diff --git a/packages/snapcompact/src/prompts/snapcompact-summary.md b/packages/snapcompact/src/prompts/snapcompact-summary.md
index 397786c16..286ee0c94 100644
--- a/packages/snapcompact/src/prompts/snapcompact-summary.md
+++ b/packages/snapcompact/src/prompts/snapcompact-summary.md
@@ -15,10 +15,10 @@ Reading HISTORY:
 {{/if}}{{/if}}{{#if includedPreviousSummary}}- HISTORY opens with a condensed digest of still-older context that predates the archived turns.
 {{/if}}{{#if truncatedChars}}- About {{truncatedChars}} characters of older middle history were dropped to fit the archive budget.
 {{/if}}- When an exact earlier detail matters and a section reads unclearly, re-derive it from the workspace (re-read files, re-run commands) rather than guessing.
-{{#if files}}
-FILES
+
+{{#if files}}FILES
 ===================
 {{files}}
-{{/if}}
-HISTORY
+
+{{/if}}HISTORY
 ===================
diff --git a/packages/tui/CHANGELOG.md b/packages/tui/CHANGELOG.md
index 317ce747b..7625b97fe 100644
--- a/packages/tui/CHANGELOG.md
+++ b/packages/tui/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- `Box` now accepts an optional `border` (box-drawing glyphs + colorizer) and exposes `setBorder()`, drawing a colored outline around its padded/background content. The border is automatically dropped at widths too narrow to frame so a bordered box never overflows its given width.
+
 ## [16.0.11] - 2026-06-19
 
 ### Breaking Changes
diff --git a/packages/tui/src/components/box.ts b/packages/tui/src/components/box.ts
index 2959147a4..1ba1c7212 100644
--- a/packages/tui/src/components/box.ts
+++ b/packages/tui/src/components/box.ts
@@ -4,10 +4,24 @@ import { applyBackgroundToLine, getPaddingX, padding, visibleWidth } from "../ut
 type Cache = {
 	width: number;
 	bgSample: string | undefined;
+	borderSample: string | undefined;
 	childLines: (readonly string[])[];
 	result: string[];
 };
 
+/** Box-drawing glyphs plus an optional colorizer for an outline drawn around a {@link Box}. */
+export interface BoxBorder {
+	chars: {
+		topLeft: string;
+		topRight: string;
+		bottomLeft: string;
+		bottomRight: string;
+		horizontal: string;
+		vertical: string;
+	};
+	color?: (text: string) => string;
+}
+
 /**
  * Box component - a container that applies padding and background to all children
  */
@@ -16,6 +30,7 @@ export class Box implements Component {
 	#paddingX: number;
 	#paddingY: number;
 	#bgFn?: (text: string) => string;
+	#border?: BoxBorder;
 
 	#ignoreTight = false;
 
@@ -28,10 +43,11 @@ export class Box implements Component {
 	// Cache for rendered output
 	#cached?: Cache;
 
-	constructor(paddingX = 1, paddingY = 1, bgFn?: (text: string) => string) {
+	constructor(paddingX = 1, paddingY = 1, bgFn?: (text: string) => string, border?: BoxBorder) {
 		this.#paddingX = paddingX;
 		this.#paddingY = paddingY;
 		this.#bgFn = bgFn;
+		this.#border = border;
 	}
 
 	addChild(component: Component): void {
@@ -72,6 +88,11 @@ export class Box implements Component {
 		// Don't invalidate here - we'll detect bgFn changes by sampling output
 	}
 
+	setBorder(border?: BoxBorder): void {
+		this.#border = border;
+		this.#invalidateCache();
+	}
+
 	#invalidateCache(): void {
 		this.#cached = undefined;
 	}
@@ -87,10 +108,18 @@ export class Box implements Component {
 		const children = this.children;
 		const count = children.length;
 		const paddingX = this.#ignoreTight ? this.#paddingX : getPaddingX(this.#paddingX);
-		const contentWidth = Math.max(1, width - paddingX * 2);
-		// bgFn output can change without the function reference changing (theme
-		// mutation); sample it so a silent palette swap still misses the cache.
+		// A border eats one column on each side; skip it unless the interior can still
+		// hold the horizontal padding plus at least one content column, so a bordered
+		// Box never overflows the width it was given.
+		const border = this.#border && width - 2 >= paddingX * 2 + 1 ? this.#border : undefined;
+		const innerWidth = border ? width - 2 : width;
+		const contentWidth = Math.max(1, innerWidth - paddingX * 2);
+		// bgFn / border output can change without the function reference changing
+		// (theme mutation); sample both so a silent palette swap still misses the cache.
 		const bgSample = this.#bgFn ? this.#bgFn("test") : undefined;
+		const borderSample = border
+			? `${border.color ? border.color("|") : "|"}${border.chars.topLeft}${border.chars.vertical}`
+			: undefined;
 
