FA-74221 / Feature flag rollout bucketing / Open access

Flag override resolution: Booleans satisfy integer flags · case 01

A remote payload of true for a numeric limit flag is served as 1.

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

ROOT CAUSE

Layer values are validated with isinstance, and bool is a subclass of int.

THE FAILURE

Layer values are validated with isinstance, and bool is a subclass of int.

Unsuccessful approach: Excluding boolean defaults from isinstance validation rejects every value for boolean flags.

Case contract

Layers in precedence order: env var FLAG_<KEY uppercased with "-" -> "_">, local overrides[key], remote[key], then the default. A layer is used only if its value is valid for the default's type, else the next layer is tried. Non-env values must have exactly the default's type (bool is not int). Env strings: bool defaults accept "true"/"false" case-insensitively; int defaults accept digits with an optional leading "-"; str defaults accept any string. Return [value, source].

Why this case matters

Local and environment overrides are how operators pin flags during incidents; precedence must be exact.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(key, default, remote, overrides, env):
    def coerce(v, from_env):
        if from_env:
            if isinstance(default, bool):
                low = v.lower()
                return (True, low == 'true') if low in ('true', 'false') else (False, None)
            if isinstance(default, int):
                body = v[1:] if v.startswith('-') else v
                return (True, int(v)) if body.isdigit() else (False, None)
            return (True, v)
        return (True, v) if isinstance(v, type(default)) else (False, None)
    name = 'FLAG_' + key.upper().replace('-', '_')
    layers = [('env', env, name, True), ('override', overrides, key, False), ('remote', remote, key, False)]
    for source, table, k, from_env in layers:
        if k in table:
            ok, value = coerce(table[k], from_env)
            if ok:
                return [value, source]
    return [default, 'default']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('boolean remote value rejected for integer flag', ['beta', 3, {'beta': True}, {}, {}], [3, 'default']),
  ('environment beats local override',
   ['new-ui', False, {}, {'new-ui': False}, {'FLAG_NEW_UI': 'true'}],
   [True, 'env']),
  ('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 1', ['beta', 7, {'beta': 1}, {}, {}], [1, 'remote']),
  ('override layer sample 2', ['new-ui', 'blue', {'new-ui': False}, {}, {}], ['blue', 'default'])],
 [('boolean remote value rejected for integer flag', ['beta', 3, {'beta': True}, {}, {}], [3, 'default']),
  ('environment beats local override',
   ['new-ui', False, {}, {'new-ui': False}, {'FLAG_NEW_UI': 'true'}],
   [True, 'env']),
  ('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 14',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {}, {'FLAG_DARK-MODE-V2': '+4'}],
   [0, 'default']),
  ('override layer sample 41',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'true'}],
   [0, 'default'])],
 [('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('override layer sample 11', ['beta', True, {'beta': -2}, {'beta': 0}, {}], [True, 'default']),
  ('override layer sample 12', ['dark-mode-v2', 'blue', {}, {'dark-mode-v2': 0}, {}], ['blue', 'default']),
  ('override layer sample 18',
   ['dark-mode-v2', 0, {}, {'dark-mode-v2': True}, {'FLAG_DARK_MODE_V2': 'true'}],
   [0, 'default'])],
 [('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 16', ['dark-mode-v2', 'blue', {'dark-mode-v2': 1}, {}, {}], ['blue', 'default']),
  ('override layer sample 17',
   ['dark-mode-v2', 'blue', {'dark-mode-v2': 'red'}, {'dark-mode-v2': 'red'}, {'FLAG_DARK-MODE-V2': 'yes'}],
   ['red', 'override']),
  ('override layer sample 31',
   ['dark-mode-v2', 7, {'dark-mode-v2': True}, {}, {'FLAG_dark_mode_v2': 'true'}],
   [7, 'default'])],
 [('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('local override beats remote', ['beta', 'a', {'beta': 'b'}, {'beta': 'c'}, {}], ['c', 'override']),
  ('override layer sample 21',
   ['dark-mode-v2', False, {}, {}, {'FLAG_DARK-MODE-V2': 'true'}],
   [False, 'default']),
  ('override layer sample 41',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'true'}],
   [0, 'default']),
  ('override layer sample 51',
   ['dark-mode-v2', 7, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'FALSE'}],
   [7, 'default'])]]
for label, args, expected in fixtures[N - 1]:
    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
boolean remote value rejected for integer flag	`[True, 'remote']`	`[3, 'default']`	Failed
environment beats local override	`[True, 'env']`	`[True, 'env']`	Passed
dashed key maps to underscored env name	`['green', 'env']`	`['green', 'env']`	Passed
invalid env value falls through to remote	`[5, 'remote']`	`[5, 'remote']`	Passed
negative integer from env	`[-3, 'env']`	`[-3, 'env']`	Passed
non-boolean env text is invalid for boolean flag	`[True, 'remote']`	`[True, 'remote']`	Passed
override layer sample 1	`[1, 'remote']`	`[1, 'remote']`	Passed
override layer sample 2	`['blue', 'default']`	`['blue', 'default']`	Passed

