Cloud Development Environment Platform · View 14 of 21 · Runtime
Decisions
- The prebuild artefact is a snapshot taken after the post-create step, rebased onto newer commits, which is what keeps a create at 25 seconds rather than four minutes (ADR-07).
- Fan-out is rate-limited per tenant: prebuilding every branch of every active repository is the easiest way to spend a fleet on environments nobody opens.
- A cache miss is visible, not silent: the requester is told which path was taken and what it cost in start latency.
Assumptions
- Create from a valid prebuild p95 ≤ 25 s; from a warm pool p95 ≤ 3 s; inline build p95 ≤ 4 min with progress from the first second.
- The most recent valid prebuild per active branch is retained; superseded ones are collected.
Risks
- A silently stale prebuild produces a workspace that differs from CI, which is worse than a slow start and much harder to debug — hence a predicate rather than a heuristic.
- Rebasing a post-create snapshot onto a newer commit is correct until a dependency change makes it wrong; the lockfile hash is the only thing standing between the two cases.
