Problem

After removing the lease concept from file operations in #136, the type guards in ToolMessage.tsx were still checking for the presence of lease in the tool arguments. This exposed a deeper architectural issue: hand-written type guards can drift from type definitions.

Root Cause

Type guards used manual property checks that TypeScript can't verify match the actual types:

// ❌ Problem: Can get out of sync with type definition
function isFileEditReplaceTool(toolName: string, args: unknown): args is FileEditReplaceToolArgs {
  return (
    toolName === "file_edit_replace" &&
    typeof args === "object" &&
    args !== null &&
    "file_path" in args &&
    "edits" in args &&
    "lease" in args  // ← TypeScript doesn't verify this matches FileEditReplaceToolArgs!
  );
}

Solution: Schema-Driven Type Guards

Use the existing Zod schemas from toolDefinitions.ts as the single source of truth:

// ✅ Solution: Uses schema validation - always in sync
import { TOOL_DEFINITIONS } from "@/utils/tools/toolDefinitions";

function isFileEditReplaceTool(toolName: string, args: unknown): args is FileEditReplaceToolArgs {
  if (toolName !== "file_edit_replace") return false;
  return TOOL_DEFINITIONS.file_edit_replace.schema.safeParse(args).success;
}

Benefits

1. Single source of truth: Zod schemas define both runtime validation and TypeScript types
2. Automatic sync: Schema changes automatically propagate to type guards
3. More robust: Validates full structure, not just key presence
4. Future-proof: Prevents entire category of drift bugs

Changes

• Import TOOL_DEFINITIONS from toolDefinitions.ts
• Replace all manual type guards with schema-based validation
• Apply to all tools: bash, file_read, file_edit_replace, file_edit_insert, propose_plan
• Net result: -33 lines of manual validation code, +13 lines of schema-driven validation

Related

• Depends on 🤖 Remove lease concept from file operations #136 (Remove lease concept from file operations)

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