multi-tenancy

A design guide for keeping multiple customers' data separate in a Cratis application. It uses Chronicle namespaces, which are independent event-store areas for each tenant.

In plain words
What is it for?
It helps configure tenant-to-namespace mapping in Arc and design isolated commands, events, projections, reducers, observers, and read models.
Why use it?
It prevents events, projections, observers, and read models from different tenants from being mixed within one deployment.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/cratis/ai/multi-tenancy
Any agent
npx skills add Cratis/AI --skill multi-tenancy
Clone the repo
git clone --depth 1 https://github.com/Cratis/AI

Made for: Claude Code, Codex.

Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 637 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00072 $0.00637
Opus 5 $0.00036 $0.00318
Sonnet 5 $0.00014 $0.00127
Haiku 4.5 $0.00007 $0.00064

Measured 2d ago against content hash d88b6633208c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

multi-tenancy scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.ai/skills/multi-tenancy/SKILL.md · 53 lines

How it starts

The opening of the file, as written. The whole thing — 53 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Multi-Tenancy with Chronicle Namespaces

Chronicle implements multi-tenancy through namespaces: each namespace is a logically separate event store. Events, projections, reducers, and observers run independently per namespace — there is no cross-namespace leakage. Not every Cratis app is multi-tenant — adopt this only when one deployment must serve multiple tenants with isolation.

Core concept

Term Meaning
Namespace a named isolation boundary in Chronicle (its own event store)
Default namespace "Default" — used when none is resolved

All appends, projections, and observers are scoped to the resolved namespace. A reactor for <Entity>Created fires once per tenant namespace that has that event — independently.

Arc tenancy integration

When using Arc with Chronicle, tenancy maps to namespaces automatically: Arc's TenantNamespaceResolver maps the current tenant id to the Chronicle namespace and falls back to the default namespace when no tenant is set. Enable Arc tenancy in startup so the tenant context resolves before each command/query handler runs; namespace wiring is then automatic — no manual resolver registration needed.

If you need custom namespace resolution outside Arc tenancy (header, subdomain, JWT claim), Chronicle supports namespace resolvers registered in priority order; the first non-null result wins, else the default namespace is used.

Observer and reactor isolation

Observers (projections, reducers, reactors) are instantiated per namespace. Consequences:

  • A [OnceOnly] reactor fires once per event source within each namespace (i.e. once per tenant), not globally once — see reactors.md.
  • Projection rewind affects only the target namespace.
  • Each namespace has its own sequence numbers.

Common pitfalls

Pitfall Why
Storing a tenant id on every event type the namespace is the tenant — events don't need a tenant property
No tenant resolution in a multi-tenant deployment every tenant lands in "Default" — no isolation
Reading one namespace and writing another in the same request accidental cross-namespace access is a bug (intentional bridging is a Translation reactor)
Expecting [OnceOnly] to be globally once it is per-namespace

Read the full file on GitHub · 53 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 53 lines · 72 tokens per session scan A d88b6633208c

Subscribe to this mod's changes

multi-tenancy is a skill published in the GitHub repository Cratis/AI (2 stars, last pushed 4d ago), licensed MIT. It adds 72 tokens to every session and 637 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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