test(corpus): a rebuild with log.md present reproduces the bundle exactly

`log.md` is written INTO a directory Door B enumerates on the next round: it
matches the concept glob and is excluded only by `index.md`'s name, so a
rebuild could have seen it as pre-existing curated content or pruned it.
Rebuild-equals-incremental is the property the segmented bundle rests on.

Measured on the real artifact, not only the synthetic: the K2 corpus was run
a second time into the same bundle and compared against a snapshot with
`diff -r`, exit 0 over all 1108 files. The test pins the same property in
seconds instead of 13 minutes.

Also corrects the report's reproduction command -- it documented plan
filenames the run did not use, and re-running it into the existing plans
directory would leave two files claiming one `source_sha256`, which
`_resolve_plans` refuses.

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

tests/test_corpus_run.py

@@ -321,3 +321,49 @@ def test_without_a_plan_directory_the_run_is_unchanged(tmp_path: Path) -> None:
     concepts = [path for path in bundle.rglob("*.md") if path.name not in ("index.md", "log.md")]
     assert len(concepts) == 1
     assert "adjudication:" not in concepts[0].read_text(encoding="utf-8")
+
+
+def test_a_second_run_into_the_same_bundle_reproduces_it_byte_for_byte(tmp_path: Path) -> None:
+    """`log.md` is a file the harness writes INTO a directory Door B enumerates
+    on the next round: it matches the concept glob and is excluded only by
+    `index.md`'s name, so a rebuild could see it as pre-existing curated content
+    or prune it. Rebuild-equals-incremental is the property the segmented bundle
+    is built on, and a log that broke it would be worse than no log.
+    """
+    root = corpus(tmp_path, {"doc.md": SEGMENTABLE, "flat.md": SUBSTANTIVE})
+    plans = tmp_path / "plans"
+    plans.mkdir()
+    _propose(root / "doc.md", plans / "doc.json")
+    bundle = tmp_path / "bundle"
+    argv = [
+        "--corpus",
+        str(root),
+        "--report",
+        str(tmp_path / "r.md"),
+        "--bundle",
+        str(bundle),
+        "--ingested-at",
+        INGESTED_AT,
+        "--plans-dir",
+        str(plans),
+        "--bundle-id",
+        "k2",
+        "--okf-version",
+        "0.2",
+    ]
+
+    assert okf_corpus_run.main(argv) == 0
+    first = {
+        path.relative_to(bundle).as_posix(): path.read_bytes()
+        for path in sorted(bundle.rglob("*"))
+        if path.is_file()
+    }
+    assert "log.md" in first
+
+    assert okf_corpus_run.main(argv) == 0
+    second = {
+        path.relative_to(bundle).as_posix(): path.read_bytes()
+        for path in sorted(bundle.rglob("*"))
+        if path.is_file()
+    }
+    assert second == first