diff --git a/packages/coding-agent/src/tools/write.ts b/packages/coding-agent/src/tools/write.ts
index 4f474b2af..3df67ea04 100644
--- a/packages/coding-agent/src/tools/write.ts
+++ b/packages/coding-agent/src/tools/write.ts
@@ -70,6 +70,8 @@ export type WriteToolInput = z.infer<typeof writeSchema>;
 export interface WriteToolDetails {
 	diagnostics?: FileDiagnosticsResult;
 	meta?: OutputMeta;
+	/** Set when the file was auto-chmod'd because content begins with a `#!` shebang. */
+	madeExecutable?: boolean;
 }
 
 /**
@@ -103,6 +105,28 @@ function appendNoteToResult(result: AgentToolResult<WriteToolDetails>, note: str
 	}
 }
 
+/**
+ * If `content` begins with a `#!` shebang, ensure the file is executable.
+ *
+ * Mirrors `chmod a+x` (adds user/group/other execute bits to existing mode).
+ * Errors are swallowed: chmod failure (e.g. Windows ACL, read-only mount)
+ * MUST NOT fail an otherwise successful write. Returns whether the mode
+ * actually changed so the caller can surface a note.
+ */
+async function maybeMarkExecutableForShebang(absolutePath: string, content: string): Promise<boolean> {
+	if (!content.startsWith("#!")) return false;
+	try {
+		const stat = await fs.stat(absolutePath);
+		const currentMode = stat.mode & 0o7777;
+		const newMode = currentMode | 0o111;
+		if (newMode === currentMode) return false;
+		await fs.chmod(absolutePath, newMode);
+		return true;
+	} catch {
+		return false;
+	}
+}
+
 // ═══════════════════════════════════════════════════════════════════════════
 // Tool Class
 // ═══════════════════════════════════════════════════════════════════════════
@@ -772,6 +796,7 @@ export class WriteTool implements AgentTool<typeof writeSchema, WriteToolDetails
 
 			const diagnostics = await this.#writethrough(absolutePath, cleanContent, signal, undefined, batchRequest);
 			invalidateFsScanAfterWrite(absolutePath);
+			const madeExecutable = await maybeMarkExecutableForShebang(absolutePath, cleanContent);
 
 			const displayPath = formatPathRelativeToCwd(absolutePath, this.session.cwd);
 			let resultText = `Successfully wrote ${cleanContent.length} bytes to ${displayPath}`;
@@ -781,7 +806,7 @@ export class WriteTool implements AgentTool<typeof writeSchema, WriteToolDetails
 			if (!diagnostics) {
 				return {
 					content: [{ type: "text", text: resultText }],
-					details: {},
+					details: { madeExecutable: madeExecutable || undefined },
 				};
 			}
 
@@ -789,6 +814,7 @@ export class WriteTool implements AgentTool<typeof writeSchema, WriteToolDetails
 				content: [{ type: "text", text: resultText }],
 				details: {
 					diagnostics,
+					madeExecutable: madeExecutable || undefined,
 					meta: outputMeta()
 						.diagnostics(diagnostics.summary, diagnostics.messages ?? [])
 						.get(),
@@ -915,13 +941,16 @@ export const writeToolRenderer = {
 		const pathDisplay = filePath ? uiTheme.fg("accent", filePath) : uiTheme.fg("toolOutput", "…");
 		const lineCount = countLines(fileContent);
 		const lineSuffix = formatLineCountSuffix(lineCount, uiTheme);
+		const execSuffix = result.details?.madeExecutable
+			? `${uiTheme.fg("dim", " · ")}${uiTheme.fg("success", "made executable!")}`
+			: "";
 
