fix(copilot): keep a drag a local selection so Auto Copy works

Copilot's TUI turns mouse tracking on itself. Under `strip-mux-only` those DECSETs reached
xterm, which then reported a plain drag to the TUI instead of selecting (only Shift+drag
selected), so Auto Copy and copy-on-select did nothing. This is the failure opencode had and
`strip-mux-and-mouse` was added for: the DECSETs are stripped, a drag is a local selection and
clicks still reach the CLI through the browser's hand-encoded tap (`cliMouseTracking`).

Stripping them also stops xterm from encoding the wheel for the CLI, so
`_shouldForwardWheelToApp` now forwards it as SGR reports while Copilot is tracking the mouse
(the same bytes xterm sent natively, which is what scrolling was verified against). Shift+wheel
stays on local scrollback and a stale flag falls back to PageUp/PageDown.

Tests: the strip flavor for copilot (stripped DECSETs, 3J kept, cliMouseTracking, direct-PTY
untouched) and the wheel gate (forwards while tracking, no other non-claude mode changes).

src/config/cli-registry/stock.ts

@@ -1749,7 +1749,13 @@ const COPILOT: CliEntry = {
   },
   capabilities: {
     ...agentDefaults(),
-    altScreen: 'strip-mux-only',
+    // A full-screen TUI that turns mouse tracking on itself (measured on 1.0.94: alt screen,
+    // mouse reporting on). Kept, xterm reports a plain drag to the TUI instead of selecting, so
+    // Auto Copy and "mark text, copy on select" silently do nothing; stripped, a drag is a local
+    // selection and clicks still reach the CLI through the browser's hand-encoded tap
+    // (`cliMouseTracking`). Same shape and reason as opencode. The wheel keeps working because
+    // `_shouldForwardWheelToApp` forwards it as SGR reports while the CLI is tracking.
+    altScreen: 'strip-mux-and-mouse',
     echo: { policy: 'buffer', anchor: { kind: 'cursor' } },
     // The composer row is a `❯` between two rules, and the submitted prompt is echoed as
     // ` ❯ <text>  <time>` above it. While a turn runs the footer's left end reads

src/config/cli-registry/types.ts

@@ -525,7 +525,7 @@ export interface CliCapabilities {
    *   own mouse support must work in the pane (htop/vim in a shell).
    *
    * Stock CLIs: `strip-full` = claude, codex, gemini (Ink TUIs); `strip-mux-and-mouse` =
-   * opencode (a full-screen TUI that enables tracking itself); `strip-mux-only` =
+   * opencode and copilot (full-screen TUIs that enable tracking themselves); `strip-mux-only` =
    * antigravity, grok, deepseek, omp; `preserve` = shell, pi.
    *
    * A fourth combination is the point to split this into flags; three is still cheaper

src/web/public/terminal-ui.js

@@ -5852,6 +5852,12 @@ Object.assign(CodemanApp.prototype, {
     if (mode && mode !== 'none') return false;
     const session = this.sessions?.get(target.sessionId || this.activeSessionId);
     const sessionMode = session?.mode || 'claude';
+    // GitHub Copilot CLI scrolls its own transcript on SGR wheel reports (checked with xterm
+    // encoding them natively). Its mouse DECSETs are stripped server-side so a drag selects
+    // locally (strip-mux-and-mouse), which also means xterm no longer encodes the wheel: send the
+    // same reports by hand, but only while the CLI is actually tracking the mouse. Not gated on a
+    // version; a stale-false flag falls through to the PageUp/PageDown fallback like claude's.
+    if (sessionMode === 'copilot') return session?.cliMouseTracking === true;
     if (sessionMode !== 'claude') return false;
     if (!this._cliVersionAtLeast(session?.cliVersion, '2.1.187')) return false;
     // Only while Claude is actually listening for the mouse. In its default