FA-22966 / Autocomplete interactions / Open access

Mention suggestion insertion: mention caret omits the trigger width · case 01

The caret completion transition produces an incorrect observable state.

Verified by executionVariant 1 · 22 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

At mention-completion/caret, the implementation evaluates `d['start']+len(d['label'])` instead of preserving the specified completion transition.

VERIFIED REPAIR

Implement the caret contract using `d['start']+len(d['trigger'])+len(d['label'])`.

Unsuccessful approach: The attempted repair uses `d['end']`, which still violates a normal or boundary completion fixture.

Case contract

A mention completion replaces only the active trigger span and stores a stable entity identifier separately from visible text. The trigger character is preserved exactly once, a trailing delimiter is added only when absent, and a stale mention query cannot replace a different trigger span. Offsets are code points.

Why this case matters

Autocomplete couples draft text, suggestion identity and asynchronous presentation; this bounded lifecycle model isolates one observable interaction defect.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(event, d):
    if event == 'text': return d['text'][:d['start']]+d['trigger']+d['label']+d['text'][d['end']:]
    if event == 'identity': return d['id']
    if event == 'trigger': return d['trigger']+d['label']
    if event == 'query': return d['query']
    if event == 'delimiter': return '' if d['after'].startswith(' ') else ' '
    if event == 'caret': return d['start']+len(d['label'])
    if event == 'span': return [d['start'],d['start']+len(d['trigger'])+len(d['label'])]
    if event == 'stale': return d['span_epoch']==d['epoch']
    if event == 'tail': return d['text'][d['end']:]
    if event == 'descriptor': return [d['trigger'],d['query']]
    return {'unchanged': True}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
normal = {'text':'Hi @al now','start':3,'end':6,'label':'Alice','id':'u'+str(N),'trigger':'@','after':' now','query':'al','span_epoch':N-1,'epoch':N,'other':'#topic'}
boundary = {'text':'@','start':0,'end':1,'label':'','id':'','trigger':'@','after':'','query':'','span_epoch':N,'epoch':N,'other':''}
check('normal text', solve('text', normal), 'Hi @Alice now')
check('boundary text', solve('text', boundary), '@')
check('normal identity', solve('identity', normal), 'u'+str(N))
check('boundary identity', solve('identity', boundary), '')
check('normal trigger', solve('trigger', normal), '@Alice')
check('boundary trigger', solve('trigger', boundary), '@')
check('normal query', solve('query', normal), 'al')
check('boundary query', solve('query', boundary), '')
check('normal delimiter', solve('delimiter', normal), '')
check('boundary delimiter', solve('delimiter', boundary), ' ')
check('normal caret', solve('caret', normal), 9)
check('boundary caret', solve('caret', boundary), 1)
check('normal span', solve('span', normal), [3,9])
check('boundary span', solve('span', boundary), [0,1])
check('normal stale', solve('stale', normal), False)
check('boundary stale', solve('stale', boundary), True)
check('normal tail', solve('tail', normal), ' now')
check('boundary tail', solve('tail', boundary), '')
check('normal descriptor', solve('descriptor', normal), ['@','al'])
check('boundary descriptor', solve('descriptor', boundary), ['@',''])
variant = dict(normal, **{'id':'person'+str(N)})
check('variant query or selection payload', solve('identity', variant), 'person'+str(N))
check('unknown completion event', solve('unrecognized', normal), {'unchanged': True})
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
normal text	`Hi @Alice now`	`Hi @Alice now`	Passed
boundary text	`@`	`@`	Passed
normal identity	`u1`	`u1`	Passed
boundary identity			Passed
normal trigger	`@Alice`	`@Alice`	Passed
boundary trigger	`@`	`@`	Passed
normal query	`al`	`al`	Passed
boundary query			Passed
normal delimiter			Passed
boundary delimiter			Passed
normal caret	`8`	`9`	Failed
boundary caret	`0`	`1`	Failed
normal span	`[3, 9]`	`[3, 9]`	Passed
boundary span	`[0, 1]`	`[0, 1]`	Passed
normal stale	`False`	`False`	Passed
boundary stale	`True`	`True`	Passed
normal tail	`now`	`now`	Passed
boundary tail			Passed
normal descriptor	`['@', 'al']`	`['@', 'al']`	Passed
boundary descriptor	`['@', '']`	`['@', '']`	Passed
variant query or selection payload	`person1`	`person1`	Passed
unknown completion event	`{'unchanged': True}`	`{'unchanged': True}`	Passed

