fix(prompts): remove stray tab before Tool Use Guidelines heading

src/core/prompts/__tests__/system-prompt.spec.ts

@@ -560,6 +560,11 @@ describe("SYSTEM_PROMPT", () => {
 		// Should contain Tool Use Guidelines section
 		expect(prompt).toContain("Tool Use Guidelines")
 
+		// The guidelines heading must start at column 0. A stray leading tab
+		// (#1415) would otherwise be sent to the model with every request.
+		expect(prompt).toContain("\n# Tool Use Guidelines\n")
+		expect(prompt).not.toContain("\t# Tool Use Guidelines")
+
 		// Should NOT contain a tool catalog / XML examples
 		expect(prompt).not.toContain("# Tools")
 		expect(prompt).not.toContain("## read_file")

src/core/prompts/system.ts

@@ -98,7 +98,7 @@ ${markdownFormattingSection()}
 
 ${getSharedToolUseSection()}${toolsCatalog}
 
-	${getToolUseGuidelinesSection()}
+${getToolUseGuidelinesSection()}
 
 ${
 	// Forward the hub only when the mode actually exposes the MCP group, and pass the per-mode