vim89 · Oct 7, 2026 · Oct 7, 2026 · Oct 7, 2026 · Oct 7, 2026 · Oct 7, 2026
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -11,6 +11,11 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.head_ref || github.ref }}
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
+# GitHub Packages authenticates reads, so sbt needs a token to resolve ctdc-core. The repo token works
+# once the package grants this repo access; CTDC_PACKAGES_TOKEN is the override if a wider token is needed.
+env:
+  GITHUB_TOKEN: ${{ secrets.CTDC_PACKAGES_TOKEN || secrets.GITHUB_TOKEN }}
+
 jobs:
   fixture-sync:
     name: Spec fixture sync
@@ -32,6 +37,7 @@ jobs:
     needs: fixture-sync
     permissions:
       contents: read
+      packages: read
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
     steps:
       - uses: actions/checkout@v6
@@ -52,7 +58,7 @@ jobs:
 
       # Core's src/main/scala-3 is only on the source path under Scala 3, so the check above never sees it.
       - name: scalafmt check (Scala 3 sources)
-        run: sbt "++3.3.3 core/scalafmtCheckAll"
+        run: sbt "++3.3.6 core/scalafmtCheckAll"
 
       - name: Guard - ban println in production sources
         run: |
@@ -161,6 +167,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     permissions:
       contents: read
+      packages: read
     strategy:
       fail-fast: false
       matrix:
@@ -180,7 +187,7 @@ jobs:
           # Core is the only module built for Scala 3, so the command is core only. The whole aggregate
           # cannot run here: the modules that stay on 2.13 fail dependency resolution under ++3.
           - os: ubuntu-latest
-            scala: 3.3.3
+            scala: 3.3.6
             java: 17
             command: core/testQuick
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
@@ -214,6 +221,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+      packages: read
     strategy:
       fail-fast: false
       max-parallel: 2
@@ -240,6 +248,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+      packages: read
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
     steps:
       - uses: actions/checkout@v6
@@ -263,6 +272,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+      packages: read
     if: |
       github.event_name == 'workflow_dispatch' ||
       (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'run-integration-tests')) ||
@@ -284,6 +294,7 @@ jobs:
     needs: quick-checks
     permissions:
       contents: read
+      packages: read
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
     steps:
       - uses: actions/checkout@v6
@@ -309,6 +320,7 @@ jobs:
     needs: test
     permissions:
       contents: read
+      packages: read
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
     steps:
       - uses: actions/checkout@v6
@@ -330,6 +342,7 @@ jobs:
     needs: [test]
     permissions:
       contents: read
+      packages: read
     if: "!contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip release]')"
     steps:
       - uses: actions/checkout@v6

diff --git a/README.md b/README.md
@@ -46,7 +46,7 @@ You get compile‑time guarantees (not CI or runtime heuristics), a small opinio
 
 ## How (principles)
 
-- **Compile‑time contracts:** `SchemaConforms[Out, Contract, Policy]` proves compatibility; policies include **Exact**, **Backward**, **Forward** (+ Ordered/CI/ByPosition). See [docs/how-it-fails.md](docs/how-it-fails.md).
+- **Compile‑time contracts:** `SchemaConforms[Out, Contract, Policy]` proves compatibility; policies include **Exact**, **Backward**, **Forward** (+ Ordered/CI/ByPosition). See [docs/how-it-fails.md](docs/how-it-fails.md). The engine behind it is [ctdc-core](https://github.com/vim89/compile-time-data-contracts), a standalone library; `com.flowforge.core.contracts` aliases its types so there is one implementation to maintain.
 - **Typestate builder:** `build()` exists only when source, transforms, and sink are present. Incomplete pipelines are unbuildable.
 - **Pure vs effect boundary:** transforms are pure functions; `F[_]` only at IO edges; engines plug into a single algebra.
 - **Pictures over prose:** see [flowchart.svg](docs/diagrams/compile-time-contracts/flowchart.svg) and [optionality.md](docs/diagrams/compile-time-contracts/optionality.md).

