diff --git a/src/libstore-tests/data/worker-substitution/ca-drv/store-after.json b/src/libstore-tests/data/worker-substitution/ca-drv/store-after.json
new file mode 100644
index 000000000..7f0f62f87
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/ca-drv/store-after.json
@@ -0,0 +1,58 @@
+{
+  "buildTrace": {
+    "gnRuK+wfbXqRPzgO5MyiBebXrV10Kzv+tkZCEuPm7pY=": {
+      "out": {
+        "dependentRealisations": {},
+        "outPath": "hrva7l0gsk67wffmks761mv4ks4vzsx7-test-ca-drv-out",
+        "signatures": []
+      }
+    }
+  },
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "hrva7l0gsk67wffmks761mv4ks4vzsx7-test-ca-drv-out": {
+      "contents": {
+        "contents": "I am the output of a CA derivation",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-l0+gmYB0AK65UWuoSh7AbVRI4rAc5/VGqzBGTHgMsiU=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-l0+gmYB0AK65UWuoSh7AbVRI4rAc5/VGqzBGTHgMsiU=",
+        "narSize": 152,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {
+    "vvyyj6h5ilinsv4q48q5y5vn7s3hxmhl-test-ca-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {},
+        "srcs": []
+      },
+      "name": "test-ca-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    }
+  }
+}
diff --git a/src/libstore-tests/data/worker-substitution/ca-drv/store-before.json b/src/libstore-tests/data/worker-substitution/ca-drv/store-before.json
new file mode 100644
index 000000000..6d64d2327
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/ca-drv/store-before.json
@@ -0,0 +1,27 @@
+{
+  "buildTrace": {},
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {},
+  "derivations": {
+    "vvyyj6h5ilinsv4q48q5y5vn7s3hxmhl-test-ca-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {},
+        "srcs": []
+      },
+      "name": "test-ca-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    }
+  }
+}
diff --git a/src/libstore-tests/data/worker-substitution/ca-drv/substituter.json b/src/libstore-tests/data/worker-substitution/ca-drv/substituter.json
new file mode 100644
index 000000000..93f4fb22a
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/ca-drv/substituter.json
@@ -0,0 +1,39 @@
+{
+  "buildTrace": {
+    "gnRuK+wfbXqRPzgO5MyiBebXrV10Kzv+tkZCEuPm7pY=": {
+      "out": {
+        "dependentRealisations": {},
+        "outPath": "hrva7l0gsk67wffmks761mv4ks4vzsx7-test-ca-drv-out",
+        "signatures": []
+      }
+    }
+  },
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "hrva7l0gsk67wffmks761mv4ks4vzsx7-test-ca-drv-out": {
+      "contents": {
+        "contents": "I am the output of a CA derivation",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-l0+gmYB0AK65UWuoSh7AbVRI4rAc5/VGqzBGTHgMsiU=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-l0+gmYB0AK65UWuoSh7AbVRI4rAc5/VGqzBGTHgMsiU=",
+        "narSize": 152,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {}
+}
diff --git a/src/libstore-tests/data/worker-substitution/issue-11928/store-after.json b/src/libstore-tests/data/worker-substitution/issue-11928/store-after.json
new file mode 100644
index 000000000..0d2cd439c
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/issue-11928/store-after.json
@@ -0,0 +1,114 @@
+{
+  "buildTrace": {
+    "8vEkprm3vQ3BE6JLB8XKfU+AdAwEFOMI/skzyj3pr5I=": {
+      "out": {
+        "dependentRealisations": {
+          "sha256:82746e2bec1f6d7a913f380ee4cca205e6d7ad5d742b3bfeb6464212e3e6ee96!out": "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out"
+        },
+        "outPath": "px7apdw6ydm9ynjy5g0bpdcylw3xz2kj-root-drv-out",
+        "signatures": []
+      }
+    },
+    "gnRuK+wfbXqRPzgO5MyiBebXrV10Kzv+tkZCEuPm7pY=": {
+      "out": {
+        "dependentRealisations": {},
+        "outPath": "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out",
+        "signatures": []
+      }
+    }
+  },
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "px7apdw6ydm9ynjy5g0bpdcylw3xz2kj-root-drv-out": {
+      "contents": {
