diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index bba3a028c..f2ea1dd3a 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `debug` launch/attach failures so `configurationDone` no longer masks the underlying DAP launch error, early stop-outcome watchers cannot emit unhandled rejections, and directory-valued launch programs are rejected before adapter selection. ([#1187](https://github.com/can1357/oh-my-pi/issues/1187))
+
 ## [15.1.6] - 2026-05-19
 
 ### Fixed
diff --git a/packages/coding-agent/src/dap/session.ts b/packages/coding-agent/src/dap/session.ts
index 29c389128..400ab5c1b 100644
--- a/packages/coding-agent/src/dap/session.ts
+++ b/packages/coding-agent/src/dap/session.ts
@@ -105,6 +105,41 @@ function toErrorMessage(value: unknown): string {
 	return String(value);
 }
 
+interface DapStartRequestFailure {
+	rejected: boolean;
+	error?: unknown;
+}
+
+function trackDapStartRequest<T>(promise: Promise<T>, failure: DapStartRequestFailure): Promise<T> {
+	return promise.catch(error => {
+		failure.rejected = true;
+		failure.error = error;
+		throw error;
+	});
+}
+
+function combineDapStartErrors(command: "launch" | "attach", startError: unknown, configurationError: unknown): Error {
+	const startMessage = toErrorMessage(startError);
+	const configurationMessage = toErrorMessage(configurationError);
+	if (startMessage === configurationMessage) {
+		return startError instanceof Error ? startError : new Error(startMessage);
+	}
+	return new Error(
+		`DAP ${command} failed: ${startMessage}\nDAP configurationDone also failed: ${configurationMessage}`,
+	);
+}
+
+async function throwPreferredDapStartError(
+	command: "launch" | "attach",
+	startFailure: DapStartRequestFailure,
+	configurationError: unknown,
+): Promise<never> {
+	await Promise.resolve();
+	if (startFailure.rejected) {
+		throw combineDapStartErrors(command, startFailure.error, configurationError);
+	}
+	throw configurationError;
+}
 function normalizePath(filePath: string): string {
 	return path.resolve(filePath);
 }
@@ -209,12 +244,20 @@ export class DapSessionManager {
 			// DAP spec: many adapters do not respond to launch until after
 			// configurationDone. Fire launch, complete the config handshake,
 			// then await the launch response.
-			const launchPromise = client.sendRequest("launch", launchArguments, signal, timeoutMs);
+			const launchFailure: DapStartRequestFailure = { rejected: false };
+			const launchPromise = trackDapStartRequest(
+				client.sendRequest("launch", launchArguments, signal, timeoutMs),
+				launchFailure,
+			);
 			// Mark handled so a fast error response doesn't become an unhandled
 			// rejection while we await the config handshake. The actual error
 			// still propagates when we await launchPromise below.
 			launchPromise.catch(() => {});
-			await this.#completeConfigurationHandshake(session, signal, timeoutMs);
+			try {
+				await this.#completeConfigurationHandshake(session, signal, timeoutMs);
+			} catch (error) {
+				await throwPreferredDapStartError("launch", launchFailure, error);
+			}
 			await launchPromise;
 			// Try to capture initial stopped state (e.g. stopOnEntry).
 			// Timeout is acceptable — the program may simply be running.
@@ -262,9 +305,17 @@ export class DapSessionManager {
 				signal,
 				Math.min(timeoutMs, STOP_CAPTURE_TIMEOUT_MS),
 			);
-			const attachPromise = client.sendRequest("attach", attachArguments, signal, timeoutMs);
+			const attachFailure: DapStartRequestFailure = { rejected: false };
+			const attachPromise = trackDapStartRequest(
+				client.sendRequest("attach", attachArguments, signal, timeoutMs),
+				attachFailure,
+			);
 			attachPromise.catch(() => {});
-			await this.#completeConfigurationHandshake(session, signal, timeoutMs);
+			try {
+				await this.#completeConfigurationHandshake(session, signal, timeoutMs);
+			} catch (error) {
+				await throwPreferredDapStartError("attach", attachFailure, error);
+			}
 			await attachPromise;
 			try {
 				await untilAborted(signal, initialStopPromise);
@@ -1085,7 +1136,9 @@ export class DapSessionManager {
 		for (const p of promises) {
 			p.catch(() => {});
 		}
-		return Promise.race(promises);
+		const outcome = Promise.race(promises);
+		outcome.catch(() => {});
+		return outcome;
 	}
 
