support appending content to the system prompt via cli argument

.gitignore

@@ -13,6 +13,7 @@ packages/*/dist-firefox/
 
 # Editor files
 .vscode/
+.zed/
 .idea/
 *.swp
 *.swo

packages/coding-agent/src/main.ts

@@ -45,6 +45,7 @@ interface Args {
 	model?: string;
 	apiKey?: string;
 	systemPrompt?: string;
+	appendSystemPrompt?: string;
 	thinking?: ThinkingLevel;
 	continue?: boolean;
 	resume?: boolean;
@@ -88,6 +89,8 @@ function parseArgs(args: string[]): Args {
 			result.apiKey = args[++i];
 		} else if (arg === "--system-prompt" && i + 1 < args.length) {
 			result.systemPrompt = args[++i];
+		} else if (arg === "--append-system-prompt" && i + 1 < args.length) {
+			result.appendSystemPrompt = args[++i];
 		} else if (arg === "--no-session") {
 			result.noSession = true;
 		} else if (arg === "--session" && i + 1 < args.length) {
@@ -235,6 +238,7 @@ ${chalk.bold("Options:")}
   --model <id>                   Model ID (default: gemini-2.5-flash)
   --api-key <key>                API key (defaults to env vars)
   --system-prompt <text>         System prompt (default: coding assistant prompt)
+  --append-system-prompt <text>  Append text or file contents to the system prompt
   --mode <mode>                  Output mode: text (default), json, or rpc
   --print, -p                    Non-interactive mode: process prompt and exit
   --continue, -c                 Continue previous session
@@ -320,19 +324,27 @@ const toolDescriptions: Record<ToolName, string> = {
 	ls: "List directory contents",
 };
 
-function buildSystemPrompt(customPrompt?: string, selectedTools?: ToolName[]): string {
+function resolvePromptInput(input: string | undefined, description: string): string | undefined {
-	// Check if customPrompt is a file path that exists
+	if (!input) {
-	if (customPrompt && existsSync(customPrompt)) {
+		return undefined;
+	}
+
+	if (existsSync(input)) {
 		try {
-			customPrompt = readFileSync(customPrompt, "utf-8");
+			return readFileSync(input, "utf-8");
 		} catch (error) {
-			console.error(chalk.yellow(`Warning: Could not read system prompt file ${customPrompt}: ${error}`));
+			console.error(chalk.yellow(`Warning: Could not read ${description} file ${input}: ${error}`));
-			// Fall through to use as literal string
+			return input;
 		}
 	}
 
-	if (customPrompt) {
+	return input;
-		// Use custom prompt as base, then add context/datetime
+}
+
+function buildSystemPrompt(customPrompt?: string, selectedTools?: ToolName[], appendSystemPrompt?: string): string {
+	const resolvedCustomPrompt = resolvePromptInput(customPrompt, "system prompt");
+	const resolvedAppendPrompt = resolvePromptInput(appendSystemPrompt, "append system prompt");
+
 	const now = new Date();
 	const dateTime = now.toLocaleString("en-US", {
 		weekday: "long",
@@ -345,7 +357,14 @@ function buildSystemPrompt(customPrompt?: string, selectedTools?: ToolName[]): s
 		timeZoneName: "short",
 	});
 
-		let prompt = customPrompt;
+	const appendSection = resolvedAppendPrompt ? `\n\n${resolvedAppendPrompt}` : "";
+
+	if (resolvedCustomPrompt) {
+		let prompt = resolvedCustomPrompt;
+
+		if (appendSection) {
+			prompt += appendSection;
+		}
 
 		// Append project context files
 		const contextFiles = loadProjectContextFiles();
@@ -364,18 +383,6 @@ function buildSystemPrompt(customPrompt?: string, selectedTools?: ToolName[]): s
 		return prompt;
 	}
 
-	const now = new Date();
-	const dateTime = now.toLocaleString("en-US", {
-		weekday: "long",
-		year: "numeric",
-		month: "long",
-		day: "numeric",
-		hour: "2-digit",
-		minute: "2-digit",
-		second: "2-digit",
-		timeZoneName: "short",
-	});
-
 	// Get absolute path to README.md
 	const readmePath = getReadmePath();
 
@@ -453,6 +460,10 @@ Documentation:
 - Your own documentation (including custom model setup and theme creation) is at: ${readmePath}
 - Read it when users ask about features, configuration, or setup, and especially if the user asks you to add a custom model or provider, or create a custom theme.`;
 
+	if (appendSection) {
+		prompt += appendSection;
+	}
+
 	// Append project context files
 	const contextFiles = loadProjectContextFiles();
 	if (contextFiles.length > 0) {
@@ -1138,7 +1149,7 @@ export async function main(args: string[]) {
 		}
 	}
 
-	const systemPrompt = buildSystemPrompt(parsed.systemPrompt, parsed.tools);
+	const systemPrompt = buildSystemPrompt(parsed.systemPrompt, parsed.tools, parsed.appendSystemPrompt);
 
 	// Load previous messages if continuing or resuming
 	// This may update initialModel if restoring from session