+        "contents": "I am the root output. I don't reference anything because the other derivation's output is just needed at build time.",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-0mlhg9y1FGb7YsHAsNOmtuW44b8TfoPaNPK6SjVYe5s=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-0mlhg9y1FGb7YsHAsNOmtuW44b8TfoPaNPK6SjVYe5s=",
+        "narSize": 232,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    },
+    "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out": {
+      "contents": {
+        "contents": "I am the dependency output",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-HK2LBzSTtwuRjc44PH3Ac1JHHPKmfnAgNxz6I5mVgL8=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-HK2LBzSTtwuRjc44PH3Ac1JHHPKmfnAgNxz6I5mVgL8=",
+        "narSize": 144,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {
+    "11yvkl84ashq63ilwc2mi4va41z2disw-root-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {
+          "vy7j6m6p5y0327fhk3zxn12hbpzkh6lp-dep-drv.drv": {
+            "dynamicOutputs": {},
+            "outputs": [
+              "out"
+            ]
+          }
+        },
+        "srcs": []
+      },
+      "name": "root-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    },
+    "vy7j6m6p5y0327fhk3zxn12hbpzkh6lp-dep-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {},
+        "srcs": []
+      },
+      "name": "dep-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    }
+  }
+}
diff --git a/src/libstore-tests/data/worker-substitution/issue-11928/store-before.json b/src/libstore-tests/data/worker-substitution/issue-11928/store-before.json
new file mode 100644
index 000000000..47a3b34be
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/issue-11928/store-before.json
@@ -0,0 +1,52 @@
+{
+  "buildTrace": {},
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {},
+  "derivations": {
+    "11yvkl84ashq63ilwc2mi4va41z2disw-root-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {
+          "vy7j6m6p5y0327fhk3zxn12hbpzkh6lp-dep-drv.drv": {
+            "dynamicOutputs": {},
+            "outputs": [
+              "out"
+            ]
+          }
+        },
+        "srcs": []
+      },
+      "name": "root-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    },
+    "vy7j6m6p5y0327fhk3zxn12hbpzkh6lp-dep-drv.drv": {
+      "args": [],
+      "builder": "",
+      "env": {},
+      "inputs": {
+        "drvs": {},
+        "srcs": []
+      },
+      "name": "dep-drv",
+      "outputs": {
+        "out": {
+          "hashAlgo": "sha256",
+          "method": "nar"
+        }
+      },
+      "system": "",
+      "version": 4
+    }
+  }
+}
diff --git a/src/libstore-tests/data/worker-substitution/issue-11928/substituter.json b/src/libstore-tests/data/worker-substitution/issue-11928/substituter.json
new file mode 100644
index 000000000..c3530b8d5
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/issue-11928/substituter.json
@@ -0,0 +1,70 @@
+{
+  "buildTrace": {
+    "8vEkprm3vQ3BE6JLB8XKfU+AdAwEFOMI/skzyj3pr5I=": {
+      "out": {
+        "dependentRealisations": {
+          "sha256:82746e2bec1f6d7a913f380ee4cca205e6d7ad5d742b3bfeb6464212e3e6ee96!out": "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out"
+        },
+        "outPath": "px7apdw6ydm9ynjy5g0bpdcylw3xz2kj-root-drv-out",
+        "signatures": []
+      }
+    },
+    "gnRuK+wfbXqRPzgO5MyiBebXrV10Kzv+tkZCEuPm7pY=": {
+      "out": {
+        "dependentRealisations": {},
+        "outPath": "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out",
+        "signatures": []
+      }
+    }
+  },
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "px7apdw6ydm9ynjy5g0bpdcylw3xz2kj-root-drv-out": {
+      "contents": {
+        "contents": "I am the root output. I don't reference anything because the other derivation's output is just needed at build time.",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-0mlhg9y1FGb7YsHAsNOmtuW44b8TfoPaNPK6SjVYe5s=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-0mlhg9y1FGb7YsHAsNOmtuW44b8TfoPaNPK6SjVYe5s=",
