing in common. The click moved Win32 focus onto
the sidebar row, and term.focus() in the page cannot take it back — only the
host can, so the shell raises TerminalFocusRequested and the window answers with
the same posted focus every other path here uses. The highlight was bash: xterm
wraps a paste in bracketed-paste markers, readline marks what arrives inside
them as an active region, and it stays in reverse video until the next
keystroke. Right for a clipboard paste, wrong for a snippet picked off a
sidebar. Single-line snips are typed rather than pasted now, which needs no
markers; multi-line still pastes, because "runs three commands unasked" is the
worse of the two failures and the markers are the whole of what prevents it.

A BLACK BAR UNDER THE TERMINAL, on Windows. xterm.css paints its scrolling
viewport #000 — its own comment explains why, and it is a macOS scrollbar
concern. Everywhere else that black is covered by the rows, except along the
bottom: the fit addon floors the row count, so the remainder below the last
whole row is bare viewport, up to a line tall, against this page's #171a26. The
light square at its right-hand end is where WebView2's classic scrollbar corner
lands. The viewport is repainted in the page's own background, and the scrollbar
with it — thin and in these colours rather than a grey Windows channel down the
side of a near-black terminal, and kept rather than hidden, because a surface
that scrolls with no sign that it does is worse than a quiet bar.

THE PINS ROW DREW A TOFU BOX. U+E946 is not in the embedded Material Icons face
at all — that file is the 2019 build and its cmap skips E944 and E946 — so the
rail's Pins row and the hosts screen's own pin badge have both been drawing a
missing-glyph rectangle since v5b picked the codepoint. push_pin in that vintage
is U+F10D, verified against the file rather than against a codepoints table for
a later release of the font. Every other icon codepoint in the repository was
audited the same way; this was the only miss.

THE KBD CHIP CUT THE CHORD IN HALF. 34 pixels is the design's width for a chip
reading ⌘K, and this build substitutes CTRL K — six characters and a space,
wider than 34 at 10.5 mono. MinWidth and padding instead, so the design's
footprint survives for the day this face has a ⌘ to draw.

---- AND THE POPOVER UNDER THE USER CHIP ----

Reported as not matching the design, and it was not: Button.poprow set a corner
radius and a padding and never touched the Background, so every row wore the
Fluent theme's own #33FFFFFF button fill. Six raised pills stacked in a menu the
design draws as six lines of text — and the hover rule underneath was already
correct and simply invisible against a fill that never went away. Set on the
ContentPresenter as well as on the Button, the same as Button.flat, because the
theme binds its brush there and a Background set only on the control loses to
it. The panel itself gets this window's own radius-12 card treatment through a
FlyoutPresenter class rather than by widening the shared context-menu rule, and
Vaults and Preferences stop being drawn one step dimmer than Settings and
Logout, which read as two disabled entries in a menu of five live ones.

---- WHAT PROVES IT ----

Three tests in the layout suite, two of them checked against the defect they
describe: the popover row's resting fill (fails with #33ffffff without the
style), and the kbd chip against the natural width of its own text, measured on
a detached copy because a TextBlock's DesiredSize is already clipped to what it
was given and reports 34 inside a 34-pixel chip either way. SessionSidebarTests
is new — the sidebar has never been laid out by a test, and it now holds a
string of unbounded length beside a button that has to stay clickable. In the
shell suite: the cross-surface row in both directions, the closed state
surviving to disk, and the focus request being made when a snip lands and not
made when it does not.

tests/DodoSSH.Client.App.Tests/ShellFlowTests.cs

@@ -6498,12 +6498,68 @@ public sealed class ShellFlowTests : IAsyncLifetime
         shell.IsTerminalShowing.ShouldBeTrue();
     }
 
