Feature: per-subagent timeout / tool-call budget — one stalled child hangs the parent indefinitely

Problem

A task that spawns subagents has no per-child wall-clock timeout or budget: when one subagent stalls (e.g. its model backend stops responding mid-call), the parent waits forever with no error and no recovery.

Measured case (OpenCode 1.18.x, Windows 11, local Ollama models via an OpenAI-compatible provider): an unattended research task spawned several subagents; one child's backend stalled and the parent hung 20 minutes until manually killed. The identical task re-run with a prompt-level instruction ("at most N tool calls, then report") completed in 169 s with full results — so the work itself was fine; only the missing guardrail made the run unsafe.

Related open reports that look like the same missing guardrail from different angles: #33028 (subagents hang indefinitely, stream never times out), #13841 (Explore subagent hangs, no timeout or recovery), #44931 (background subagents hang silently on repeated upstream 429s).

Proposal

• A configurable per-subagent wall-clock timeout (config default + per-agent override), after which the child is cancelled and the parent receives a structured "subagent timed out" result it can act on.
• Optionally a tool-call budget per subagent as a second, cheaper guardrail (deterministic, model-independent).

Prompt discipline works as a workaround but shouldn't be the only line of defense for unattended runs — a stalled child currently converts into an unbounded parent hang.