🤖 Validate bash tool script parameter and fix typecheck target (#114)

## Changes

**Bash tool validation:**
- Empty or whitespace-only scripts now fail immediately with a clear
error
- Prevents confusing behavior from malformed tool calls
- Returns `exitCode: -1` and `wall_duration_ms: 0` for instant feedback

**Makefile fix:**
- `make typecheck` now depends on `dist/version.txt` 
- Automatically generates version file before type checking
- Eliminates "Cannot find module './version'" errors

## Testing

Added two tests in `bash.test.ts`:
- Empty script (`""`)
- Whitespace-only script (`"   \n\t  "`)

All 233 tests pass ✅

_Generated with `cmux`_

Author: ammar-agent

Makefile

@@ -91,7 +91,7 @@ fmt-check: ## Check code formatting
 fmt-shell: ## Format shell scripts with shfmt
 	@./scripts/fmt.sh --shell
 
-typecheck: ## Run TypeScript type checking
+typecheck: dist/version.txt ## Run TypeScript type checking
 	@./scripts/typecheck.sh
 
 ## Testing

src/services/tools/bash.test.ts

@@ -560,4 +560,42 @@ describe("bash tool", () => {
       expect(result.exitCode).toBe(-1);
     }
   });
+
+  it("should fail immediately when script is empty", async () => {
+    const tool = createBashTool({ cwd: process.cwd() });
+    const args: BashToolArgs = {
+      script: "",
+      timeout_secs: 5,
+      max_lines: 100,
+    };
+
+    const result = (await tool.execute!(args, mockToolCallOptions)) as BashToolResult;
+
+    expect(result.success).toBe(false);
+    if (!result.success) {
+      expect(result.error).toContain("Script parameter is empty");
+      expect(result.error).toContain("malformed tool call");
+      expect(result.exitCode).toBe(-1);
+      expect(result.wall_duration_ms).toBe(0);
+    }
+  });
+
+  it("should fail immediately when script is only whitespace", async () => {
+    const tool = createBashTool({ cwd: process.cwd() });
+    const args: BashToolArgs = {
+      script: "   \n\t  ",
+      timeout_secs: 5,
+      max_lines: 100,
+    };
+
+    const result = (await tool.execute!(args, mockToolCallOptions)) as BashToolResult;
+
+    expect(result.success).toBe(false);
+    if (!result.success) {
+      expect(result.error).toContain("Script parameter is empty");
+      expect(result.exitCode).toBe(-1);
+      expect(result.wall_duration_ms).toBe(0);
+    }
+  });
+
 });

src/services/tools/bash.ts

@@ -46,6 +46,16 @@ export const createBashTool: ToolFactory = (config: ToolConfiguration) => {
       { script, timeout_secs, max_lines = BASH_DEFAULT_MAX_LINES, stdin },
       { abortSignal }
     ): Promise<BashToolResult> => {
+      // Validate script is not empty - likely indicates a malformed tool call
+      if (!script || script.trim().length === 0) {
+        return {
+          success: false,
+          error: "Script parameter is empty. This likely indicates a malformed tool call.",
+          exitCode: -1,
+          wall_duration_ms: 0,
+        };
+      }
+
       const startTime = performance.now();
       const normalizedMaxLines = Math.max(1, Math.floor(max_lines));
       const effectiveMaxLines = Math.min(normalizedMaxLines, BASH_HARD_MAX_LINES);