Re-audit round 2: 5 blind reviewers, 17 fixes, +12 tests

The re-run confirmed round 1 held and then caught second-order bugs in
its own fixes plus two long-standing ones everyone missed. TUI decisions
after a mid-session reload were counted but never written (rows are now
re-adopted into the fresh list on every save, preferring undecided slots
on duplicate keys); row_ix was computed by equality so duplicate rows
shared an ordinal (identity now, merges included, veto sends it); upload
job keys collided for two same-version copies (completions are counted
per key, so --limit or an interrupt can no longer strand the second
copy); diff consumes collids on exact-version matches (a vetoed
same-version second copy was silently swallowed) and splits mismatches:
report-only disagreement while an unclaimed copy exists, second-copy add
only when every copy is claimed.

Also: XML responses are validated and written atomically before caching
(a torn or truncated 200 body can never poison a re-run), JSON artifacts
write atomically, thing/search parsers refuse missing ids like the
collection parser, empty game names are refused by the upload queue, a
never-rendering version picker fails retryably instead of terminally,
the systemic-failure abort compares exception types, blocked same-title
entries defer as a group so positional pairing can't misalign,
truncation heads pick the earliest separator, diff messages tell the
truth when a token exists without a username, and the shared-constant
sweep now actually covers every module (statuses, search types, marker
names, client_for, ports). pydantic declared as a direct dependency.

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

scripts/fixture_common.py

@@ -9,6 +9,8 @@ from __future__ import annotations
 
 from pathlib import Path
 
+from bggpipe.config import STUB_CACHE_MARKER_NAME, STUB_DATA_MARKER_NAME
+
 CACHE_MARKER_TEXT = (
     "This cache contains hand-written stub XML, not real BGG "
     "responses. Data resolved from it must not be uploaded.\n"
@@ -28,9 +30,9 @@ def esc(text: str) -> str:
 
 
 def write_cache_marker(target: Path) -> None:
-    (target / "STUB_FIXTURES.marker").write_text(CACHE_MARKER_TEXT)
+    (target / STUB_CACHE_MARKER_NAME).write_text(CACHE_MARKER_TEXT)
 
 
 def write_data_marker(data_dir: Path = Path("data")) -> None:
     data_dir.mkdir(parents=True, exist_ok=True)
-    (data_dir / "STUB_DATA.marker").write_text(DATA_MARKER_TEXT)
+    (data_dir / STUB_DATA_MARKER_NAME).write_text(DATA_MARKER_TEXT)