What the Nexus engine does for you
These are the platform-enforced behaviours you get out of the box, on top of the specialised-agents + shared-Configuration + tools model described in the Harness overview.
| Area | Nexus change | Why it matters |
|---|---|---|
| Routing | Two-stage LLM call - a small Context Expert picks the agent from each agent's Trigger description only, then a Conversation Agent runs that agent's instructions + tools. | Faster routing (smaller Stage 1 model), narrower Stage 2 prompt, fewer wrong-tool calls. |
| Continuity | The platform enforces a fixed continuity rule every turn - keep on the same agent unless the user has clearly switched topics. | Fewer mid-flow drop-offs without writing defensive "stay here" logic. |
| Numbered steps | If your Agent instructions list Step 1: / Step 2: …, the platform auto-injects sequential-execution rules: one step per turn, with step progress tracked automatically. | Multi-step procedures stay on track without per-flow boilerplate. |
| Parent-child agent triggers | A parent agent can call a child agent: the platform snapshots the parent's state, runs the child, and auto-restores the parent when the child completes. 1 level deep. | Reusable sub-tasks (verify identity, capture payment) callable from any parent without writing return logic. |
| Conversation history | Once history exceeds ~15 messages / ~10K characters, older turns are automatically summarised; the last 2 user turns stay verbatim. | Long support conversations don't blow context; recent turns stay verbatim. |
| Tool failure | Platform rule: don't retry the same tool. Return the error as the tool result so the LLM phrases a recovery message. | Predictable failure UX; no silent retries. |
| Execution trace | Every turn stores a structured executionTrace - tool calls + results, memory writes, intent classifications, the Context Expert decision. | Testing lab and Copilot Debug share one underlying record. A buggy production conversation becomes a regression test in one click. |
| Routing Logic surface | New sub-page under Configuration (Configuration → Routing logic) where you write optional plain-English rules ("if billing → billing-agent"). | Deterministic handoff when you want it; routing falls back to each agent's Trigger when you don't. |
| Widget Builder | New top-level surface for designing custom in-conversation UI (forms, pickers, multi-step wizards). | Custom UI without channel-specific code. |
| AI Trust Centre | New top-level menu - Testing lab + Evaluators & Rules (Quality / Safety scoring with thresholds). | Durable regression coverage and automated scoring. |
| Versioned configuration | Every Configuration change is versioned with history. | Roll back; review behaviour shifts over time. |
@-mentions in prompts | Type @ in most prompt fields (bot identity, conversation rules, welcome/fallback - Routing Logic rules are the one exception, plain text only) to insert a live reference to an agent, workflow, tool, or rich-media item. Chips stay linked through renames. | Prompts don't go stale when you rename a target. |
| Welcome / Fallback options | Welcome supports Instruct, Send message, or any welcome workflow you've defined (each workflow shows up as its own option). Fallback supports Instruct + a retry count for validation failures. | Cleaner UX; workflows attach as options instead of via a generic "Trigger a flow" item. |
Back to: Harness overview