diff --git a/AGENTS.md b/AGENTS.md
index c0e326a..31e26be 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -101,6 +101,7 @@ parity is golden rule 3.
 | `PROPERTY_PHASES` | Always (`false`/`''` = unset) | Comma-separated phase names, case-insensitive: `examples`, `corpus`, `random`, `shrink` | Stages of every run, in run order — **overrides** `phases()` | `InvalidArgumentException` naming the accepted values |
 | `PROPERTY_DERANDOMIZE` | Always | Any value except `''` and `'0'` enables | Derives every unset seed from the property id — **overrides** `derandomize()` | n/a (falsy values disable) |
 | `PROPERTY_PATH` | Only when `path()` was not called (explicit path wins) | A recorded `CounterExample::$path` | Replays that shrink descent instead of searching for it; needs the seed of the run that produced it | engine rejects a path that would be a silent no-op |
+| `PROPERTY_EDGE_CASES` | Always (`false`/`''` = unset) | `mixin` or `none`, case-insensitive, trimmed | Numeric boundary bias for every run — **overrides** `edgeCases()` | `InvalidArgumentException` naming the accepted values |
 
 The split is deliberate and worth stating: **the environment dials the suite,
 the code pins the property.** `PROPERTY_RUNS`, `PROPERTY_PHASES` and
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f2a6a7..cf3521a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # Changelog
 
+## Unreleased
+
+- Added `PropertyCheck::edgeCases()` and `PROPERTY_EDGE_CASES` (`mixin` or
+  `none`), reaching core 0.3's switch for the numeric boundary bias. Turning it
+  off stops a property that cannot use `0`, `±1` or a range's ends from
+  spending one run in five on a value it discards. The variable overrides the
+  chain, like every other CI-facing knob, and an unknown value throws rather
+  than silently keeping the bias it was told to drop.
+- **Requires `rasuvaeff/property-testing-core` `^0.3`.**
+
 ## 0.2.0 — 2026-08-14
 
 - Added the 0.2 run knobs, as fluent setters and as environment variables:
diff --git a/README.md b/README.md
index b276024..e545d74 100644
--- a/README.md
+++ b/README.md
@@ -110,6 +110,7 @@ Reproduce the exact run by pinning the reported seed: `->seed(7382910)`.
 | `phases(array)` | Stages to perform (`Phase::Examples`, `Corpus`, `Random`, `Shrink`) — a subset trades coverage for time on purpose |
 | `derandomize(bool)` | Derives an unset seed from the property id instead of drawing one; an explicit `seed()` still wins |
 | `path(string)` | Replays a recorded shrink descent instead of searching for it; needs the seed that produced it |
+| `edgeCases(EdgeCases)` | `None` turns off the numeric boundary bias — for a property the edges only cost runs |
 | `output($stdout, $stderr)` | Redirects the distribution report, discard warning and verbose trace (used by this package's own tests) |
 
 ### Naming a property (`id()`)
@@ -162,6 +163,7 @@ Byte-for-byte parity with the Testo adapter — one contract across adapters:
 | `PROPERTY_PHASES` | Comma-separated stage list (`examples,corpus,random,shrink`, case-insensitive) that overrides `phases()` — an unknown name throws rather than skipping a stage. `examples,corpus` is the fast pull-request gate |
 | `PROPERTY_DERANDOMIZE` | Any value except `''`/`'0'` derives every unset seed from the property id, making a whole suite reproducible without editing it |
 | `PROPERTY_PATH` | A recorded shrink descent (`CounterExample::$path`) replayed instead of searched for. Needs the seed that produced it; an explicit `path()` wins |
+| `PROPERTY_EDGE_CASES` | `mixin` or `none` (case-insensitive) — the numeric boundary bias for the whole suite, overriding `edgeCases()`. An unknown value throws |
 
