The Git-target grammar (slug, branch, and SHA rules plus the derived
origin URL) was implemented twice with no shared code path: once in
server admission and again in sandbox start, so the two could drift and
disagree about which persisted targets are valid.
Own it once as RunTarget::validate() in fabro-types, next to the
primitives it uses, returning the canonical target together with its
derived GitContext projection. Admission consumes it directly, and the
start path re-derives the expected clone source from the same rules
before checking the persisted projection against it. The start path now
also moves the derived strings into the sandbox spec instead of cloning
them.
While reordering admission around the shared validator, run the pure,
in-memory checks (target grammar, environment id) before the blob-store
closure fetch and lowering so malformed requests no longer pay for
version-store I/O.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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