refactor(tools): narrow optional values

Avoid non-null assertions in tool and doctor code by preserving narrowed locals through each use site.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/cli/doctor/checks/dependencies.ts

@@ -6,7 +6,11 @@ import type { DependencyInfo } from "../types"
 import { spawnWithTimeout } from "../spawn-with-timeout"
 import { getCachedBinaryPath } from "../../../hooks/comment-checker/downloader"
 
-async function checkBinaryExists(binary: string): Promise<{ exists: boolean; path: string | null }> {
+type BinaryCheck =
+  | { exists: true; path: string }
+  | { exists: false; path: null }
+
+async function checkBinaryExists(binary: string): Promise<BinaryCheck> {
   try {
     const path = Bun.which(binary)
     if (path) {
@@ -44,7 +48,7 @@ export async function checkAstGrepCli(): Promise<DependencyInfo> {
     }
   }
 
-  const version = await getBinaryVersion(binary.path!)
+  const version = await getBinaryVersion(binary.path)
 
   return {
     name: "AST-Grep CLI",