specialist: no hard maximum depth limit on Task / nested specialists

[euxaristia]

Problem

Specialist / Task tool nesting has no hard upper bound.

// internal/specialist/exec.go
if options.CurrentDepth < 0 { ... }
// then always:
args = append(..., "--depth", strconv.Itoa(input.CurrentDepth+1), ...)

Only a negative check. Depth is just metadata passed down to child zero processes.

Impact

• A specialist (or the model) can recursively spawn more specialists indefinitely.
• Leads to process explosion, high CPU/memory, stack overflow, or runaway costs.
• No protection against accidental or adversarial deep recursion.

Suggested fix

• Add a hard MaxDepth (e.g. 5-8) in TaskRunOptions / Executor.Run / swarm launcher.
• Return clear error when exceeded.
• Document and expose via CLI flag if needed.
• Consider a global per-run limit in the main agent loop.

[Vasanthdev2004]

Handled now — #491 added a hard cap (maxSpecialistDepth = 8) in internal/specialist/exec.go, and Executor.Run rejects any call whose CurrentDepth is at or past the cap with a clear error before it launches a child. That's the hard MaxDepth + clear error this issue asked for.

Worth noting the recursive path isn't actually reachable through today's normal flow — specialist/swarm children are tagged specialist and don't get the Task tool — so this is really defense-in-depth against that gating ever being loosened, rather than a live-exploit fix. But the cap you suggested is in main, so closing this out. Thanks for the writeup.