werkdock: import the rootfs archive, fall back to load -i on an older werkdock

Werkdock's docker-compat branch names the verb for rootfs archives
'import' (docker import semantics) and keeps 'load -i --name' only as
a compatibility path. Werkator now runs 'werkdock import ARCHIVE IMAGE'
and falls back to 'load -i --name' on exactly the unknown-verb
signature (exit 125, 'unknown command' on stderr), so Werkator and
werkdock can be updated in either order. Any other import failure
propagates as before. The image name stays untagged: it equals
werkator-buildenv-<hash>:latest in werkdock's naming, and the existing
store needs no re-import. PR-doc under docs/prs/ with the PR#000
placeholder.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/configuration.md

@@ -475,7 +475,9 @@ The section was called `bwrap` and its binary key `bwrap.werkdock` until v1.2.0;
 `werkdock.rootfs` names the prepared root filesystem archive — a Debian-base rootfs with the build tools (JDK, git, locales, project-specific tooling) built elsewhere, since `debootstrap` is unavailable on the target.
 It is a local path or an `http(s)` URL; a URL is downloaded once into `.git/werkator/buildenv/`.
 Build the archive with `tools/build-bwrap-rootfs.sh` on any machine with Docker.
-The archive is loaded once per source as the werkdock image `werkator-buildenv-<hash>` into werkdock's store (`$WERKDOCK_HOME`, default `~/.werkdock`) — shared by every repository of this OS user; the hash derives from the source string, so a changed `rootfs` loads a fresh image and stale ones can be removed from the store.
+The archive is imported once per source as the werkdock image `werkator-buildenv-<hash>` into werkdock's store (`$WERKDOCK_HOME`, default `~/.werkdock`) — shared by every repository of this OS user; the hash derives from the source string, so a changed `rootfs` imports a fresh image and stale ones can be removed from the store.
+Werkator uses `werkdock import ARCHIVE IMAGE` (docker import semantics) and falls back to the older `werkdock load -i ARCHIVE --name IMAGE` when the installed werkdock does not know the verb yet, so Werkator and werkdock can be updated in either order.
+The image keeps its untagged name (it equals `werkator-buildenv-<hash>:latest` in werkdock's docker-style naming), so an existing store needs no re-import.
 Per-repo Gradle caches persist in `.git/werkator/buildenv/home`, bound as `/root`.
 `werkdock.env` adds environment variables inside the sandbox; the environment is otherwise cleared (docker semantics) — the server's environment does not leak in.
 Files created inside the sandbox are owned by the host user, because uid 0 maps back to the unprivileged webspace user.

docs/deployment.md

@@ -342,7 +342,7 @@ tools/remote --env-file .env.mih34 port-forward start            # browser tunne
 
 Layout on the host: the watched repository at `$WERKATOR_PATH/werkator/`, the unpacked runtime at `$WERKATOR_PATH/.werkator/werkator/`, the werkdock binary at `$WERKATOR_PATH/.werkator/bin/werkdock`.
 That is the default, not a requirement: `WERKATOR_REPO_DIR`, `WERKATOR_INSTALL_DIR` and `WERKATOR_SANDBOX` bend it to an installation that predates the script, see [Updating an Existing Installation](#updating-an-existing-installation).
-The rootfs archive is loaded once per source into werkdock's image store (`~/.werkdock`), shared by every repository of the user.
+The rootfs archive is imported once per source into werkdock's image store (`~/.werkdock`), shared by every repository of the user.
 Fill `git.account`/`git.token` in the machine config when the origin is private, and make the user's services survive logout with `loginctl enable-linger`.
 
 Updates are one command, refused while a build runs (`FORCE=1` overrides):

