diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 3bef17718..5c5fc4523 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -19,6 +19,7 @@
 
 ### Fixed
 
+- Fixed signal-terminated local shell commands being reported as successful with partial output ([#9577](https://github.com/earendil-works/pi/issues/9577)).
 - Fixed local clipboard failures reporting success when the terminal ignored the fallback OSC 52 write, and added platform-specific setup guidance when no clipboard backend works ([#9618](https://github.com/earendil-works/pi/issues/9618)).
 - Capped agent-level retry backoff at `retry.maxAgentDelayMs` (60s by default) so long retry runs stay responsive during prolonged transient outages ([#8826](https://github.com/earendil-works/pi/issues/8826)).
 - Fixed direct RPC `steer` and `follow_up` commands bypassing extension `input` handlers ([#8718](https://github.com/earendil-works/pi/issues/8718)).
diff --git a/packages/coding-agent/src/core/tools/bash.ts b/packages/coding-agent/src/core/tools/bash.ts
index b7c9973a4..bde6ecb91 100644
--- a/packages/coding-agent/src/core/tools/bash.ts
+++ b/packages/coding-agent/src/core/tools/bash.ts
@@ -1,5 +1,6 @@
 import { constants } from "node:fs";
 import { access as fsAccess } from "node:fs/promises";
+import { constants as osConstants } from "node:os";
 import type { AgentTool } from "@earendil-works/pi-agent-core";
 import { spawn } from "child_process";
 import { type Static, Type } from "typebox";
@@ -61,7 +62,8 @@ export interface BashOperations {
 	 * @param command The command to execute
 	 * @param cwd Working directory
 	 * @param options Execution options
-	 * @returns Promise resolving to exit code (null if killed)
+	 * @returns Promise resolving to the exit code. Report signal terminations as 128 + signal number;
+	 * a null exit code is treated as a failed command.
 	 */
 	exec: (
 		command: string,
@@ -134,7 +136,10 @@ export function createLocalShellOperations(shellName: string, resolveShellConfig
 				if (timedOut) {
 					throw new Error(`timeout:${timeout}`);
 				}
-				return { exitCode };
+				// A signal-killed shell has no exit code. Use the standard shell convention so
+				// callers do not mistake the termination for a successful command.
+				const signalCode = child.signalCode;
+				return { exitCode: exitCode ?? (signalCode ? 128 + (osConstants.signals[signalCode] ?? 0) : 1) };
 			} finally {
 				if (child.pid) untrackDetachedChildPid(child.pid);
 				if (timeoutHandle) clearTimeout(timeoutHandle);
@@ -360,7 +365,10 @@ export function createShellToolDefinition(
 
 				const snapshot = await finishOutput();
 				const { text: outputText, details } = formatOutput(snapshot);
-				if (exitCode !== 0 && exitCode !== null) {
+				if (exitCode === null) {
+					throw new Error(appendStatus(outputText, "Command terminated without an exit code"));
+				}
+				if (exitCode !== 0) {
 					throw new Error(appendStatus(outputText, `Command exited with code ${exitCode}`));
 				}
 				return { content: [{ type: "text", text: outputText }], details };
diff --git a/packages/coding-agent/test/tools.test.ts b/packages/coding-agent/test/tools.test.ts
index bb71dfead..e63b6747e 100644
--- a/packages/coding-agent/test/tools.test.ts
+++ b/packages/coding-agent/test/tools.test.ts
@@ -496,6 +496,52 @@ describe("Coding Agent Tools", () => {
 			);
 		});
 
+		// Regression tests for https://github.com/earendil-works/pi/issues/9577
+		it.skipIf(process.platform === "win32")(
+			"should map signal-killed commands to 128 plus the signal number",
+			async () => {
+				const operations = createLocalBashOperations();
+				for (const { signal, exitCode } of [
+					{ signal: "KILL", exitCode: 137 },
+					{ signal: "TERM", exitCode: 143 },
+				]) {
+					const result = await operations.exec(`kill -${signal} $$`, testDir, { onData: () => {} });
+					expect(result.exitCode).toBe(exitCode);
+				}
+			},
+		);
+
+		it.skipIf(process.platform === "win32")(
+			"should reject signal-killed commands while preserving partial output",
+			async () => {
+				for (const { signal, exitCode } of [
+					{ signal: "KILL", exitCode: 137 },
+					{ signal: "TERM", exitCode: 143 },
+				]) {
+					const execution = bashTool.execute(`test-call-signal-${signal}`, {
+						command: `printf 'before-kill\\n'; kill -${signal} $$`,
+					});
+					await expect(execution).rejects.toThrow(
+						new RegExp(`before-kill\\s+Command exited with code ${exitCode}$`),
+					);
+				}
+			},
+		);
+
+		it("should reject a null exit code from custom operations", async () => {
+			const operations: BashOperations = {
+				exec: async (_command, _cwd, { onData }) => {
+					onData(Buffer.from("partial\n", "utf-8"));
+					return { exitCode: null };
+				},
+			};
+			const bash = createBashTool(testDir, { operations });
+
+			await expect(bash.execute("test-call-null-exit", { command: "remote" })).rejects.toThrow(
+				/partial\s+Command terminated without an exit code$/,
+			);
+		});
+
 		it("should respect timeout", async () => {
 			const command = `${JSON.stringify(process.execPath)} -e ${JSON.stringify("setInterval(() => {}, 1000)")}`;
 			await expect(bashTool.execute("test-call-10", { command, timeout: 0.05 })).rejects.toThrow(/timed out/i);