 The corpus format is exactly the one `rasuvaeff/property-testing` 2.8 wrote —
 a corpus recorded under Testo (or under 2.x) replays here and vice versa. On
diff --git a/README.ru.md b/README.ru.md
index 20d8902..1f6048b 100644
--- a/README.ru.md
+++ b/README.ru.md
@@ -110,6 +110,7 @@ Property falsified after 12 successful run(s); seed=7382910
 | `phases(array)` | Какие стадии выполнять (`Phase::Examples`, `Corpus`, `Random`, `Shrink`); подмножество осознанно обменивает покрытие на время прогона |
 | `derandomize(bool)` | Выводит незаданный seed из id property вместо случайного; явный `seed()` всё равно побеждает |
 | `path(string)` | Воспроизводит записанный спуск shrink вместо повторного поиска; нужен seed того прогона |
+| `edgeCases(EdgeCases)` | `None` выключает граничное смещение числовых генераторов — для property, которой края стоят только прогонов |
 | `output($stdout, $stderr)` | Перенаправляет отчёт распределения, предупреждение о discard'ах и verbose-трассу (используется тестами самого пакета) |
 
 ### Имя property (`id()`)
@@ -162,6 +163,7 @@ $this->forAll(['values' => Gen::arrayOf(Gen::int())])
 | `PROPERTY_PHASES` | Список стадий через запятую (`examples,corpus,random,shrink`, регистр не важен), перекрывающий `phases()`; неизвестное имя — исключение, а не пропуск стадии. `examples,corpus` — быстрый гейт для pull request |
 | `PROPERTY_DERANDOMIZE` | Любое значение, кроме `''`/`'0'`, выводит каждый незаданный seed из id property: весь сьют становится воспроизводимым без правки кода |
 | `PROPERTY_PATH` | Записанный спуск shrink (`CounterExample::$path`) воспроизводится вместо повторного поиска. Нужен seed того прогона; явный `path()` побеждает |
+| `PROPERTY_EDGE_CASES` | `mixin` или `none` (регистр не важен) — граничное смещение для всего сьюта, перекрывает `edgeCases()`. Неизвестное значение — исключение |
 
 Формат корпуса — ровно тот, что писал `rasuvaeff/property-testing` 2.8:
 корпус, записанный под Testo (или под 2.x), реплеится здесь, и наоборот. При
diff --git a/composer.json b/composer.json
index 42d15d7..6fcd58e 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     "require": {
         "php": "8.3 - 8.5",
         "phpunit/phpunit": "^11.5 || ^12.0 || ^13.0",
-        "rasuvaeff/property-testing-core": "^0.2"
+        "rasuvaeff/property-testing-core": "^0.3"
     },
     "require-dev": {
         "ergebnis/composer-normalize": "^2.51",
diff --git a/infection.json5 b/infection.json5
index 24f7135..a8738ea 100644
--- a/infection.json5
+++ b/infection.json5
@@ -7,7 +7,7 @@
         "text": "php://stderr",
         "summary": "build/infection-summary.log"
     },
-    // 146 of 154 mutants are killed; the remaining eight are equivalent
+    // 160 of 168 mutants are killed; the remaining eight are equivalent
     // (report wording and ordering that no observable behaviour distinguishes),
     // so 100 is unreachable without ignores — which are forbidden here.
     "minMsi": 90,
diff --git a/llms.txt b/llms.txt
index d249ce4..d31f152 100644
--- a/llms.txt
+++ b/llms.txt
@@ -64,6 +64,7 @@ public function shrinkBudgetMs(int $ms): self;       // wall-clock budget for th
 public function phases(array $phases): self;         // list<Phase>: Examples, Corpus, Random, Shrink
 public function derandomize(bool $on = true): self;  // unset seed derived from the property id
 public function path(string $path): self;            // replay a recorded shrink descent; needs its seed
+public function edgeCases(EdgeCases $mode): self;    // Mixin (default) | None = no numeric boundary bias
 public function seed(int $seed): self;               // pin the random phase; disables corpus replay
 public function maxShrinks(int $maxShrinks): self;   // cap accepted shrink steps; 0 = no shrinking
 public function maxDiscards(int $maxDiscards): self; // discard budget; default runs * 10
@@ -112,6 +113,7 @@ final class SortPropertyTest extends TestCase
 | `PROPERTY_PHASES` | `examples,corpus,random,shrink` (comma-separated, case-insensitive) | Stages to run; OVERRIDES `phases()`; unknown name throws |
 | `PROPERTY_DERANDOMIZE` | anything but `''`/`'0'` | Unset seeds derived from the property id; `seed()`/`PROPERTY_SEED` still win |
 | `PROPERTY_PATH` | recorded `CounterExample::$path` | Replays that shrink descent; needs the seed of that run; explicit `path()` wins |
+| `PROPERTY_EDGE_CASES` | `mixin` \| `none` (case-insensitive) | Numeric boundary bias; OVERRIDES `edgeCases()`; unknown value throws |
 
