Stop the terminal's Enter key dismissing the keyboard it was typed on

The first device run of ADR 0015 found the premise held and the field misconfigured
in a second way: the suggestion strip, autocorrect and predictive text were all
gone, and every Enter closed the keyboard. On a terminal that is every command, so
the phone asked for a tap between each one.

TerminalInputSurface had been left with Avalonia's default ReturnKeyType, and the
same OnCreateInputConnection that carries the inputType fix maps that default, on a
field that is not Multiline, to IME_ACTION_DONE:

    _ => options.Multiline ? 1073741824 : 6,   // 6 is IME_ACTION_DONE

Done means done. The keyboard performs the action and dismisses itself, which is
right for the text box the default was written for and wrong for a surface where
Enter is punctuation rather than submission.

TextInputReturnKeyType.Return is the member that maps to IME_ACTION_NONE — value 1,
so `returnKeyType - 1 => 0 => 1073741824` — leaving Enter a plain newline with no
action attached and no reason for the IME to hide.

◆ THE TRAP, WHICH IS THE ONE 11.10b ALREADY WARNED ABOUT FROM THE OTHER SIDE.

Multiline=true also reaches IME_ACTION_NONE, through that same default arm, and is
the obvious fix and the wrong one. It ORs TYPE_TEXT_FLAG_MULTI_LINE into InputType,
which moves it off 1 and silently fails the ShowSuggestions guard the whole ADR
turns on. Taking the obvious route to a working Enter would have handed the
suggestion strip back and looked like the premise had failed rather than like the
fix had. ReturnKeyType touches imeOptions only, which is why it is what is set.

Enter's byte was never the problem and is not what changed: IME_ACTION_DONE was
already synthesising KEYCODE_ENTER through AvaloniaInputConnection.PerformEditorAction,
so commands did run — the keyboard just left afterwards.

OnTextInput now also normalises line endings to CR. Belt and braces for the case
this change makes newly possible: a keyboard with no editor action attached may
commit "\n" as ordinary text rather than sending KEYCODE_ENTER, and a shell handed
LF for Enter looks like a shell that ignored the key. Normalising rather than
special-casing also stops a pasted "\r\n" running its line twice.

Check 11.10e is the regression test, and says in as many words not to fix a
recurrence with Multiline.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/manual-checks.md

@@ -1919,6 +1919,24 @@ could not pass *before* ADR 0015 and is not a regression test but a new capabili
 only to the accessory row's own keys, because everything typed went straight into the page and never passed
 the code that holds the latch.
 
+### 11.10e Enter runs the command and the keyboard stays where it is
+
+With a shell open and the software keyboard up, type `pwd` and press Enter. Then type another command.
+
+**Pass:** the command runs and **the keyboard is still up**, unmoved, ready for the next one. The Enter key
+reads as a return arrow rather than as `DONE` or a tick. Ten commands in a row cost ten Enters and no taps
+to bring the keyboard back.
+
+**Failure means:** `TextInputOptions.ReturnKeyType` is not `Return` on `TerminalInputSurface`, so Avalonia
+has mapped the field's default to `IME_ACTION_DONE` and the keyboard is doing exactly what Done means. This
+was the first defect the first device run found. **Do not fix it with `Multiline = true`** — that reaches
+the same `IME_ACTION_NONE` by a route that ORs `TYPE_TEXT_FLAG_MULTI_LINE` into `InputType`, which fails the
+`ShowSuggestions` guard and hands the suggestion strip back; check 11.10b would then start failing and the
+cause would look unrelated. See the correction in [ADR 0015](adr/0015-android-terminal-input.md).
+
+Worth pressing Enter on an empty prompt a few times too: each one should give a fresh prompt and nothing
+else. A doubled prompt per press means a line ending is arriving as both CR and LF.
+
 ### 11.11 Closing a connection and opening a new one both take you somewhere real
 
 Open a shell, close its tab, then open a different one from HOSTS.