docs/prs/2026-09-05-PR#000-werkdock-import-verb.md

@@ -0,0 +1,102 @@
+> **WARNING:** This document describes only the change applied in this PR.
+> It may already be outdated once the next PR is merged.
+> Historic PR-documentation is not maintained along with new PRs — treat it as a snapshot, not as current documentation.
+
+## Related Links
+
+- Werkdock `CHANGELOG.md` on its `docker-compat` branch — the release notes this PR adapts to: `import` replaces `load -i --name` for rootfs archives, `load` is reserved for docker/OCI image archives, image names gained docker-style tags.
+- ADR 0008 — the bwrap build runtime; `docs/configuration.md`, notes on `builds.<name>.werkdock`.
+
+## The Problem
+
+Werkdock moves its CLI closer to `docker run --rm`.
+For the rootfs archives Werkator uses, the verb is now `werkdock import ARCHIVE IMAGE` (docker import semantics).
+`werkdock load -i ARCHIVE --name IMAGE` still works but is a compatibility path with a note on stderr, and is announced to go away once Werkator has switched.
+Werkator ships the werkdock binary with its deployment, but nothing forces the two to be updated together: an installation may run a new Werkator against an older werkdock for a while, or the other way round.
+
+## Non-Goals
+
+- No switch of the existence check from `werkdock images` to `werkdock inspect`: `images` prints the bare name for untagged images on every werkdock version, the exact-line match keeps working, and `inspect` would tie Werkator to the new werkdock.
+- No tagged image name (`werkator-buildenv:<hash>`): it would re-import every build environment on the webspace and orphan the old image, for no functional gain today.
+- None of the new `run` flags (`--mount`, `--entrypoint`, `--network host`): Werkator's invocation needs none of them.
+
+## The Scenarios
+
+### Feature: rootfs archives are imported with werkdock's docker-shaped verb
+
+#### Background
+
+- The build environment is a rootfs archive named by `builds.<name>.werkdock.rootfs`.
+- Werkator creates the werkdock image `werkator-buildenv-<hash>` from it once per source.
+- Werkdock answers an unknown verb with `werkdock: unknown command "import"` and exit code 125, its code for its own errors.
+
+#### Scenario#000.01: A missing image is imported with `werkdock import`
+
+So that Werkator uses the verb werkdock names for rootfs archives, and the deprecated path can be removed on werkdock's side.
+
+- **Given** `werkdock images` does not list the image
+- **When** a build starts
+- **Then** Werkator runs `werkdock import ARCHIVE werkator-buildenv-<hash>`
+  - **and** runs no `werkdock load`.
+
+##### Verified by
+
+- [WerkdockBuildRunnerTest "imports the image once when werkdock does not know it yet"](../../src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt)
+- [WerkdockBuildRunnerTest "downloads a URL rootfs once before importing it"](../../src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt)
+
+#### Scenario#000.02: An older werkdock without the verb still works
+
+So that Werkator and werkdock can be updated in either order.
+
+- **Given** the installed werkdock answers `import` with `unknown command` and exit 125
+- **When** a build starts with a missing image
+- **Then** Werkator falls back to `werkdock load -i ARCHIVE --name werkator-buildenv-<hash>`
+  - **and** logs the fallback.
+
+##### Verified by
+
+- [WerkdockBuildRunnerTest "falls back to load -i --name on a werkdock without the import verb"](../../src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt)
+
+#### Scenario#000.03: A real import failure is not masked by the fallback
+
+So that a broken archive fails the build with werkdock's message, as before.
+
+- **Given** `werkdock import` fails for any other reason (any other exit code, or exit 125 without `unknown command`)
+- **When** a build starts with a missing image
+- **Then** the build fails with that command's output
+  - **and** no `werkdock load` runs.
+
+##### Verified by
+
+- [WerkdockBuildRunnerTest "propagates an import failure that is not a missing verb"](../../src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt)
+
+#### Scenario#000.04: An existing image is neither imported nor loaded
+
+- **Given** `werkdock images` lists the image
+- **When** a build starts
+- **Then** neither `import` nor `load` runs.
+
+##### Verified by
+
+- [WerkdockBuildRunnerTest "does not import an image werkdock already has"](../../src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt)
+
+## The Solution
+
+`WerkdockBuildRunner.ensureImage` calls the new `importImage`: `werkdock import ARCHIVE IMAGE` through the non-throwing `run`, then either returns, falls back to `load -i --name` on exactly the unknown-verb signature (exit 125 plus `unknown command` on stderr), or rethrows the import's result as a `GitCommandException` — the same exception and message the old code produced.
+The fallback is keyed on werkdock's own error signature rather than on a version string, because werkdock's version output does not yet distinguish the two builds.
+
+## Open Questions
+
+- When to drop the fallback: once every installation runs a werkdock with `import`, the `load -i --name` branch and its test go, and werkdock can remove the compatibility path.
+
+## Additional Changes
+
+- `docs/configuration.md` and `docs/deployment.md` say "imported" where they said "loaded", and name the fallback and the reason the image name stays untagged.
+
+## Prerequisite PRs
+
+- Werkdock's `docker-compat` branch (repository `mi/werkdock`), which introduces `import`; without it the fallback path runs.
+
+## Follow-up PRs
+
+- Remove the fallback (see Open Questions).

