Land staged session/MCP/chrome work + sidebar clear-J fix

This batches the in-flight [Unreleased] block from CHANGELOG.md into a
single commit. Highlights:

- Real MCP protocol layer (initialize / tools/list / tools/call) so
  vendor MCP clients can complete the handshake against the per-PID
  socket. Legacy direct-dispatch preserved for the harness.
- New mcp_injection kinds — cli_override for codex, config_env for
  opencode — joining the existing env-var and config_file paths so
  patterm can slot into more agents without touching their real
  config or auth.
- Ctrl+A/D and Ctrl+W/S focus navigation across tabs and intra-tab
  process lists, recognised in legacy / kitty CSI u / xterm
  modifyOtherKeys encodings.
- Palette macros (sw / k / sp ) and reordering so open sessions
  surface above spawn-new entries.
- Two-row tab bar, sidebar/tabbar/status chrome cache, viewport-wipe
  on agent spawn, CR-terminated orchestrator injections, and split-
  Enter PTY writes so paste-detecting TUIs see Enter as a key event.

Also fixes the bug logged in TODO: claude's Ctrl+O tool-call expansion
emits CSI 0 J, which the viewport renderer was forwarding verbatim —
wiping the sidebar to the right of the cursor and leaving the chrome
cache convinced nothing had changed. CSI 0 J and CSI 1 J are now
translated into per-row ECH sequences clamped to the viewport, same
as CSI 2 J and CSI K already were.

Agent guides (CLAUDE.md / AGENTS.md) now spell out the
TODO->CHANGELOG workflow so completed items land in the changelog
rather than as ticked entries left behind in TODO.

internal/app/viewport_renderer.go

@@ -161,6 +161,10 @@ func (vr *viewportRenderer) emitCSI() {
 			return
 		}
 		switch n {
+		case 0:
+			vr.pending.WriteString(vr.clearViewportFromCursor())
+		case 1:
+			vr.pending.WriteString(vr.clearViewportToCursor())
 		case 2, 3:
 			vr.pending.WriteString(vr.clearViewport())
 		default:
@@ -203,6 +207,54 @@ func (vr *viewportRenderer) clearViewport() string {
 	return b.String()
 }
 
+// clearViewportFromCursor implements `CSI 0 J` clamped to the viewport.
+// Without clamping, the child's "clear to end of screen" would reach the
+// rightmost columns and erase the sidebar.
+func (vr *viewportRenderer) clearViewportFromCursor() string {
+	row, col := vr.row, vr.col
+	cols := int(vr.layout.childCols())
+	rows := int(vr.layout.childRows())
+	if row < 1 {
+		row = 1
+	}
+	if col < 1 {
+		col = 1
+	}
+	var b strings.Builder
+	b.WriteString("\x1b7")
+	if remaining := cols - col + 1; remaining > 0 {
+		fmt.Fprintf(&b, "\x1b[%dX", remaining)
+	}
+	for r := row + 1; r <= rows; r++ {
+		fmt.Fprintf(&b, "\x1b[%d;%dH\x1b[%dX",
+			int(vr.layout.mainTop)+r-1, int(vr.layout.mainLeft), cols)
+	}
+	b.WriteString("\x1b8")
+	return b.String()
+}
+
+// clearViewportToCursor implements `CSI 1 J` clamped to the viewport.
+func (vr *viewportRenderer) clearViewportToCursor() string {
+	row, col := vr.row, vr.col
+	cols := int(vr.layout.childCols())
+	if row < 1 {
+		row = 1
+	}
+	if col < 1 {
+		col = 1
+	}
+	var b strings.Builder
+	b.WriteString("\x1b7")
+	for r := 1; r < row; r++ {
+		fmt.Fprintf(&b, "\x1b[%d;%dH\x1b[%dX",
+			int(vr.layout.mainTop)+r-1, int(vr.layout.mainLeft), cols)
+	}
+	fmt.Fprintf(&b, "\x1b[%d;%dH\x1b[%dX",
+		int(vr.layout.mainTop)+row-1, int(vr.layout.mainLeft), col)
+	b.WriteString("\x1b8")
+	return b.String()
+}
+
 func (vr *viewportRenderer) clearLine(n int) string {
 	right := int(vr.layout.childCols())
 	if vr.col < 1 {