+        "narSize": 232,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    },
+    "w0yjpwh59kpbyc7hz9jgmi44r9br908i-dep-drv-out": {
+      "contents": {
+        "contents": "I am the dependency output",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-HK2LBzSTtwuRjc44PH3Ac1JHHPKmfnAgNxz6I5mVgL8=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-HK2LBzSTtwuRjc44PH3Ac1JHHPKmfnAgNxz6I5mVgL8=",
+        "narSize": 144,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {}
+}
diff --git a/src/libstore-tests/data/worker-substitution/single/substituter.json b/src/libstore-tests/data/worker-substitution/single/substituter.json
new file mode 100644
index 000000000..f22d4c7df
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/single/substituter.json
@@ -0,0 +1,31 @@
+{
+  "buildTrace": {},
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "axqic2q30v0sqvcpiqxs139q8w6zd4n8-hello": {
+      "contents": {
+        "contents": "Hello, world!",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-KShIJtIwWG1gMSpvPMt5drppc1h5WMwHWzVpNJiVqGI=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-KShIJtIwWG1gMSpvPMt5drppc1h5WMwHWzVpNJiVqGI=",
+        "narSize": 128,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {}
+}
diff --git a/src/libstore-tests/data/worker-substitution/with-dep/store.json b/src/libstore-tests/data/worker-substitution/with-dep/store.json
new file mode 100644
index 000000000..3f2994dfb
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/with-dep/store.json
@@ -0,0 +1,55 @@
+{
+  "buildTrace": {},
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "4k79i02avcckr96r97lqnswn75fi1gv7-dependency": {
+      "contents": {
+        "contents": "I am a dependency",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-miJnClL0Ai/HAmX1G/pz7P2TIaeFjP5D/VN1rhYf354=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-miJnClL0Ai/HAmX1G/pz7P2TIaeFjP5D/VN1rhYf354=",
+        "narSize": 136,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    },
+    "k09ldq9fvxb6vfwq0cmv6j1jgqx08y1n-main": {
+      "contents": {
+        "contents": "I depend on /nix/store/4k79i02avcckr96r97lqnswn75fi1gv7-dependency",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-CBfMK3HkqiXjpI8HNL1spWD/US4RnQHwI67Ojl50XoQ=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-CBfMK3HkqiXjpI8HNL1spWD/US4RnQHwI67Ojl50XoQ=",
+        "narSize": 184,
+        "references": [
+          "4k79i02avcckr96r97lqnswn75fi1gv7-dependency"
+        ],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {}
+}
diff --git a/src/libstore-tests/data/worker-substitution/with-dep/substituter.json b/src/libstore-tests/data/worker-substitution/with-dep/substituter.json
new file mode 100644
index 000000000..3f2994dfb
--- /dev/null
+++ b/src/libstore-tests/data/worker-substitution/with-dep/substituter.json
@@ -0,0 +1,55 @@
+{
+  "buildTrace": {},
+  "config": {
+    "store": "/nix/store"
+  },
+  "contents": {
+    "4k79i02avcckr96r97lqnswn75fi1gv7-dependency": {
+      "contents": {
+        "contents": "I am a dependency",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-miJnClL0Ai/HAmX1G/pz7P2TIaeFjP5D/VN1rhYf354=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-miJnClL0Ai/HAmX1G/pz7P2TIaeFjP5D/VN1rhYf354=",
+        "narSize": 136,
+        "references": [],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    },
+    "k09ldq9fvxb6vfwq0cmv6j1jgqx08y1n-main": {
+      "contents": {
+        "contents": "I depend on /nix/store/4k79i02avcckr96r97lqnswn75fi1gv7-dependency",
+        "executable": false,
+        "type": "regular"
+      },
+      "info": {
+        "ca": {
+          "hash": "sha256-CBfMK3HkqiXjpI8HNL1spWD/US4RnQHwI67Ojl50XoQ=",
+          "method": "nar"
+        },
+        "deriver": null,
+        "narHash": "sha256-CBfMK3HkqiXjpI8HNL1spWD/US4RnQHwI67Ojl50XoQ=",
+        "narSize": 184,
+        "references": [
+          "4k79i02avcckr96r97lqnswn75fi1gv7-dependency"
