Composite patternAI engineeringMCP

A harness for dozens of copilots to become testable software.

This composite architecture shows how teams can share prompts, tools, traces, evaluations, model routing and policy gates—without forcing every copilot into the same framework. Benchmarks below are illustrative targets pending client-approved evidence.

42Copilots onboarded
14d→2hRelease proof
41%Token cost cut
73%Eval coverage
01 · Constraint

Every team had an AI stack. Nobody had an AI release contract.

Prompts lived in application code, tools had inconsistent schemas, and quality was judged from a handful of chat transcripts. A provider or prompt change could improve one workflow and silently break another.

Invisible regressions

There was no repeatable corpus for task success, refusal, safety and groundedness.

Unbounded tools

Tool descriptions, permissions and side effects varied by framework.

No cost envelope

Accuracy, latency and token usage were measured in separate systems.

02 · Harness

A release candidate became an evidence bundle.

DefineVersioned behavior

Prompt, model policy and tool allow-list

ConnectMCP contracts

Typed tools with scoped identity and risk hints

ExerciseGolden datasets

Happy path, adversarial and edge cases

ObserveGenAI traces

Model, retrieval and tool spans

GateRisk-weighted evals

Quality, safety, latency and cost budgets

Failure path: a failed critical evaluation blocked promotion. Production anomalies could pin traffic to the prior behavior bundle without rolling back unrelated application code.
03 · Decisions

The harness standardized evidence, not creativity.

D-01Framework-neutral envelope

LangGraph, provider SDKs and custom orchestrators emitted the same run and evaluation contract.

D-02Risk-tiered gates

A writing assistant and an account-action agent did not share the same approval burden.

D-03Model routing by task

Quality floors came first; the least costly passing route served production traffic.

04 · Outcome

AI changes became inspectable and reversible.

MeasureBeforeAfter
Release evidenceUp to 14 daysUnder 2 hours
Evaluation coverageAd hoc examples73% critical paths
Token cost per taskBaseline41% lower
Tool governancePer applicationVersioned MCP contracts
Model Context ProtocolLangGraphOpenTelemetryGolden datasetsPrompt registryPolicy engineModel router
Current-tech choice: MCP tools were pinned to an explicit protocol version, and GenAI telemetry stayed behind a translation layer so evolving semantic conventions could not leak into product code.

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