Summary

Adds narrow coercion for spawn-agent params values when models emit a valid JSON object as a string. This covers both batched spawn_agents entries and spawn_agent_inline, while leaving malformed strings, arrays, and primitives to fail normal schema validation.

Also updates Freebuff e2e tests to use execFileSync instead of shell-quoted execSync for simple binary flag checks.

Why

Some providers can produce nested agent params as a JSON string even when the top-level tool call input is otherwise valid. That caused validation failures before the agent-specific params schema could run.

Validation

• bun test common/src/tools/params/__tests__/coerce-to-array.test.ts
• bun test packages/agent-runtime/src/__tests__/tool-validation-error.test.ts
• bun run typecheck in common/
• bun run typecheck in packages/agent-runtime/
• git diff --check

Note: Freebuff e2e tests were not run because cli/bin/freebuff is not present in this workspace.