The problem
Every flagship agentic project at a large regulated enterprise, from front-line assistance to financial crime screening and credit adjudication, was about to build its own ingestion, its own retrieval and its own governance. That does not scale, it is hard to defend to a regulator, and it rebuilds the very silos the programme existed to remove. The enterprise's customer knowledge content was not mastered in one place, the incumbent knowledge tooling offered neither the guardrails nor the prompt control needed to generate customer-facing content, and public-website content sat outside central governance entirely.
I wrote the architecture decision paper for the shared layer at CTO level and designed the platform it selected: a governed context backbone that every agentic use case consumes rather than rebuilds.
Why it was hard
Part of the confusion was linguistic. The word "context" was carrying four different meanings at once, from the documents an agent retrieves to the session state it accumulates, and teams were talking past each other while committing budgets. The design had to fix the vocabulary before it could fix the architecture: knowledge is what an agent retrieves; context is how it decides what to retrieve and how to process it.
The technical tension was between commitment and reversibility. A shared layer has to fix contracts early enough that five projects can build against it, while leaving components swappable, because the vector index or graph store chosen this year will not be the best one available in three years. And a single retrieval mechanism forced on everything fails quietly: relationship questions want a graph, factual lookups want a key, policy questions want semantic search, and a platform that offers only one of these pushes teams back into building their own.
Key decisions
Rather than argue from preference, five candidate architectures were scored against nine signals using structured multi-criteria methods, ranked three independent ways, with a simulation sweep across the wider priority space. One option, the governed backbone, led across the overwhelming majority of the sampled weight space and won every ranking. The losing options each failed instructively: a single enterprise ontology front-loads years of modelling before the first use case ships, per-project builds rebuild the silos, and renting the whole layer from a vendor puts the enterprise's most defensible asset, its own governed knowledge, on someone else's roadmap.
The core commitments were contracts, not products: a knowledge-object contract that every store honours, a small ontology instead of an enterprise one, intent-routed retrieval across four modes, and a context assembly service that returns a governed envelope. The guiding principle was blunt: build the durable, own the truth, govern every turn, rent the rest.
Architecture
A single seven-stage pipeline carries content from source systems through validation, enrichment and approval to publication as governed knowledge objects. Objects land in four stores, each holding a different projection of the same truth: a graph for relationships, a vector index for meaning, a content store for payloads and lineage, and a catalogue for ownership and versioning. Retrieval is routed by intent across deterministic lookup, structured query, semantic search and graph traversal, and any low-confidence object is quarantined rather than loaded. The context assembly service composes what retrieval returns into a governed envelope that reasoning agents consume.
The context assembly service is deliberately reconstructive. Each turn is assembled fresh from the governed envelope rather than accumulated across a session, so a contaminated retrieval dies at the end of the turn instead of living quietly inside a conversation.
Trade-offs
A shared layer is slower for the first project than building its own pipeline, and the design accepts that openly; the payback arrives with the second consumer and compounds after that. The small ontology trades semantic completeness for shipping: it models only what the live use cases need, and grows by accretion. Per-turn reconstruction costs assembly work on every turn that an accumulating design would amortise, but it buys containment and replayability, and in a regulated setting those are worth more than the tokens. Renting less means operating more, and the platform carries a real operating model as a consequence.
Governance
Every knowledge object carries an owner, a version, provenance and entitlements, enforced before retrieval rather than checked after. Low-confidence objects are quarantined rather than loaded. Lineage runs unbroken from source system to published object to assembled envelope to rendered answer, which is what lets the enterprise show a reviewer exactly where any statement came from. Customer-facing agents and the internal knowledge estate consume the same governed layer, so there is one assurance story rather than several.
Outcome
The result is a funded platform layer that the enterprise's flagship agentic projects consume rather than rebuild, proven end to end by a six-week vertical slice and carried by an operating model and a regulator-ready assurance story. The decision paper itself became a reusable artefact: the scoring method and the option analysis have been picked up beyond the original programme.
What I learned
Fix the vocabulary before the architecture; half of the disagreement dissolved once knowledge and context stopped meaning four things. Structured option scoring is not bureaucracy, it is how you make an architecture decision survive the people who were not in the room. And the most defensible asset a regulated organisation owns in this space is not a model or a platform, it is its own governed knowledge, which is exactly the thing never to rent.