Credibility pass: comments state constraints, not development history

A skeptical-cloner review flagged the patterns that read as AI-iteration
residue: test comments and section headers narrating the review process
that produced them, "legacy format" framing in a days-old repo, shadow
re-imports appended without reading file headers, one genuine machine
leftover (FIXTURE_CACHE = FIXTURE_CACHE), and a few register slips.
Every history-narrating comment is rewritten as the timeless invariant
it was guarding, test sections are grouped by behavior, function-local
imports are hoisted, and the README loses its one marketing clause and
heaviest dash runs. No behavior changes; 176 tests unchanged and green.

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

tests/test_diff.py

@@ -3,11 +3,19 @@ snapshots as parsing fixtures. No network anywhere."""
 
 from __future__ import annotations
 
+import shutil
 from pathlib import Path
 
 from bggpipe.config import Config
-from bggpipe.diff import SNAPSHOT_FILES, compute_diff, load_snapshot_collection
+from bggpipe.diff import (
+    SNAPSHOT_FILES,
+    compute_diff,
+    load_snapshot_collection,
+    run_diff,
+)
 from bggpipe.models import CollectionItem
+from bggpipe.resolve import write_matches
+from bggpipe.upload import run_upload
 
 FIXTURES = Path(__file__).parent / "fixtures"
 
@@ -171,16 +179,15 @@ def test_unvetoed_bare_duplicate_stays_owned():
 
 
 def test_earlier_disagreement_cannot_steal_a_later_rows_exact_match():
-    # round-3 ordering bug: row A (v3, no match) must not consume the v2
-    # copy that row B exactly matches — exact matches settle first
+    # row A (v3, no match) must not consume the v2 copy that row B exactly
+    # matches — exact-version claims settle before disagreements
     rows = [
         _match("Catan", "13", vstatus="version_auto", vid="3", vname="v3"),
         _match("Catan", "13", vstatus="version_auto", vid="2", vname="v2"),
     ]
     result = compute_diff(rows, [_item(13, 900, version_id=2)])
     assert result.already_owned == ["Catan"]  # B's exact match claims the copy
-    # A's v3 box exists on the shelf and matches no collection entry: a
-    # genuine new copy — NOT a spurious v2 duplicate, NOT a false disagreement
+    # A's v3 box matches no collection entry: a genuine new copy
     assert [r["version_id"] for r in result.to_add] == ["3"]
     assert result.disagreements == []
 
@@ -276,11 +283,6 @@ def test_versionless_copies_exhaust_then_second_copy_becomes_add():
 def test_run_diff_outputs_feed_upload_unchanged(tmp_path, monkeypatch):
     # the cross-stage contract: whatever run_diff writes, run_upload must
     # read — a column rename on either side has to fail HERE
-    import shutil
-
-    from bggpipe.diff import run_diff
-    from bggpipe.resolve import write_matches
-    from bggpipe.upload import run_upload
 
     monkeypatch.delenv("BGG_API_TOKEN", raising=False)
     cfg = Config(data_dir=tmp_path)
@@ -307,10 +309,6 @@ def test_run_diff_outputs_feed_upload_unchanged(tmp_path, monkeypatch):
 
 
 def test_token_without_username_says_so(tmp_path, monkeypatch, capsys):
-    import shutil
-
-    from bggpipe.diff import run_diff
-    from bggpipe.resolve import write_matches
 
     monkeypatch.setenv("BGG_API_TOKEN", "tok")
     monkeypatch.delenv("BGG_USERNAME", raising=False)
@@ -322,7 +320,7 @@ def test_token_without_username_says_so(tmp_path, monkeypatch, capsys):
     run_diff(cfg)
     out = capsys.readouterr().out
     assert "BGG_API_TOKEN is set but BGG_USERNAME is not" in out
-    assert "No BGG_API_TOKEN" not in out  # the old message was a lie here
+    assert "No BGG_API_TOKEN" not in out  # the token IS set; blame the username
 
 
 class _LiveClient:
@@ -346,9 +344,6 @@ def test_live_diff_fetches_fresh_collection(tmp_path, monkeypatch):
     # the branch that runs the day the token arrives: must call
     # collection_full with refresh=True, not serve resolve-era cache
 
-    from bggpipe.diff import run_diff
-    from bggpipe.resolve import write_matches
-
     monkeypatch.setenv("BGG_API_TOKEN", "tok")
     monkeypatch.setenv("BGG_USERNAME", "eric")
     cfg = Config(bgg_username="eric", data_dir=tmp_path)
@@ -360,10 +355,6 @@ def test_live_diff_fetches_fresh_collection(tmp_path, monkeypatch):
 
 
 def test_live_diff_falls_back_to_snapshots_on_auth_failure(tmp_path, monkeypatch):
-    import shutil
-
-    from bggpipe.diff import run_diff
-    from bggpipe.resolve import write_matches
 
     monkeypatch.setenv("BGG_API_TOKEN", "bad")
     monkeypatch.setenv("BGG_USERNAME", "eric")