diff --git a/Dockerfile b/Dockerfile
index b51a2cfa97..901289778e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -103,14 +103,6 @@ RUN rm -rf packages/paperclip-runner/runner/target
 FROM base AS production
 ARG USER_UID=1000
 ARG USER_GID=1000
-# Real version for this build, computed from `git describe` on the CI runner
-# (the image has no .git, so the server cannot derive it at runtime). Empty for
-# local `docker build`, which just leaves the server on its normal fallbacks.
-ARG PAPERCLIP_BUILD_VERSION=""
-# The exact commit this image was built from, for the same reason: server-info
-# falls back to PAPERCLIP_BUILD_COMMIT when git is unavailable, which feeds the
-# /api/health `commit` field that deploy tooling verifies. Empty locally.
-ARG PAPERCLIP_BUILD_COMMIT=""
 # Refreshes the tool layer below when it changes (CI stamps an ISO week, so
 # the @latest CLI tools advance weekly). Without it the cached layer would
 # freeze the tools until an unrelated cache bust.
@@ -133,6 +125,13 @@ RUN chmod +x /usr/local/bin/docker-entrypoint.sh
 
 COPY --chown=node:node --from=build /app /app
 
+# Declare per-build metadata after the stable RUN layers. Docker includes
+# in-scope ARG values in a RUN's environment even when its command does not
+# mention them; declaring these earlier invalidates the weekly tool cache.
+# The build stage still receives the commit before writing dist/build-info.json.
+# Empty for local builds, preserving the server's normal version fallbacks.
+ARG PAPERCLIP_BUILD_VERSION=""
+ARG PAPERCLIP_BUILD_COMMIT=""
 ENV NODE_ENV=production \
   HOME=/paperclip \
   HOST=0.0.0.0 \
diff --git a/doc/DOCKER.md b/doc/DOCKER.md
index 93ffe55554..c89664fd0a 100644
--- a/doc/DOCKER.md
+++ b/doc/DOCKER.md
@@ -18,6 +18,14 @@ Build arguments:
 |-----|---------|---------|
 | `USER_UID` | `1000` | UID for the container `node` user (match your host UID to avoid permission issues on bind mounts) |
 | `USER_GID` | `1000` | GID for the container `node` group |
+| `CLI_TOOLS_CACHE_EPOCH` | empty | Refresh the CLI-install layer; CI supplies the current ISO week |
+| `PAPERCLIP_BUILD_VERSION` | empty | Runtime version when Git metadata is unavailable |
+| `PAPERCLIP_BUILD_COMMIT` | empty | Source commit written into the server build stamp and runtime environment |
+
+Changing the build version or commit preserves the CLI-install cache. The
+tool layer refreshes when its weekly epoch, base image, installation command,
+or earlier build inputs change. Local builds can set a new epoch explicitly
+to refresh tools without clearing the entire build cache.
 
 ```sh
 docker build -t paperclip-local \
diff --git a/server/src/__tests__/docker-build-stamp.test.ts b/server/src/__tests__/docker-build-stamp.test.ts
index f013d30ec6..454b8b912e 100644
--- a/server/src/__tests__/docker-build-stamp.test.ts
+++ b/server/src/__tests__/docker-build-stamp.test.ts
@@ -35,6 +35,25 @@ function stageBody(source: string, stageName: string): string {
   return source.slice(start, end);
 }
 
+it("keeps per-build runtime metadata out of the weekly CLI-install cache", () => {
+  const production = stageBody(dockerfile, "production");
+  const tools = production.search(/^RUN echo "cli-tools-epoch:/m);
+  const entrypoint = production.search(/^RUN chmod \+x \/usr\/local\/bin\/docker-entrypoint\.sh/m);
+  const runtime = production.search(/^ENV NODE_ENV=production/m);
+  const epoch = production.search(/^ARG CLI_TOOLS_CACHE_EPOCH\b/m);
+  expect(tools).toBeGreaterThanOrEqual(0);
+  expect(entrypoint).toBeGreaterThan(tools);
+  expect(epoch).toBeGreaterThanOrEqual(0);
+  expect(epoch).toBeLessThan(tools);
+  for (const name of ["PAPERCLIP_BUILD_VERSION", "PAPERCLIP_BUILD_COMMIT"]) {
+    const declarations = [...production.matchAll(new RegExp(`^ARG ${name}\\b`, "gm"))];
+    expect(declarations).toHaveLength(1);
+    expect(declarations[0].index).toBeGreaterThan(entrypoint);
+    expect(declarations[0].index).toBeLessThan(runtime);
+    expect(production.slice(runtime)).toContain(`${name}=\${${name}}`);
+  }
+});
+
 describe("docker build-stamp wiring", () => {
   it("declares PAPERCLIP_BUILD_COMMIT in the build stage before the server build", () => {
     const build = stageBody(dockerfile, "build");