fix(coding-agent): keep empty quoted prompt template arguments

Empty quoted arguments ("" or '') were dropped, shifting later positional
arguments and preventing positional defaults from applying.

closes #10867

packages/coding-agent/CHANGELOG.md

@@ -14,6 +14,7 @@
 - Fixed repeated codemode timeouts or aborts accumulating surviving workers; admission now limits live workers to two across sessions, counting cancelled workers until actual exit ([#10748](https://github.com/earendil-works/pi/issues/10748))
 - Fixed `--model` choosing a provider by catalog order when several providers offer the match; Pi now prefers the provider with credentials and otherwise reports the ambiguity. `--models` and `enabledModels` add a model for each provider that offers it and warn about the ambiguity ([#10160](https://github.com/earendil-works/pi/issues/10160))
 - Fixed `read` line-range labels for numeric-string or null arguments in the TUI, session tree, HTML exports, and examples ([#9887](https://github.com/earendil-works/pi/issues/9887))
+- Fixed prompt templates dropping empty quoted arguments (`""` or `''`), which shifted later positional arguments and prevented positional defaults from applying ([#10867](https://github.com/earendil-works/pi/issues/10867))
 
 ## [1.2.0] - 2026-10-12
 

packages/coding-agent/src/core/prompt-templates.ts

@@ -25,6 +25,8 @@ export interface PromptTemplate {
 export function parseCommandArgs(argsString: string): string[] {
 	const args: string[] = [];
 	let current = "";
+	// Tracks whether a token has started, so quoted empty strings ("" or '') are kept as arguments
+	let hasToken = false;
 	let inQuote: string | null = null;
 
 	for (let i = 0; i < argsString.length; i++) {
@@ -38,17 +40,20 @@ export function parseCommandArgs(argsString: string): string[] {
 			}
 		} else if (char === '"' || char === "'") {
 			inQuote = char;
+			hasToken = true;
 		} else if (/\s/.test(char)) {
-			if (current) {
+			if (hasToken) {
 				args.push(current);
 				current = "";
+				hasToken = false;
 			}
 		} else {
 			current += char;
+			hasToken = true;
 		}
 	}
 
-	if (current) {
+	if (hasToken) {
 		args.push(current);
 	}
 

packages/coding-agent/test/prompt-templates.test.ts

@@ -383,8 +383,10 @@ describe("parseCommandArgs", () => {
 	});
 
 	test("should handle quoted empty string", () => {
-		// Note: Empty quotes are skipped by current implementation
-		expect(parseCommandArgs('"" " "')).toEqual([" "]);
+		// Empty quotes keep their position as an empty argument (#10867)
+		expect(parseCommandArgs('"" " "')).toEqual(["", " "]);
+		expect(parseCommandArgs("a '' c")).toEqual(["a", "", "c"]);
+		expect(parseCommandArgs('a ""')).toEqual(["a", ""]);
 	});
 
 	test("should handle arguments with special characters", () => {
@@ -433,6 +435,24 @@ describe("parseCommandArgs", () => {
 // ============================================================================
 
 describe("expandPromptTemplate", () => {
+	// #10867
+	test("should use positional default for empty quoted argument without shifting later args", () => {
+		const template = {
+			name: "review",
+			description: "test",
+			content: `Review $2. Focus: \${1:-correctness}.`,
+			sourceInfo: { path: "/tmp/review.md", source: "local", scope: "temporary", origin: "top-level" } as const,
+			filePath: "/tmp/review.md",
+		};
+
+		expect(expandPromptTemplate('/review "" src/index.ts', [template])).toBe(
+			"Review src/index.ts. Focus: correctness.",
+		);
+		expect(expandPromptTemplate("/review '' src/index.ts", [template])).toBe(
+			"Review src/index.ts. Focus: correctness.",
+		);
+	});
+
 	test("should split template arguments on unquoted newlines", () => {
 		const result = expandPromptTemplate("/arg-test label-2\n\nHere is some description #2.", [
 			{