FA-21401 / Assistive announcements / Open access

Undo restores the oldest edit instead of latest · case 01

The announcement trace violates the stated edit-narration contract.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Fault site: text,cursor=history.pop() is implemented as text,cursor=history.pop(0)

VERIFIED REPAIR

Restore the stated transition: text,cursor=history.pop()

Unsuccessful approach: The attempted repair substitutes text,cursor=history[-1] and still violates a regression oracle.

Case contract

Document announcement state stores text and a cursor. Insert inserts at clamped cursor and announces inserted span. Backspace removes up to count before cursor and announces removed span in original order. Delete removes after cursor without moving it. Move clamps cursor. Replace range uses sorted clamped endpoints, announces old/new, moves cursor to replacement end. Undo restores text and cursor from last mutating edit and announces restored text. Silent toggles suppress cues but not state or undo. Return cues,text,cursor.

Why this case matters

Deterministic controlled model of assistive announcement delivery.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events):
    text=''; cursor=0; history=[]; silent=False; out=[]
    for e in events:
        op=e[0]
        if op=='move': cursor=max(0,min(len(text),e[1]))
        elif op=='silent': silent=e[1]
        elif op=='undo' and history:
            text,cursor=history.pop(0)
            if not silent: out.append(['undo',text])
        elif op in ('insert','backspace','delete','replace'):
            history.append([text,cursor])
            if op=='insert':
                text=text[:cursor]+e[1]+text[cursor:]; cursor+=len(e[1]); cue=['insert',e[1]]
            elif op=='backspace':
                start=max(0,cursor-e[1]); cue=['remove',text[start:cursor]]
                text=text[:start]+text[cursor:]; cursor=start
            elif op=='delete':
                end=min(len(text),cursor+e[1]); cue=['remove',text[cursor:end]]
                text=text[:cursor]+text[end:]
            else:
                a,b=sorted([max(0,min(len(text),e[1])),max(0,min(len(text),e[2]))])
                cue=['replace',text[a:b],e[3]]; text=text[:a]+e[3]+text[b:]; cursor=a+len(e[3])
            if not silent: out.append(cue)
    return [out,text,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = ["[['insert','abcd'*N],['move',2],['insert','XY'],['backspace',2],['undo'],['undo']]", "[['insert','abcdef'*N],['move',4],['backspace',2]]", "[['insert','abcdef'*N],['move',2],['delete',2]]", "[['insert','abcdef'*N],['replace',5,2,'Z']]", "[['insert','abcdef'*N],['replace',5,2,'Z'],['undo']]", "[['silent',True],['insert','secret'*N],['silent',False],['move',99],['insert','!']]", "[['insert','x'*N],['move',-5],['backspace',4],['delete',99],['undo']]", '[]']
expected = {1: [[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3], [[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6], [[['insert', '!']], 'secret!', 7], [[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0], [[], '', 0]], 2: [[[['insert', 'abcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcd'], ['undo', 'abcdabcd']], 'abcdabcd', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdef', 3], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdef']], 'abcdefabcdef', 12], [[['insert', '!']], 'secretsecret!', 13], [[['insert', 'xx'], ['remove', ''], ['remove', 'xx'], ['undo', 'xx']], 'xx', 0], [[], '', 0]], 3: [[[['insert', 'abcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcd'], ['undo', 'abcdabcdabcd']], 'abcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdef']], 'abcdefabcdefabcdef', 18], [[['insert', '!']], 'secretsecretsecret!', 19], [[['insert', 'xxx'], ['remove', ''], ['remove', 'xxx'], ['undo', 'xxx']], 'xxx', 0], [[], '', 0]], 4: [[[['insert', 'abcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcd']], 'abcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdef', 24], [[['insert', '!']], 'secretsecretsecretsecret!', 25], [[['insert', 'xxxx'], ['remove', ''], ['remove', 'xxxx'], ['undo', 'xxxx']], 'xxxx', 0], [[], '', 0]], 5: [[[['insert', 'abcdabcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcdabcd']], 'abcdabcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdefabcdef', 30], [[['insert', '!']], 'secretsecretsecretsecretsecret!', 31], [[['insert', 'xxxxx'], ['remove', ''], ['remove', 'xxxxx'], ['undo', 'xxxxx']], 'xxxxx', 0], [[], '', 0]]}[N]
for i, expression in enumerate(fixtures):
    check("trace-"+str(i+1), solve(eval(expression)), expected[i])
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
trace-1	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', ''], ['undo', 'abcd']], 'abcd', 2]`	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2]`	Failed
trace-2	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-3	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-4	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	Passed
trace-5	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', '']], '', 0]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6]`	Failed
trace-6	`[[['insert', '!']], 'secret!', 7]`	`[[['insert', '!']], 'secret!', 7]`	Passed
trace-7	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', '']], '', 0]`	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0]`	Failed
trace-8	`[[], '', 0]`	`[[], '', 0]`	Passed