+        ],
+        "registrationTime": null,
+        "signatures": [],
+        "storeDir": "/nix/store",
+        "ultimate": false,
+        "version": 2
+      }
+    }
+  },
+  "derivations": {}
+}
diff --git a/src/libstore-tests/meson.build b/src/libstore-tests/meson.build
index 58f624611..123bccb90 100644
--- a/src/libstore-tests/meson.build
+++ b/src/libstore-tests/meson.build
@@ -85,6 +85,7 @@ sources = files(
   'store-reference.cc',
   'uds-remote-store.cc',
   'worker-protocol.cc',
+  'worker-substitution.cc',
   'write-derivation.cc',
 )
 
diff --git a/src/libstore-tests/worker-substitution.cc b/src/libstore-tests/worker-substitution.cc
new file mode 100644
index 000000000..016f6207b
--- /dev/null
+++ b/src/libstore-tests/worker-substitution.cc
@@ -0,0 +1,449 @@
+#include <gtest/gtest.h>
+#include <nlohmann/json.hpp>
+
+#include "nix/store/build/worker.hh"
+#include "nix/store/derivations.hh"
+#include "nix/store/dummy-store-impl.hh"
+#include "nix/store/globals.hh"
+#include "nix/util/memory-source-accessor.hh"
+
+#include "nix/store/tests/libstore.hh"
+#include "nix/util/tests/json-characterization.hh"
+
+namespace nix {
+
+class WorkerSubstitutionTest : public LibStoreTest, public JsonCharacterizationTest<ref<DummyStore>>
+{
+    std::filesystem::path unitTestData = getUnitTestData() / "worker-substitution";
+
+protected:
+    ref<DummyStore> dummyStore;
+    ref<DummyStore> substituter;
+
+    WorkerSubstitutionTest()
+        : LibStoreTest([] {
+            auto config = make_ref<DummyStoreConfig>(DummyStoreConfig::Params{});
+            config->readOnly = false;
+            return config->openDummyStore();
+        }())
+        , dummyStore(store.dynamic_pointer_cast<DummyStore>())
+        , substituter([] {
+            auto config = make_ref<DummyStoreConfig>(DummyStoreConfig::Params{});
+            config->readOnly = false;
+            config->isTrusted = true;
+            return config->openDummyStore();
+        }())
+    {
+    }
+
+public:
+    std::filesystem::path goldenMaster(std::string_view testStem) const override
+    {
+        return unitTestData / testStem;
+    }
+
+    static void SetUpTestSuite()
+    {
+        initLibStore(false);
+    }
+};
+
+TEST_F(WorkerSubstitutionTest, singleStoreObject)
+{
+    // Add a store path to the substituter
+    auto pathInSubstituter = substituter->addToStore(
+        "hello",
+        SourcePath{
+            [] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents = "Hello, world!",
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256);
+
+    // Snapshot the substituter (has one store object)
+    checkpointJson("single/substituter", substituter);
+
+    // Snapshot the destination store before (should be empty)
+    checkpointJson("../dummy-store/empty", dummyStore);
+
+    // The path should not exist in the destination store yet
+    ASSERT_FALSE(dummyStore->isValidPath(pathInSubstituter));
+
+    // Create a worker with our custom substituter
+    Worker worker{*dummyStore, *dummyStore};
+
+    // Override the substituters to use our dummy store substituter
+    ref<Store> substituerAsStore = substituter;
+    worker.getSubstituters = [substituerAsStore]() -> std::list<ref<Store>> { return {substituerAsStore}; };
+
+    // Create a substitution goal for the path
+    auto goal = worker.makePathSubstitutionGoal(pathInSubstituter);
+
+    // Run the worker with -j0 semantics (no local builds, only substitution)
+    // The worker.run() takes a set of goals
+    Goals goals;
+    goals.insert(upcast_goal(goal));
+    worker.run(goals);
+
+    // Snapshot the destination store after (should match the substituter)
+    checkpointJson("single/substituter", dummyStore);
+
+    // The path should now exist in the destination store
+    ASSERT_TRUE(dummyStore->isValidPath(pathInSubstituter));
+
+    // Verify the goal succeeded
+    ASSERT_EQ(upcast_goal(goal)->exitCode, Goal::ecSuccess);
+}
+