src/main/kotlin/de/hoennig/werkator/build/WerkdockBuildRunner.kt

@@ -2,6 +2,7 @@ package de.hoennig.werkator.build
 
 import de.hoennig.werkator.config.BranchConfig
 import de.hoennig.werkator.config.WerkdockConfig
+import de.hoennig.werkator.git.GitCommandException
 import de.hoennig.werkator.git.GitCommandRunner
 import org.slf4j.LoggerFactory
 import org.springframework.stereotype.Component
@@ -16,9 +17,9 @@ import java.security.MessageDigest
  * it shells out to the `werkdock` CLI (`werkdock.binary`, default via PATH) — the same
  * pattern as git and docker, CLI, no library.
  *
- * The rootfs archive becomes a werkdock *image*, loaded once per source
+ * The rootfs archive becomes a werkdock *image*, imported once per source
  * (`werkator-buildenv-<hash>`, the hash over the source string, so a changed source
- * loads a fresh image) into werkdock's own store (`$WERKDOCK_HOME`, default
+ * imports a fresh image) into werkdock's own store (`$WERKDOCK_HOME`, default
  * `~/.werkdock`) — shared by every repository of this OS user, unlike the old
  * per-repo unpack. Only the download cache for URL sources and the persistent
  * toolchain home (bound to `/root` for Gradle/Go caches) stay under
@@ -66,9 +67,11 @@ class WerkdockBuildRunner(
     }
 
     /**
-     * Loads the rootfs archive into the werkdock image store once per source.
+     * Imports the rootfs archive into the werkdock image store once per source.
      * `werkdock images` answers existence through the CLI, like `docker image
-     * inspect` does for the Docker runner.
+     * inspect` does for the Docker runner; it prints the bare name for an untagged
+     * image on every werkdock version, so the exact-line match holds across the
+     * werkdock upgrade that introduced tags.
      */
     private fun ensureImage(
         werkdock: String,
@@ -84,7 +87,33 @@ class WerkdockBuildRunner(
         val envDir = repoDir.resolve(BUILDENV_DIR).resolve(sourceKey(sandbox.rootfs))
         Files.createDirectories(envDir)
         val archive = localArchive(sandbox.rootfs, envDir, repoDir, onAuxProcess)
-        log.info("loading build environment {} as werkdock image {}", sandbox.rootfs, image)
+        log.info("importing build environment {} as werkdock image {}", sandbox.rootfs, image)
+        importImage(werkdock, archive, image, repoDir, onAuxProcess)
+    }
+
+    /**
+     * `werkdock import ARCHIVE IMAGE` (docker import semantics) creates the image from a
+     * rootfs archive. A werkdock that predates the verb answers `unknown command` with
+     * exit 125; then the older `load -i ARCHIVE --name IMAGE` does the same job, so an
+     * installation can update Werkator and werkdock in either order. Any other failure
+     * is the import's own and propagates as it did before.
+     */
+    private fun importImage(
+        werkdock: String,
+        archive: String,
+        image: String,
+        repoDir: Path,
+        onAuxProcess: (Process) -> Unit,
+    ) {
+        val importCommand = listOf(werkdock, "import", archive, image)
+        val imported = commandRunner.run(importCommand, repoDir, onProcess = onAuxProcess)
+        if (imported.isSuccess) {
+            return
+        }
+        if (imported.exitCode != WERKDOCK_CLI_ERROR || "unknown command" !in imported.stderr) {
+            throw GitCommandException(importCommand, imported)
+        }
+        log.info("this werkdock has no import verb yet, falling back to load -i --name")
         commandRunner.runOrThrow(
             listOf(werkdock, "load", "-i", archive, "--name", image),
             repoDir,
@@ -209,5 +238,8 @@ class WerkdockBuildRunner(
     companion object {
         const val BUILDENV_DIR = ".git/werkator/buildenv"
         const val HOME_DIR = "home"
+
+        /** werkdock's exit code for its own errors (docker's 125), as opposed to the sandboxed command's. */
+        const val WERKDOCK_CLI_ERROR = 125
     }
 }

src/test/kotlin/de/hoennig/werkator/build/WerkdockBuildRunnerTest.kt

@@ -2,6 +2,7 @@ package de.hoennig.werkator.build
 
 import de.hoennig.werkator.config.BranchConfig
 import de.hoennig.werkator.config.WerkdockConfig
+import de.hoennig.werkator.git.GitCommandException
 import de.hoennig.werkator.git.GitCommandResult
 import de.hoennig.werkator.git.GitCommandRunner
 import io.kotest.assertions.throwables.shouldThrow
@@ -37,7 +38,11 @@ class WerkdockBuildRunnerTest : FunSpec() {
 
     private fun imageName(rootfs: String = "/srv/buildenv.tar.zst"): String = "werkator-buildenv-${rootfs.sha12()}"
 
