fix(tools): resolve extensionful specifiers in the boundary guard

`resolveSpecifier` probed `base + ext` and `base/index + ext` but never `base`
itself, so an already-extensioned specifier resolved to null and its edge
vanished from the walk — `import { tools } from '@/tools/registry.ts'` would
have passed the guard silently.

Not theoretical: `executor/execution/block-executor.ts` already imports
`@/executor/human-in-the-loop/utils.ts` with the extension, so real edges were
being dropped. Counts rise slightly now that they are followed (canvas
2,023 -> 2,029).

Verified: the extensionful import exits 1, and removing it returns to 0.

Author: waleedlatif1

scripts/check-tool-registry-boundary.ts

@@ -71,6 +71,11 @@ function resolveSpecifier(specifier: string, importer: string): string | null {
   else if (specifier.startsWith('.')) base = resolve(dirname(importer), specifier)
   else return null
 
+  // An already-extensioned specifier (`@/tools/registry.ts`) resolves as-is.
+  // Probing only `base + ext` would miss it and silently drop the edge — and
+  // extensionful `@/` imports do exist in this repo.
+  if (existsSync(base) && statSync(base).isFile()) return base
+
   for (const ext of EXTENSIONS) {
     if (existsSync(base + ext)) return base + ext
   }