FA-75981 / Chat ordering and read receipts / Open access

Filter read receipts by privacy settings and chat kind: channel admin override · case 01

Channel admins lose receipts of members who disabled them, or non-admins see channel receipts.

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

ROOT CAUSE

The channel admin override decision evaluates `ok = viewer in admins and enabled(u)` where the contract requires `ok = viewer in admins`.

VERIFIED REPAIR

Use `ok = viewer in admins` for the channel admin override decision and keep every other rule of the model unchanged.

Unsuccessful approach: Using the reader flag in channels shows receipts to every non-admin viewer. The attempted `ok = enabled(u)` still disagrees with a fixture.

Case contract

settings[u] is a user's "send read receipts" flag (default True). In direct chats a reader is shown only when both the reader and the viewer have receipts enabled (reciprocity). In group chats only the reader's flag matters. In channels only admins see receipts and they see every reader regardless of settings. The viewer never sees their own receipt. Result: sorted visible readers.

Why this case matters

Receipt privacy rules differ by conversation type; mistakes leak receipts users disabled or hide ones they may see.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(viewer, readers, settings, chat_kind, admins):
    enabled = lambda u: settings.get(u, True)
    out = []
    for u in readers:
        if u == viewer:
            continue
        if chat_kind == 'channel':
            ok = viewer in admins and enabled(u)
        elif chat_kind == 'direct':
            ok = enabled(u) and enabled(viewer)
        else:
            ok = enabled(u)
        if ok:
            out.append(u)
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('missing settings default on', ('v', ['r1'], {}, 'direct', []), ['r1']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r1'], {}, 'group', []), ['r1']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 2: [('missing settings default on', ('v', ['r2'], {}, 'direct', []), ['r2']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r2'], {}, 'group', []), ['r2']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 3: [('missing settings default on', ('v', ['r3'], {}, 'direct', []), ['r3']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r3'], {}, 'group', []), ['r3']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 4: [('missing settings default on', ('v', ['r4'], {}, 'direct', []), ['r4']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r4'], {}, 'group', []), ['r4']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 5: [('missing settings default on', ('v', ['r5'], {}, 'direct', []), ['r5']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r5'], {}, 'group', []), ['r5']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
missing settings default on	`['r1']`	`['r1']`	Passed
viewer disabled in direct chat	`[]`	`[]`	Passed
viewer disabled in group	`['r']`	`['r']`	Passed
reader disabled in direct chat	`[]`	`[]`	Passed
channel admin	`['p', 'q']`	`['p', 'q', 'r']`	Failed
channel non-admin	`[]`	`[]`	Passed
own receipt in group	`['r1']`	`['r1']`	Passed
own receipt in channel as admin	`[]`	`[]`	Passed

SHA-256 / eafdcf052959a081e7388e9124796556c78e685d68ee7e722502c2e81ed6f042

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(viewer, readers, settings, chat_kind, admins):
    enabled = lambda u: settings.get(u, True)
    out = []
    for u in readers:
        if u == viewer:
            continue
        if chat_kind == 'channel':
            ok = enabled(u)
        elif chat_kind == 'direct':
            ok = enabled(u) and enabled(viewer)
        else:
            ok = enabled(u)
        if ok:
            out.append(u)
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('missing settings default on', ('v', ['r1'], {}, 'direct', []), ['r1']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r1'], {}, 'group', []), ['r1']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 2: [('missing settings default on', ('v', ['r2'], {}, 'direct', []), ['r2']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r2'], {}, 'group', []), ['r2']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 3: [('missing settings default on', ('v', ['r3'], {}, 'direct', []), ['r3']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r3'], {}, 'group', []), ['r3']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 4: [('missing settings default on', ('v', ['r4'], {}, 'direct', []), ['r4']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r4'], {}, 'group', []), ['r4']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 5: [('missing settings default on', ('v', ['r5'], {}, 'direct', []), ['r5']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r5'], {}, 'group', []), ['r5']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
missing settings default on	`['r1']`	`['r1']`	Passed
viewer disabled in direct chat	`[]`	`[]`	Passed
viewer disabled in group	`['r']`	`['r']`	Passed
reader disabled in direct chat	`[]`	`[]`	Passed
channel admin	`['p', 'q']`	`['p', 'q', 'r']`	Failed
channel non-admin	`['r']`	`[]`	Failed
own receipt in group	`['r1']`	`['r1']`	Passed
own receipt in channel as admin	`[]`	`[]`	Passed

SHA-256 / b5df47bf5110962065b720d12d8898a059f1691e8b6d4676013b79f194449e51

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(viewer, readers, settings, chat_kind, admins):
    enabled = lambda u: settings.get(u, True)
    out = []
    for u in readers:
        if u == viewer:
            continue
        if chat_kind == 'channel':
            ok = viewer in admins
        elif chat_kind == 'direct':
            ok = enabled(u) and enabled(viewer)
        else:
            ok = enabled(u)
        if ok:
            out.append(u)
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('missing settings default on', ('v', ['r1'], {}, 'direct', []), ['r1']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r1'], {}, 'group', []), ['r1']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 2: [('missing settings default on', ('v', ['r2'], {}, 'direct', []), ['r2']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r2'], {}, 'group', []), ['r2']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 3: [('missing settings default on', ('v', ['r3'], {}, 'direct', []), ['r3']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r3'], {}, 'group', []), ['r3']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 4: [('missing settings default on', ('v', ['r4'], {}, 'direct', []), ['r4']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r4'], {}, 'group', []), ['r4']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])], 5: [('missing settings default on', ('v', ['r5'], {}, 'direct', []), ['r5']), ('viewer disabled in direct chat', ('v', ['r'], {'v': False}, 'direct', []), []), ('viewer disabled in group', ('v', ['r', 'q'], {'v': False, 'q': False}, 'group', []), ['r']), ('reader disabled in direct chat', ('v', ['r'], {'r': False, 'v': True}, 'direct', []), []), ('channel admin', ('v', ['r', 'q', 'p'], {'r': False}, 'channel', ['v']), ['p', 'q', 'r']), ('channel non-admin', ('v', ['r'], {}, 'channel', ['a']), []), ('own receipt in group', ('v', ['v', 'r5'], {}, 'group', []), ['r5']), ('own receipt in channel as admin', ('v', ['v'], {}, 'channel', ['v']), [])]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
missing settings default on	`['r1']`	`['r1']`	Passed
viewer disabled in direct chat	`[]`	`[]`	Passed
viewer disabled in group	`['r']`	`['r']`	Passed
reader disabled in direct chat	`[]`	`[]`	Passed
channel admin	`['p', 'q', 'r']`	`['p', 'q', 'r']`	Passed
channel non-admin	`[]`	`[]`	Passed
own receipt in group	`['r1']`	`['r1']`	Passed
own receipt in channel as admin	`[]`	`[]`	Passed

SHA-256 / cc76d3fff826f13ffbe45e088089ff8ba069ab5926a314a4b0cb1ca2919a9d60

Verification & scope

Stipulated offline chat model; not a complete messaging protocol, client or server implementation. 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 2026-09-29T14:49:12.065696+00:00.

Case digest / 010d667987f8b7f8bc42a52e639cb06df3aef2b55ced11bfda759076081fbaa9