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FA-34851 / Notification interfaces / Open access

Inbox history pagination presentation: empty-page from loading-older · case 01

The empty-page event leaves a notification in older-appended instead of end-of-history.

Verified by executionVariant 1 · 37 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Empty terminal page leaves a load-more affordance active.

VERIFIED REPAIR

Commit the loading-older / empty-page transition to end-of-history; preserve the other explicitly stipulated transitions.

Unsuccessful approach: Resetting to the first page allows repeated terminal requests.

Case contract

Inbox history pagination presentation is a bounded visual-notification workflow with mutable policy state {'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True}. Its default transition relation is {('first-page', 'load-older'): 'loading-older', ('loading-older', 'nonempty-page'): 'older-appended', ('loading-older', 'empty-page'): 'end-of-history', ('loading-older', 'page-failure'): 'older-error', ('older-error', 'retry-older'): 'loading-older', ('older-appended', 'new-head-arrives'): 'head-update-pending', ('head-update-pending', 'show-new-head'): 'head-restoring', ('head-restoring', 'head-anchor-ready'): 'first-page', ('loading-older', 'filter-changed'): 'new-filter-loading', ('new-filter-loading', 'old-page-arrives'): 'new-filter-loading'}; domain inputs can suppress or redirect transitions and update policy fields, as specified in solve. Different-generation events are inert. Batches apply in order. Optional observe returns the selected policy field alongside the phase.