 	/**
diff --git a/packages/coding-agent/src/prompts/tools/debug.md b/packages/coding-agent/src/prompts/tools/debug.md
index f9abcb226..9817f97c7 100644
--- a/packages/coding-agent/src/prompts/tools/debug.md
+++ b/packages/coding-agent/src/prompts/tools/debug.md
@@ -4,6 +4,7 @@ Use for launching or attaching debuggers, setting breakpoints, stepping through
 <instruction>
 - Prefer over bash for program state, breakpoints, stepping, thread inspection, or interrupting a running process.
 - `action: "launch"` starts a session; `program` is required, `adapter` optional (auto-selected from target path and workspace).
+  For Python, set `adapter: "debugpy"` and `program` to the target `.py` file; put interpreter/script flags in `args`.
 - `action: "attach"` connects to an existing process: `pid` for local attach, `port` for remote attach (where the adapter supports it), `adapter` to force a specific debugger.
 - **Breakpoints**: `set_breakpoint`/`remove_breakpoint` with source (`file`+`line`) or function (`function`); optional `condition` for conditional breakpoints.
 - **Flow control**: `continue` (resumes; briefly waits to observe whether the program stops or keeps running), `step_over`/`step_in`/`step_out` (single-step), `pause` (interrupt a running program so you can inspect state).
@@ -15,6 +16,7 @@ Use for launching or attaching debuggers, setting breakpoints, stepping through
 - Only one active debug session is supported at a time.
 - Some adapters require a launched session to receive `configurationDone` before the target actually runs; if the tool says configuration is pending, set breakpoints and then call `continue`.
 - Adapter availability depends on local binaries. Common built-ins: `gdb`, `lldb-dap`, `python -m debugpy.adapter`, `dlv dap`.
+- `program` must be an executable file or debug target, not a directory or interpreter name that resolves to a workspace directory.
 </caution>
 
 <examples>
@@ -25,6 +27,9 @@ Use for launching or attaching debuggers, setting breakpoints, stepping through
 4. If the program appears hung: `debug(action: "pause")`
 5. Inspect state with `threads`, `stack_trace`, `scopes`, and `variables`
 
+
+# Launch a Python script with debugpy
+`debug(action: "launch", adapter: "debugpy", program: "scripts/job.py", args: ["--flag"])`
 # Raw debugger command through repl
 `debug(action: "evaluate", expression: "info registers", context: "repl")`
 </examples>
diff --git a/packages/coding-agent/src/tools/debug.ts b/packages/coding-agent/src/tools/debug.ts
index 04a87e09c..c940dafce 100644
--- a/packages/coding-agent/src/tools/debug.ts
+++ b/packages/coding-agent/src/tools/debug.ts
@@ -1,3 +1,4 @@
+import * as fs from "node:fs/promises";
 import type {
 	AgentTool,
 	AgentToolContext,
@@ -6,7 +7,7 @@ import type {
 	RenderResultOptions,
 } from "@oh-my-pi/pi-agent-core";
 import { type Component, Text } from "@oh-my-pi/pi-tui";
-import { prompt } from "@oh-my-pi/pi-utils";
+import { isEnoent, prompt } from "@oh-my-pi/pi-utils";
 import * as z from "zod/v4";
 import {
 	type DapBreakpointRecord,
@@ -37,7 +38,7 @@ import { renderStatusLine } from "../tui";
 import { CachedOutputBlock } from "../tui/output-block";
 import type { ToolSession } from ".";
 import type { OutputMeta } from "./output-meta";
-import { resolveToCwd } from "./path-utils";
+import { formatPathRelativeToCwd, resolveToCwd } from "./path-utils";
 import {
 	formatExpandHint,
 	formatStatusIcon,
@@ -469,6 +470,21 @@ function getConfiguredAdapters(cwd: string): string {
 	const adapters = getAvailableAdapters(cwd).map(adapter => adapter.name);
 	return adapters.length > 0 ? adapters.join(", ") : "none";
 }
+async function validateLaunchProgram(program: string, cwd: string): Promise<void> {
+	let isDirectory: boolean;
+	try {
+		isDirectory = (await fs.stat(program)).isDirectory();
+	} catch (error) {
+		if (isEnoent(error)) return;
+		throw error;
+	}
+	if (!isDirectory) return;
+
+	const displayPath = formatPathRelativeToCwd(program, cwd, { trailingSlash: true });
+	throw new ToolError(
+		`launch program resolves to a directory: ${displayPath}. Pass an executable file path, or for Python use adapter "debugpy" with program set to the .py file.`,
+	);
+}
 
