diff --git a/packages/shared/src/agent-command.test.ts b/packages/shared/src/agent-command.test.ts
index 6796358105d..8480d45baca 100644
--- a/packages/shared/src/agent-command.test.ts
+++ b/packages/shared/src/agent-command.test.ts
@@ -60,4 +60,21 @@ describe("buildAgentPromptCommand", () => {
 		expect(command).toStartWith("pi \"$(cat <<'SUPERSET_PROMPT_pi1234'");
 		expect(command).not.toContain("pi -p");
 	});
+
+	it("passes copilot prompts via --prompt flag, not as positional", () => {
+		// Repro for #3862: `copilot -i ... "<prompt>"` errors with
+		// "Expected 0 arguments but got 1." because interactive mode does
+		// not accept a positional prompt. The prompt must be passed via
+		// the --prompt flag.
+		const command = buildAgentPromptCommand({
+			prompt: "hello",
+			randomId: "copilot-1234",
+			agent: "copilot",
+		});
+
+		expect(command).not.toMatch(/\bcopilot\b[^"]*\s-i\b/);
+		expect(command).toStartWith(
+			"copilot --allow-tool=write --prompt \"$(cat <<'SUPERSET_PROMPT_copilot1234'",
+		);
+	});
 });
diff --git a/packages/shared/src/agent-permissions-migration.ts b/packages/shared/src/agent-permissions-migration.ts
index cda447361c9..89236644f4d 100644
--- a/packages/shared/src/agent-permissions-migration.ts
+++ b/packages/shared/src/agent-permissions-migration.ts
@@ -41,7 +41,7 @@ export const LEGACY_BUILTIN_TERMINAL_AGENT_OVERRIDES: Readonly<
 	},
 	copilot: {
 		command: "copilot --allow-all",
-		promptCommand: "copilot -i --allow-all",
+		promptCommand: "copilot --allow-all --prompt",
 		promptCommandSuffix: "--yolo",
 	},
 	"cursor-agent": {
diff --git a/packages/shared/src/builtin-terminal-agents.ts b/packages/shared/src/builtin-terminal-agents.ts
index 294098270ae..649822cfa68 100644
--- a/packages/shared/src/builtin-terminal-agents.ts
+++ b/packages/shared/src/builtin-terminal-agents.ts
@@ -121,7 +121,7 @@ export const BUILTIN_TERMINAL_AGENTS = [
 		description:
 			"GitHub's coding agent for planning, editing, and building in your repo.",
 		command: "copilot --allow-tool=write",
-		promptCommand: "copilot -i --allow-tool=write",
+		promptCommand: "copilot --allow-tool=write --prompt",
 		includeInDefaultTerminalPresets: true,
 	}),
 	createBuiltinTerminalAgent({