diff --git a/tests/tools/test_dockerfile_pid1_reaping.py b/tests/tools/test_dockerfile_pid1_reaping.py
index 52532a78..a922171c 100644
--- a/tests/tools/test_dockerfile_pid1_reaping.py
+++ b/tests/tools/test_dockerfile_pid1_reaping.py
@@ -106,8 +106,18 @@ def test_dockerfile_entrypoint_routes_through_the_init(dockerfile_text):
 
 
 def test_dockerfile_installs_tui_dependencies(dockerfile_text):
+    """The Dockerfile must install ui-tui's npm dependencies during build,
+    and must copy the @hermes/ink workspace tree (not just its manifests)
+    so npm can resolve the ``file:`` workspace dep without falling back to
+    the bare manifest. See PR #16690 + a49f4c6 for the design.
+    """
     assert "ui-tui/package.json" in dockerfile_text
-    assert "ui-tui/packages/hermes-ink/package-lock.json" in dockerfile_text
+    # ui-tui/packages/hermes-ink/ is referenced as a `file:` workspace dep
+    # from ui-tui/package.json. Copying the FULL tree (rather than just
+    # package.json + package-lock.json as in earlier revisions) is what lets
+    # npm resolve the workspace to real content. This assertion catches a
+    # regression that reverts to manifest-only copies.
+    assert "COPY ui-tui/packages/hermes-ink/ ui-tui/packages/hermes-ink/" in dockerfile_text
     assert any(
         "ui-tui" in step and "npm" in step and (" install" in step or " ci" in step)
         for step in _run_steps(dockerfile_text)
@@ -121,17 +131,33 @@ def test_dockerfile_builds_tui_assets(dockerfile_text):
     )
 
 
-def test_dockerfile_materializes_local_tui_ink_package(dockerfile_text):
-    assert any(
-        "ui-tui" in step
-        and "node_modules/@hermes/ink" in step
-        and "packages/hermes-ink" in step
-        and "rm -rf packages/hermes-ink/node_modules" in step
-        and "npm install --omit=dev" in step
-        and "--prefix node_modules/@hermes/ink" in step
-        and "rm -rf node_modules/@hermes/ink/node_modules/react" in step
-        and "await import('@hermes/ink')" in step
-        for step in _run_steps(dockerfile_text)
+def test_dockerfile_forces_npm_install_links_false_for_workspace_resolution(dockerfile_text):
+    """The Dockerfile must force npm to install ``file:`` deps as symlinks
+    rather than copies.
+
+    Debian's bundled npm 9.x defaults to ``install-links=true`` (deps
+    installed as copies). The host-side ``ui-tui/package-lock.json`` is
+    generated by npm 10+ which uses symlinks, so an install-as-copy in the
+    image produces a hidden ``node_modules/.package-lock.json`` that
+    permanently disagrees with the root lockfile on the @hermes/ink entry.
+    That disagreement trips the TUI launcher's ``_tui_need_npm_install()``
+    check on every startup and triggers a runtime ``npm install`` that
+    fails with EACCES (node_modules/ is root-owned from build time).
+
+    This assertion replaces the older ``--prefix node_modules/@hermes/ink``
+    materialization smoke test (PR #16690), which was retired in a49f4c6
+    in favour of ``install-links=false`` because the materialization step
+    rebuilt TUI assets unnecessarily on every container start.
+    """
+    instructions = _dockerfile_instructions(dockerfile_text)
+    has_env_directive = any(
+        instr.startswith("ENV ") and "npm_config_install_links=false" in instr
+        for instr in instructions
+    )
+    assert has_env_directive, (
+        "ENV npm_config_install_links=false missing — without it, Debian npm 9.x "
+        "installs `file:` deps as copies, breaking @hermes/ink workspace "
+        "resolution at runtime. See PR #16690 + a49f4c6."
     )