diff --git a/build.sbt b/build.sbt
@@ -38,15 +38,26 @@
 ThisBuild / coverageHighlighting := true
 
 // ===== REPOSITORY RESOLVERS =====
-resolvers ++= Resolver.sonatypeOssRepos("public") ++ Seq(
+// ThisBuild and not the root project: every module is defined separately below, so a root-only setting
+// would not reach them and `core` could not resolve ctdc-core.
+ThisBuild / resolvers ++= Resolver.sonatypeOssRepos("public") ++ Seq(
   Resolver.mavenCentral,
   "Confluent" at "https://packages.confluent.io/maven/",
   "Apache Releases" at "https://repository.apache.org/content/repositories/releases/",
   "Google Cloud" at "https://maven-central.storage-download.googleapis.com/maven2/",
   "AWS SDK" at "https://repo1.maven.org/maven2/software/amazon/awssdk/",
   "Spark Packages" at "https://repos.spark-packages.org/",
+  // The contract engine, published from github.com/vim89/compile-time-data-contracts.
+  "ctdc GitHub Packages" at "https://maven.pkg.github.com/vim89/compile-time-data-contracts",
 )
 
+// GitHub Packages authenticates reads, not just writes, so resolving ctdc-core needs a token. Absent
+// locally, where ctdc is resolved from `~/.ivy2/local` after a `publishLocal` instead.
+ThisBuild / credentials ++= (for {
+  user  <- sys.env.get("GITHUB_ACTOR")
+  token <- sys.env.get("GITHUB_TOKEN")
+} yield Credentials("GitHub Package Registry", "maven.pkg.github.com", user, token)).toSeq
+
 // Compiler settings for all projects
 
 val scala3CompilerOptions = Seq(
@@ -204,52 +215,14 @@
     coverageExcludedPackages := Seq(
       "com.flowforge.core.examples.*",
     ).mkString(";"),
-    // The macros run in the compiler rather than in a test, so the instrumentation never sees them. The
-    // comparison they share lives in the same package and is ordinary code with its own tests, which is
-    // why these are excluded by file instead of by package.
-    coverageExcludedFiles := Seq(
-      ".*/ContractMacros.scala",
-      ".*/SchemaConformsMaterializer.scala",
-      ".*/ShapeDerivation.scala",
-      ".*/TypeShapes.scala",
-    ).mkString(";"),
     // Core module requires 90% coverage (foundational code)
     coverageMinimumStmtTotal := 90,
     coverageMinimumBranchTotal := 85,
     coverageFailOnMinimum := enforceCoverageThreshold,
-    // Section 13.3 - Version-specific dependencies for Scala 2/3 cross-build
-    libraryDependencies ++= {
-      CrossVersion.partialVersion(scalaVersion.value) match {
-        case Some((2, _)) =>
-          Seq(
-            "com.softwaremill.magnolia1_2" %% "magnolia"      % "1.1.10",
-            "org.scala-lang"                % "scala-reflect" % scalaVersion.value,
-          )
-        case Some((3, _)) =>
-          Seq(
-            // Scala 3 derives and inspects types with the compiler's own quotes reflection, so there is
-            // no Magnolia or scala-reflect to add here.
-          )
-        case _ => Seq.empty
-      }
-    },
-    // Section 13.3 - Version-specific source directories for Scala 2/3 cross-build
-    Compile / unmanagedSourceDirectories ++= {
-      val base = (Compile / sourceDirectory).value
-      CrossVersion.partialVersion(scalaVersion.value) match {
-        case Some((2, _)) => Seq(base / "scala-2")
-        case Some((3, _)) => Seq(base / "scala-3")
-        case _            => Nil
-      }
-    },
-    Test / unmanagedSourceDirectories ++= {
-      val base = (Test / sourceDirectory).value
-      CrossVersion.partialVersion(scalaVersion.value) match {
-        case Some((2, _)) => Seq(base / "scala-2")
-        case Some((3, _)) => Seq(base / "scala-3")
-        case _            => Nil
-      }
-    },
+    // Magnolia, scala-reflect and the scala-2/scala-3 source directories used to be wired here, because the
+    // contract macro is spelled differently on each Scala version. That macro now ships in ctdc-core, which
+    // carries its own per-version sources and dependencies, so everything left in this module is ordinary
+    // version-agnostic Scala.
   )
   .settings(mimaSettings("core"): _*)
 