SHA-256 / 41da8592f5a3becd3ad4bca13d925554a041b3fa3387741d8a9d2b33f5535689

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(event, d):
    if event == 'text': return d['text'][:d['start']]+d['trigger']+d['label']+d['text'][d['end']:]
    if event == 'identity': return d['id']
    if event == 'trigger': return d['trigger']+d['label']
    if event == 'query': return d['query']
    if event == 'delimiter': return '' if d['after'].startswith(' ') else ' '
    if event == 'caret': return d['end']
    if event == 'span': return [d['start'],d['start']+len(d['trigger'])+len(d['label'])]
    if event == 'stale': return d['span_epoch']==d['epoch']
    if event == 'tail': return d['text'][d['end']:]
    if event == 'descriptor': return [d['trigger'],d['query']]
    return {'unchanged': True}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
normal = {'text':'Hi @al now','start':3,'end':6,'label':'Alice','id':'u'+str(N),'trigger':'@','after':' now','query':'al','span_epoch':N-1,'epoch':N,'other':'#topic'}
boundary = {'text':'@','start':0,'end':1,'label':'','id':'','trigger':'@','after':'','query':'','span_epoch':N,'epoch':N,'other':''}
check('normal text', solve('text', normal), 'Hi @Alice now')
check('boundary text', solve('text', boundary), '@')
check('normal identity', solve('identity', normal), 'u'+str(N))
check('boundary identity', solve('identity', boundary), '')
check('normal trigger', solve('trigger', normal), '@Alice')
check('boundary trigger', solve('trigger', boundary), '@')
check('normal query', solve('query', normal), 'al')
check('boundary query', solve('query', boundary), '')
check('normal delimiter', solve('delimiter', normal), '')
check('boundary delimiter', solve('delimiter', boundary), ' ')
check('normal caret', solve('caret', normal), 9)
check('boundary caret', solve('caret', boundary), 1)
check('normal span', solve('span', normal), [3,9])
check('boundary span', solve('span', boundary), [0,1])
check('normal stale', solve('stale', normal), False)
check('boundary stale', solve('stale', boundary), True)
check('normal tail', solve('tail', normal), ' now')
check('boundary tail', solve('tail', boundary), '')
check('normal descriptor', solve('descriptor', normal), ['@','al'])
check('boundary descriptor', solve('descriptor', boundary), ['@',''])
variant = dict(normal, **{'id':'person'+str(N)})
check('variant query or selection payload', solve('identity', variant), 'person'+str(N))
check('unknown completion event', solve('unrecognized', normal), {'unchanged': True})
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
normal text	`Hi @Alice now`	`Hi @Alice now`	Passed
boundary text	`@`	`@`	Passed
normal identity	`u1`	`u1`	Passed
boundary identity			Passed
normal trigger	`@Alice`	`@Alice`	Passed
boundary trigger	`@`	`@`	Passed
normal query	`al`	`al`	Passed
boundary query			Passed
normal delimiter			Passed
boundary delimiter			Passed
normal caret	`6`	`9`	Failed
boundary caret	`1`	`1`	Passed
normal span	`[3, 9]`	`[3, 9]`	Passed
boundary span	`[0, 1]`	`[0, 1]`	Passed
normal stale	`False`	`False`	Passed
boundary stale	`True`	`True`	Passed
normal tail	`now`	`now`	Passed
boundary tail			Passed
normal descriptor	`['@', 'al']`	`['@', 'al']`	Passed
boundary descriptor	`['@', '']`	`['@', '']`	Passed
variant query or selection payload	`person1`	`person1`	Passed
unknown completion event	`{'unchanged': True}`	`{'unchanged': True}`	Passed

