FA-7966 / Selection controls / Open access
Anchored range selection: Backward shift selection produces an empty range · case 01
Backward shift selection produces an empty range.
ROOT CAUSE
The reverse operation uses `(items.index(anchor), items.index(target))` where the contract requires `sorted((items.index(anchor), items.index(target)))`.
VERIFIED REPAIR
Implement the reverse operation as `sorted((items.index(anchor), items.index(target)))`.
Unsuccessful approach: Swapping endpoints without normalization instead breaks forward ranges.
Case contract
Ranges include both endpoints in document order; plain clicks replace; additive selection unions; missing targets preserve selection.
Why this case matters
A deterministic model of anchored range selection; this isolates one interface invariant without requiring a browser.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, selected, anchor, target, extend, additive):
if target not in items: return sorted(selected)
if not extend or anchor not in items: span = {target}
else:
a, b = (items.index(anchor), items.index(target))
span = set(items[a:b+1])
return sorted(set(selected) | span if additive else span)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('removed', solve(['a','b'], ['a'], 'a', 'x', False, False), ['a'])
check('plain', solve(['a','b','c'], ['a'], 'a', 'c', False, False), ['c'])
check('forward', solve(['a','b','c'], [], 'a', 'c', True, False), ['a', 'b', 'c'])
check('backward', solve(['a','b','c'], [], 'c', 'a', True, False), ['a', 'b', 'c'])
check('union', solve(['a','b','c'], ['a'], 'b', 'c', True, True), ['a', 'b', 'c'])
check('replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
check('parameterized inclusive range', solve(list(range(N+2)), [], 0, N, True, False), list(range(N+1)))
for repetition in range(N):
check('repeat replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| removed | ['a'] | ['a'] | Passed |
| plain | ['c'] | ['c'] | Passed |
| forward | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| backward | [] | ['a', 'b', 'c'] | Failed |
| union | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| replace | ['b', 'c'] | ['b', 'c'] | Passed |
| parameterized inclusive range | [0, 1] | [0, 1] | Passed |
| repeat replace | ['b', 'c'] | ['b', 'c'] | Passed |
SHA-256 / 2bde1c04c1dda16b1cffe6a4d23e838a1bf7843bf072a8335e992a50b5fa2b93
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, selected, anchor, target, extend, additive):
if target not in items: return sorted(selected)
if not extend or anchor not in items: span = {target}
else:
a, b = (items.index(target), items.index(anchor))
span = set(items[a:b+1])
return sorted(set(selected) | span if additive else span)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('removed', solve(['a','b'], ['a'], 'a', 'x', False, False), ['a'])
check('plain', solve(['a','b','c'], ['a'], 'a', 'c', False, False), ['c'])
check('forward', solve(['a','b','c'], [], 'a', 'c', True, False), ['a', 'b', 'c'])
check('backward', solve(['a','b','c'], [], 'c', 'a', True, False), ['a', 'b', 'c'])
check('union', solve(['a','b','c'], ['a'], 'b', 'c', True, True), ['a', 'b', 'c'])
check('replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
check('parameterized inclusive range', solve(list(range(N+2)), [], 0, N, True, False), list(range(N+1)))
for repetition in range(N):
check('repeat replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| removed | ['a'] | ['a'] | Passed |
| plain | ['c'] | ['c'] | Passed |
| forward | [] | ['a', 'b', 'c'] | Failed |
| backward | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| union | ['a'] | ['a', 'b', 'c'] | Failed |
| replace | [] | ['b', 'c'] | Failed |
| parameterized inclusive range | [] | [0, 1] | Failed |
| repeat replace | [] | ['b', 'c'] | Failed |
SHA-256 / 089a422365375b953fb867ff06f73b93077ea156219305b38db3d919d2d405e4
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(items, selected, anchor, target, extend, additive):
if target not in items: return sorted(selected)
if not extend or anchor not in items: span = {target}
else:
a, b = sorted((items.index(anchor), items.index(target)))
span = set(items[a:b+1])
return sorted(set(selected) | span if additive else span)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('removed', solve(['a','b'], ['a'], 'a', 'x', False, False), ['a'])
check('plain', solve(['a','b','c'], ['a'], 'a', 'c', False, False), ['c'])
check('forward', solve(['a','b','c'], [], 'a', 'c', True, False), ['a', 'b', 'c'])
check('backward', solve(['a','b','c'], [], 'c', 'a', True, False), ['a', 'b', 'c'])
check('union', solve(['a','b','c'], ['a'], 'b', 'c', True, True), ['a', 'b', 'c'])
check('replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
check('parameterized inclusive range', solve(list(range(N+2)), [], 0, N, True, False), list(range(N+1)))
for repetition in range(N):
check('repeat replace', solve(['a','b','c'], ['a'], 'b', 'c', True, False), ['b', 'c'])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| removed | ['a'] | ['a'] | Passed |
| plain | ['c'] | ['c'] | Passed |
| forward | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| backward | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| union | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| replace | ['b', 'c'] | ['b', 'c'] | Passed |
| parameterized inclusive range | [0, 1] | [0, 1] | Passed |
| repeat replace | ['b', 'c'] | ['b', 'c'] | Passed |
SHA-256 / caeebbec1387af3a4eff6775092231c4860974fc3c1fee025be129f473c5877c
Verification & scope
This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:38:16.874388+00:00.
Case digest / 8482a317e506783021f0d57c24c5ad6441a41f11af1518761d5fbe28e84ea0b1