 		// Render every child every frame (renders may carry side effects); the
 		// memo only skips re-deriving the padded/background rows. Per the
@@ -101,6 +130,7 @@ export class Box implements Component {
 			cached !== undefined &&
 			cached.width === width &&
 			cached.bgSample === bgSample &&
+			cached.borderSample === borderSample &&
 			cached.childLines.length === count;
 		const childLines: (readonly string[])[] = new Array(count);
 		let contentRows = 0;
@@ -115,23 +145,39 @@ export class Box implements Component {
 		const result: string[] = [];
 		if (contentRows > 0) {
 			const leftPad = padding(paddingX);
+			const interior: string[] = [];
 			// Top padding
 			for (let i = 0; i < this.#paddingY; i++) {
-				result.push(this.#applyBg("", width));
+				interior.push(this.#applyBg("", innerWidth));
 			}
 			// Content
 			for (const lines of childLines) {
 				for (const line of lines) {
-					result.push(this.#applyBg(leftPad + line, width));
+					interior.push(this.#applyBg(leftPad + line, innerWidth));
 				}
 			}
 			// Bottom padding
 			for (let i = 0; i < this.#paddingY; i++) {
-				result.push(this.#applyBg("", width));
+				interior.push(this.#applyBg("", innerWidth));
+			}
+
+			if (border) {
+				const paint = border.color ?? (s => s);
+				const rule = border.chars.horizontal.repeat(Math.max(0, innerWidth));
+				const side = paint(border.chars.vertical);
+				result.push(paint(border.chars.topLeft + rule + border.chars.topRight));
+				for (const row of interior) {
+					result.push(side + row + side);
+				}
+				result.push(paint(border.chars.bottomLeft + rule + border.chars.bottomRight));
+			} else {
+				for (const row of interior) {
+					result.push(row);
+				}
 			}
 		}
 
-		this.#cached = { width, bgSample, childLines, result };
+		this.#cached = { width, bgSample, borderSample, childLines, result };
 		return result;
 	}
 
diff --git a/packages/tui/test/box-border.test.ts b/packages/tui/test/box-border.test.ts
new file mode 100644
index 000000000..4ee0f487b
--- /dev/null
+++ b/packages/tui/test/box-border.test.ts
@@ -0,0 +1,73 @@
+import { describe, expect, it } from "bun:test";
+import { Box, type BoxBorder, Text } from "@oh-my-pi/pi-tui";
+
+const CHARS: BoxBorder["chars"] = {
+	topLeft: "+",
+	topRight: "+",
+	bottomLeft: "+",
+	bottomRight: "+",
+	horizontal: "-",
+	vertical: "|",
+};
+
+function borderedBox(border?: Partial<BoxBorder>): Box {
+	// paddingY 0 keeps the row count predictable; ignoreTight pins paddingX to exactly 1.
+	// Real SGR escapes so Bun.stripANSI removes both bg and border color before width checks.
+	const box = new Box(1, 0, t => `\x1b[48;5;236m${t}\x1b[49m`, { chars: CHARS, color: t => `\x1b[31m${t}\x1b[39m`, ...border });
+	box.setIgnoreTight(true);
+	box.addChild(new Text("hi", 0, 0));
+	return box;
+}
+
+const widths = (rows: readonly string[]): number[] => rows.map(r => Bun.stringWidth(Bun.stripANSI(r)));
+const plain = (rows: readonly string[]): string[] => rows.map(r => Bun.stripANSI(r));
+
+describe("Box border", () => {
+	it("frames content without exceeding the given width", () => {
+		const rows = borderedBox().render(20);
+		// top rule + single content row + bottom rule
+		expect(rows.length).toBe(3);
+		for (const w of widths(rows)) expect(w).toBe(20);
+
+		const flat = plain(rows);
+		expect(flat[0]).toBe(`+${"-".repeat(18)}+`);
+		expect(flat[2]).toBe(`+${"-".repeat(18)}+`);
+		// Interior rows are wrapped by the vertical glyph on both edges.
+		expect(flat[1]!.startsWith("|")).toBe(true);
+		expect(flat[1]!.endsWith("|")).toBe(true);
+		expect(flat[1]).toContain("hi");
+	});
+
+	it("paints border glyphs with the supplied colorizer", () => {
+		const rows = borderedBox().render(20);
+		// The top rule is emitted through the color fn (red SGR), the interior is not.
+		expect(rows[0]).toContain("\x1b[31m");
+	});
+
+	it("recomputes width when the border is toggled off", () => {
+		const box = borderedBox();
+		expect(widths(box.render(20))).toEqual([20, 20, 20]);
+
+		box.setBorder(undefined);
+		const rows = box.render(20);
+		// No border rows now; the single content row fills the full width.
+		expect(rows.length).toBe(1);
+		expect(Bun.stringWidth(Bun.stripANSI(rows[0]!))).toBe(20);
+		expect(Bun.stripANSI(rows[0]!)).not.toContain("+");
+	});
+
+	it("frames at the boundary width without overflowing", () => {
+		// paddingX 1 → the border needs width >= 5 (2 borders + 2 padding + 1 content col).
+		const rows = borderedBox().render(5);
+		for (const w of widths(rows)) expect(w).toBe(5);
+		expect(plain(rows)[0]).toBe(`+${"-".repeat(3)}+`);
+	});
+
+	it("drops the border when the interior can't fit padding + content", () => {
+		for (const width of [3, 4]) {
+			const rows = borderedBox().render(width);
+			for (const w of widths(rows)) expect(w).toBeLessThanOrEqual(width);
+			for (const line of plain(rows)) expect(line).not.toContain("+");
+		}
+	});
+});