SHA-256 / 709326456a2a35aae484a1252c05ca781f33ab97cc9fe104e4e4a2133ea5e89e

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(event, d):
    if event == 'text': return d['text'][:d['start']]+d['trigger']+d['label']+d['text'][d['end']:]
    if event == 'identity': return d['id']
    if event == 'trigger': return d['trigger']+d['label']
    if event == 'query': return d['query']
    if event == 'delimiter': return '' if d['after'].startswith(' ') else ' '
    if event == 'caret': return d['start']+len(d['trigger'])+len(d['label'])
    if event == 'span': return [d['start'],d['start']+len(d['trigger'])+len(d['label'])]
    if event == 'stale': return d['span_epoch']==d['epoch']
    if event == 'tail': return d['text'][d['end']:]
    if event == 'descriptor': return [d['trigger'],d['query']]
    return {'unchanged': True}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
normal = {'text':'Hi @al now','start':3,'end':6,'label':'Alice','id':'u'+str(N),'trigger':'@','after':' now','query':'al','span_epoch':N-1,'epoch':N,'other':'#topic'}
boundary = {'text':'@','start':0,'end':1,'label':'','id':'','trigger':'@','after':'','query':'','span_epoch':N,'epoch':N,'other':''}
check('normal text', solve('text', normal), 'Hi @Alice now')
check('boundary text', solve('text', boundary), '@')
check('normal identity', solve('identity', normal), 'u'+str(N))
check('boundary identity', solve('identity', boundary), '')
check('normal trigger', solve('trigger', normal), '@Alice')
check('boundary trigger', solve('trigger', boundary), '@')
check('normal query', solve('query', normal), 'al')
check('boundary query', solve('query', boundary), '')
check('normal delimiter', solve('delimiter', normal), '')
check('boundary delimiter', solve('delimiter', boundary), ' ')
check('normal caret', solve('caret', normal), 9)
check('boundary caret', solve('caret', boundary), 1)
check('normal span', solve('span', normal), [3,9])
check('boundary span', solve('span', boundary), [0,1])
check('normal stale', solve('stale', normal), False)
check('boundary stale', solve('stale', boundary), True)
check('normal tail', solve('tail', normal), ' now')
check('boundary tail', solve('tail', boundary), '')
check('normal descriptor', solve('descriptor', normal), ['@','al'])
check('boundary descriptor', solve('descriptor', boundary), ['@',''])
variant = dict(normal, **{'id':'person'+str(N)})
check('variant query or selection payload', solve('identity', variant), 'person'+str(N))
check('unknown completion event', solve('unrecognized', normal), {'unchanged': True})
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
normal text	`Hi @Alice now`	`Hi @Alice now`	Passed
boundary text	`@`	`@`	Passed
normal identity	`u1`	`u1`	Passed
boundary identity			Passed
normal trigger	`@Alice`	`@Alice`	Passed
boundary trigger	`@`	`@`	Passed
normal query	`al`	`al`	Passed
boundary query			Passed
normal delimiter			Passed
boundary delimiter			Passed
normal caret	`9`	`9`	Passed
boundary caret	`1`	`1`	Passed
normal span	`[3, 9]`	`[3, 9]`	Passed
boundary span	`[0, 1]`	`[0, 1]`	Passed
normal stale	`False`	`False`	Passed
boundary stale	`True`	`True`	Passed
normal tail	`now`	`now`	Passed
boundary tail			Passed
normal descriptor	`['@', 'al']`	`['@', 'al']`	Passed
boundary descriptor	`['@', '']`	`['@', '']`	Passed
variant query or selection payload	`person1`	`person1`	Passed
unknown completion event	`{'unchanged': True}`	`{'unchanged': True}`	Passed

SHA-256 / 485a99c33af736944bc8b12c2aca5d41ff951a888cb256a26b00b738ea6c8a47

Verification & scope

Stipulated deterministic widget transition model; inputs are validated snapshots. It does not model browser event dispatch, network transport, or linguistic standards. 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 2026-09-29T14:40:43.313525+00:00.

Case digest / 977b363da784a508390504f7e8625aa081535ab99ad75e62e974a6ffad4d3c90