Why this case matters

Visual notification lifecycle ordering can leave an inbox or toast showing the wrong actionable state even when transport succeeds.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, events, generation, payload=None, observe=None):
    table = {('first-page', 'load-older'): 'loading-older', ('loading-older', 'nonempty-page'): 'older-appended', ('loading-older', 'empty-page'): 'older-appended', ('loading-older', 'page-failure'): 'older-error', ('older-error', 'retry-older'): 'loading-older', ('older-appended', 'new-head-arrives'): 'head-update-pending', ('head-update-pending', 'show-new-head'): 'head-restoring', ('head-restoring', 'head-anchor-ready'): 'first-page', ('loading-older', 'filter-changed'): 'new-filter-loading', ('new-filter-loading', 'old-page-arrives'): 'new-filter-loading'}
    data = json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})) if payload is None else {**json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})), **json.loads(json.dumps(payload))}
    state = initial
    for delivery in events:
        event, event_generation = delivery[:2]
        arg = delivery[2] if len(delivery) > 2 else {}
        if event_generation == generation:
            previous = state
            if event in ('nonempty-page','empty-page','old-page-arrives') and arg.get('filter',data['filter']) != data['filter']: event = 'unknown-event'
            if event == 'nonempty-page': data['rows'] += [x for x in arg.get('rows',['older']) if x not in data['rows']]
            if event == 'filter-changed': data['filter'] += 1
            state = table.get((state, event), state)
            if state == 'end-of-history': data['has_more'] = False
            if state == 'first-page': data['anchor'] = data['rows'][0] if data['rows'] else None
            if state == 'new-filter-loading': data['rows'] = []
    return {'phase': state, 'value': data[observe]} if observe else state
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('first-page / load-older', solve('first-page', [('load-older', N)], N), 'loading-older')
check('loading-older / nonempty-page', solve('loading-older', [('nonempty-page', N)], N), 'older-appended')
check('loading-older / empty-page', solve('loading-older', [('empty-page', N)], N), 'end-of-history')
check('loading-older / page-failure', solve('loading-older', [('page-failure', N)], N), 'older-error')
check('older-error / retry-older', solve('older-error', [('retry-older', N)], N), 'loading-older')
check('older-appended / new-head-arrives', solve('older-appended', [('new-head-arrives', N)], N), 'head-update-pending')
check('head-update-pending / show-new-head', solve('head-update-pending', [('show-new-head', N)], N), 'head-restoring')
check('head-restoring / head-anchor-ready', solve('head-restoring', [('head-anchor-ready', N)], N), 'first-page')
check('loading-older / filter-changed', solve('loading-older', [('filter-changed', N)], N), 'new-filter-loading')
check('new-filter-loading / old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N)], N), 'new-filter-loading')
check('older notification incarnation', solve('first-page', [('load-older', N - 1)], N), 'first-page')
check('future notification incarnation', solve('first-page', [('load-older', N + 1)], N), 'first-page')
check('unknown event is inert', solve('first-page', [('unknown-event', N)], N), 'first-page')
check('empty delivery batch', solve('first-page', [], N), 'first-page')
check('N stale deliveries before current delivery', solve('first-page', [('load-older', N - 1)] * N + [('load-older', N)], N), 'loading-older')
check('trace load-older then nonempty-page', solve('first-page', [('load-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace load-older then empty-page', solve('first-page', [('load-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace load-older then page-failure', solve('first-page', [('load-older', N), ('page-failure', N)], N), 'older-error')
check('trace load-older then filter-changed', solve('first-page', [('load-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace nonempty-page then new-head-arrives', solve('loading-older', [('nonempty-page', N), ('new-head-arrives', N)], N), 'head-update-pending')
check('trace page-failure then retry-older', solve('loading-older', [('page-failure', N), ('retry-older', N)], N), 'loading-older')
check('trace retry-older then nonempty-page', solve('older-error', [('retry-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace retry-older then empty-page', solve('older-error', [('retry-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace retry-older then page-failure', solve('older-error', [('retry-older', N), ('page-failure', N)], N), 'older-error')
