Build once, test many: cross-compiled binaries verified by self-install on target machines #652

Epic: #444. Depends on: #639 (pin the host toolchain so a cross-compile build completes at all).

The goal, stated by USER 2026-08-24: build on one machine and test on many. No maintained Linux or Windows environment on every box being targeted — instead, cross-compile the binaries once, ship them to the target, and verify by self-installing there.

Today the only cross-platform gate is make vet, which compiles and runs nothing. That is precisely why #639 hid: a defect that only manifests when a binary executes cannot be caught by a gate that never executes one.

What exists already

• dist (Makefile:286-287) cross-compiles under explicit GOOS/GOARCH/CGO_ENABLED=0 — but only writ and lore, 2 of the 7 binaries make build produces (lore, star, writ, devlore-test, devlore-docs, devlore-index, devlore-inventory).
• TestSelfInstallScenario (cmd/scenario) already drives self-install end to end, and make test-scenario runs it on all three platforms in CI — but against binaries built on each platform, which is the workflow this issue replaces.
• Product recipes (Makefile:136-142) already carry $(GOEXE), so they anticipate cross-compilation.

What has to be worked out

1. Which binaries ship. All seven, or the user-facing subset? devlore-inventory and star are build tools — a target machine has no obvious use for them, but devlore-test may be exactly what runs on the target.
2. How binaries reach the target. Artifact upload, a release, a shared path, scp — and whether that is CI's job or a local make target.
3. What "verify" means on the target. Self-install and exit 0, or self-install and then run a scenario subset? The stronger form needs devlore-test and its data/*.star fixtures on the target too.
4. Where it runs. CI matrix job, or an operator-driven flow the user invokes by hand across their own boxes. The stated motivation — not maintaining environments — points away from CI runners and toward real machines.
5. CGO_ENABLED. dist forces 0. Whether every binary tolerates that, and whether it should be uniform, is unverified.
6. The regression guard. Independent of the full workflow, CI should run a cross-compile build so Cross-compiling the product cross-compiles the build tools too #639 cannot silently return. That is the cheap half and could land well before the rest.

Suggested first cut

Item 6 alone, immediately after #639: a CI step that runs GOOS=linux make build and GOOS=windows make build. It protects the fix, costs one job, and needs none of the decisions above settled.