Preserve exact integer differences in claim distances

agent-notes/fix-integer-distance-issue-3.md

@@ -0,0 +1,21 @@
+# Assignment-selection issue 3
+
+## Goal
+Fix integer distance precision and open a draft PR without merging or changing Propstore pins/source.
+
+## State
+Separate worktree/branch fix/integer-distance-issue-3, based on published d855496. Global instructions and repo source/tests/CI read; no local AGENTS.md/CLAUDE.md found. Focused dependency fixes and regression tests explicitly authorized by parent delegation.
+
+## Smallest change and decision
+About four source lines: subtract int/int endpoints exactly, then convert the difference to the existing float distance type. Preserve float/numeric-coercion/categorical behavior for all other input pairs. About forty regression-test lines cover adjacent signed-64-bit integers and SIGMA's unique majority winner. No new metric policy or broader numeric redesign.
+
+## Next step
+The new tests failed in all six cases before the change (four unit-distance cases and two SIGMA winner cases). After the four-line source fix, the same command passed all six in 0.49s:
+
+`uv run --no-project --offline --python C:/Users/Q/code/assignment-selection/.venv/Scripts/python.exe python -B -m pytest -p no:cacheprovider tests/test_integer_distances.py -q`
+
+PYTHONPATH selected this worktree's src; UV_CACHE_DIR selected its isolated cache. No dependencies installed. Full suite and typing will run in PR CI.
+
+Q separately approved the citation-only edit to issue #3. Replaced only the Propstore solve-owner line anchor 265 with 236, fetched the issue, and verified exact body equality with that one substitution.
+
+Published draft PR https://github.com/ctoth/assignment-selection/pull/4 at source commit 175d32533dc233cb25969154b9f8ca383a996294. Fetched the PR and verified its draft status and exact head. CI run 39339378017 passed all typing/test jobs on Python 3.11, 3.12, and 3.13. No merge or ready transition performed. This final note update records that outcome; verify the note-only final head before handoff.

src/assignment_selection/solver.py

@@ -25,7 +25,10 @@ class EnumerationExceeded:
 def claim_distance(a: Any, b: Any) -> float:
     """Distance between two claim values."""
     try:
-        distance = abs(float(a) - float(b))
+        if isinstance(a, int) and isinstance(b, int):
+            distance = float(abs(a - b))
+        else:
+            distance = abs(float(a) - float(b))
     except (ValueError, TypeError):
         return 0.0 if a == b else 1.0
     if not isfinite(distance):

tests/test_integer_distances.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+import pytest
+
+from assignment_selection import Assignment, Problem, SourceAssignment, solve
+from assignment_selection.solver import claim_distance
+
+
+@pytest.mark.parametrize(
+    "left,right",
+    [
+        (2**53, 2**53 + 1),
+        (2**63 - 2, 2**63 - 1),
+        (-(2**53), -(2**53) - 1),
+        (-(2**63), -(2**63) + 1),
+    ],
+)
+def test_adjacent_large_integers_have_unit_distance(left: int, right: int) -> None:
+    assert claim_distance(left, right) == 1.0
+    assert claim_distance(right, left) == 1.0
+
+
+@pytest.mark.parametrize("majority", [2**53, -(2**63)])
+def test_sigma_selects_the_majority_of_adjacent_large_integers(majority: int) -> None:
+    minority = majority + 1
+    sources = tuple(
+        SourceAssignment(str(index), Assignment({"x": value}))
+        for index, value in enumerate((majority, majority, minority))
+    )
+
+    result = solve(Problem(("x",), sources))
+
+    assert tuple(winner.value_for("x") for winner in result.winners) == (majority,)
+    assert tuple(
+        (candidate.assignment.value_for("x"), candidate.score)
+        for candidate in result.scored_candidates
+    ) == ((majority, 1.0), (minority, 2.0))