diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index d249a7093..2a9d17ab9 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -625,8 +625,9 @@ object Defaults extends BuildCommon with DefExtra {
     sources := Classpaths.concatDistinct(unmanagedSources, managedSources).value,
     sourcesVF := Def.uncached {
       val conv = fileConverter.value
-      sources.value.toVector.map: x =>
+      val vs = sources.value.toVector.map: x =>
         (conv.toVirtualFile(x.toPath()): HashedVirtualFileRef)
+      vs.sortBy(_.id)
     },
   )
   lazy val resourceConfigPaths = Seq(
@@ -2046,7 +2047,7 @@ object Defaults extends BuildCommon with DefExtra {
   lazy val packageConfigurationTask: Initialize[Task[Pkg.Configuration]] =
     Def.task {
       Pkg.Configuration(
-        mappings.value,
+        mappings.value.sortBy(_._2),
         artifactPath.value,
         packageOptions.value,
       )
diff --git a/sbt-app/src/sbt-test/cache/input-order/build.sbt b/sbt-app/src/sbt-test/cache/input-order/build.sbt
new file mode 100644
index 000000000..099c5ea10
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/build.sbt
@@ -0,0 +1,72 @@
+import sbt.internal.util.CacheEventSummary
+
+val delClasses = taskKey[Unit]("deletes the classes directory")
+val delJar = taskKey[Unit]("deletes the packaged jar")
+val saveJar = taskKey[Unit]("copies the packaged jar aside for later comparison")
+val checkNoMiss = taskKey[Unit]("asserts the previous command was served entirely from the cache")
+val checkClasses = taskKey[Unit]("asserts class files exist")
+val checkJarMatches = taskKey[Unit]("asserts the jar is byte-identical to the saved one")
+
+Global / localCacheDirectory := baseDirectory.value / "diskcache"
+
+// A distinct project id keeps this fixture's output paths from colliding with same-named
+// sibling fixtures in scripted's shared batch directory.
+lazy val inputOrder = project
+  .in(file("."))
+  .settings(
+    scalaVersion := "3.8.4",
+    // Reversing stands in for a second filesystem's readdir order, which is the only part of
+    // this that cannot be reproduced on a single machine.
+    Compile / sources := {
+      val ss = (Compile / sources).value
+      if ((baseDirectory.value / "reverse.marker").exists) ss.reverse else ss
+    },
+    Compile / packageBin / mappings := {
+      val ms = (Compile / packageBin / mappings).value
+      if ((baseDirectory.value / "reverse.marker").exists) ms.reverse else ms
+    },
+  )
+
+delClasses := Def.uncached {
+  val dir = (inputOrder / Compile / classDirectory).value
+  IO.delete(dir)
+  streams.value.log.info(s"deleted $dir")
+}
+
+delJar := Def.uncached {
+  val conv = fileConverter.value
+  val jar = conv.toPath((inputOrder / Compile / packageBin / artifactPath).value).toFile()
+  IO.delete(jar)
+  streams.value.log.info(s"deleted $jar")
+}
+
+saveJar := Def.uncached {
+  val conv = fileConverter.value
+  val jar = conv.toPath((inputOrder / Compile / packageBin).value).toFile()
+  IO.copyFile(jar, baseDirectory.value / "expected.jar")
+}
+
+checkJarMatches := Def.uncached {
+  val conv = fileConverter.value
+  val jar = conv.toPath((inputOrder / Compile / packageBin).value).toFile()
+  val expected = baseDirectory.value / "expected.jar"
+  assert(
+    java.util.Arrays.equals(IO.readBytes(jar), IO.readBytes(expected)),
+    s"jar bytes changed after reordering packageBin / mappings"
+  )
+}
+
+checkNoMiss := Def.uncached {
+  val config = Def.cacheConfiguration.value
+  val prev = config.cacheEventLog.previous match
+    case data: CacheEventSummary.Data => data
+    case _                            => sys.error("empty event log")
+  streams.value.log.info(s"prev hitCount=${prev.hitCount} missCount=${prev.missCount}")
+  assert(prev.missCount == 0, s"expected no cache misses but missCount=${prev.missCount}")
+}
+
+checkClasses := Def.uncached {
+  val dir = (inputOrder / Compile / classDirectory).value
+  val classes = (dir ** "*.class").get()
+  assert(classes.nonEmpty, s"no class files under $dir")
+}
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/alpha.properties b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/alpha.properties
new file mode 100644
index 000000000..73cdb8bcc
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/alpha.properties
@@ -0,0 +1 @@
+a=1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/zeta.properties b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/zeta.properties
new file mode 100644
index 000000000..7fc3e8577
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/cfg/zeta.properties
@@ -0,0 +1 @@
+z=1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/resources/root.properties b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/root.properties
new file mode 100644
index 000000000..efe74750c
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/resources/root.properties
@@ -0,0 +1 @@
+r=1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha1.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha1.scala
new file mode 100644
index 000000000..fec7ed1ae
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha1.scala
@@ -0,0 +1,3 @@
+package com.example.alpha
+
+class Calpha1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha2.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha2.scala
new file mode 100644
index 000000000..409600928
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha2.scala
@@ -0,0 +1,3 @@
+package com.example.alpha
+
+class Calpha2
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha3.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha3.scala
new file mode 100644
index 000000000..ee12e0954
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/alpha/Calpha3.scala
@@ -0,0 +1,3 @@
+package com.example.alpha
+
+class Calpha3
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci1.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci1.scala
new file mode 100644
index 000000000..3357791cd
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci1.scala
@@ -0,0 +1,3 @@
+package com.example.ci
+
+class Cci1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci2.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci2.scala
new file mode 100644
index 000000000..011fab70a
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci2.scala
@@ -0,0 +1,3 @@
+package com.example.ci
+
+class Cci2
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci3.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci3.scala
new file mode 100644
index 000000000..a87b32674
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/ci/Cci3.scala
@@ -0,0 +1,3 @@
+package com.example.ci
+
+class Cci3
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib1.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib1.scala
new file mode 100644
index 000000000..e60398771
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib1.scala
@@ -0,0 +1,3 @@
+package com.example.lib
+
+class Clib1
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib2.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib2.scala
new file mode 100644
index 000000000..424f619c4
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib2.scala
@@ -0,0 +1,3 @@
+package com.example.lib
+
+class Clib2
diff --git a/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib3.scala b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib3.scala
new file mode 100644
index 000000000..3a414f624
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/src/main/scala/com/example/lib/Clib3.scala
@@ -0,0 +1,3 @@
+package com.example.lib
+
+class Clib3
diff --git a/sbt-app/src/sbt-test/cache/input-order/test b/sbt-app/src/sbt-test/cache/input-order/test
new file mode 100644
index 000000000..be57e3037
--- /dev/null
+++ b/sbt-app/src/sbt-test/cache/input-order/test
@@ -0,0 +1,22 @@
+# Regression for #9645: neither the traversal order of Compile / sources nor of
+# packageBin / mappings may take part in a cache key. When it does, a macOS developer and a
+# Linux CI runner hash an identical tree into different keys and neither can use the other's
+# entries.
+
+# Populate the cache with both input lists in filesystem traversal order.
+> compile
+> packageBin
+> saveJar
+
+# Reverse both lists. No key may move.
+$ touch reverse.marker
+
+> delClasses
+> compile
+> checkNoMiss
+> checkClasses
+
+> delJar
+> packageBin
+> checkNoMiss
+> checkJarMatches