SHA-256 / e2a0269bf1d82592a1f537d3d1d9b51e78ff7eb04958d99978f8cdad8d1a83bf

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events):
    text=''; cursor=0; history=[]; silent=False; out=[]
    for e in events:
        op=e[0]
        if op=='move': cursor=max(0,min(len(text),e[1]))
        elif op=='silent': silent=e[1]
        elif op=='undo' and history:
            text,cursor=history[-1]
            if not silent: out.append(['undo',text])
        elif op in ('insert','backspace','delete','replace'):
            history.append([text,cursor])
            if op=='insert':
                text=text[:cursor]+e[1]+text[cursor:]; cursor+=len(e[1]); cue=['insert',e[1]]
            elif op=='backspace':
                start=max(0,cursor-e[1]); cue=['remove',text[start:cursor]]
                text=text[:start]+text[cursor:]; cursor=start
            elif op=='delete':
                end=min(len(text),cursor+e[1]); cue=['remove',text[cursor:end]]
                text=text[:cursor]+text[end:]
            else:
                a,b=sorted([max(0,min(len(text),e[1])),max(0,min(len(text),e[2]))])
                cue=['replace',text[a:b],e[3]]; text=text[:a]+e[3]+text[b:]; cursor=a+len(e[3])
            if not silent: out.append(cue)
    return [out,text,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = ["[['insert','abcd'*N],['move',2],['insert','XY'],['backspace',2],['undo'],['undo']]", "[['insert','abcdef'*N],['move',4],['backspace',2]]", "[['insert','abcdef'*N],['move',2],['delete',2]]", "[['insert','abcdef'*N],['replace',5,2,'Z']]", "[['insert','abcdef'*N],['replace',5,2,'Z'],['undo']]", "[['silent',True],['insert','secret'*N],['silent',False],['move',99],['insert','!']]", "[['insert','x'*N],['move',-5],['backspace',4],['delete',99],['undo']]", '[]']
expected = {1: [[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3], [[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6], [[['insert', '!']], 'secret!', 7], [[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0], [[], '', 0]], 2: [[[['insert', 'abcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcd'], ['undo', 'abcdabcd']], 'abcdabcd', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdef', 3], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdef']], 'abcdefabcdef', 12], [[['insert', '!']], 'secretsecret!', 13], [[['insert', 'xx'], ['remove', ''], ['remove', 'xx'], ['undo', 'xx']], 'xx', 0], [[], '', 0]], 3: [[[['insert', 'abcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcd'], ['undo', 'abcdabcdabcd']], 'abcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdef']], 'abcdefabcdefabcdef', 18], [[['insert', '!']], 'secretsecretsecret!', 19], [[['insert', 'xxx'], ['remove', ''], ['remove', 'xxx'], ['undo', 'xxx']], 'xxx', 0], [[], '', 0]], 4: [[[['insert', 'abcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcd']], 'abcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdef', 24], [[['insert', '!']], 'secretsecretsecretsecret!', 25], [[['insert', 'xxxx'], ['remove', ''], ['remove', 'xxxx'], ['undo', 'xxxx']], 'xxxx', 0], [[], '', 0]], 5: [[[['insert', 'abcdabcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcdabcd']], 'abcdabcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdefabcdef', 30], [[['insert', '!']], 'secretsecretsecretsecretsecret!', 31], [[['insert', 'xxxxx'], ['remove', ''], ['remove', 'xxxxx'], ['undo', 'xxxxx']], 'xxxxx', 0], [[], '', 0]]}[N]
for i, expression in enumerate(fixtures):
    check("trace-"+str(i+1), solve(eval(expression)), expected[i])
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
trace-1	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abXYcd']], 'abXYcd', 4]`	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2]`	Failed
trace-2	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-3	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-4	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	Passed
trace-5	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6]`	Passed
trace-6	`[[['insert', '!']], 'secret!', 7]`	`[[['insert', '!']], 'secret!', 7]`	Passed
trace-7	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0]`	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0]`	Passed
trace-8	`[[], '', 0]`	`[[], '', 0]`	Passed