 interface DebugRenderArgs extends Partial<DebugParams> {}
 
@@ -628,6 +644,7 @@ export class DebugTool implements AgentTool<typeof debugSchema, DebugToolDetails
 				}
 				const commandCwd = params.cwd ? resolveToCwd(params.cwd, this.session.cwd) : this.session.cwd;
 				const program = resolveToCwd(params.program, commandCwd);
+				await validateLaunchProgram(program, commandCwd);
 				const adapter = selectLaunchAdapter(program, commandCwd, params.adapter);
 				if (!adapter) {
 					throw new ToolError(
diff --git a/packages/coding-agent/test/debug/dap-launch-failures.test.ts b/packages/coding-agent/test/debug/dap-launch-failures.test.ts
new file mode 100644
index 000000000..604746c65
--- /dev/null
+++ b/packages/coding-agent/test/debug/dap-launch-failures.test.ts
@@ -0,0 +1,208 @@
+import { afterEach, describe, expect, it, spyOn, vi } 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 "../../src/config/settings";
+import { DapClient } from "../../src/dap/client";
+import { DapSessionManager } from "../../src/dap/session";
+import type { DapCapabilities, DapClientState, DapEventMessage, DapResolvedAdapter } from "../../src/dap/types";
+import type { ToolSession } from "../../src/tools";
+import { DebugTool } from "../../src/tools/debug";
+
+const TEST_ADAPTER: DapResolvedAdapter = {
+	name: "lldb-dap",
+	command: "lldb-dap",
+	args: [],
+	resolvedCommand: "lldb-dap",
+	languages: [],
+	fileTypes: [],
+	rootMarkers: [],
+	launchDefaults: {},
+	attachDefaults: {},
+	connectMode: "stdio",
+};
+
+type DapEventHandler = (body: unknown, event: DapEventMessage) => void | Promise<void>;
+
+class FakeDapClient {
+	readonly proc: DapClientState["proc"];
+	readonly #exited = Promise.withResolvers<void>();
+	readonly #handlers = new Map<string, Set<DapEventHandler>>();
+	#alive = true;
+
+	constructor(
+		readonly adapter: DapResolvedAdapter,
+		readonly cwd: string,
+		readonly options: {
+			launchError?: string;
+			attachError?: string;
+			configurationDoneError?: string;
+			rejectStopWaiters?: boolean;
+		},
+	) {
+		this.proc = {
+			exited: this.#exited.promise,
+			exitCode: null,
+			stdin: { write: () => 0, flush: () => undefined },
+			stdout: new ReadableStream<Uint8Array>(),
+			stderr: new ReadableStream<Uint8Array>(),
+			peekStderr: () => "",
+			kill: () => {
+				this.#alive = false;
+				this.#exited.resolve();
+				return true;
+			},
+		} as unknown as DapClientState["proc"];
+	}
+
+	async initialize(): Promise<DapCapabilities> {
+		queueMicrotask(() => this.#emit("initialized", {}));
+		return { supportsConfigurationDoneRequest: true };
+	}
+
+	async sendRequest(command: string): Promise<unknown> {
+		if (command === "launch" && this.options.launchError) {
+			throw new Error(this.options.launchError);
+		}
+		if (command === "attach" && this.options.attachError) {
+			throw new Error(this.options.attachError);
+		}
+		if (command === "configurationDone" && this.options.configurationDoneError) {
+			throw new Error(this.options.configurationDoneError);
+		}
+		return {};
+	}
+
+	waitForEvent(event: string): Promise<unknown> {
+		if (this.options.rejectStopWaiters && (event === "stopped" || event === "terminated" || event === "exited")) {
+			return Promise.reject(new Error(`DAP event ${event} timed out after 1ms`));
+		}
+		const { promise, resolve } = Promise.withResolvers<unknown>();
+		const unsubscribe = this.onEvent(event, body => {
+			unsubscribe();
+			resolve(body);
+		});
+		return promise;
+	}
+
+	onEvent(event: string, handler: DapEventHandler): () => void {
+		let handlers = this.#handlers.get(event);
+		if (!handlers) {
+			handlers = new Set<DapEventHandler>();
+			this.#handlers.set(event, handlers);
+		}
+		handlers.add(handler);
+		return () => handlers?.delete(handler);
+	}
+
