#ADR 0003: Compile-time composition, one Worker per venture

Status: accepted, 2026-09-05

#Context

Requirements: modules are packages used while compiling; each venture is independent; the harness is open source, some modules private.

#Decision

A venture backend is a Cargo project (from venture-backend-template) whose src/lib.rs builds a Harness from module crates. The wasm binary contains exactly those modules. There is no runtime plugin loading and no multi-tenant deployment.

#Consequences

Private modules are private crates pulled by git dependency; the harness does not know or care.
Each venture has its own D1 database, secrets and custom domain.
Route prefix, table name and HARNESS_API mismatches are caught by Harness::build(), which the template runs under cargo test.

Mirrored from docs/adr/0003-compile-time-composition.md at b6f50cd. The harness is the source of truth: a correction goes there first.