fix: Task dependency graph should validate cycles at creation time, not at runtime

[tcconnally]

Problem

When tasks are defined with circular dependencies (A -> B -> C -> A), CrewAI does not detect the cycle until runtime, when it causes a RecursionError or infinite hang.

Steps

1. Define Task A with depends_on=[Task B]
2. Define Task B with depends_on=[Task C]
3. Define Task C with depends_on=[Task A]
4. Run the crew -> hangs or crashes

Expected

Cycle detection at graph construction time with a clear ValueError.

[Sehlani042]

I can take a narrow pass at this, but I want to confirm the current API surface before opening a PR.

When you say cyclic depends_on, should this map to cycles through Task.context=[...] in the current codebase? For example:

task_a.context = [task_c]
task_b.context = [task_a]
task_c.context = [task_b]

If that is the intended dependency graph, I can add a focused regression that constructs A -> B -> C -> A through task context and expects an early ValueError with a clear cycle message, then implement a small DFS validator around the task-context graph.

[tcconnally]

Closing this. I filed it without verifying the API and it's wrong: crewAI Task has no depends_on field, dependencies are expressed via context: list[Task], so the reproduction steps here don't apply. Apologies for the noise.