[upstream #612] agents#612: redesign stop hooks with structured exit status and per-lane state #387

Follow-up from LibreChat-AI/agents#612: the opt-in verify-before-stop (Stop) and stop-on-passing-check (PostToolBatch) hooks were moved out of that PR because review kept finding shell forms their text heuristic misreads.

Redesign once before reopening:

• Pass the bash tool's exit status, timeout and kill state as structured data to hooks instead of parsing output text.
• Keep verification state per agent lane, since parallel agents share one Run and their batches overlap.
• Count only the hook's own continuations, while honoring continuationBudgetRemaining.
• Treat tests in the same tool batch as an edit as concurrent with it.

Open review findings to carry over: LibreChat-AI/agents#612 (comment), #discussion_r4296257768, #discussion_r4296257788, #discussion_r4296257802.