The problem
Front-line staff at a large regulated enterprise prepare for dozens of client meetings a week, each taking the better part of an hour to research across six or more systems. The obvious answer, an assistant inside the collaboration workspace they already use, has a quiet flaw: most of the decision-weighted data a coverage team needs lives outside that workspace boundary, in performance reporting, the credit-risk workflow, core lending systems and external market feeds. A single-vendor chat agent reaches one ring of that data and answers a fraction of what the role actually demands.
I wrote the architecture decision paper and designed the recommended hybrid: the workspace stays the surface; the reasoning runs on a system the enterprise owns and verifies on every turn.
Why it was hard
The data falls into three rings with different owners, different security regimes and different freshness: the workspace estate, the enterprise's internal cloud estate, and external market data. No single platform spans all three with the entitlements intact, and pretending otherwise fails at the assurance gate, because where a model is allowed to run and what data may cross which boundary are fixed by security policy, not preference.
The question range was the second trap. A declarative topic bot is really a rules engine: fine for a handful of intents, broken across the spread of questions a front-line staff actually asks. But a fully agentic system across this surface would never clear governance. The design had to place agency precisely, not everywhere.
And the answers carry numbers into client conversations. A wrong figure in a meeting brief is not a quality problem, it is a conduct problem, so grounding had to be enforced rather than encouraged.
Key decisions
Six candidate options were scored against ten weighted dimensions covering capability, strategic fit and execution. The recommended hybrid led clearly, and the ranking held under any reasonable re-weighting. The split is clean: the collaboration workspace remains the workspace surface, the reasoning brain runs on the enterprise's own cloud estate, and vector and graph retrieval sit together as one layer.
Only the root planner is genuinely agentic. Every other step is tiered on the enterprise's autonomy taxonomy and behaves as a bounded component. Each model choice is made against an explicit acceptance bar rather than preference: a small encoder for intent classification against an accuracy and latency bar, small generative models for sub-agent summarisation against a faithfulness bar, a frontier model only for root synthesis and compliance review, where the small models fell short of the completeness bar.
Failure modes were engineered before features. The planner runs on a bounded replan budget, so a pathological question degrades into a partial, cited answer rather than an open-ended token spend.
Architecture
The staff asks in the workspace. The request crosses an identity-federated boundary to the root orchestrator, which runs plan, act, observe, replan, gated on sufficiency. Thin domain agents fan out over an allow-listed topology and reach data through governed tool contracts. They stand on a four-projection knowledge layer: a graph for who is connected, a vector store for what the text says, structured marts for how much, and a live tier for what just changed. The synthesis passes a blocking citation guardrail before anything renders back on the surface.
Internal structured data is never queried at source by agents; it is replicated into curated, row-level-secured views that the knowledge layer serves. Retrieval is hybrid, dense and sparse fused and reranked, because front-line questions swing between the precise and the vague within a single session.
Trade-offs
The hybrid costs more to integrate than an all-in single-vendor design, and the decision paper says so plainly; it wins because the all-in options fail on data reach and on the assurance gate, and no integration saving compensates for answering a fifth of the question space. Small-model-first routing holds inference cost down sharply but adds calibration and escalation machinery. The bounded replan budget means some hard questions come back partial, by design: a partial answer with citations beats a complete answer without them.
Governance
Every step carries an autonomy tier and a numeric evaluation gate, feeding the enterprise's certification process. The citation guardrail is blocking, not advisory: an answer with an unsourced number does not render. The platform monitors each agent's tool-selection distribution over time, because behavioural drift shows up before verbal drift. The architecture decision, the autonomy artefact and the model evaluations were accepted as the enterprise's assurance reference for work of this class.
Outcome
The decision paper drove the build, and the recovered preparation time is modelled as hours per staff per week, which is material across a large coverage population. More durable than the capacity case: the surface strategy lets the vendor assistant and the enterprise-owned brain advance without conflict, and the same pattern is extending to adjacent front-line workflows such as schedule automation in commercial lending and quote preparation inside pricing thresholds.
What I learned
The surface is not the system. Conflating the two is the single most common error I see in enterprise assistant design. Acceptance bars ended the model arguments: once every step had a numeric bar, model selection became an engineering decision instead of a taste war. And designing the failure modes first, the replan budget, the topology, the blocking guardrail, made the feature conversations easier, because everyone knew what the system would refuse to do.