SHA-256 / cd38e902c345400f1e780ca742e60e56d32277276a2c8249c566d79e7e3c6bee

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(key, default, remote, overrides, env):
    def coerce(v, from_env):
        if from_env:
            if isinstance(default, bool):
                low = v.lower()
                return (True, low == 'true') if low in ('true', 'false') else (False, None)
            if isinstance(default, int):
                body = v[1:] if v.startswith('-') else v
                return (True, int(v)) if body.isdigit() else (False, None)
            return (True, v)
        return (True, v) if isinstance(v, type(default)) and not isinstance(default, bool) else (False, None)
    name = 'FLAG_' + key.upper().replace('-', '_')
    layers = [('env', env, name, True), ('override', overrides, key, False), ('remote', remote, key, False)]
    for source, table, k, from_env in layers:
        if k in table:
            ok, value = coerce(table[k], from_env)
            if ok:
                return [value, source]
    return [default, 'default']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('boolean remote value rejected for integer flag', ['beta', 3, {'beta': True}, {}, {}], [3, 'default']),
  ('environment beats local override',
   ['new-ui', False, {}, {'new-ui': False}, {'FLAG_NEW_UI': 'true'}],
   [True, 'env']),
  ('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 1', ['beta', 7, {'beta': 1}, {}, {}], [1, 'remote']),
  ('override layer sample 2', ['new-ui', 'blue', {'new-ui': False}, {}, {}], ['blue', 'default'])],
 [('boolean remote value rejected for integer flag', ['beta', 3, {'beta': True}, {}, {}], [3, 'default']),
  ('environment beats local override',
   ['new-ui', False, {}, {'new-ui': False}, {'FLAG_NEW_UI': 'true'}],
   [True, 'env']),
  ('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 14',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {}, {'FLAG_DARK-MODE-V2': '+4'}],
   [0, 'default']),
  ('override layer sample 41',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'true'}],
   [0, 'default'])],
 [('dashed key maps to underscored env name',
   ['dark-mode-v2', 'blue', {}, {}, {'FLAG_DARK_MODE_V2': 'green'}],
   ['green', 'env']),
  ('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('override layer sample 11', ['beta', True, {'beta': -2}, {'beta': 0}, {}], [True, 'default']),
  ('override layer sample 12', ['dark-mode-v2', 'blue', {}, {'dark-mode-v2': 0}, {}], ['blue', 'default']),
  ('override layer sample 18',
   ['dark-mode-v2', 0, {}, {'dark-mode-v2': True}, {'FLAG_DARK_MODE_V2': 'true'}],
   [0, 'default'])],
 [('invalid env value falls through to remote',
   ['beta', 0, {'beta': 5}, {}, {'FLAG_BETA': 'lots'}],
   [5, 'remote']),
  ('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('override layer sample 16', ['dark-mode-v2', 'blue', {'dark-mode-v2': 1}, {}, {}], ['blue', 'default']),
  ('override layer sample 17',
   ['dark-mode-v2', 'blue', {'dark-mode-v2': 'red'}, {'dark-mode-v2': 'red'}, {'FLAG_DARK-MODE-V2': 'yes'}],
   ['red', 'override']),
  ('override layer sample 31',
   ['dark-mode-v2', 7, {'dark-mode-v2': True}, {}, {'FLAG_dark_mode_v2': 'true'}],
   [7, 'default'])],
 [('negative integer from env', ['beta', 0, {}, {}, {'FLAG_BETA': '-3'}], [-3, 'env']),
  ('plus sign is not a valid integer', ['beta', 0, {'beta': 9}, {}, {'FLAG_BETA': '+4'}], [9, 'remote']),
  ('env boolean is case-insensitive', ['beta', False, {}, {}, {'FLAG_BETA': 'TRUE'}], [True, 'env']),
  ('non-boolean env text is invalid for boolean flag',
   ['beta', True, {'beta': True}, {}, {'FLAG_BETA': 'yes'}],
   [True, 'remote']),
  ('local override beats remote', ['beta', 'a', {'beta': 'b'}, {'beta': 'c'}, {}], ['c', 'override']),
  ('override layer sample 21',
   ['dark-mode-v2', False, {}, {}, {'FLAG_DARK-MODE-V2': 'true'}],
   [False, 'default']),
  ('override layer sample 41',
   ['dark-mode-v2', 0, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'true'}],
   [0, 'default']),
  ('override layer sample 51',
   ['dark-mode-v2', 7, {'dark-mode-v2': False}, {'dark-mode-v2': 'x'}, {'FLAG_DARK-MODE-V2': 'FALSE'}],
   [7, 'default'])]]
for label, args, expected in fixtures[N - 1]:
    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
boolean remote value rejected for integer flag	`[True, 'remote']`	`[3, 'default']`	Failed
environment beats local override	`[True, 'env']`	`[True, 'env']`	Passed
dashed key maps to underscored env name	`['green', 'env']`	`['green', 'env']`	Passed
invalid env value falls through to remote	`[5, 'remote']`	`[5, 'remote']`	Passed
negative integer from env	`[-3, 'env']`	`[-3, 'env']`	Passed
non-boolean env text is invalid for boolean flag	`[True, 'default']`	`[True, 'remote']`	Failed
override layer sample 1	`[1, 'remote']`	`[1, 'remote']`	Passed
override layer sample 2	`['blue', 'default']`	`['blue', 'default']`	Passed

SHA-256 / af0c932e4c3e77cf8be2afdda5dbe2a23a605909719bdee07031e21c4f2da01e

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic toy flag-evaluation model with a stipulated contract; it does not reproduce any vendor SDK byte for byte. 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 2026-09-29T14:48:54.599073+00:00.

Case digest / 7c32cde1f53f16b58913910f8850220bb186a5d07a4eeee92cf71129deeb386c