+TEST_F(WorkerSubstitutionTest, singleRootStoreObjectWithSingleDepStoreObject)
+{
+    // First, add a dependency store path to the substituter
+    auto dependencyPath = substituter->addToStore(
+        "dependency",
+        SourcePath{
+            [] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents = "I am a dependency",
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256);
+
+    // Now add a store path that references the dependency
+    auto mainPath = substituter->addToStore(
+        "main",
+        SourcePath{
+            [&] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                // Include a reference to the dependency path in the contents
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents = "I depend on " + substituter->printStorePath(dependencyPath),
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256,
+        StorePathSet{dependencyPath});
+
+    // Snapshot the substituter (has two store objects)
+    checkpointJson("with-dep/substituter", substituter);
+
+    // Snapshot the destination store before (should be empty)
+    checkpointJson("../dummy-store/empty", dummyStore);
+
+    // Neither path should exist in the destination store yet
+    ASSERT_FALSE(dummyStore->isValidPath(dependencyPath));
+    ASSERT_FALSE(dummyStore->isValidPath(mainPath));
+
+    // Create a worker with our custom substituter
+    Worker worker{*dummyStore, *dummyStore};
+
+    // Override the substituters to use our dummy store substituter
+    ref<Store> substituterAsStore = substituter;
+    worker.getSubstituters = [substituterAsStore]() -> std::list<ref<Store>> { return {substituterAsStore}; };
+
+    // Create a substitution goal for the main path only
+    // The worker should automatically substitute the dependency as well
+    auto goal = worker.makePathSubstitutionGoal(mainPath);
+
+    // Run the worker
+    Goals goals;
+    goals.insert(upcast_goal(goal));
+    worker.run(goals);
+
+    // Snapshot the destination store after (should match the substituter)
+    checkpointJson("with-dep/substituter", dummyStore);
+
+    // Both paths should now exist in the destination store
+    ASSERT_TRUE(dummyStore->isValidPath(dependencyPath));
+    ASSERT_TRUE(dummyStore->isValidPath(mainPath));
+
+    // Verify the goal succeeded
+    ASSERT_EQ(upcast_goal(goal)->exitCode, Goal::ecSuccess);
+}
+
+TEST_F(WorkerSubstitutionTest, floatingDerivationOutput)
+{
+    // Enable CA derivations experimental feature
+    experimentalFeatureSettings.set("extra-experimental-features", "ca-derivations");
+
+    // Create a CA floating output derivation
+    Derivation drv;
+    drv.name = "test-ca-drv";
+    drv.outputs = {
+        {
+            "out",
+            DerivationOutput{DerivationOutput::CAFloating{
+                .method = ContentAddressMethod::Raw::NixArchive,
+                .hashAlgo = HashAlgorithm::SHA256,
+            }},
+        },
+    };
+
+    // Write the derivation to the destination store
+    auto drvPath = writeDerivation(*dummyStore, drv);
+
+    // Snapshot the destination store before
+    checkpointJson("ca-drv/store-before", dummyStore);
+
+    // Compute the hash modulo of the derivation
+    // For CA floating derivations, the kind is Deferred since outputs aren't known until build
+    auto hashModulo = hashDerivationModulo(*dummyStore, drv, true);
+    ASSERT_EQ(hashModulo.kind, DrvHash::Kind::Deferred);
+    auto drvHash = hashModulo.hashes.at("out");
+
+    // Create the output store object
+    auto outputPath = substituter->addToStore(
+        "test-ca-drv-out",
+        SourcePath{
+            [] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents = "I am the output of a CA derivation",
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256);
+
+    // Add the realisation (build trace) to the substituter
+    substituter->buildTrace.insert_or_assign(
+        drvHash,
+        std::map<std::string, UnkeyedRealisation>{
+            {
+                "out",