diff --git a/docs/contracts/policy-cookbook.md b/docs/contracts/policy-cookbook.md
@@ -8,7 +8,7 @@ Notes
 
 - All examples use `PipelineBuilder` + `TypedSource/TypedSink` so the compiler must materialize `SchemaConforms[Out, Contract, P]` evidence.
 - On mismatch, compilation aborts with a diff like:
-  FlowForge: Contract drift (policy: com.flowforge.core.contracts.SchemaPolicy.Exact).
+  FlowForge: Contract drift (policy: ctdc.SchemaPolicy.Exact).
   Out: Producer vs Contract: Contract
   Missing: email:string
   Extra: age:int

diff --git a/docs/how-it-fails.md b/docs/how-it-fails.md
@@ -127,7 +127,7 @@ implicitly[SchemaConforms[Out, Contract, SchemaPolicy.Exact]]
 Indicative error message shape:
 
 ```
-Compile-time contract drift (policy: com.flowforge.core.contracts.SchemaPolicy.Exact).
+Compile-time contract drift (policy: ctdc.SchemaPolicy.Exact).
 Out: List[Option[Int]] vs Contract: List[Int]
 Mismatch attributes: []? expected Int, found optional Int
 ```

diff --git a/docs/migration/guide.md b/docs/migration/guide.md
@@ -2,8 +2,9 @@
 
 Plan for moving FlowForge's compile-time contracts from Scala 2.13 to Scala 3.
 
-> Status: part plan, part record. `core` now cross-builds Scala 2.13.16 and 3.3.3, with the Scala 3
-> derivation in `modules/core/src/main/scala-3`, and CI runs `core/testQuick` on 3.3.3. Every other
+> Status: part plan, part record. `core` now cross-builds Scala 2.13.16 and 3.3.6, with the per-version
+> derivation living in the ctdc-core library rather than in FlowForge, and CI runs `core/testQuick` on
+> 3.3.6. Every other
 > module is 2.13.16 only. Snippets below that are marked proposed are still proposals. Readiness for
 > v1.0 is tracked in [v1.0 readiness](../plan/v1.0-readiness.md).
 

diff --git a/docs/plan/v1.0-readiness.md b/docs/plan/v1.0-readiness.md
@@ -9,7 +9,7 @@ change before the version number means anything.
 ## Where the build stands
 
 - Scala 2.13.16 is the only version the whole build is cross-built for. `core` also builds and tests on
-  3.3.3, which CI runs as `core/testQuick`. Nothing is cross-published, so the Scala 3 build comes from
+  3.3.6, which CI runs as `core/testQuick`. Nothing is cross-published, so the Scala 3 build comes from
   source.
 - JDK 17 is the baseline. CI runs 17. Spark 3.5.x does not support a newer JDK.
 - Spark 3.5.x is the engine that runs. `engines-spark/test` runs on every CI build; the Delta integration

diff --git a/modules/core/src/main/scala-2/com/flowforge/core/contracts/SchemaConformsMaterializer.scala b/modules/core/src/main/scala-2/com/flowforge/core/contracts/SchemaConformsMaterializer.scala
diff --git a/modules/core/src/main/scala-2/com/flowforge/core/contracts/derive/ShapeDerivation.scala b/modules/core/src/main/scala-2/com/flowforge/core/contracts/derive/ShapeDerivation.scala