feat(project): --gate reaches the build, and the bundle says which one

`project.create` called `build()` with five keyword arguments and no `gate=`,
so `okf project` screened by the package default and nothing anywhere said
that was a choice rather than the only option. The gate is not a segmentation
rule -- it is a screen about whether a document may be persisted at all -- so
it is the one flag this command owns that may move a bundle's bytes, and the
module docstring, the README paragraph and the test file's own claim are
corrected rather than left standing beside the new flag.

The default is `okf build`'s default, so an unflagged `okf project` is the
bytes it always was; the byte-equality invariant against `okf build` holds
unchanged. An unknown gate name still raises `gate_invalid` rather than
falling back -- a fallback reproduces the defect with an extra step.

Tests first, all three red: the gate name read back out of the bundle's own
`log.md` (not out of the call), the flag parsed by this command's parser, and
the unknown name refused.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_okf_project.py

@@ -1,9 +1,10 @@
 """`okf project`: one folder in, one bundle plus one skill out.
 
-The command adds no rule and owns no flag that changes a bundle's bytes, so
-these tests are mostly about that: the project bundle must be the SAME bytes
-`okf build` writes for the same folder at the same stamp, or there are two
-build paths and the reports are pinned to one of them.
+The command adds no rule, and owns exactly ONE flag that changes a bundle's
+bytes -- `--gate`, which is a screen and not a segmentation rule. These tests
+are mostly about the rest: the project bundle must be the SAME bytes `okf
+build` writes for the same folder at the same stamp, or there are two build
+paths and the reports are pinned to one of them.
 """
 
 from __future__ import annotations
@@ -267,3 +268,36 @@ def test_a_sheet_reaches_the_project_bundle_as_it_reaches_the_build_command(
         == 0
     )
     assert tree(bundle) == tree(reference)
+
+
+def test_the_gate_reaches_the_build_and_the_bundle_says_which_one(
+    folder: Path, tmp_path: Path
+) -> None:
+    """`okf project --gate` is the one flag here that MAY move a bundle's bytes.
+
+    `project.create` called `build()` with five keyword arguments and no
+    `gate=`, so the gate name was unreachable from this command: every project
+    bundle was screened by the package default and nothing said so was a
+    choice. The gate's name is written into the bundle's own `log.md`, so the
+    check is the bundle's, not the call's.
+    """
+    out = tmp_path / "project"
+    bundle, _, _ = project.create(folder, out=out, gate="none")
+    log = (bundle / "log.md").read_text(encoding="utf-8")
+    assert "NOTHING WAS SCREENED" in log
+
+    default = tmp_path / "default"
+    other, _, _ = project.create(folder, out=default)
+    assert "NOTHING WAS SCREENED" not in (other / "log.md").read_text(encoding="utf-8")
+
+
+def test_the_gate_flag_is_parsed_by_the_project_command(folder: Path, tmp_path: Path) -> None:
+    args = project.parse_args([str(folder), "--out", str(tmp_path), "--gate", "none"])
+    assert args.gate == "none"
+
+
+def test_an_unknown_gate_name_does_not_start_the_run(folder: Path, tmp_path: Path) -> None:
+    """A fallback would reproduce the defect the gate was added to close."""
+    with pytest.raises(IngestError) as caught:
+        project.create(folder, out=tmp_path / "project", gate="guard-nonesuch")
+    assert caught.value.code == "gate_invalid"