+                UnkeyedRealisation{
+                    .outPath = outputPath,
+                },
+            },
+        });
+
+    // Snapshot the substituter
+    checkpointJson("ca-drv/substituter", substituter);
+
+    // The realisation should not exist in the destination store yet
+    DrvOutput drvOutput{drvHash, "out"};
+    ASSERT_FALSE(dummyStore->queryRealisation(drvOutput));
+
+    // Create a worker with our custom substituter
+    Worker worker{*dummyStore, *dummyStore};
+
+    // Override the substituters to use our dummy store substituter
+    ref<Store> substituterAsStore = substituter;
+    worker.getSubstituters = [substituterAsStore]() -> std::list<ref<Store>> { return {substituterAsStore}; };
+
+    // Create a derivation goal for the CA derivation output
+    // The worker should substitute the output rather than building
+    auto goal = worker.makeDerivationGoal(drvPath, drv, "out", bmNormal, true);
+
+    // Run the worker
+    Goals goals;
+    goals.insert(upcast_goal(goal));
+    worker.run(goals);
+
+    // Snapshot the destination store after
+    checkpointJson("ca-drv/store-after", dummyStore);
+
+    // The output path should now exist in the destination store
+    ASSERT_TRUE(dummyStore->isValidPath(outputPath));
+
+    // The realisation should now exist in the destination store
+    auto realisation = dummyStore->queryRealisation(drvOutput);
+    ASSERT_TRUE(realisation);
+    ASSERT_EQ(realisation->outPath, outputPath);
+
+    // Verify the goal succeeded
+    ASSERT_EQ(upcast_goal(goal)->exitCode, Goal::ecSuccess);
+
+    // Disable CA derivations experimental feature
+    experimentalFeatureSettings.set("extra-experimental-features", "");
+}
+
+/**
+ * Test for issue #11928: substituting a CA derivation output should not
+ * require fetching the output of an input derivation when that output
+ * is not referenced.
+ */
+TEST_F(WorkerSubstitutionTest, floatingDerivationOutputWithDepDrv)
+{
+    // Enable CA derivations experimental feature
+    experimentalFeatureSettings.set("extra-experimental-features", "ca-derivations");
+
+    // Create the dependency CA floating derivation
+    Derivation depDrv;
+    depDrv.name = "dep-drv";
+    depDrv.outputs = {
+        {
+            "out",
+            DerivationOutput{DerivationOutput::CAFloating{
+                .method = ContentAddressMethod::Raw::NixArchive,
+                .hashAlgo = HashAlgorithm::SHA256,
+            }},
+        },
+    };
+
+    // Write the dependency derivation to the destination store
+    auto depDrvPath = writeDerivation(*dummyStore, depDrv);
+
+    // Compute the hash modulo for the dependency derivation
+    auto depHashModulo = hashDerivationModulo(*dummyStore, depDrv, true);
+    ASSERT_EQ(depHashModulo.kind, DrvHash::Kind::Deferred);
+    auto depDrvHash = depHashModulo.hashes.at("out");
+
+    // Create the output store object for the dependency in the substituter
+    auto depOutputPath = substituter->addToStore(
+        "dep-drv-out",
+        SourcePath{
+            [] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents = "I am the dependency output",
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256);
+
+    // Add the realisation for the dependency to the substituter
+    substituter->buildTrace.insert_or_assign(
+        depDrvHash,
+        std::map<std::string, UnkeyedRealisation>{
+            {
+                "out",
+                UnkeyedRealisation{
+                    .outPath = depOutputPath,
+                },
+            },
+        });
+
+    // Create the root CA floating derivation that depends on depDrv
+    Derivation rootDrv;
+    rootDrv.name = "root-drv";
+    rootDrv.outputs = {
+        {
+            "out",
+            DerivationOutput{DerivationOutput::CAFloating{
+                .method = ContentAddressMethod::Raw::NixArchive,
+                .hashAlgo = HashAlgorithm::SHA256,
+            }},
+        },
+    };
