tests: fix the flaky heartbeat coverage assertion

test_search_fills_progress_with_live_positions_and_total asserted 100%
coverage after searching for a DOI that EXISTS. Once every queried DOI is
found the consumer signals TERM and the producers stop mid-file, so the
recorded offsets reach an arbitrary point - the assertion was racing the
scan and failed roughly one full-suite run in two.

Split into the two things that are actually deterministic: coverage is now
measured with an ABSENT DOI (nothing can stop the scan early, so 100% is
guaranteed), and the found-target case asserts what holds regardless of
where the producers stopped - the total is known, progress is bounded and
sane, and the hit is reported.

Verified: 5 consecutive runs of the file and 3 consecutive full integration
runs, all green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/integration/test_librarian_heartbeat.py

@@ -60,25 +60,49 @@ def test_current_search_registration_round_trip():
         assert not lib._current_search
 
 
-def test_search_fills_progress_with_live_positions_and_total(tmp_path, monkeypatch):
-    # End to end against the real scan: total_bytes matches the chunk files on
-    # disk, and once finished the recorded offsets cover them.
-    monkeypatch.setattr(search_bot, "DATABASE_PATH", str(tmp_path) + "/")
+def _write_two_chunks(tmp_path):
     (tmp_path / "0_chunk.txt").write_text("10.1/a\n10.1/b\n", encoding="utf-8")
     (tmp_path / "1_chunk.txt").write_text("10.1/c\n", encoding="utf-8")
-    expected_total = sum(
+    return sum(
         (tmp_path / name).stat().st_size for name in ("0_chunk.txt", "1_chunk.txt")
     )
 
+
+def test_search_fills_progress_and_reaches_full_coverage(tmp_path, monkeypatch):
+    # Coverage must be measured on a search that CANNOT stop early. Once every
+    # queried DOI is found the consumer signals TERM and the producers stop
+    # mid-file, so a search for a DOI that exists reaches an arbitrary offset -
+    # asserting 100% there is a race (it failed roughly one run in two).
+    # An absent DOI forces the whole database to be read.
+    monkeypatch.setattr(search_bot, "DATABASE_PATH", str(tmp_path) + "/")
+    expected_total = _write_two_chunks(tmp_path)
+
+    progress = {}
+    search_bot.search_for_doi([("10.9/absent", "DATA")], [], _LOG, progress=progress)
+
+    assert progress["total_bytes"] == expected_total
+    assert progress["chunk_files"] == 2
+    done, total, percent = lib._progress_summary(progress)
+    assert total == expected_total
+    assert done == expected_total          # nothing stopped it: whole DB scanned
+    assert percent == pytest.approx(100.0)
+
+
+def test_progress_is_populated_for_a_search_that_finds_its_target(tmp_path, monkeypatch):
+    # The early-termination case: the target is found, so coverage is whatever
+    # the producers reached. Assert what IS deterministic - the total is known,
+    # progress is bounded and sane, and the hit is reported.
+    monkeypatch.setattr(search_bot, "DATABASE_PATH", str(tmp_path) + "/")
+    expected_total = _write_two_chunks(tmp_path)
+
     progress = {}
     result, _positions, _interrupted = search_bot.search_for_doi(
         [("10.1/c", "DATA")], [], _LOG, progress=progress
     )
 
     assert progress["total_bytes"] == expected_total
-    assert progress["chunk_files"] == 2
     done, total, percent = lib._progress_summary(progress)
     assert total == expected_total
-    assert done == expected_total          # whole DB scanned
-    assert percent == pytest.approx(100.0)
+    assert 0 <= done <= total              # bounded, never nonsense
+    assert 0.0 <= percent <= 100.0
     assert [r for r in result if r["DOI"] == "10.1/c" and r["exists"]]