diff --git a/go/delivery/fingerprint.go b/go/delivery/fingerprint.go
index 443039e..8966d67 100644
--- a/go/delivery/fingerprint.go
+++ b/go/delivery/fingerprint.go
@@ -10,7 +10,9 @@ import (
 // SourceInputs are what a module's source fingerprint is of (novox/hq ADR 0437 §5): the module, the git tree of
 // its directory, its bases (references, of which only the digest counts), the root tree of each repository its
 // artifacts read (by artifact), each artifact's toolchain line, and the reason the source does not pin the build
-// when it does not (a build that resolves packages when built).
+// when it does not (a build that resolves packages when built). A context is the value the builder records for it:
+// a repository's root tree, or for an image that compiles a Go program the `narrow:` hash of the build source it was
+// handed (mesh-controller internal/builder/builder.go:1146-1156).
 type SourceInputs struct {
 	Module     string
 	Tree       string
diff --git a/go/delivery/fingerprint_test.go b/go/delivery/fingerprint_test.go
index a7fd036..198862d 100644
--- a/go/delivery/fingerprint_test.go
+++ b/go/delivery/fingerprint_test.go
@@ -114,3 +114,65 @@ func TestReferenceDigest(t *testing.T) {
 		}
 	}
 }
+
+// 1203/AC1: three builds the live builder recorded a source fingerprint for. Each value is captured, never written
+// by hand: the recorded fingerprint was read with mesh-controller.builds (after issues 1204 and 1208 were
+// delivered); each tree is `git rev-parse <commit>:<dir>` in the repository's clone; the bases are from the
+// build's `[bases]` log lines; the toolchain lines are mesh-controller's toolchainOf over its toolchains values.
+func TestFingerprintLiveBuilds(t *testing.T) {
+	const ts = "typescript sha256:4b81682df5665c1f461d3f720a3a0fd7593f4aa71e4fc272dbfdc4bbd235b489 20125bd590041690"
+	for _, c := range []struct {
+		name     string
+		in       SourceInputs
+		recorded string
+	}{
+		{
+			// mailu, build-1792391134620131370: mesh-catalog at b4527d9091e972f28cb365623d9280045e7741a3, dir modules/mailu.
+			name: "mailu",
+			in: SourceInputs{
+				Module:     "mailu",
+				Tree:       "cfc6fa8ff5fc1e220132e51ade653b9d3f387b3e",
+				Bases:      []string{"sha256:25f3cfeaceca14921366af4d1240b56457ef46273bdb508c7b0e8f469f6fd228"},
+				Toolchains: map[string]string{"code": ts},
+			},
+			recorded: "src1:539f2e64000d436c572ef53b40e524012455945f8c5a1c6bb173ee0707e88ef4",
+		},
+		{
+			// radarr, build-1792391147149753355: mesh-media-catalog at 197abb061d9b77d67c7f11e9e567528ea7a85436,
+			// dir modules/radarr; no bases.
+			name: "radarr",
+			in: SourceInputs{
+				Module: "radarr",
+				Tree:   "42b9c918b5af75cba2bbc75845012e7f64e16df9",
+				Toolchains: map[string]string{
+					"code":     ts,
+					"tools-go": "go sha256:2054591ca034b68323d87ec887ba34f56819cb3364034360c0777da4b314dd54 0995d85edc9a6a23",
+				},
+			},
+			recorded: "src1:b3c150d39c395b99dd68974a48490e9a42467aa5d486d0c604d6ef1e8e9c910a",
+		},
+		{
+			// build-agent, build-1792395447088936520: mesh-controller at 7a74cee83f88e6585a5511c3cc53bdf0f5303d20,
+			// dir modules/build-agent; the context is narrowTree's hash of the 185 paths GoBuildSource gave for
+			// cmd/mesh-builder at 7a74cee8.
+			name: "build-agent",
+			in: SourceInputs{
+				Module: "build-agent",
+				Tree:   "11c0b4f90cae0d6e4ef9cc48cbfdf9f6dbe52bca",
+				Bases: []string{
+					"sha256:d9e853e87e55526f6b2917df91a2115c36dd7c696a35be12163d44e6e2a4b6bc",
+					"sha256:8ac98ca534ac3f51e1f420a1dd2c15e74c75cfa0f23f3ad27eb5d7236c349a0c",
+				},
+				Contexts: map[string]string{"server": "narrow:d51ca744fd11af59d616c858f76c27b3e58e16e11fbdc0c720eb9d7d19d55fac"},
+			},
+			recorded: "src1:e846efe73716b78e80860baaac96153de2cb76551325753838ca245d2160a3d7",
+		},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			fp, none := SourceFingerprint(c.in)
+			if none != "" || fp != c.recorded {
+				t.Errorf("fingerprint = %q (none %q), the live builder recorded %q", fp, none, c.recorded)
+			}
+		})
+	}
+}