-    /** The image is already loaded: `werkdock images` lists it, so no load runs. */
+    private fun importCommand(): List<String> = listOf("werkdock", "import", "/srv/buildenv.tar.zst", imageName())
+
+    private fun loadCommand(): List<String> = listOf("werkdock", "load", "-i", "/srv/buildenv.tar.zst", "--name", imageName())
+
+    /** The image is already there: `werkdock images` lists it, so no import runs. */
     private fun givenImageLoaded(rootfs: String = "/srv/buildenv.tar.zst") {
         every { commandRunner.runOrThrow(listOf("werkdock", "images"), repoDir, any(), any()) } returns
             GitCommandResult(0, imageName(rootfs) + "\n", "")
@@ -88,34 +93,47 @@ class WerkdockBuildRunnerTest : FunSpec() {
                 )
         }
 
-        test("loads the image once when werkdock does not know it yet") {
+        test("imports the image once when werkdock does not know it yet") {
             givenImageMissing()
-            every {
+            every { commandRunner.run(importCommand(), repoDir, any(), any()) } returns GitCommandResult(0, "", "")
-                commandRunner.runOrThrow(
-                    listOf("werkdock", "load", "-i", "/srv/buildenv.tar.zst", "--name", imageName()),
-                    repoDir,
-                    any(),
-                    any(),
-                )
-            } returns GitCommandResult(0, "", "")
 
             runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, werkdockBranchConfig())
 
-            verify {
+            verify { commandRunner.run(importCommand(), repoDir, any(), any()) }
-                commandRunner.runOrThrow(
+            verify(exactly = 0) { commandRunner.runOrThrow(match { "load" in it }, any(), any(), any()) }
-                    listOf("werkdock", "load", "-i", "/srv/buildenv.tar.zst", "--name", imageName()),
-                    repoDir,
-                    any(),
-                    any(),
-                )
-            }
         }
 
-        test("does not load an image werkdock already has") {
+        test("falls back to load -i --name on a werkdock without the import verb") {
+            givenImageMissing()
+            every { commandRunner.run(importCommand(), repoDir, any(), any()) } returns
+                GitCommandResult(125, "", "werkdock: unknown command \"import\"\n")
+            every { commandRunner.runOrThrow(loadCommand(), repoDir, any(), any()) } returns GitCommandResult(0, "", "")
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, werkdockBranchConfig())
+
+            verify { commandRunner.runOrThrow(loadCommand(), repoDir, any(), any()) }
+        }
+
+        test("propagates an import failure that is not a missing verb") {
+            givenImageMissing()
+            every { commandRunner.run(importCommand(), repoDir, any(), any()) } returns
+                GitCommandResult(125, "", "werkdock: unpacking /srv/buildenv.tar.zst failed\n")
+
+            val exception =
+                shouldThrow<GitCommandException> {
+                    runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, werkdockBranchConfig())
+                }
+
+            exception.message shouldContain "unpacking"
+            verify(exactly = 0) { commandRunner.runOrThrow(match { "load" in it }, any(), any(), any()) }
+        }
+
+        test("does not import an image werkdock already has") {
             givenImageLoaded()
 
             runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, werkdockBranchConfig())
 
+            verify(exactly = 0) { commandRunner.run(match { "import" in it }, any(), any(), any()) }
             verify(exactly = 0) { commandRunner.runOrThrow(match { "load" in it }, any(), any(), any()) }
         }
 
@@ -209,7 +227,7 @@ class WerkdockBuildRunnerTest : FunSpec() {
             exception.message shouldContain "werkdock.rootfs"
         }
 
-        test("downloads a URL rootfs once before loading it") {
+        test("downloads a URL rootfs once before importing it") {
             val url = "https://example.test/buildenv.tar.zst"
             val downloadTarget =
                 repoDir
@@ -219,7 +237,7 @@ class WerkdockBuildRunnerTest : FunSpec() {
             givenImageMissing()
             every { commandRunner.runOrThrow(listOf("curl", "-fsSL", "-o", downloadTarget.toString(), url), repoDir, any(), any()) } returns
                 GitCommandResult(0, "", "")
-            every { commandRunner.runOrThrow(match { "load" in it }, any(), any(), any()) } returns
+            every { commandRunner.run(match { "import" in it }, any(), any(), any()) } returns
                 GitCommandResult(0, "", "")
 
             runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, werkdockBranchConfig(rootfs = url))
@@ -228,8 +246,8 @@ class WerkdockBuildRunnerTest : FunSpec() {
                 commandRunner.runOrThrow(listOf("curl", "-fsSL", "-o", downloadTarget.toString(), url), repoDir, any(), any())
             }
             verify {
-                commandRunner.runOrThrow(
+                commandRunner.run(
-                    listOf("werkdock", "load", "-i", downloadTarget.toString(), "--name", "werkator-buildenv-${url.sha12()}"),
+                    listOf("werkdock", "import", downloadTarget.toString(), "werkator-buildenv-${url.sha12()}"),
                     repoDir,
                     any(),
                     any(),