Let the terminal's text be made bigger, and remember how big

Taking pinch-zoom off the phone left nothing in its place, and there was nothing on the desktop
either. This is the replacement, and it is deliberately not the thing that was removed: zoom scales
what has already been drawn, so the remote goes on wrapping to a width that is no longer on screen.
Changing the font size refits the grid and reports the new column count, so the far end is told it
has fewer columns. That round trip is the feature.

The size is one number, owned by the shell. It has to be, for two reasons that pull the same way: it
must survive a relaunch, and it must be reachable from a phone that has no Ctrl key to press. So the
page asks and the host decides — a signed step over a new client opcode, answered with a size over a
new server opcode. The phone's buttons and the desktop's chords arrive at the same place, and a size
set by either is the size both remember.

Stored in settings.json beside the cache rather than in it, and that is not laziness about a
migration. The cache is encrypted and unreadable until a vault is unlocked, and the first terminal of
a locked launch needs the size already. Nothing secret may go in that file; ClientSettings says so
out loud, because the next person to add a preference is the one who needs to read it.

Where it is reachable from differs per head, and only here. The phone gets A− and A+ on the
connection line — not in the accessory row, which scrolls, and a control that fixes unreadable text
must never be the thing that is off-screen. The desktop gets the three chords every terminal
emulator has, answered by the page while a terminal has focus and by the window when it does not,
plus a row in preferences that shows the current value and names the chords rather than replacing
them. Someone whose terminal is too small to read is not in a position to go looking.

Clamped 8 to 32. Below eight a monospace grid stops being legible and becomes a texture, and every
column of it is still a column the remote is being told exists; above thirty-two a phone in portrait
has too few columns to hold a prompt. The buttons disable at the ends rather than accepting presses
that do nothing, which on a terminal reads as the application having stopped responding.

The preferences screen's header comment claimed none of the design's terminal settings could be
saved, and listed the three things that were missing to make one work. All three now exist, so it
says which one is real and why the other five still are not.

Verified with the protocol suite — including that the step byte round-trips signed, since read
unsigned a step down arrives as 255 and clamps to the largest font, making "smaller" do the most
dramatic available version of "larger" — a data-plane test that the chord is heard with no session
registered, and five shell tests: the default matches the renderer's, both clamps hold, reset works,
and a size chosen in one shell is there in a second one over the same profile directory. Layout
suite and both heads build.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/DodoSSH.Client.Terminal/TerminalFrame.cs

@@ -76,6 +76,25 @@ public enum TerminalServerOpcode : byte
     /// </para>
     /// </remarks>
     Paste = 6,
+
+    /// <summary>
+    /// What size every pane should draw at. Payload is one byte, the size in CSS pixels.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Not per session, although the frame carries a session id as every frame does: a font size is a
+    /// preference about reading rather than a property of one remote, and somebody who makes the text
+    /// bigger means all of it. The id is sent as zero and ignored.
+    /// </para>
+    /// <para>
+    /// <b>Changing it reflows the remote, and that is the point.</b> The page refits after applying, which
+    /// changes the column and row count and sends <see cref="TerminalClientOpcode.Resize"/> back — so a
+    /// larger font is a terminal with fewer columns, and the far end is told about it. That is why this is
+    /// a font size rather than a zoom: zoom scales pixels and leaves the remote wrapping to a width that
+    /// is no longer on screen, which is what made the phone's pinch-zoom worse than useless.
+    /// </para>
+    /// </remarks>
+    FontSize = 7,
 }
 
 /// <summary>Frames the renderer sends to the host.</summary>
@@ -94,6 +113,24 @@ public enum TerminalClientOpcode : byte
 
     /// <summary>The terminal was resized. Payload is four big-endian <see cref="ushort"/> values.</summary>
     Resize = 3,
+
+    /// <summary>
+    /// The page asking for a different font size. Payload is one signed byte: a step, or zero to reset.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// A request rather than a statement, and the direction matters. The page owns the keyboard whenever a
+    /// terminal has focus — the host's window sees no key events at all then — so Ctrl+plus and Ctrl+minus
+    /// can only be <em>heard</em> there. But the size has to be remembered across launches and shown in a
+    /// control the page knows nothing about, so it is <em>decided</em> here. The page asks, the host
+    /// clamps, stores and answers with <see cref="TerminalServerOpcode.FontSize"/>.
+    /// </para>
+    /// <para>
+    /// Which also means one path, not two: the phone's buttons and the desktop's chords arrive at the same
+    /// place, and a size set by either is the size both remember.
+    /// </para>
+    /// </remarks>
+    FontSizeStep = 4,
 }
 
 /// <summary>
@@ -230,6 +267,31 @@ public static class TerminalFrame
         return payload;
     }
 
+    /// <summary>Reads a <see cref="TerminalClientOpcode.FontSizeStep"/> payload.</summary>
+    /// <remarks>
+    /// Signed, because the one byte carries a direction as well as a magnitude — and zero means reset,
+    /// which is why this cannot be a flag pair.
+    /// </remarks>
+    public static bool TryReadFontSizeStep(ReadOnlySpan<byte> payload, out int step)
+    {
+        step = 0;
+
+        if (payload.Length != 1)
+        {
+            return false;
+        }
+
+        step = (sbyte)payload[0];
+
+        return true;
+    }
+
+    /// <summary>Writes a <see cref="TerminalClientOpcode.FontSizeStep"/> payload.</summary>
+    public static byte[] CreateFontSizeStepPayload(int step) => [(byte)(sbyte)Math.Clamp(step, -128, 127)];
+
+    /// <summary>Writes a <see cref="TerminalServerOpcode.FontSize"/> payload.</summary>
+    public static byte[] CreateFontSizePayload(int pixels) => [(byte)Math.Clamp(pixels, 1, 255)];
+
     /// <summary>Writes an <see cref="TerminalClientOpcode.Acknowledge"/> payload.</summary>
     public static byte[] CreateAcknowledgementPayload(uint rendered)
     {