Fix viewport width issues in thinking selector and text rendering

Thinking selector fix:
- Replace hardcoded 50-character borders with DynamicBorder component
  that adjusts to viewport width
- Prevents crash when terminal is resized narrow

Text/Markdown rendering fixes:
- Fix Markdown wrapSingleLine to check if adding next character would
  exceed width BEFORE adding it (was checking AFTER, causing lines to
  be 1 character too long)
- Add word truncation in Text component for words longer than
  contentWidth (prevents long unbreakable words from exceeding width)

These fixes prevent "Rendered line exceeds terminal width" errors.

packages/coding-agent/src/tui/thinking-selector.ts

@@ -1,7 +1,16 @@
 import type { ThinkingLevel } from "@mariozechner/pi-agent";
-import { Container, type SelectItem, SelectList, Text } from "@mariozechner/pi-tui";
+import { type Component, Container, type SelectItem, SelectList } from "@mariozechner/pi-tui";
 import chalk from "chalk";
 
+/**
+ * Dynamic border component that adjusts to viewport width
+ */
+class DynamicBorder implements Component {
+	render(width: number): string[] {
+		return [chalk.blue("─".repeat(Math.max(1, width)))];
+	}
+}
+
 /**
  * Component that renders a thinking level selector with borders
  */
@@ -20,7 +29,7 @@ export class ThinkingSelectorComponent extends Container {
 		];
 
 		// Add top border
-		this.addChild(new Text(chalk.blue("─".repeat(50)), 0, 0));
+		this.addChild(new DynamicBorder());
 
 		// Create selector
 		this.selectList = new SelectList(thinkingLevels, 5);
@@ -42,7 +51,7 @@ export class ThinkingSelectorComponent extends Container {
 		this.addChild(this.selectList);
 
 		// Add bottom border
-		this.addChild(new Text(chalk.blue("─".repeat(50)), 0, 0));
+		this.addChild(new DynamicBorder());
 	}
 
 	getSelectList(): SelectList {

packages/tui/src/components/markdown.ts

@@ -404,7 +404,11 @@ export class Markdown implements Component {
 				}
 			} else {
 				// Regular character
-				if (currentLength >= width) {
+				const char = line[i];
+				const charWidth = visibleWidth(char);
+
+				// Check if adding this character would exceed width
+				if (currentLength + charWidth > width) {
 					// Need to wrap - close current line with reset if needed
 					if (activeAnsiCodes.length > 0) {
 						wrapped.push(currentLine + "\x1b[0m");
@@ -416,10 +420,9 @@ export class Markdown implements Component {
 					}
 					currentLength = 0;
 				}
-				const char = line[i];
+
 				currentLine += char;
-				// Count actual terminal column width, not string length
-				currentLength += visibleWidth(char);
+				currentLength += charWidth;
 				i++;
 			}
 		}

packages/tui/src/components/text.ts

@@ -84,13 +84,27 @@ export class Text implements Component {
 					const currentVisible = visibleWidth(currentLine);
 					const wordVisible = visibleWidth(word);
 
+					// If word is too long, truncate it
+					let finalWord = word;
+					if (wordVisible > contentWidth) {
+						// Truncate word to fit
+						let truncated = "";
+						for (const char of word) {
+							if (visibleWidth(truncated + char) > contentWidth) {
+								break;
+							}
+							truncated += char;
+						}
+						finalWord = truncated;
+					}
+
 					if (currentVisible === 0) {
-						currentLine = word;
-					} else if (currentVisible + 1 + wordVisible <= contentWidth) {
-						currentLine += " " + word;
+						currentLine = finalWord;
+					} else if (currentVisible + 1 + visibleWidth(finalWord) <= contentWidth) {
+						currentLine += " " + finalWord;
 					} else {
 						lines.push(currentLine);
-						currentLine = word;
+						currentLine = finalWord;
 					}
 				}