+    // Add the dependency derivation as an input
+    rootDrv.inputDrvs = {.map = {{depDrvPath, {.value = {"out"}}}}};
+
+    // Write the root derivation to the destination store
+    auto rootDrvPath = writeDerivation(*dummyStore, rootDrv);
+
+    // Snapshot the destination store before
+    checkpointJson("issue-11928/store-before", dummyStore);
+
+    // Compute the hash modulo for the root derivation
+    auto rootHashModulo = hashDerivationModulo(*dummyStore, rootDrv, true);
+    ASSERT_EQ(rootHashModulo.kind, DrvHash::Kind::Deferred);
+    auto rootDrvHash = rootHashModulo.hashes.at("out");
+
+    // Create the output store object for the root derivation
+    // Note: it does NOT reference the dependency's output
+    auto rootOutputPath = substituter->addToStore(
+        "root-drv-out",
+        SourcePath{
+            [] {
+                auto sc = make_ref<MemorySourceAccessor>();
+                sc->root = MemorySourceAccessor::File{MemorySourceAccessor::File::Regular{
+                    .executable = false,
+                    .contents =
+                        "I am the root output. "
+                        "I don't reference anything because the other derivation's output is just needed at build time.",
+                }};
+                return sc;
+            }(),
+        },
+        ContentAddressMethod::Raw::NixArchive,
+        HashAlgorithm::SHA256);
+
+    // The DrvOutputs for both derivations
+    DrvOutput depDrvOutput{depDrvHash, "out"};
+    DrvOutput rootDrvOutput{rootDrvHash, "out"};
+
+    // Add the realisation for the root derivation to the substituter
+    // Include the dependency realisation in dependentRealisations
+    substituter->buildTrace.insert_or_assign(
+        rootDrvHash,
+        std::map<std::string, UnkeyedRealisation>{
+            {
+                "out",
+                UnkeyedRealisation{
+                    .outPath = rootOutputPath,
+                    .dependentRealisations = {{depDrvOutput, depOutputPath}},
+                },
+            },
+        });
+
+    // Snapshot the substituter
+    // Note: it has realisations for both drvs, but only the root's output store object
+    checkpointJson("issue-11928/substituter", substituter);
+
+    // The realisations should not exist in the destination store yet
+    ASSERT_FALSE(dummyStore->queryRealisation(depDrvOutput));
+    ASSERT_FALSE(dummyStore->queryRealisation(rootDrvOutput));
+
+    // Create a worker with our custom substituter
+    Worker worker{*dummyStore, *dummyStore};
+
+    // Override the substituters to use our dummy store substituter
+    ref<Store> substituterAsStore = substituter;
+    worker.getSubstituters = [substituterAsStore]() -> std::list<ref<Store>> { return {substituterAsStore}; };
+
+    // Create a derivation goal for the root derivation output
+    // The worker should substitute the output rather than building
+    auto goal = worker.makeDerivationGoal(rootDrvPath, rootDrv, "out", bmNormal, false);
+
+    // Run the worker
+    Goals goals;
+    goals.insert(upcast_goal(goal));
+    worker.run(goals);
+
+    // Snapshot the destination store after
+    checkpointJson("issue-11928/store-after", dummyStore);
+
+    // The root output path should now exist in the destination store
+    ASSERT_TRUE(dummyStore->isValidPath(rootOutputPath));
+
+    // The root realisation should now exist in the destination store
+    auto rootRealisation = dummyStore->queryRealisation(rootDrvOutput);
+    ASSERT_TRUE(rootRealisation);
+    ASSERT_EQ(rootRealisation->outPath, rootOutputPath);
+
+    // The dependency's REALISATION should have been fetched
+    auto depRealisation = dummyStore->queryRealisation(depDrvOutput);
+    ASSERT_TRUE(depRealisation);
+    ASSERT_EQ(depRealisation->outPath, depOutputPath);
+
+    // TODO #11928: The dependency's OUTPUT should NOT be fetched (not referenced
+    // by root output). Once #11928 is fixed, change ASSERT_TRUE to ASSERT_FALSE.
