A module built once is not built again

Every package that ships a module used to be compiled, packed and tested from scratch on every run that reached it: once on the pull request, again on the push to main minutes later, and once more in every concurrent pull request that happened to touch the same module. A platform release rebuilt every module in the fleet, whether or not the release changed anything the module could see.

The lane now writes a module build ledger on the registry portal. Every selected module gets a content address — the package's content hash, the source of every in-repo project the bundle carries or its tests reach, both image digests, the platform commit and the lane's own recipe — and the ledger says, per address, what has already happened: built, tested, published, failed, or in progress right now in another run.

• Same address, built before? The run downloads that bundle and runs only what is still missing — the tests if nobody recorded a verdict, the hand-over to the registry if nobody published it.
• Same address, another run is on it? The run waits for that one to finish rather than building the same thing beside it.
• Same address, compile failed? The run stops with the other run's evidence — the same inputs give the same result. A test failure is allowed one more attempt, so a flaky suite does not pin the fleet.

The registry portal being unavailable never turns a green build red: the lane then builds without coordination and says so in the job summary.

Where the design decisions live: Module Build Architecture → "Content-addressed outputs".