+	onReverseRequest(): () => void {
+		return () => {};
+	}
+
+	isAlive(): boolean {
+		return this.#alive;
+	}
+
+	async dispose(): Promise<void> {
+		this.#alive = false;
+		this.#exited.resolve();
+	}
+
+	#emit(event: string, body: unknown): void {
+		const message: DapEventMessage = { seq: 1, type: "event", event, body };
+		for (const handler of this.#handlers.get(event) ?? []) {
+			void handler(body, message);
+		}
+	}
+}
+
+afterEach(() => {
+	vi.restoreAllMocks();
+});
+
+describe("DAP launch failure handling", () => {
+	it("surfaces the launch failure when configurationDone also fails", async () => {
+		const manager = new DapSessionManager();
+		const fake = new FakeDapClient(TEST_ADAPTER, process.cwd(), {
+			launchError: "launch: 'C:\\repo\\python' is not a valid executable",
+			configurationDoneError: "configurationDone: Expected process to be stopped.",
+		});
+		spyOn(DapClient, "spawn").mockResolvedValue(fake as unknown as DapClient);
+
+		let message = "";
+		try {
+			await manager.launch({ adapter: TEST_ADAPTER, program: "C:\\repo\\python", cwd: process.cwd() });
+		} catch (error) {
+			expect(error).toBeInstanceOf(Error);
+			message = (error as Error).message;
+		}
+
+		expect(message).toContain("launch: 'C:\\repo\\python' is not a valid executable");
+		expect(message).toContain("configurationDone: Expected process to be stopped.");
+	});
+
+	it("surfaces the attach failure when configurationDone also fails", async () => {
+		const manager = new DapSessionManager();
+		const fake = new FakeDapClient(TEST_ADAPTER, process.cwd(), {
+			attachError: "attach: target process exited",
+			configurationDoneError: "configurationDone: Expected process to be stopped.",
+		});
+		spyOn(DapClient, "spawn").mockResolvedValue(fake as unknown as DapClient);
+
+		let message = "";
+		try {
+			await manager.attach({ adapter: TEST_ADAPTER, cwd: process.cwd(), pid: 123 });
+		} catch (error) {
+			expect(error).toBeInstanceOf(Error);
+			message = (error as Error).message;
+		}
+
+		expect(message).toContain("attach: target process exited");
+		expect(message).toContain("configurationDone: Expected process to be stopped.");
+	});
+
+	it("does not emit an unhandled rejection when launch fails before initial stop watchers settle", async () => {
+		const manager = new DapSessionManager();
+		const fake = new FakeDapClient(TEST_ADAPTER, process.cwd(), {
+			launchError: "launch: failed before stop outcome",
+			rejectStopWaiters: true,
+		});
+		const unhandled: unknown[] = [];
+		const onUnhandled = (reason: unknown) => unhandled.push(reason);
+		process.on("unhandledRejection", onUnhandled);
+		spyOn(DapClient, "spawn").mockResolvedValue(fake as unknown as DapClient);
+
+		try {
+			await expect(
+				manager.launch({ adapter: TEST_ADAPTER, program: "/bin/echo", cwd: process.cwd() }),
+			).rejects.toThrow("launch: failed before stop outcome");
+			await Bun.sleep(10);
+			expect(unhandled).toEqual([]);
+		} finally {
+			process.off("unhandledRejection", onUnhandled);
+		}
+	});
+});
+
+describe("DebugTool launch validation", () => {
+	it("rejects directory-valued launch programs before adapter selection", async () => {
+		const cwd = await fs.mkdtemp(path.join(os.tmpdir(), "omp-debug-program-"));
+		try {
+			await fs.mkdir(path.join(cwd, "python"));
+			const session: ToolSession = {
+				cwd,
+				hasUI: false,
+				getSessionFile: () => null,
+				getSessionSpawns: () => "*",
+				settings: Settings.isolated({ "debug.enabled": true }),
+			};
+			const tool = new DebugTool(session);
+
+			await expect(tool.execute("call", { action: "launch", program: "python" })).rejects.toThrow(
+				/launch program resolves to a directory.*python/,
+			);
+		} finally {
+			await fs.rm(cwd, { recursive: true, force: true });
+		}
+	});
+});