fix(pfs,cli): the CPT parser imports rex lazily so the stack CLI starts in the api image (no fsspec there) — the nightly Zotero sync and mail poller run inside it (refs #718)

src/pfs/cpt_epub.py

@@ -47,7 +47,6 @@ from pfs.cpt_model import (
     CptReference,
     CptSection,
 )
-from rex.comments.epub_text import content_root
 
 # One CPT code: 4 digits + a digit/letter (99490, 0202U, 99213F, 0042T, 0001A).
 _CODE = re.compile(r"\b\d{4}[0-9A-Z]\b")
@@ -906,6 +905,11 @@ def parse_epub(path: Path, *, year: int | None = None) -> CptEdition:
         # Resolved once via container.xml -> the OPF's own path, not
         # hard-coded — falls back to "OPS/" (every edition checked so
         # far) when container.xml is missing/malformed (F2).
+        # Lazy: importing rex.comments pulls in the rex package (fsspec),
+        # which the api image's `cli` extra does not carry — the CLI must
+        # import without it (tests/cli/test_cli_import_without_optional_deps.py).
+        from rex.comments.epub_text import content_root
+
         root = content_root(zf)
 
         toc_ranges: dict[str, tuple[str, str]] = {}

tests/cli/test_cli_import_without_optional_deps.py

@@ -0,0 +1,32 @@
+"""The api image installs the ``cli`` extra only (no fsspec/s3fs/obstore —
+those belong to the lake/rex extras). ``stack`` must still start there:
+the nightly Zotero sync and the mail poller run inside that image. On
+2026-09-11 a module-level ``pfs.cpt_load → pfs.cpt_epub → rex`` import
+chain made every ``stack`` invocation in the api image die with
+``ModuleNotFoundError: fsspec``."""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+
+_PROBE = """
+import builtins
+_real = builtins.__import__
+def _fake(name, *a, **k):
+    if name.split('.')[0] in {'fsspec', 's3fs', 'obstore'}:
+        raise ModuleNotFoundError(name)
+    return _real(name, *a, **k)
+builtins.__import__ = _fake
+import cli            # the `stack` entry point package
+import cli.pfs, cli.bib, cli.llm
+print('cli ok')
+"""
+
+
+def test_stack_cli_imports_without_lake_extras():
+    r = subprocess.run(
+        [sys.executable, "-c", _PROBE], capture_output=True, text=True, check=False
+    )
+    assert r.returncode == 0, r.stderr[-1200:]
+    assert "cli ok" in r.stdout