Fix mouse interactions in terminal.

README.md

@@ -113,7 +113,7 @@ Window.zig     sidebar + GtkStack of views, tab management, shortcuts
 View.zig       one tab's content: its panes, their layout, and drag handling
 Layout.zig     the split tree: nodes, rearranging, GtkPaned materialization
 Pane.zig       content plus its header, drag source, and drop target
-Terminal.zig   GtkDrawingArea: Cairo/Pango renderer + input handling
+Terminal.zig   GtkDrawingArea: Cairo/Pango renderer, keyboard, mouse, selection
 Browser.zig    WebKitWebView plus a nav/address bar and a find bar
 webkit.zig     hand-written bindings for the WebKitGTK calls we make
 Layouts.zig    saved tab templates: model, JSON on disk, {{substitution}}
@@ -403,6 +403,7 @@ in principle, but a terminal grid is small.
 | `Ctrl+Shift+W` | close the focused pane (closes the tab with its last one) |
 | `Ctrl+Shift+←/→/↑/↓` | move the focused pane within its view |
 | `Ctrl+Shift+V` | paste into a terminal (bracketed-paste aware, refuses unsafe pastes) |
+| `Ctrl+Shift+C` | copy the terminal selection |
 | `Ctrl+Shift+R` | rename the current tab (empty name = follow the terminal) |
 | `Ctrl+Shift+Z` | zoom the focused pane to fill the tab, and back |
 | `Ctrl+F` | find in the focused web page (web panes only — see [Find in page](#find-in-page)) |
@@ -418,6 +419,31 @@ competes with the content's own mouse handling.
 Both add-pane shortcuts are also buttons in every pane header, which is how you
 open a web view without remembering the chord.
 
+## The mouse in a terminal
+
+A terminal's pointer has two possible owners, and which one has it depends on
+what is running.
+
+Ordinarily it is the window's. Dragging selects text, double-click takes a
+word and triple-click a line, `Ctrl` while dragging selects a rectangle, and
+the wheel moves through the scrollback. Selecting fills the primary selection,
+so middle-click pastes what was last highlighted; `Ctrl+Shift+C` puts it on the
+clipboard proper.
+
+But a full-screen program can ask for the mouse itself (DEC modes 1000-1003),
+and from then on clicks, drags and wheel notches are encoded and handed
+straight to it. That is what makes a TUI's buttons clickable and what makes
+Claude Code scroll. While a program holds the pointer the cursor goes back to
+an arrow, as a reminder that a drag will not select anything. **Holding shift
+takes it back** for the length of that drag, so there is always a way to copy
+text out of a full-screen application.
+
+One case sits between the two. Pagers — `less`, `man`, anything built on them —
+run on the alternate screen, which has no scrollback for the wheel to move
+through, and most of them never ask for the mouse. There the wheel becomes
+arrow keys (DEC mode 1007), which is what those programs are waiting for
+anyway.
+
 ## Zoom
 
 A split that was the right shape for watching two things at once is usually the