 ### Classification output
 
diff --git a/src/PhpUnit/PropertyCheck.php b/src/PhpUnit/PropertyCheck.php
index 3a81a19..647e9d2 100644
--- a/src/PhpUnit/PropertyCheck.php
+++ b/src/PhpUnit/PropertyCheck.php
@@ -11,6 +11,7 @@
 use Rasuvaeff\PropertyTesting\PropertyListener;
 use Rasuvaeff\PropertyTesting\Runner\CallableTrialExecutor;
 use Rasuvaeff\PropertyTesting\Runner\CoverageFailed;
+use Rasuvaeff\PropertyTesting\Runner\EdgeCases;
 use Rasuvaeff\PropertyTesting\Runner\FilesystemCorpus;
 use Rasuvaeff\PropertyTesting\Runner\GaveUp;
 use Rasuvaeff\PropertyTesting\Runner\Passed;
@@ -70,6 +71,7 @@ final class PropertyCheck
     private ?ShrinkMode $shrink = null;
     private ?int $shrinkBudgetMs = null;
     private ?string $path = null;
+    private ?EdgeCases $edgeCases = null;
     private ?bool $derandomize = null;
 
     /** @var ?list<Phase> */
@@ -234,6 +236,22 @@ public function derandomize(bool $derandomize = true): self
         return $this;
     }
 
+    /**
+     * Whether the numeric generators keep biasing toward their boundary values
+     * ({@see EdgeCases::Mixin}, the default) or generate uniformly
+     * ({@see EdgeCases::None}).
+     *
+     * Turn them off when the edges are what this property cannot use — a body
+     * discarding `0`, a range end that violates a precondition — so the
+     * discard budget stops paying for one run in five.
+     */
+    public function edgeCases(EdgeCases $edgeCases): self
+    {
+        $this->edgeCases = $edgeCases;
+
+        return $this;
+    }
+
     /**
      * Replays the shrink descent of an earlier failure, as reported by
      * `CounterExample::$path`, instead of searching for it again. It needs the
@@ -318,6 +336,7 @@ public function check(\Closure $property): void
                 phases: $this->envPhases() ?? $this->phases,
                 derandomize: $this->envDerandomize() ?? $this->derandomize ?? false,
                 path: $this->path ?? $this->envPath(),
+                edgeCases: $this->envEdgeCases() ?? $this->edgeCases ?? EdgeCases::Mixin,
             ),
             examples: $this->examples,
             replayRegressions: $this->seed === null,
@@ -463,6 +482,31 @@ private function envPhases(): ?array
         return $phases;
     }
 
+    /**
+     * `PROPERTY_EDGE_CASES` selects the numeric boundary bias for the whole
+     * suite: `mixin` (the default) or `none`, case-insensitive. It overrides
+     * the chain, like every other CI-facing knob, and an unknown value is an
+     * error rather than a silent fallback — a suite that quietly kept the bias
+     * it was told to drop would spend the discard budget it was trying to save.
+     */
+    private function envEdgeCases(): ?EdgeCases
+    {
+        $env = getenv('PROPERTY_EDGE_CASES');
+
+        if ($env === false || $env === '') {
+            return null;
+        }
+
+        return match (strtolower(trim($env))) {
+            'mixin' => EdgeCases::Mixin,
+            'none' => EdgeCases::None,
+            default => throw new \InvalidArgumentException(sprintf(
+                'PROPERTY_EDGE_CASES must be one of mixin, none, got "%s"',
+                trim($env),
+            )),
+        };
+    }
+
     /**
      * `PROPERTY_DERANDOMIZE` (any value except '' and '0') derives every
      * unset seed from the property id, which makes a whole suite reproducible
diff --git a/tests/EnvironmentParityTest.php b/tests/EnvironmentParityTest.php
index d98bdbd..6b654f7 100644
--- a/tests/EnvironmentParityTest.php
+++ b/tests/EnvironmentParityTest.php
@@ -18,6 +18,7 @@
 use Rasuvaeff\PropertyTesting\PhpUnit\Tests\Support\RecordingListener;
 use Rasuvaeff\PropertyTesting\PropertyViolationException;
 use Rasuvaeff\PropertyTesting\RegressionViolationException;
+use Rasuvaeff\PropertyTesting\Runner\EdgeCases;
 use Rasuvaeff\PropertyTesting\Runner\Phase;
 
