multi-session-build

Multi-session build

A large build spread across many sessions leans on a harness: per-session briefs, a definition of done, handoff notes, a pre-build design review. That harness enforces discipline. It does not prove the assembled, deployed system is correct or that it matches its own claims.

The core failure: value-ranked vertical slices are per-component by construction. Each slice owns one component and ships it end-to-end. But whole-system properties -- global fairness, a global rate limit, N-instance liveness, failover, back-pressure across services -- belong to no single slice. Nothing owns them, so nothing tests them. They pass review, pass every per-slice test, and fail in production the first time the real topology runs.

Process rigor is not coverage. Add the gates below so emergent properties get an owner, deferrals get burned down, and "done" is validated by someone who did not build it.

When to use

• A build planned as more than ~3 sessions or handed across agents.
• Any system with cross-component invariants (multiple instances, shared quotas, coordination, failover, ordering, exactly-once).
• Any build where a design doc or brief makes claims the code must honor.

When not to

• A single-slice change fully covered by its own tests.
• A throwaway spike with no correctness bar and no downstream reader.

The gates

1. Claims-vs-built ledger

Every load-bearing design claim carries one tag, kept in the design doc itself (the artifact a reviewer opens first), reconciled every session:

• BUILT+TESTED -- code exists and a test or invariant exercises it.
• BUILT-UNTESTED -- code exists, nothing proves it.
• DESIGN-ONLY -- described, no slice will build it.

Rules:

• A claim no scheduled slice will build must read DESIGN-ONLY loudly, not sit in prose implying it is real.
• BUILT-UNTESTED is a standing debt; it must move to BUILT+TESTED or get an explicit deferral entry (gate 5).
• Reconcile the ledger at the start and end of every session. A claim whose tag no longer matches the code is a bug in the ledger; fix it before coding.