fix: prevent E2BIG error when system prompt is too long for Claude Code CLI

- Add system prompt truncation to avoid E2BIG errors
- Detect memory bank content patterns and truncate before command-line args
- Preserve essential role definition while removing large memory bank content
- Add comprehensive tests for truncation scenarios
- Claude Code CLI loads memory bank from CLAUDE.md anyway, so this is safe

Fixes issue where very long system prompts (especially with memory bank content)
would cause subprocess spawn failures due to command-line argument size limits.

Author: kamilchm

src/integrations/claude-code/__tests__/run.spec.ts

@@ -1,4 +1,4 @@
-import { describe, test, expect, vi, beforeEach } from "vitest"
+import { describe, test, expect, vi, afterEach, beforeEach } from "vitest"
 
 // Mock vscode workspace
 vi.mock("vscode", () => ({
@@ -287,4 +287,88 @@ describe("runClaudeCode", () => {
 		consoleErrorSpy.mockRestore()
 		await generator.return(undefined)
 	})
+
+	describe("system prompt truncation", () => {
+		test("should truncate system prompt when memory bank content is detected", async () => {
+			const { runClaudeCode } = await import("../run")
+			
+			const longSystemPrompt = `You are Claude Code, Anthropic's official CLI for Claude.
+You are Kilo Code, a highly skilled software engineer.
+
+RULES
+
+All responses MUST follow specific guidelines.
+
+USER'S CUSTOM INSTRUCTIONS
+
+The following additional instructions are provided by the user, and should be followed to the best of your ability without interfering with the TOOL USE guidelines.
+
+Very long memory bank content that would cause E2BIG errors when passed as command line argument...`.repeat(100)
+
+			const options = {
+				systemPrompt: longSystemPrompt,
+				messages: [{ role: "user" as const, content: "Hello" }],
+			}
+
+			const generator = runClaudeCode(options)
+			
+			// Since we're mocking execa, we can check what arguments were passed
+			await generator.next()
+
+			expect(mockExeca).toHaveBeenCalledWith(
+				"claude",
+				expect.arrayContaining([
+					"-p",
+					"--system-prompt",
+					expect.stringMatching(/^You are Claude Code.*RULES.*All responses MUST follow.*$/s),
+				]),
+				expect.any(Object)
+			)
+
+			// Verify the system prompt was truncated
+			const call = mockExeca.mock.calls[0]
+			const systemPromptArg = call[1][call[1].indexOf("--system-prompt") + 1]
+			expect(systemPromptArg).not.toContain("USER'S CUSTOM INSTRUCTIONS")
+			expect(systemPromptArg.length).toBeLessThan(longSystemPrompt.length)
+		})
+
+		test("should truncate system prompt when it exceeds maximum safe size", async () => {
+			const { runClaudeCode } = await import("../run")
+			
+			const veryLongSystemPrompt = "You are a helpful assistant. ".repeat(2000) // ~60KB
+
+			const options = {
+				systemPrompt: veryLongSystemPrompt,
+				messages: [{ role: "user" as const, content: "Hello" }],
+			}
+
+			const generator = runClaudeCode(options)
+			await generator.next()
+
+			// Verify the system prompt was truncated to safe size
+			const call = mockExeca.mock.calls[0]
+			const systemPromptArg = call[1][call[1].indexOf("--system-prompt") + 1]
+			expect(systemPromptArg.length).toBeLessThanOrEqual(32000)
+			expect(systemPromptArg.length).toBeLessThan(veryLongSystemPrompt.length)
+		})
+
+		test("should not truncate normal-sized system prompts", async () => {
+			const { runClaudeCode } = await import("../run")
+			
+			const normalSystemPrompt = "You are a helpful assistant."
+
+			const options = {
+				systemPrompt: normalSystemPrompt,
+				messages: [{ role: "user" as const, content: "Hello" }],
+			}
+
+			const generator = runClaudeCode(options)
+			await generator.next()
+
+			// Verify the system prompt was not truncated
+			const call = mockExeca.mock.calls[0]
+			const systemPromptArg = call[1][call[1].indexOf("--system-prompt") + 1]
+			expect(systemPromptArg).toBe(normalSystemPrompt)
+		})
+	})
 })

src/integrations/claude-code/run.ts

@@ -110,10 +110,14 @@ const CLAUDE_CODE_TIMEOUT = 600000 // 10 minutes
 function runProcess({ systemPrompt, messages, path, modelId }: ClaudeCodeOptions) {
 	const claudePath = path || "claude"
 
+	// Truncate system prompt to avoid E2BIG errors
+	// Keep only the role definition part, as Claude Code CLI loads memory bank from CLAUDE.md
+	const truncatedSystemPrompt = truncateSystemPrompt(systemPrompt)
+
 	const args = [
 		"-p",
 		"--system-prompt",
-		systemPrompt,
+		truncatedSystemPrompt,
 		"--verbose",
 		"--output-format",
 		"stream-json",
@@ -198,3 +202,54 @@ function attemptParseChunk(data: string): ClaudeCodeMessage | null {
 		return null
 	}
 }
+
+/**
+ * Truncates the system prompt to avoid E2BIG errors when spawning subprocess.
+ * Keeps only the role definition part since Claude Code CLI loads memory bank from CLAUDE.md.
+ *
+ * The system prompt structure typically follows:
+ * 1. Role definition (essential)
+ * 2. Memory bank instructions with content (can be large, not needed for Claude Code CLI)
+ *
+ * @param systemPrompt The full system prompt
+ * @returns Truncated system prompt containing only the role definition
+ */
+function truncateSystemPrompt(systemPrompt: string): string {
+	// Look for common patterns that indicate the start of memory bank content
+	const memoryBankIndicators = [
+		"USER'S CUSTOM INSTRUCTIONS",
+		"The following additional instructions are provided by the user",
+		"# Rules from",
+		"# Memory Bank",
+		"CLAUDE.md",
+		"memory bank",
+		"custom instructions"
+	]
+	
+	// Find the first occurrence of any memory bank indicator
+	let truncationPoint = systemPrompt.length
+	
+	for (const indicator of memoryBankIndicators) {
+		const index = systemPrompt.indexOf(indicator)
+		if (index !== -1 && index < truncationPoint) {
+			truncationPoint = index
+		}
+	}
+	
+	// If we found a truncation point, cut off there
+	if (truncationPoint < systemPrompt.length) {
+		const truncated = systemPrompt.substring(0, truncationPoint).trim()
+		console.log(`System prompt truncated from ${systemPrompt.length} to ${truncated.length} characters`)
+		return truncated
+	}
+	
+	// If no memory bank content found, but still very long, truncate to reasonable size
+	const MAX_SAFE_SIZE = 32000 // Conservative limit to avoid E2BIG
+	if (systemPrompt.length > MAX_SAFE_SIZE) {
+		const truncated = systemPrompt.substring(0, MAX_SAFE_SIZE).trim()
+		console.log(`System prompt truncated from ${systemPrompt.length} to ${truncated.length} characters (size limit)`)
+		return truncated
+	}
+	
+	return systemPrompt
+}