+    ASSERT_TRUE(dummyStore->isValidPath(depOutputPath));
+
+    // Verify the goal succeeded
+    ASSERT_EQ(upcast_goal(goal)->exitCode, Goal::ecSuccess);
+
+    // Disable CA derivations experimental feature
+    experimentalFeatureSettings.set("extra-experimental-features", "");
+}
+
+} // namespace nix
diff --git a/src/libstore/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
index 03ebb38bb..171aa900a 100644
--- a/src/libstore/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -3,8 +3,6 @@
 #include "nix/store/build/worker.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/util/callback.hh"
-#include "nix/store/store-open.hh"
-#include "nix/store/globals.hh"
 
 namespace nix {
 
@@ -25,7 +23,7 @@ Goal::Co DrvOutputSubstitutionGoal::init()
         co_return amDone(ecSuccess);
     }
 
-    auto subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
+    auto subs = worker.getSubstituters();
 
     bool substituterFailed = false;
 
diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index 51dc87e8d..b1273835c 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -1,5 +1,4 @@
 #include "nix/store/build/worker.hh"
-#include "nix/store/store-open.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/store/nar-info.hh"
 #include "nix/util/finally.hh"
@@ -60,7 +59,7 @@ Goal::Co PathSubstitutionGoal::init()
         throw Error(
             "cannot substitute path '%s' - no write access to the Nix store", worker.store.printStorePath(storePath));
 
-    auto subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
+    auto subs = worker.getSubstituters();
 
     bool substituterFailed = false;
     std::optional<Error> lastStoresException = std::nullopt;
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 754f4b1cc..593319d03 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -1,5 +1,6 @@
 #include "nix/store/local-store.hh"
 #include "nix/store/machines.hh"
+#include "nix/store/store-open.hh"
 #include "nix/store/build/worker.hh"
 #include "nix/store/build/substitution-goal.hh"
 #include "nix/store/build/drv-output-substitution-goal.hh"
@@ -21,6 +22,7 @@ Worker::Worker(Store & store, Store & evalStore)
     , actSubstitutions(*logger, actCopyPaths)
     , store(store)
     , evalStore(evalStore)
+    , getSubstituters{[] { return settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>{}; }}
 {
     nrLocalBuilds = 0;
     nrSubstitutions = 0;
diff --git a/src/libstore/include/nix/store/build/worker.hh b/src/libstore/include/nix/store/build/worker.hh
index 173f7b222..65408429c 100644
--- a/src/libstore/include/nix/store/build/worker.hh
+++ b/src/libstore/include/nix/store/build/worker.hh
@@ -8,6 +8,7 @@
 #include "nix/store/realisation.hh"
 #include "nix/util/muxable-pipe.hh"
 
+#include <functional>
 #include <future>
 #include <thread>
 
@@ -171,6 +172,14 @@ public:
     Store & store;
     Store & evalStore;
 
+    /**
+     * Function to get the substituters to use for path substitution.
+     *
+     * Defaults to `getDefaultSubstituters`. This allows tests to
+     * inject custom substituters.
+     */
+    std::function<std::list<ref<Store>>()> getSubstituters;
+
 #ifndef _WIN32 // TODO Enable building on Windows
     std::unique_ptr<HookInstance> hook;
 #endif
diff --git a/src/libutil-test-support/include/nix/util/tests/json-characterization.hh b/src/libutil-test-support/include/nix/util/tests/json-characterization.hh
index 6db32c4b6..744880f38 100644
--- a/src/libutil-test-support/include/nix/util/tests/json-characterization.hh
+++ b/src/libutil-test-support/include/nix/util/tests/json-characterization.hh
@@ -83,6 +83,31 @@ void checkpointJson(CharacterizationTest & test, PathView testStem, const T & go
     }
 }
 
+/**
+ * Specialization for when we need to do "JSON -> `ref<T>`" in one
+ * direction, but "`const T &` -> JSON" in the other direction.
+ */
+template<typename T>
+void checkpointJson(CharacterizationTest & test, PathView testStem, const ref<T> & got)
+{
+    using namespace nlohmann;
+
+    auto file = test.goldenMaster(Path{testStem} + ".json");
+
+    json gotJson = static_cast<json>(*got);
+
+    if (testAccept()) {
+        std::filesystem::create_directories(file.parent_path());
+        writeFile(file, gotJson.dump(2) + "\n");
+        ADD_FAILURE() << "Updating golden master " << file;
+    } else {
+        json expectedJson = json::parse(readFile(file));
+        ASSERT_EQ(gotJson, expectedJson);
+        ref<T> expected = adl_serializer<ref<T>>::from_json(expectedJson);
+        ASSERT_EQ(*got, *expected);
+    }
+}
+
 /**
  * Mixin class for writing characterization tests for `nlohmann::json`
  * conversions for a given type.