fix(builtin): disable tools during continue/retry to force frontmatter output

Agent was using all continue turns to keep calling tools instead of
outputting the required frontmatter. Now continue runs with noTools=true,
forcing LLM to emit text-only response.

Also supports null tools in chatCompletionWithTools to omit tools from
the API request entirely.

package.json

@@ -9,7 +9,7 @@
     "check": "bunx tsc --build && biome check . && bash scripts/lint-log-tags.sh",
     "typecheck": "bunx tsc --build",
     "format": "biome format --write .",
-    "test": "bun run --filter '*' test",
+    "test": "bun run --filter './packages/*' test",
     "changeset": "bunx changeset",
     "version": "bunx changeset version",
     "release": "bun run build && bun test && node scripts/publish-all.mjs"