mesh-build-go: give each ask a cache layer in its workspace, so what its digest and vet compile its tests find compiled

Pins mesh-sdk fix/check-speed-s2 (2a867018), whose Isolation.CacheLayer keeps what one
command of an ask writes into the caches for the ask's later commands, the shared cache
unchanged. A trunk build and the lint's vet still write the shared cache directly.
Ported from feat/try-speed S2 (issue 1921; ADR 0541 §2).

modules/mesh-build-go/cmd/mesh-build-go/isolate.go

@@ -43,15 +43,16 @@ func (m *Module) isolation(workspace string, write bool) buildstep.Isolation {
 		Env:         append([]string{"PATH=" + path, "LC_ALL=C"}, m.threadEnv()...),
 	}
 	if !write {
-		// What one command of the ask compiles into the build cache is kept for its later commands (the digests, the unit
-		// tests, the integration level's compile), beside the workspace, out of every step's reach, and gone with it
-		// (issue 1921, try speed S2); the module cache keeps its throwaway layer.
-		iso.CacheLayer = m.spaces().CacheLayer(workspace)
-		iso.LayerCaches = []string{filepath.Join(m.Cache, "gobuild")}
+		// What one command of the ask compiles is kept for its later commands (the vet, the unit tests, the integration
+		// level's compile), in the workspace and gone with it (issue 1921, try speed S2).
+		iso.CacheLayer = filepath.Join(iso.Workspace, cacheLayerDir)
 	}
 	return iso
 }
 
+// cacheLayerDir is the directory in a workspace's root where an ask keeps what its commands wrote into the caches.
+const cacheLayerDir = "cachelayer"
+
 // stepRunner is the runner of a run step of the workspace: buildstep.Isolated over m.Run, so every command it runs is
 // shut off; write is true for a trunk build and for a check's go vet, compile steps that run nothing of the change (ADR 0541 §2). Inside is the
 // integration level's own process, already running shut off (level.go): it runs its commands as they are.

modules/mesh-build-go/cmd/mesh-build-go/isolate_test.go

@@ -111,12 +111,9 @@ func checkShutOff(t *testing.T, m *Module, s shutOff, write bool) {
 			t.Errorf("a trunk build's %s does not write the shared cache %s (bound %v, layered %v)", s.command, c, bound, layered)
 		case !write && (bound || !layered):
 			t.Errorf("%s may write the shared cache %s (bound %v, layered %v): only a trunk build does", s.command, c, bound, layered)
-		case !write && c == filepath.Join(m.Cache, "gobuild") && !strings.HasPrefix(s.uppers[c], filepath.Join(m.Work, "ws1.cachelayer")+"/"):
-			// 1921/S2: what one command of the ask compiles is kept for its later commands, beside the workspace
-			t.Errorf("%s writes the build cache %s into %q, not the ask's cache layer beside its workspace", s.command, c, s.uppers[c])
-		case !write && c != filepath.Join(m.Cache, "gobuild") && s.uppers[c] != "":
-			// the module cache keeps its throwaway layer
-			t.Errorf("%s keeps what it writes into the module cache %s (in %q)", s.command, c, s.uppers[c])
+		case !write && !strings.HasPrefix(s.uppers[c], filepath.Join(m.Work, "ws1", "cachelayer")+"/"):
+			// 1921/S2: what one command of the ask compiles is kept for its later commands, in the workspace
+			t.Errorf("%s writes the cache %s into %q, not the ask's cache layer in its workspace", s.command, c, s.uppers[c])
 		}
 	}
 	if want := filepath.Join(m.Work, "ws1"); !slices.Contains(s.binds, want) {

modules/mesh-build-go/go.mod

@@ -3,7 +3,7 @@ module meshbuildgo
 go 1.26.0
 
 require (
-	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235126-2a8670189188
 	github.com/distribution/distribution/v3 v3.1.2
 	github.com/nats-io/nats-server/v2 v2.11.17
 	github.com/nats-io/nats.go v1.54.0

modules/mesh-build-go/go.sum

@@ -1,9 +1,7 @@
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028230718-261f41aec1ae h1:bwcj9NnfGk/DP0sbTRInPAA4aMUnvr8+CmQLhnDvV9w=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028230718-261f41aec1ae/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235320-62a50ebcf822 h1:od9tMSw9yHRLe4c03/u9EVr7TpXZ+pEJa2XY5evx6Ho=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235320-62a50ebcf822/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819 h1:ypKERyJAbbsydMKLlPmWKU++wU2YCPLzGC0nzdw6QvQ=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028190821-9e5666b4d6f5 h1:L7EJbCPZfJRCYHyco5Ck3ui+pWc//sp+h5nnPqSarng=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028190821-9e5666b4d6f5/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235126-2a8670189188 h1:0ZJZmp4wqiJlBlVHAdGonVIRaLf0Z79Ql4DFR2k8E8c=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235126-2a8670189188/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
 github.com/alicebob/miniredis/v2 v2.35.0 h1:QwLphYqCEAo1eu1TqPRN2jgVMPBweeQcR21jeqDCONI=
 github.com/alicebob/miniredis/v2 v2.35.0/go.mod h1:TcL7YfarKPGDAthEtl5NBeHZfeUQj6OXMm/+iu5cLMM=
 github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=

modules/mesh-build-node/go.mod

@@ -3,7 +3,7 @@ module meshbuildnode
 go 1.26.0
 
 require (
-	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028190821-9e5666b4d6f5
 	github.com/distribution/distribution/v3 v3.1.2
 	github.com/nats-io/nats.go v1.54.0
 )

modules/mesh-build-node/go.sum

@@ -1,9 +1,5 @@
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028230718-261f41aec1ae h1:bwcj9NnfGk/DP0sbTRInPAA4aMUnvr8+CmQLhnDvV9w=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028230718-261f41aec1ae/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235320-62a50ebcf822 h1:od9tMSw9yHRLe4c03/u9EVr7TpXZ+pEJa2XY5evx6Ho=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028235320-62a50ebcf822/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819 h1:ypKERyJAbbsydMKLlPmWKU++wU2YCPLzGC0nzdw6QvQ=
-git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261029000420-979f2cd71819/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028190821-9e5666b4d6f5 h1:L7EJbCPZfJRCYHyco5Ck3ui+pWc//sp+h5nnPqSarng=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261028190821-9e5666b4d6f5/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
 github.com/alicebob/miniredis/v2 v2.35.0 h1:QwLphYqCEAo1eu1TqPRN2jgVMPBweeQcR21jeqDCONI=
 github.com/alicebob/miniredis/v2 v2.35.0/go.mod h1:TcL7YfarKPGDAthEtl5NBeHZfeUQj6OXMm/+iu5cLMM=
 github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=