fix(tui): clamp editor height and overlays on small terminals

Two bounded TUI overlap fixes:

- Editor max-height (coding-agent): the [6,18] clamp's floor of 6 exceeded
  available space on terminals <=18 rows, letting the editor crowd the
  transcript/status. Extracted a pure computeEditorMaxHeight(rows) with an
  EDITOR_MIN_CHROME_ROWS=4 upper bound; identical for rows >=18.
- Overlay overflow (tui): #resolveOverlayLayout left maxHeight undefined when
  the option was unset, so a tall overlay's bottom rows were dropped
  off-screen. maxHeight now defaults to availHeight so every overlay is
  sliced to fit and re-clamps on resize.

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed the editor input box claiming a disproportionate share of small terminals (<=18 rows): the editor max-height floor (6 rows) ignored the available space. The height now yields to terminal size (`EDITOR_MIN_CHROME_ROWS`), always reserving rows for the transcript and status line.
+
 ## [15.12.5] - 2026-06-13
 ### Changed
 

packages/coding-agent/src/modes/interactive-mode.ts

@@ -210,6 +210,14 @@ const EDITOR_MAX_HEIGHT_MIN = 6;
 const EDITOR_MAX_HEIGHT_MAX = 18;
 const EDITOR_RESERVED_ROWS = 12;
 const EDITOR_FALLBACK_ROWS = 24;
+const EDITOR_MIN_CHROME_ROWS = 4; // rows reserved for transcript + status + chrome on tiny terms
+
+export function computeEditorMaxHeight(terminalRows: number): number {
+	const rows = Number.isFinite(terminalRows) && terminalRows > 0 ? terminalRows : EDITOR_FALLBACK_ROWS;
+	const desired = Math.max(EDITOR_MAX_HEIGHT_MIN, Math.min(EDITOR_MAX_HEIGHT_MAX, rows - EDITOR_RESERVED_ROWS));
+	// Never let the editor crowd out the rest of the UI on small terminals.
+	return Math.max(1, Math.min(desired, rows - EDITOR_MIN_CHROME_ROWS));
+}
 
 const HUD_NOTE_SUP_DIGITS: Record<string, string> = {
 	"0": "\u2070",
@@ -1156,10 +1164,7 @@ export class InteractiveMode implements InteractiveModeContext {
 	}
 
 	#computeEditorMaxHeight(): number {
-		const rows = this.ui.terminal.rows;
-		const terminalRows = Number.isFinite(rows) && rows > 0 ? rows : EDITOR_FALLBACK_ROWS;
-		const maxHeight = terminalRows - EDITOR_RESERVED_ROWS;
-		return Math.max(EDITOR_MAX_HEIGHT_MIN, Math.min(EDITOR_MAX_HEIGHT_MAX, maxHeight));
+		return computeEditorMaxHeight(this.ui.terminal.rows);
 	}
 
 	#syncEditorMaxHeight(): void {

packages/coding-agent/test/editor-max-height.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from "bun:test";
+import { computeEditorMaxHeight } from "@oh-my-pi/pi-coding-agent/modes/interactive-mode";
+
+describe("computeEditorMaxHeight", () => {
+	it("caps the editor while preserving chrome rows on small terminals", () => {
+		expect(computeEditorMaxHeight(30)).toBe(18);
+		expect(computeEditorMaxHeight(18)).toBe(6);
+		expect(computeEditorMaxHeight(8)).toBe(4);
+		expect(computeEditorMaxHeight(5)).toBe(1);
+		expect(computeEditorMaxHeight(Number.NaN)).toBe(12);
+		expect(computeEditorMaxHeight(0)).toBe(12);
+
+		for (let rows = 5; rows <= 18; rows += 1) {
+			expect(rows - computeEditorMaxHeight(rows)).toBeGreaterThanOrEqual(4);
+		}
+	});
+});

packages/tui/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed overlays without an explicit `maxHeight` dropping their bottom rows off-screen when taller than the terminal: `#resolveOverlayLayout` now defaults the height cap to the available rows, so a tall overlay is sliced to fit (and re-clamps on resize) instead of overflowing the visible region.
+
 ## [15.12.5] - 2026-06-13
 ### Added
 

packages/tui/src/tui.ts

@@ -1902,11 +1902,8 @@ export class TUI extends Container {
 		width = Math.max(1, Math.min(width, availWidth));
 
 		// === Resolve maxHeight ===
-		let maxHeight = parseSizeValue(opt.maxHeight, termHeight);
-		// Clamp to available space
-		if (maxHeight !== undefined) {
-			maxHeight = Math.max(1, Math.min(maxHeight, availHeight));
-		}
+		let maxHeight = parseSizeValue(opt.maxHeight, termHeight) ?? availHeight;
+		maxHeight = Math.max(1, Math.min(maxHeight, availHeight));
 
 		// Effective overlay height (may be clamped by maxHeight)
 		const effectiveHeight = maxHeight !== undefined ? Math.min(overlayHeight, maxHeight) : overlayHeight;

packages/tui/test/overlay-scroll.test.ts

@@ -140,6 +140,49 @@ describe("TUI overlays", () => {
 		expect(term.getScrollBuffer().length).toBeLessThan(200);
 	});
 
+	it("clamps tall overlays without an explicit maxHeight to the available rows", async () => {
+		const term = new VirtualTerminal(80, 24);
+		const tui = new TUI(term);
+
+		tui.addChild(new LineComponent("base-", 3));
+
+		tui.start();
+		await flushRender(term);
+
+		// A bottom margin reserves rows the overlay must NOT paint into. The overlay
+		// has no explicit maxHeight, so before the fix it rendered all 40 lines and
+		// the compositor only skipped rows past the terminal edge — ov-0..ov-(rows-1)
+		// were painted, including the reserved bottom band. The maxHeight=availHeight
+		// default slices the overlay to availHeight = rows - marginBottom.
+		const marginBottom = 6;
+		tui.showOverlay(new LineComponent("ov-", 40), { anchor: "top-center", margin: { bottom: marginBottom } });
+		await flushRender(term);
+
+		const maxVisibleOverlayIndex = (): number => {
+			let max = -1;
+			for (const line of term.getViewport()) {
+				const match = line.trim().match(/^ov-(\d+)$/);
+				if (!match) continue;
+				max = Math.max(max, Number.parseInt(match[1], 10));
+			}
+			return max;
+		};
+
+		// availHeight = 24 - 6 = 18 → overlay sliced to ov-0..ov-17, nothing in the
+		// reserved bottom 6 rows. The old unclamped behavior surfaced ov-18..ov-23.
+		expect(maxVisibleOverlayIndex()).toBeGreaterThanOrEqual(0);
+		expect(maxVisibleOverlayIndex()).toBeLessThan(24 - marginBottom);
+
+		term.resize(80, 10);
+		await settleResize(term);
+
+		// availHeight = 10 - 6 = 4 → overlay re-clamped to ov-0..ov-3.
+		expect(maxVisibleOverlayIndex()).toBeGreaterThanOrEqual(0);
+		expect(maxVisibleOverlayIndex()).toBeLessThan(10 - marginBottom);
+
+		tui.stop();
+	});
+
 	it("clears stale viewport content on launch", async () => {
 		const term = new VirtualTerminal(40, 4);
 		term.write("shell-0\r\nshell-1\r\nshell-2\r\nshell-3\r\nshell-4\r\n");