fix(workflows): reject bool max_iterations in engine re-eval guard

[Noor-ul-ain001]

Summary

The while / do-while step validators already reject max_iterations: true as a type error — bool is a subclass of int, so a boolean passes a bare isinstance(..., int) check, and since True - 1 == 0 it would silently cap the loop at a single iteration (0 re-iterations).

The engine's re-evaluation guard in WorkflowEngine, however, still used the older shape:

if not isinstance(max_iters, int) or max_iters < 1:
    max_iters = 10

On an unvalidated run (executing a definition without first calling the validators), a boolean max_iterations slipped through this guard and ran the loop body just once instead of falling back to the safe default of 10.

Fix

Add the explicit isinstance(max_iters, bool) rejection so the engine guard matches WhileStep.validate() / DoWhileStep.validate(). An unvalidated run now degrades to the default of 10 rather than silently under-running the loop.

Testing

• Added test_while_loop_bool_max_iterations_falls_back_to_default, which runs a while step with max_iterations: true through the engine and asserts the body executes 10 times (not 1).
• Verified the test fails without the engine change and passes with it (test-the-test via git stash).
• Full while/do-while/loop suite: 16 passed.

🤖 Generated with Claude Code