check('trace retry-older then filter-changed', solve('older-error', [('retry-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace new-head-arrives then show-new-head', solve('older-appended', [('new-head-arrives', N), ('show-new-head', N)], N), 'head-restoring')
check('trace show-new-head then head-anchor-ready', solve('head-update-pending', [('show-new-head', N), ('head-anchor-ready', N)], N), 'first-page')
check('trace head-anchor-ready then load-older', solve('head-restoring', [('head-anchor-ready', N), ('load-older', N)], N), 'loading-older')
check('trace filter-changed then old-page-arrives', solve('loading-older', [('filter-changed', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('trace old-page-arrives then old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('domain state regression 1: rows', solve('loading-older', [('nonempty-page', N, {'filter': 1, 'rows': ['stale']})], N, {}, 'rows'), {'phase': 'loading-older', 'value': ['head']})
check('domain state regression 2: rows', solve('loading-older', [('nonempty-page', N, {'rows': ['head', 'old']})], N, {}, 'rows'), {'phase': 'older-appended', 'value': ['head', 'old']})
check('domain state regression 3: has_more', solve('loading-older', [('empty-page', N, {})], N, {}, 'has_more'), {'phase': 'end-of-history', 'value': False})
check('domain state regression 4: rows', solve('loading-older', [('filter-changed', N, {})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
check('domain state regression 5: filter', solve('loading-older', [('filter-changed', N, {})], N, {}, 'filter'), {'phase': 'new-filter-loading', 'value': 3})
check('domain state regression 6: anchor', solve('older-appended', [('new-head-arrives', N, {})], N, {'anchor': 'old'}, 'anchor'), {'phase': 'head-update-pending', 'value': 'old'})
check('domain state regression 7: rows', solve('first-page', [('load-older', N, {}), ('filter-changed', N, {}), ('old-page-arrives', N, {'filter': 2, 'rows': ['old']})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
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 fixtureActualExpectedOutcome
first-page / load-olderloading-olderloading-olderPassed
loading-older / nonempty-pageolder-appendedolder-appendedPassed
loading-older / empty-pageolder-appendedend-of-historyFailed
loading-older / page-failureolder-errorolder-errorPassed
older-error / retry-olderloading-olderloading-olderPassed
older-appended / new-head-arriveshead-update-pendinghead-update-pendingPassed
head-update-pending / show-new-headhead-restoringhead-restoringPassed
head-restoring / head-anchor-readyfirst-pagefirst-pagePassed
loading-older / filter-changednew-filter-loadingnew-filter-loadingPassed
new-filter-loading / old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
older notification incarnationfirst-pagefirst-pagePassed
future notification incarnationfirst-pagefirst-pagePassed
unknown event is inertfirst-pagefirst-pagePassed
empty delivery batchfirst-pagefirst-pagePassed
N stale deliveries before current deliveryloading-olderloading-olderPassed
trace load-older then nonempty-pageolder-appendedolder-appendedPassed
trace load-older then empty-pageolder-appendedend-of-historyFailed
trace load-older then page-failureolder-errorolder-errorPassed
trace load-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace nonempty-page then new-head-arriveshead-update-pendinghead-update-pendingPassed
trace page-failure then retry-olderloading-olderloading-olderPassed
trace retry-older then nonempty-pageolder-appendedolder-appendedPassed
trace retry-older then empty-pageolder-appendedend-of-historyFailed
trace retry-older then page-failureolder-errorolder-errorPassed
trace retry-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace new-head-arrives then show-new-headhead-restoringhead-restoringPassed
trace show-new-head then head-anchor-readyfirst-pagefirst-pagePassed
trace head-anchor-ready then load-olderloading-olderloading-olderPassed
trace filter-changed then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
trace old-page-arrives then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
domain state regression 1: rows{'phase': 'loading-older', 'value': ['head']}{'phase': 'loading-older', 'value': ['head']}Passed
domain state regression 2: rows{'phase': 'older-appended', 'value': ['head', 'old']}{'phase': 'older-appended', 'value': ['head', 'old']}Passed
domain state regression 3: has_more{'phase': 'older-appended', 'value': True}{'phase': 'end-of-history', 'value': False}Failed
domain state regression 4: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed
domain state regression 5: filter{'phase': 'new-filter-loading', 'value': 3}{'phase': 'new-filter-loading', 'value': 3}Passed
domain state regression 6: anchor{'phase': 'head-update-pending', 'value': 'old'}{'phase': 'head-update-pending', 'value': 'old'}Passed
domain state regression 7: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed

SHA-256 / 892575245a46e1f493a20218751f00fb80a68e7b5b67811a6962c34722c33603

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, events, generation, payload=None, observe=None):
    table = {('first-page', 'load-older'): 'loading-older', ('loading-older', 'nonempty-page'): 'older-appended', ('loading-older', 'empty-page'): 'first-page', ('loading-older', 'page-failure'): 'older-error', ('older-error', 'retry-older'): 'loading-older', ('older-appended', 'new-head-arrives'): 'head-update-pending', ('head-update-pending', 'show-new-head'): 'head-restoring', ('head-restoring', 'head-anchor-ready'): 'first-page', ('loading-older', 'filter-changed'): 'new-filter-loading', ('new-filter-loading', 'old-page-arrives'): 'new-filter-loading'}
    data = json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})) if payload is None else {**json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})), **json.loads(json.dumps(payload))}
    state = initial
    for delivery in events:
        event, event_generation = delivery[:2]
        arg = delivery[2] if len(delivery) > 2 else {}
        if event_generation == generation:
            previous = state
            if event in ('nonempty-page','empty-page','old-page-arrives') and arg.get('filter',data['filter']) != data['filter']: event = 'unknown-event'
            if event == 'nonempty-page': data['rows'] += [x for x in arg.get('rows',['older']) if x not in data['rows']]
            if event == 'filter-changed': data['filter'] += 1
            state = table.get((state, event), state)
            if state == 'end-of-history': data['has_more'] = False
            if state == 'first-page': data['anchor'] = data['rows'][0] if data['rows'] else None
            if state == 'new-filter-loading': data['rows'] = []
    return {'phase': state, 'value': data[observe]} if observe else state
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('first-page / load-older', solve('first-page', [('load-older', N)], N), 'loading-older')
check('loading-older / nonempty-page', solve('loading-older', [('nonempty-page', N)], N), 'older-appended')
check('loading-older / empty-page', solve('loading-older', [('empty-page', N)], N), 'end-of-history')
check('loading-older / page-failure', solve('loading-older', [('page-failure', N)], N), 'older-error')
check('older-error / retry-older', solve('older-error', [('retry-older', N)], N), 'loading-older')
check('older-appended / new-head-arrives', solve('older-appended', [('new-head-arrives', N)], N), 'head-update-pending')
check('head-update-pending / show-new-head', solve('head-update-pending', [('show-new-head', N)], N), 'head-restoring')
check('head-restoring / head-anchor-ready', solve('head-restoring', [('head-anchor-ready', N)], N), 'first-page')
check('loading-older / filter-changed', solve('loading-older', [('filter-changed', N)], N), 'new-filter-loading')
check('new-filter-loading / old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N)], N), 'new-filter-loading')
check('older notification incarnation', solve('first-page', [('load-older', N - 1)], N), 'first-page')
check('future notification incarnation', solve('first-page', [('load-older', N + 1)], N), 'first-page')
check('unknown event is inert', solve('first-page', [('unknown-event', N)], N), 'first-page')
check('empty delivery batch', solve('first-page', [], N), 'first-page')
check('N stale deliveries before current delivery', solve('first-page', [('load-older', N - 1)] * N + [('load-older', N)], N), 'loading-older')
check('trace load-older then nonempty-page', solve('first-page', [('load-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace load-older then empty-page', solve('first-page', [('load-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace load-older then page-failure', solve('first-page', [('load-older', N), ('page-failure', N)], N), 'older-error')
check('trace load-older then filter-changed', solve('first-page', [('load-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace nonempty-page then new-head-arrives', solve('loading-older', [('nonempty-page', N), ('new-head-arrives', N)], N), 'head-update-pending')
check('trace page-failure then retry-older', solve('loading-older', [('page-failure', N), ('retry-older', N)], N), 'loading-older')
check('trace retry-older then nonempty-page', solve('older-error', [('retry-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace retry-older then empty-page', solve('older-error', [('retry-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace retry-older then page-failure', solve('older-error', [('retry-older', N), ('page-failure', N)], N), 'older-error')
check('trace retry-older then filter-changed', solve('older-error', [('retry-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace new-head-arrives then show-new-head', solve('older-appended', [('new-head-arrives', N), ('show-new-head', N)], N), 'head-restoring')