SHA-256 / e6fe4782beafc6b80b69a7595ad5c931fa2fd8e3c8810102fea82b527ee57c97

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events):
    text=''; cursor=0; history=[]; silent=False; out=[]
    for e in events:
        op=e[0]
        if op=='move': cursor=max(0,min(len(text),e[1]))
        elif op=='silent': silent=e[1]
        elif op=='undo' and history:
            text,cursor=history.pop()
            if not silent: out.append(['undo',text])
        elif op in ('insert','backspace','delete','replace'):
            history.append([text,cursor])
            if op=='insert':
                text=text[:cursor]+e[1]+text[cursor:]; cursor+=len(e[1]); cue=['insert',e[1]]
            elif op=='backspace':
                start=max(0,cursor-e[1]); cue=['remove',text[start:cursor]]
                text=text[:start]+text[cursor:]; cursor=start
            elif op=='delete':
                end=min(len(text),cursor+e[1]); cue=['remove',text[cursor:end]]
                text=text[:cursor]+text[end:]
            else:
                a,b=sorted([max(0,min(len(text),e[1])),max(0,min(len(text),e[2]))])
                cue=['replace',text[a:b],e[3]]; text=text[:a]+e[3]+text[b:]; cursor=a+len(e[3])
            if not silent: out.append(cue)
    return [out,text,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = ["[['insert','abcd'*N],['move',2],['insert','XY'],['backspace',2],['undo'],['undo']]", "[['insert','abcdef'*N],['move',4],['backspace',2]]", "[['insert','abcdef'*N],['move',2],['delete',2]]", "[['insert','abcdef'*N],['replace',5,2,'Z']]", "[['insert','abcdef'*N],['replace',5,2,'Z'],['undo']]", "[['silent',True],['insert','secret'*N],['silent',False],['move',99],['insert','!']]", "[['insert','x'*N],['move',-5],['backspace',4],['delete',99],['undo']]", '[]']
expected = {1: [[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2], [[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3], [[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6], [[['insert', '!']], 'secret!', 7], [[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0], [[], '', 0]], 2: [[[['insert', 'abcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcd'], ['undo', 'abcdabcd']], 'abcdabcd', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['remove', 'cd']], 'abefabcdef', 2], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdef', 3], [[['insert', 'abcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdef']], 'abcdefabcdef', 12], [[['insert', '!']], 'secretsecret!', 13], [[['insert', 'xx'], ['remove', ''], ['remove', 'xx'], ['undo', 'xx']], 'xx', 0], [[], '', 0]], 3: [[[['insert', 'abcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcd'], ['undo', 'abcdabcdabcd']], 'abcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdef']], 'abcdefabcdefabcdef', 18], [[['insert', '!']], 'secretsecretsecret!', 19], [[['insert', 'xxx'], ['remove', ''], ['remove', 'xxx'], ['undo', 'xxx']], 'xxx', 0], [[], '', 0]], 4: [[[['insert', 'abcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcd']], 'abcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdef', 24], [[['insert', '!']], 'secretsecretsecretsecret!', 25], [[['insert', 'xxxx'], ['remove', ''], ['remove', 'xxxx'], ['undo', 'xxxx']], 'xxxx', 0], [[], '', 0]], 5: [[[['insert', 'abcdabcdabcdabcdabcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcdabcdabcdabcdabcd'], ['undo', 'abcdabcdabcdabcdabcd']], 'abcdabcdabcdabcdabcd', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['remove', 'cd']], 'abefabcdefabcdefabcdefabcdef', 2], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z']], 'abZfabcdefabcdefabcdefabcdef', 3], [[['insert', 'abcdefabcdefabcdefabcdefabcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdefabcdefabcdefabcdefabcdef']], 'abcdefabcdefabcdefabcdefabcdef', 30], [[['insert', '!']], 'secretsecretsecretsecretsecret!', 31], [[['insert', 'xxxxx'], ['remove', ''], ['remove', 'xxxxx'], ['undo', 'xxxxx']], 'xxxxx', 0], [[], '', 0]]}[N]
for i, expression in enumerate(fixtures):
    check("trace-"+str(i+1), solve(eval(expression)), expected[i])
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
trace-1	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2]`	`[[['insert', 'abcd'], ['insert', 'XY'], ['remove', 'XY'], ['undo', 'abXYcd'], ['undo', 'abcd']], 'abcd', 2]`	Passed
trace-2	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-3	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	`[[['insert', 'abcdef'], ['remove', 'cd']], 'abef', 2]`	Passed
trace-4	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z']], 'abZf', 3]`	Passed
trace-5	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6]`	`[[['insert', 'abcdef'], ['replace', 'cde', 'Z'], ['undo', 'abcdef']], 'abcdef', 6]`	Passed
trace-6	`[[['insert', '!']], 'secret!', 7]`	`[[['insert', '!']], 'secret!', 7]`	Passed
trace-7	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0]`	`[[['insert', 'x'], ['remove', ''], ['remove', 'x'], ['undo', 'x']], 'x', 0]`	Passed
trace-8	`[[], '', 0]`	`[[], '', 0]`	Passed

SHA-256 / 57f754d7870db9131c713c229503e67479461553944d07f3e8188446c5bfd29d

Verification & scope

Stipulated bounded policy, not a browser, speech engine, platform API, or standards conformance claim. 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 2026-09-29T14:40:28.497221+00:00.

Case digest / 3414231bb3455bcc1a70b6117f78af74ad660d38331274df64d87341b96c55b5