 		// Build header with status icon
 		const header = renderStatusLine(
 			{
 				icon: "success",
 				title: "Write",
-				description: `${langIcon} ${pathDisplay}${lineSuffix}`,
+				description: `${langIcon} ${pathDisplay}${lineSuffix}${execSuffix}`,
 			},
 			uiTheme,
 		);
diff --git a/packages/coding-agent/test/write-shebang-chmod.test.ts b/packages/coding-agent/test/write-shebang-chmod.test.ts
new file mode 100644
index 000000000..2a58962bf
--- /dev/null
+++ b/packages/coding-agent/test/write-shebang-chmod.test.ts
@@ -0,0 +1,95 @@
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from "bun:test";
+import * as fs from "node:fs/promises";
+import * as os from "node:os";
+import * as path from "node:path";
+import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
+import type { ToolSession } from "@oh-my-pi/pi-coding-agent/tools";
+import { WriteTool } from "@oh-my-pi/pi-coding-agent/tools/write";
+
+function createSession(cwd: string): ToolSession {
+	return {
+		cwd,
+		hasUI: false,
+		getSessionFile: () => path.join(cwd, "session.jsonl"),
+		getSessionSpawns: () => "*",
+		getArtifactsDir: () => path.join(cwd, "artifacts"),
+		allocateOutputArtifact: async () => ({ id: "artifact-1", path: path.join(cwd, "artifact-1.log") }),
+		settings: Settings.isolated(),
+		enableLsp: false,
+	};
+}
+
+function resultText(result: { content: { type: string; text?: string }[] }): string {
+	return result.content
+		.filter((b): b is { type: "text"; text: string } => b.type === "text" && typeof b.text === "string")
+		.map(b => b.text)
+		.join("\n");
+}
+
+function details(result: { details?: { madeExecutable?: boolean } }): { madeExecutable?: boolean } {
+	return result.details ?? {};
+}
+
+describe("write tool shebang chmod", () => {
+	let tmpDir: string;
+
+	beforeAll(async () => {
+		await Settings.init({ inMemory: true });
+	});
+
+	beforeEach(async () => {
+		tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), "write-shebang-test-"));
+	});
+
+	afterEach(async () => {
+		await fs.rm(tmpDir, { recursive: true, force: true });
+	});
+
+	it("marks files starting with #! as executable and flags the result", async () => {
+		const filePath = path.join(tmpDir, "run.sh");
+		const tool = new WriteTool(createSession(tmpDir));
+
+		const result = await tool.execute("call-1", {
+			path: filePath,
+			content: "#!/bin/sh\necho hi\n",
+		});
+
+		const stat = await fs.stat(filePath);
+		// All three execute bits flipped on (chmod a+x semantics).
+		expect(stat.mode & 0o111).toBe(0o111);
+		// Notice surfaces on details, not in the model-facing text.
+		expect(details(result).madeExecutable).toBe(true);
+		expect(resultText(result)).not.toContain("executable");
+	});
+
+	it("does not chmod files without a shebang", async () => {
+		const filePath = path.join(tmpDir, "data.txt");
+		const tool = new WriteTool(createSession(tmpDir));
+
+		const result = await tool.execute("call-2", {
+			path: filePath,
+			content: "no shebang here\n",
+		});
+
+		const stat = await fs.stat(filePath);
+		expect(stat.mode & 0o111).toBe(0);
+		expect(details(result).madeExecutable).toBeUndefined();
+	});
+
+	it("does not re-flag when file is already executable", async () => {
+		const filePath = path.join(tmpDir, "preexec.sh");
+		await fs.writeFile(filePath, "#!/bin/sh\nold\n");
+		await fs.chmod(filePath, 0o755);
+
+		const tool = new WriteTool(createSession(tmpDir));
+		const result = await tool.execute("call-3", {
+			path: filePath,
+			content: "#!/usr/bin/env python3\nprint('hi')\n",
+		});
+
+		const stat = await fs.stat(filePath);
+		expect(stat.mode & 0o111).toBe(0o111);
+		// Mode didn't change, so no flag.
+		expect(details(result).madeExecutable).toBeUndefined();
+	});
+});