+    /// <remarks>
+    /// v5c-4 retired the session shell's own header row and moved its cross-surface button into the sidebar,
+    /// where one control is drawn on both surfaces — so the two directions above are reached through one
+    /// command and one label, resolved by the shell. This is that resolution: the same two outcomes the two
+    /// tests above assert, from the row a user actually clicks now.
+    /// </remarks>
+    [Fact]
+    public async Task TheSidebarsCrossSurfaceRow_NamesAndOpensWhicheverSurfaceIsNotShowing()
+    {
+        await ConnectedHostWithAPinAsync();
+
+        shell.IsTerminalSurface.ShouldBeTrue();
+        shell.SessionCrossSurfaceLabel.ShouldBe("Open SFTP");
+
+        await shell.OpenOtherSurfaceCommand.ExecuteAsync(null);
+
+        shell.IsTransfersShowing.ShouldBeTrue();
+        shell.Transfers.SelectedHost.ShouldNotBeNull().Label.ShouldBe("prod-db");
+        shell.SessionCrossSurfaceLabel.ShouldBe("Open terminal", "the row turns over with the surface");
+
+        var tabsBefore = shell.Tabs.Count;
+
+        await shell.OpenOtherSurfaceCommand.ExecuteAsync(null);
+
+        shell.Tabs.Count.ShouldBe(tabsBefore + 1, "the other direction dials a terminal at the browsed host");
+        shell.IsTerminalShowing.ShouldBeTrue();
+    }
+
+    /// <remarks>
+    /// Closing the sidebar is a preference about this machine, so it outlives the window — see
+    /// <c>ClientSettings.SessionSidebarOpen</c>. Asserted against the store rather than against a second
+    /// shell built over the same profile: what a fresh launch reads is exactly what is on disk, and building
+    /// another shell here would prove the constructor twice and the storage once.
+    /// </remarks>
+    [Fact]
+    public async Task ClosingTheSidebar_IsRememberedForTheNextLaunch()
+    {
+        await ConnectedHostWithAPinAsync();
+
+        shell.IsSessionSidebarOpen.ShouldBeTrue("open is the default, and nothing has closed it");
+
+        shell.ToggleSessionSidebarCommand.Execute(null);
+
+        shell.IsSessionSidebarOpen.ShouldBeFalse();
+        new ClientSettingsStore(paths).Read().SessionSidebarOpen.ShouldBeFalse();
+
+        shell.ToggleSessionSidebarCommand.Execute(null);
+
+        shell.IsSessionSidebarOpen.ShouldBeTrue();
+        new ClientSettingsStore(paths).Read().SessionSidebarOpen.ShouldBeTrue("and reopening is remembered too");
+    }
+
     /// <remarks>
     /// The sidebar's SNIPS row, wired through <c>SnippetsViewModel.InsertCommand</c> rather than a second
     /// insert path — see the deviation recorded on <c>MainWindowViewModel.InsertSnippetCommand</c>. Proven
     /// through a real connected tab and a real renderer, the same fixture <c>InsertingASnippet_...</c> above
     /// uses for the standalone screen, because what is worth proving here is that the shell's command reaches
     /// that same mechanism rather than reimplementing it.
+    ///
+    /// The focus request is asserted here rather than in a test of its own because it is part of what this
+    /// click does: the row that typed the command took the keyboard with it, and only the window can give it
+    /// back. See <c>MainWindowViewModel.TerminalFocusRequested</c>.
     /// </remarks>
     [Fact]
     public async Task InsertingASnippetFromTheSidebarTypesItIntoTheSelectedTab()
@@ -6515,9 +6571,38 @@ public sealed class ShellFlowTests : IAsyncLifetime
 
         var row = snippets.Visible.ShouldHaveSingleItem();
 
+        var focusRequests = 0;
+        shell.TerminalFocusRequested += (_, _) => focusRequests++;
+
         await shell.InsertSnippetCommand.ExecuteAsync(row);
 
         snippets.Selected.ShouldBe(row, "the sidebar row picks the same selection INSERT reads");
+        focusRequests.ShouldBe(1, "the keyboard goes back to the terminal the command landed in");
+    }
+
+    /// <remarks>
+    /// The other half of the rule above: nothing was typed, so nothing asks for the keyboard. A snip clicked
+    /// with no terminal to put it in lands on the snippets screen instead — see
+    /// <c>MainWindowViewModel.InsertSnippetCommand</c> — and stealing focus into a collapsed WebView on the
+    /// way would leave that screen unable to be typed on.
+    /// </remarks>
+    [Fact]
+    public async Task InsertingASnippetWithNothingToInsertInto_DoesNotAskForTheTerminal()
+    {
+        await UnlockedAsync();
+
+        var snippets = shell.SnippetsScreen.ShouldNotBeNull();
+        await AddSnippetAsync(snippets, "uptime", "uptime", runs: false);
+
+        var row = snippets.Visible.ShouldHaveSingleItem();
+
+        var focusRequests = 0;
+        shell.TerminalFocusRequested += (_, _) => focusRequests++;
+
+        await shell.InsertSnippetCommand.ExecuteAsync(row);
+
+        shell.Screen.ShouldBe(ShellScreen.Snippets);
+        focusRequests.ShouldBe(0);
     }
 
     [Fact]