 /**
@@ -473,6 +474,84 @@ public function testANamedPropertyWarnsAboutNothing(): void
         self::assertSame('', (string) stream_get_contents($stderr));
     }
 
+    public function testEdgeCasesOffKeepsBoundaryValuesOutOfTheRun(): void
+    {
+        // The knob's whole purpose: a property that cannot use the edges would
+        // otherwise throw away one run in five.
+        self::assertSame(0, $this->edgesSeen(static fn(PropertyCheck $check): PropertyCheck => $check->edgeCases(EdgeCases::None)));
+    }
+
+    public function testByDefaultTheBoundaryValuesAreStillGenerated(): void
+    {
+        self::assertGreaterThan(10, $this->edgesSeen(static fn(PropertyCheck $check): PropertyCheck => $check));
+    }
+
+    public function testPropertyEdgeCasesOverridesTheChain(): void
+    {
+        putenv('PROPERTY_EDGE_CASES=none');
+
+        self::assertSame(0, $this->edgesSeen(static fn(PropertyCheck $check): PropertyCheck => $check->edgeCases(EdgeCases::Mixin)));
+    }
+
+    public function testPropertyEdgeCasesIgnoresSpacingAndCase(): void
+    {
+        putenv('PROPERTY_EDGE_CASES=  NONE  ');
+
+        self::assertSame(0, $this->edgesSeen(static fn(PropertyCheck $check): PropertyCheck => $check));
+    }
+
+    public function testPropertyEdgeCasesCanTurnThemBackOn(): void
+    {
+        putenv('PROPERTY_EDGE_CASES=mixin');
+
+        self::assertGreaterThan(10, $this->edgesSeen(static fn(PropertyCheck $check): PropertyCheck => $check->edgeCases(EdgeCases::None)));
+    }
+
+    public function testPropertyEdgeCasesRejectsAnUnknownValue(): void
+    {
+        // Spaces on purpose: the message quotes the trimmed value, so a
+        // reader sees what was compared rather than what was typed.
+        putenv('PROPERTY_EDGE_CASES=  sometimes  ');
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('PROPERTY_EDGE_CASES must be one of mixin, none, got "sometimes"');
+
+        $this->forAll(['value' => Gen::intBetween(0, 10)])
+            ->check(static function (int $value): void {
+                self::assertGreaterThanOrEqual(0, $value);
+            });
+    }
+
+    /**
+     * How many runs generated an in-range boundary value.
+     *
+     * @param \Closure(PropertyCheck): PropertyCheck $configure
+     */
+    private function edgesSeen(\Closure $configure): int
+    {
+        $listener = new RecordingListener();
+
+        $configure(
+            $this->forAll(['value' => Gen::intBetween(-1_000_000, 1_000_000)])
+                ->id('parity::edge-cases')
+                ->runs(200)
+                ->seed(5)
+                ->listeners($listener),
+        )->check(static function (int $value): void {
+            self::assertIsInt($value);
+        });
+
+        $edges = 0;
+
+        foreach ($listener->events as $event) {
+            if ($event instanceof RunStarted && in_array($event->arguments['value'] ?? null, [0, 1, -1, -1_000_000, 1_000_000], true)) {
+                ++$edges;
+            }
+        }
+
+        return $edges;
+    }
+
     /**
      * The seed the engine actually ran with, as the PropertyStarted event
      * reports it — the one observable that says what a seed knob decided.
diff --git a/tests/Support/Env.php b/tests/Support/Env.php
index 7955155..4fe89c2 100644
--- a/tests/Support/Env.php
+++ b/tests/Support/Env.php
@@ -72,6 +72,7 @@ public static function isolateProperty(): \Closure
             'PROPERTY_PHASES' => null,
             'PROPERTY_DERANDOMIZE' => null,
             'PROPERTY_PATH' => null,
+            'PROPERTY_EDGE_CASES' => null,
         ]);
     }
 }