feat!: configure through shipyard-cmake; one locator, not three

[schmonz]

Part of the 14-repo shipyard-cmake flag day.

Do not merge until shipyard has landed bc3082a. Until then shipyard-cmake exists on no runner, so this PR's own CI is expected to fail at the first configure. That red is the merge-order hold, not a defect.

What changed

• msc.sh (repo root — check 17 accepts build/msc.sh or a root msc.sh, and this repo's lives at the root) replaced wholesale by shipyard's canonical template. Verified byte-identical.
• Two more locators, which the survey did not anticipate. package.sh:26-35 and scripts/guard.sh:14-23 each carried their own four-entry fallback chain, and both named $HOME/.local/share/cmake/MavericksShipyard/scripts — the prefix a cmake --install used to produce, which the pkg does not create. Neither read ~/.cmake/packages, so neither was flagged by check 16 or by a registry sweep; both were about to resolve nothing off CI. package.sh's chain also overwrote the $SHIPYARD that msc.sh had set eleven lines earlier. Both now use $SHIPYARD.
• scripts/guard.sh keeps its exit 4 for the case that is genuinely its own — shipyard found, assert_binary_compatible.sh missing from it — which is a different failure from msc.sh's "no shipyard at all" (exit 1). Both were proven by running them.
• Four call sites now use shipyard-cmake: the updater configure and --build in release.yml, build.sh:143's stdlib configure, and the build it: cmake --build build/updater recipe package.sh prints when the updater is absent.
• build.sh's prerequisites line named plain cmake; it now names the shipyard pkg. Two release.yml comments named the user package registry and ${MavericksShipyard_SCRIPTS} (a variable this PR removes); they now name the pkg and $SHIPYARD_SCRIPTS.

The one the gate cannot see

package.sh:55 prints its recipe from inside (... build it: ...). Check 18 deliberately treats a bare ( as not command position, so it was invisible to the gate. Found by sweeping every tracked file, not just the gate's subset.

Verification

• check-family-conventions.sh (from shipyard-cmake-collapsed): 4 failures -> ok, exit 0.
• Whole-tree sweep with check 18's own regex over git ls-files: clean, no exceptions needed. A wider sweep leaves only prose (MANIFEST's "key cmake flags", two build.sh comments about CMake build trees).
• No registry reference, no .local/share/cmake path and no MavericksShipyard_SCRIPTS survives anywhere in the tree.
• Also green: check-shell-portability.sh, check-comments.sh, sh -n on every tracked *.sh, all three workflows parse as YAML.
• scripts/guard.sh run three ways: with $SHIPYARD_SCRIPTS set it reaches the shared guard; with an empty shipyard it exits 4 with its own message; with no shipyard it exits 1 from msc.sh.
• No workflow step was added; install@v1's default mode already puts shipyard-cmake on PATH.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GTxFde2TJMmp5p64DhvDSK