check('trace show-new-head then head-anchor-ready', solve('head-update-pending', [('show-new-head', N), ('head-anchor-ready', N)], N), 'first-page')
check('trace head-anchor-ready then load-older', solve('head-restoring', [('head-anchor-ready', N), ('load-older', N)], N), 'loading-older')
check('trace filter-changed then old-page-arrives', solve('loading-older', [('filter-changed', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('trace old-page-arrives then old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('domain state regression 1: rows', solve('loading-older', [('nonempty-page', N, {'filter': 1, 'rows': ['stale']})], N, {}, 'rows'), {'phase': 'loading-older', 'value': ['head']})
check('domain state regression 2: rows', solve('loading-older', [('nonempty-page', N, {'rows': ['head', 'old']})], N, {}, 'rows'), {'phase': 'older-appended', 'value': ['head', 'old']})
check('domain state regression 3: has_more', solve('loading-older', [('empty-page', N, {})], N, {}, 'has_more'), {'phase': 'end-of-history', 'value': False})
check('domain state regression 4: rows', solve('loading-older', [('filter-changed', N, {})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
check('domain state regression 5: filter', solve('loading-older', [('filter-changed', N, {})], N, {}, 'filter'), {'phase': 'new-filter-loading', 'value': 3})
check('domain state regression 6: anchor', solve('older-appended', [('new-head-arrives', N, {})], N, {'anchor': 'old'}, 'anchor'), {'phase': 'head-update-pending', 'value': 'old'})
check('domain state regression 7: rows', solve('first-page', [('load-older', N, {}), ('filter-changed', N, {}), ('old-page-arrives', N, {'filter': 2, 'rows': ['old']})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
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 fixtureActualExpectedOutcome
first-page / load-olderloading-olderloading-olderPassed
loading-older / nonempty-pageolder-appendedolder-appendedPassed
loading-older / empty-pagefirst-pageend-of-historyFailed
loading-older / page-failureolder-errorolder-errorPassed
older-error / retry-olderloading-olderloading-olderPassed
older-appended / new-head-arriveshead-update-pendinghead-update-pendingPassed
head-update-pending / show-new-headhead-restoringhead-restoringPassed
head-restoring / head-anchor-readyfirst-pagefirst-pagePassed
loading-older / filter-changednew-filter-loadingnew-filter-loadingPassed
new-filter-loading / old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
older notification incarnationfirst-pagefirst-pagePassed
future notification incarnationfirst-pagefirst-pagePassed
unknown event is inertfirst-pagefirst-pagePassed
empty delivery batchfirst-pagefirst-pagePassed
N stale deliveries before current deliveryloading-olderloading-olderPassed
trace load-older then nonempty-pageolder-appendedolder-appendedPassed
trace load-older then empty-pagefirst-pageend-of-historyFailed
trace load-older then page-failureolder-errorolder-errorPassed
trace load-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace nonempty-page then new-head-arriveshead-update-pendinghead-update-pendingPassed
trace page-failure then retry-olderloading-olderloading-olderPassed
trace retry-older then nonempty-pageolder-appendedolder-appendedPassed
trace retry-older then empty-pagefirst-pageend-of-historyFailed
trace retry-older then page-failureolder-errorolder-errorPassed
trace retry-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace new-head-arrives then show-new-headhead-restoringhead-restoringPassed
trace show-new-head then head-anchor-readyfirst-pagefirst-pagePassed
trace head-anchor-ready then load-olderloading-olderloading-olderPassed
trace filter-changed then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
trace old-page-arrives then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
domain state regression 1: rows{'phase': 'loading-older', 'value': ['head']}{'phase': 'loading-older', 'value': ['head']}Passed
domain state regression 2: rows{'phase': 'older-appended', 'value': ['head', 'old']}{'phase': 'older-appended', 'value': ['head', 'old']}Passed
domain state regression 3: has_more{'phase': 'first-page', 'value': True}{'phase': 'end-of-history', 'value': False}Failed
domain state regression 4: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed
domain state regression 5: filter{'phase': 'new-filter-loading', 'value': 3}{'phase': 'new-filter-loading', 'value': 3}Passed
domain state regression 6: anchor{'phase': 'head-update-pending', 'value': 'old'}{'phase': 'head-update-pending', 'value': 'old'}Passed
domain state regression 7: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed

SHA-256 / 1b5d5973646eec211830d83ef5b7d1846ffe57bb4a0bdd95edaa6219aa1ed0ea

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, events, generation, payload=None, observe=None):
    table = {('first-page', 'load-older'): 'loading-older', ('loading-older', 'nonempty-page'): 'older-appended', ('loading-older', 'empty-page'): 'end-of-history', ('loading-older', 'page-failure'): 'older-error', ('older-error', 'retry-older'): 'loading-older', ('older-appended', 'new-head-arrives'): 'head-update-pending', ('head-update-pending', 'show-new-head'): 'head-restoring', ('head-restoring', 'head-anchor-ready'): 'first-page', ('loading-older', 'filter-changed'): 'new-filter-loading', ('new-filter-loading', 'old-page-arrives'): 'new-filter-loading'}
    data = json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})) if payload is None else {**json.loads(json.dumps({'rows': ['head'], 'filter': 2, 'anchor': 'head', 'has_more': True})), **json.loads(json.dumps(payload))}
    state = initial
    for delivery in events:
        event, event_generation = delivery[:2]
        arg = delivery[2] if len(delivery) > 2 else {}
        if event_generation == generation:
            previous = state
            if event in ('nonempty-page','empty-page','old-page-arrives') and arg.get('filter',data['filter']) != data['filter']: event = 'unknown-event'
            if event == 'nonempty-page': data['rows'] += [x for x in arg.get('rows',['older']) if x not in data['rows']]
            if event == 'filter-changed': data['filter'] += 1
            state = table.get((state, event), state)
            if state == 'end-of-history': data['has_more'] = False
            if state == 'first-page': data['anchor'] = data['rows'][0] if data['rows'] else None
            if state == 'new-filter-loading': data['rows'] = []
    return {'phase': state, 'value': data[observe]} if observe else state
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('first-page / load-older', solve('first-page', [('load-older', N)], N), 'loading-older')
check('loading-older / nonempty-page', solve('loading-older', [('nonempty-page', N)], N), 'older-appended')
check('loading-older / empty-page', solve('loading-older', [('empty-page', N)], N), 'end-of-history')
check('loading-older / page-failure', solve('loading-older', [('page-failure', N)], N), 'older-error')
check('older-error / retry-older', solve('older-error', [('retry-older', N)], N), 'loading-older')
check('older-appended / new-head-arrives', solve('older-appended', [('new-head-arrives', N)], N), 'head-update-pending')
check('head-update-pending / show-new-head', solve('head-update-pending', [('show-new-head', N)], N), 'head-restoring')
check('head-restoring / head-anchor-ready', solve('head-restoring', [('head-anchor-ready', N)], N), 'first-page')
check('loading-older / filter-changed', solve('loading-older', [('filter-changed', N)], N), 'new-filter-loading')
check('new-filter-loading / old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N)], N), 'new-filter-loading')
check('older notification incarnation', solve('first-page', [('load-older', N - 1)], N), 'first-page')
check('future notification incarnation', solve('first-page', [('load-older', N + 1)], N), 'first-page')
check('unknown event is inert', solve('first-page', [('unknown-event', N)], N), 'first-page')
check('empty delivery batch', solve('first-page', [], N), 'first-page')
check('N stale deliveries before current delivery', solve('first-page', [('load-older', N - 1)] * N + [('load-older', N)], N), 'loading-older')
check('trace load-older then nonempty-page', solve('first-page', [('load-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace load-older then empty-page', solve('first-page', [('load-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace load-older then page-failure', solve('first-page', [('load-older', N), ('page-failure', N)], N), 'older-error')
check('trace load-older then filter-changed', solve('first-page', [('load-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace nonempty-page then new-head-arrives', solve('loading-older', [('nonempty-page', N), ('new-head-arrives', N)], N), 'head-update-pending')
check('trace page-failure then retry-older', solve('loading-older', [('page-failure', N), ('retry-older', N)], N), 'loading-older')
check('trace retry-older then nonempty-page', solve('older-error', [('retry-older', N), ('nonempty-page', N)], N), 'older-appended')
check('trace retry-older then empty-page', solve('older-error', [('retry-older', N), ('empty-page', N)], N), 'end-of-history')
check('trace retry-older then page-failure', solve('older-error', [('retry-older', N), ('page-failure', N)], N), 'older-error')
check('trace retry-older then filter-changed', solve('older-error', [('retry-older', N), ('filter-changed', N)], N), 'new-filter-loading')
check('trace new-head-arrives then show-new-head', solve('older-appended', [('new-head-arrives', N), ('show-new-head', N)], N), 'head-restoring')
check('trace show-new-head then head-anchor-ready', solve('head-update-pending', [('show-new-head', N), ('head-anchor-ready', N)], N), 'first-page')
