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>

docs/2026-09-03-k2-bundle-rebuild.md

@@ -61,22 +61,33 @@ Three commits, each test-first.
 
 ## The rebuild
 
-Bundle: `~/corpora/okf-telling-20260829/K2-bundle-20260903/` (5.5 MB, 29
+Bundle: `~/corpora/okf-telling-20260829/K2-bundle-20260903/` — 5.5 MB, 1108
-directories). Plans: `~/corpora/okf-telling-20260829/K2-plans-20260903/`.
+files: 629 concepts, 478 `index.md` (one per directory, the profile sets
-Both outside the repository, both durable.
+`per_directory`), and one `log.md`. Plans:
+`~/corpora/okf-telling-20260829/K2-plans-20260903/` — 28 of them, one per
+document that had something to propose. Both outside the repository, both
+durable.
+
+**Reproduce into a FRESH plans directory.** A plan is selected by
+`source_sha256`, so re-running the proposer into a directory that already holds
+these plans leaves two files claiming the same hash, and `_resolve_plans`
+refuses that rather than picking one:
 
 ```
+PLANS=~/corpora/okf-telling-20260829/K2-plans-$(date +%Y%m%d-%H%M%S); mkdir -p "$PLANS"
+i=0
 for f in ~/corpora/okf-telling-20260829/K2/trinn1/*; do
-  b=$(basename "$f"); .venv/bin/python tools/okf_propose_segments.py "$f" \
+  i=$((i+1)); b=$(basename "$f")
-    --out ~/corpora/okf-telling-20260829/K2-plans-20260903/"${b%.*}".json \
+  .venv/bin/python tools/okf_propose_segments.py "$f" \
+    --out "$PLANS/$(printf '%02d' $i).json" \
     --path-prefix "${b%.*}" --proposed-at 2026-09-03T00:00:00Z
-done
+done   # exit 1 for the 11 with nothing to propose, exit 2 for the 4 unreadable
 .venv/bin/python tools/okf_corpus_run.py \
   --corpus ~/corpora/okf-telling-20260829/K2/trinn1 \
   --report ~/corpora/okf-telling-20260829/K2-bundle-20260903-report.md \
   --bundle ~/corpora/okf-telling-20260829/K2-bundle-20260903 \
   --ingested-at 2026-09-03T00:00:00Z \
-  --plans-dir ~/corpora/okf-telling-20260829/K2-plans-20260903 \
+  --plans-dir "$PLANS" \
   --bundle-id k2-trinn1-20260903 --okf-version 0.2
 ```
 
@@ -97,10 +108,18 @@ Converter as the harness resolved it: the vendored `pypandoc` binary, version
 | concepts over 100 000 characters | 4/629 |
 | wall time | 784.29 s total, 18.239 s per file |
 | K1b | `39 + 4 = 43 = N`, run exited `0` |
+| rebuild == incremental | `diff -r` exit `0` over all 1108 files |
 
 The previous bundle, re-measured here rather than quoted: 39 concepts, **0/39**
 carrying `adjudication`, max body 267 548 characters, no `log.md`.
 
+`log.md` is a file the run path writes into a directory Door B enumerates on
+the next round, so the rebuild property was re-measured rather than assumed:
+the whole corpus was run a second time into the same bundle and compared
+against a snapshot with `diff -r`, which exited `0`. A test in
+`tests/test_corpus_run.py` pins the same property on a synthetic corpus, so it
+fails in seconds rather than in 13 minutes.
+
 **K1b is now recoverable from the bundle alone**, which was the point of §9:
 
 ```

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