fix(pi-tui): make debug logging robust on Windows

.changeset/fix-pi-tui-debug-redraw-log-dir.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/pi-tui": patch
+---
+
+Make the TUI's debug logging robust on Windows: the `PI_DEBUG_REDRAW` and `PI_TUI_DEBUG` diagnostics no longer crash the render loop on a filesystem error, and `PI_TUI_DEBUG` writes render dumps to the OS temp dir instead of a hardcoded `/tmp`.

packages/pi-tui/src/tui.ts

@@ -1353,7 +1353,13 @@ export class TUI extends Container {
 			if (!debugRedraw) return;
 			const logPath = path.join(os.homedir(), ".pi", "agent", "pi-debug.log");
 			const msg = `[${new Date().toISOString()}] fullRender: ${reason} (prev=${this.previousLines.length}, new=${newLines.length}, height=${height})\n`;
-			fs.appendFileSync(logPath, msg);
+
+			try {
+				fs.mkdirSync(path.dirname(logPath), { recursive: true });
+				fs.appendFileSync(logPath, msg);
+			} catch {
+				// never let debug logging break rendering
+			}
 		};
 
 		// First render - just output everything without clearing (assumes clean screen)
@@ -1566,8 +1572,7 @@ export class TUI extends Container {
 		buffer += "\x1b[?2026l"; // End synchronized output
 
 		if (process.env['PI_TUI_DEBUG'] === "1") {
-			const debugDir = "/tmp/tui";
-			fs.mkdirSync(debugDir, { recursive: true });
+			const debugDir = path.join(os.tmpdir(), "tui");
 			const debugPath = path.join(debugDir, `render-${Date.now()}-${Math.random().toString(36).slice(2)}.log`);
 			const debugData = [
 				`firstChanged: ${firstChanged}`,
@@ -1591,7 +1596,13 @@ export class TUI extends Container {
 				"=== buffer ===",
 				JSON.stringify(buffer),
 			].join("\n");
-			fs.writeFileSync(debugPath, debugData);
+
+			try {
+				fs.mkdirSync(debugDir, { recursive: true });
+				fs.writeFileSync(debugPath, debugData);
+			} catch {
+				//never let debug logging break rendering.
+			}
 		}
 
 		// Write entire buffer at once

packages/pi-tui/test/tui-render.test.ts

@@ -1,4 +1,7 @@
 import assert from "node:assert";
+import * as fs from "node:fs/promises";
+import * as os from "node:os";
+import * as path from "node:path";
 import { describe, it } from "node:test";
 import type { Terminal as XtermTerminalType } from "@xterm/headless";
 import { Image } from "../src/components/image.ts";
@@ -402,6 +405,75 @@ describe("TUI resize handling", () => {
 	});
 });
 
+describe("TUI debug logging", () => {
+	it("does not crash the render loop when the debug-redraw log directory is missing", async () => {
+		const fakeHome = await fs.mkdtemp(path.join(os.tmpdir(), "pi-tui-debug-redraw-"));
+		try {
+			// `fakeHome` exists but `fakeHome/.pi/agent` does not — this mirrors a
+			// fresh machine that has never written to ~/.pi/agent before.
+			await withEnv({ PI_DEBUG_REDRAW: "1", HOME: fakeHome, USERPROFILE: fakeHome }, async () => {
+				const terminal = new VirtualTerminal(40, 10);
+				const tui = new TUI(terminal);
+				const component = new TestComponent();
+				tui.addChild(component);
+
+				component.lines = ["Line 0", "Line 1"];
+				tui.start();
+				await terminal.waitForRender();
+
+				// A width change forces `logRedraw` to run, which previously threw
+				// ENOENT (missing parent directory) and crashed the whole TUI as an
+				// uncaughtException.
+				terminal.resize(60, 10);
+				await terminal.waitForRender();
+
+				const viewport = terminal.getViewport();
+				assert.ok(viewport[0]?.includes("Line 0"), "TUI keeps rendering after the debug log write");
+
+				tui.stop();
+			});
+
+			const logPath = path.join(fakeHome, ".pi", "agent", "pi-debug.log");
+			const contents = await fs.readFile(logPath, "utf8");
+			assert.ok(contents.includes("terminal width changed"), "the debug log should still be written");
+		} finally {
+			await fs.rm(fakeHome, { recursive: true, force: true });
+		}
+	});
+
+	it("writes PI_TUI_DEBUG render dumps into the OS temp dir, not a hardcoded /tmp", async () => {
+		const fakeTmp = await fs.mkdtemp(path.join(os.tmpdir(), "pi-tui-debug-render-"));
+		try {
+			await withEnv(
+				{ PI_TUI_DEBUG: "1", TMPDIR: fakeTmp, TEMP: fakeTmp, TMP: fakeTmp },
+				async () => {
+					const terminal = new VirtualTerminal(40, 10);
+					const tui = new TUI(terminal);
+					const component = new TestComponent();
+					tui.addChild(component);
+					component.lines = ["Line 0", "Line 1"];
+					tui.start();
+					await terminal.waitForRender();
+					component.lines = ["Line 0", "CHANGED"];
+					tui.requestRender();
+					await terminal.waitForRender();
+					const viewport = terminal.getViewport();
+					assert.ok(viewport[1]?.includes("CHANGED"), "TUI keeps rendering with PI_TUI_DEBUG on");
+					tui.stop();
+				},
+			);
+			const dumpDir = path.join(fakeTmp, "tui");
+			const files = await fs.readdir(dumpDir);
+			assert.ok(
+				files.some((name) => name.startsWith("render-")),
+				"a render dump should be written under the OS temp dir",
+			);
+		} finally {
+			await fs.rm(fakeTmp, { recursive: true, force: true });
+		}
+	});
+});
+
 describe("TUI content shrinkage", () => {
 	it("clears empty rows when content shrinks significantly", async () => {
 		const terminal = new VirtualTerminal(40, 10);