Notify the view when a full reset replaces the buffer

resetToInitialState() rebuilds the buffer and then calls syncScrollArea()
so the view can recompute its scroll geometry, but that method is an empty
stub. On iOS contentSize/contentOffset are only recomputed by
TerminalView.updateScroller(), and none of its four callers fire on this
path: there is no buffer switch, no scrolled line, no keystroke and no
resize. The scroll view therefore keeps the geometry of a buffer that no
longer exists and renders blank until an unrelated layout pass corrects it.

Quitting a full-screen TUI with Ctrl+C reproduces it: the program emits RIS
while tearing down, and ensureCaretIsVisible() has already run at keypress
time, before the reset.

Notify bufferActivated instead of implementing syncScrollArea() itself:
five of its eight call sites are keypad-mode changes that do not touch the
buffer, and on iOS bufferActivated resets the scroll-follow state, so
routing those through it would pull a user who has scrolled back down to
the bottom.

Author: OwnDing

Sources/SwiftTerm/Terminal.swift

@@ -5578,6 +5578,14 @@ open class Terminal {
         cursorHidden = savedCursorHidden
         refresh (startRow: 0, endRow: rows-1)
         syncScrollArea ()
+        // A full reset replaces the buffer, so the view's scroll geometry — which
+        // is derived from `lines.count` and `yDisp` — is stale. `syncScrollArea()`
+        // is a no-op stub, and none of the other paths that recompute it fire
+        // here (no buffer switch, no scrolled line, no keystroke, no resize), so
+        // notify explicitly. Without this the view keeps the contentSize and
+        // contentOffset of a buffer that no longer exists and renders blank until
+        // some unrelated layout pass happens to correct it.
+        tdel?.bufferActivated (source: self)
     }
 
     // Support for:

Tests/SwiftTermTests/ResetScrollAreaTests.swift

@@ -0,0 +1,48 @@
+import Testing
+@testable import SwiftTerm
+
+/// A full reset (RIS, `ESC c`) replaces the buffer, so any view that derives its
+/// scroll geometry from `lines.count` / `yDisp` has to be told about it.
+/// `syncScrollArea()` is a no-op stub, and none of the other paths that make a
+/// view recompute that geometry run here — there is no buffer switch, no scrolled
+/// line, no keystroke and no resize — so `resetToInitialState()` notifies
+/// explicitly. Without that, a view keeps the contentSize/contentOffset of the
+/// buffer that was just discarded and renders blank.
+@Suite("Full reset scroll area")
+struct ResetScrollAreaTests {
+    @Test("RIS notifies the delegate that the buffer changed")
+    func fullResetNotifiesDelegate() {
+        let (terminal, delegate) = TerminalTestHarness.makeTerminal(cols: 80, rows: 24, scrollback: 500)
+
+        // Build up scrollback so the reset is a real change in buffer size.
+        for i in 0..<200 {
+            terminal.feed(text: "line \(i)\r\n")
+        }
+        #expect(terminal.buffer.lines.count > terminal.rows)
+
+        let before = delegate.bufferActivatedCount
+        terminal.feed(text: "\u{1b}c")
+
+        // The buffer really did shrink back to a single screen...
+        #expect(terminal.buffer.lines.count == terminal.rows)
+        #expect(terminal.buffer.yBase == 0)
+        #expect(terminal.buffer.yDisp == 0)
+        // ...and the delegate heard about it exactly once.
+        #expect(delegate.bufferActivatedCount == before + 1)
+    }
+
+    @Test("Keypad mode changes do not claim the buffer changed")
+    func keypadModeDoesNotNotify() {
+        let (terminal, delegate) = TerminalTestHarness.makeTerminal(cols: 80, rows: 24, scrollback: 500)
+
+        let before = delegate.bufferActivatedCount
+        terminal.feed(text: "\u{1b}=")   // application keypad
+        terminal.feed(text: "\u{1b}>")   // numeric keypad
+
+        // These also call syncScrollArea(), but they do not touch the buffer, so
+        // they must not be reported as a buffer activation: on iOS that resets
+        // the scroll-follow state and would yank a user who has scrolled back
+        // down to the bottom.
+        #expect(delegate.bufferActivatedCount == before)
+    }
+}

Tests/SwiftTermTests/TerminalTestHarness.swift

@@ -3,6 +3,7 @@ import Testing
 
 final class TerminalTestDelegate: TerminalDelegate {
     private(set) var sentData: [[UInt8]] = []
+    private(set) var bufferActivatedCount = 0
     var cellSizeInPixelsValue: (width: Int, height: Int)? = nil
 
     func showCursor(source: Terminal) {}
@@ -13,7 +14,7 @@ final class TerminalTestDelegate: TerminalDelegate {
     func sizeChanged(source: Terminal) {}
     func scrolled(source: Terminal, yDisp: Int) {}
     func linefeed(source: Terminal) {}
-    func bufferActivated(source: Terminal) {}
+    func bufferActivated(source: Terminal) { bufferActivatedCount += 1 }
     func bell(source: Terminal) {}
 
     func send(source: Terminal, data: ArraySlice<UInt8>) {