check('trace head-anchor-ready then load-older', solve('head-restoring', [('head-anchor-ready', N), ('load-older', N)], N), 'loading-older')
check('trace filter-changed then old-page-arrives', solve('loading-older', [('filter-changed', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('trace old-page-arrives then old-page-arrives', solve('new-filter-loading', [('old-page-arrives', N), ('old-page-arrives', N)], N), 'new-filter-loading')
check('domain state regression 1: rows', solve('loading-older', [('nonempty-page', N, {'filter': 1, 'rows': ['stale']})], N, {}, 'rows'), {'phase': 'loading-older', 'value': ['head']})
check('domain state regression 2: rows', solve('loading-older', [('nonempty-page', N, {'rows': ['head', 'old']})], N, {}, 'rows'), {'phase': 'older-appended', 'value': ['head', 'old']})
check('domain state regression 3: has_more', solve('loading-older', [('empty-page', N, {})], N, {}, 'has_more'), {'phase': 'end-of-history', 'value': False})
check('domain state regression 4: rows', solve('loading-older', [('filter-changed', N, {})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
check('domain state regression 5: filter', solve('loading-older', [('filter-changed', N, {})], N, {}, 'filter'), {'phase': 'new-filter-loading', 'value': 3})
check('domain state regression 6: anchor', solve('older-appended', [('new-head-arrives', N, {})], N, {'anchor': 'old'}, 'anchor'), {'phase': 'head-update-pending', 'value': 'old'})
check('domain state regression 7: rows', solve('first-page', [('load-older', N, {}), ('filter-changed', N, {}), ('old-page-arrives', N, {'filter': 2, 'rows': ['old']})], N, {}, 'rows'), {'phase': 'new-filter-loading', 'value': []})
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 fixtureActualExpectedOutcome
first-page / load-olderloading-olderloading-olderPassed
loading-older / nonempty-pageolder-appendedolder-appendedPassed
loading-older / empty-pageend-of-historyend-of-historyPassed
loading-older / page-failureolder-errorolder-errorPassed
older-error / retry-olderloading-olderloading-olderPassed
older-appended / new-head-arriveshead-update-pendinghead-update-pendingPassed
head-update-pending / show-new-headhead-restoringhead-restoringPassed
head-restoring / head-anchor-readyfirst-pagefirst-pagePassed
loading-older / filter-changednew-filter-loadingnew-filter-loadingPassed
new-filter-loading / old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
older notification incarnationfirst-pagefirst-pagePassed
future notification incarnationfirst-pagefirst-pagePassed
unknown event is inertfirst-pagefirst-pagePassed
empty delivery batchfirst-pagefirst-pagePassed
N stale deliveries before current deliveryloading-olderloading-olderPassed
trace load-older then nonempty-pageolder-appendedolder-appendedPassed
trace load-older then empty-pageend-of-historyend-of-historyPassed
trace load-older then page-failureolder-errorolder-errorPassed
trace load-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace nonempty-page then new-head-arriveshead-update-pendinghead-update-pendingPassed
trace page-failure then retry-olderloading-olderloading-olderPassed
trace retry-older then nonempty-pageolder-appendedolder-appendedPassed
trace retry-older then empty-pageend-of-historyend-of-historyPassed
trace retry-older then page-failureolder-errorolder-errorPassed
trace retry-older then filter-changednew-filter-loadingnew-filter-loadingPassed
trace new-head-arrives then show-new-headhead-restoringhead-restoringPassed
trace show-new-head then head-anchor-readyfirst-pagefirst-pagePassed
trace head-anchor-ready then load-olderloading-olderloading-olderPassed
trace filter-changed then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
trace old-page-arrives then old-page-arrivesnew-filter-loadingnew-filter-loadingPassed
domain state regression 1: rows{'phase': 'loading-older', 'value': ['head']}{'phase': 'loading-older', 'value': ['head']}Passed
domain state regression 2: rows{'phase': 'older-appended', 'value': ['head', 'old']}{'phase': 'older-appended', 'value': ['head', 'old']}Passed
domain state regression 3: has_more{'phase': 'end-of-history', 'value': False}{'phase': 'end-of-history', 'value': False}Passed
domain state regression 4: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed
domain state regression 5: filter{'phase': 'new-filter-loading', 'value': 3}{'phase': 'new-filter-loading', 'value': 3}Passed
domain state regression 6: anchor{'phase': 'head-update-pending', 'value': 'old'}{'phase': 'head-update-pending', 'value': 'old'}Passed
domain state regression 7: rows{'phase': 'new-filter-loading', 'value': []}{'phase': 'new-filter-loading', 'value': []}Passed

SHA-256 / c4a1ca0d5b3fa3ee6da3f9771af70c65595eebef03e090e86fc811e85d99cc21

Verification & scope

Stipulated single-notification state and policy model only. Event delivery and acknowledgements are explicit test inputs. No DOM, accessibility announcements, live timers, networking, actual rendering, or production-platform conformance is simulated. 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 2026-09-29T14:42:35.894982+00:00.

Case digest / bb81be7f57794e50bc82869ec98724adbfc0b35efb3fdeb86af73d7432805651