diff --git a/core/tests/golden.rs b/core/tests/golden.rs
new file mode 100644
index 0000000..7c462a3
--- /dev/null
+++ b/core/tests/golden.rs
@@ -0,0 +1,147 @@
+//! Pinned values for everything that must not change unnoticed.
+//!
+//! Every other test compares two computations inside the same build, so a
+//! change that affects both sides alike stays green. This file compares
+//! against values recorded once. If one of them fails, rules or encodings
+//! changed, on purpose or by accident. If saves or recordings are affected,
+//! raise the version constant named in the failure message, then update the
+//! value here deliberately.
+
+use grovewright_core::command::Command;
+use grovewright_core::hash::fnv1a64;
+use grovewright_core::map::Pos;
+use grovewright_core::mapgen::outcrop_origin;
+use grovewright_core::player::PlayerId;
+use grovewright_core::replay::Recording;
+use grovewright_core::world::World;
+
+const SEED: u64 = 2026;
+
+/// The commands of a session of 60 ticks. It is built from literal values
+/// and the outcrop origin of the map, not from constants such as
+/// `DIG_COOLDOWN_TICKS`, so that changing a rule changes the result and not
+/// the script.
+///
+/// Never change or extend this script. To pin more, add a new script and a
+/// new pinned value instead.
+fn frozen_script(world: &World) -> Vec<Vec<Command>> {
+    let origin = outcrop_origin(world.map());
+    let right_of_origin = Pos::new(origin.x + 1, origin.y);
+    // Pairs of (tick, command). Commands of the same tick are applied in the
+    // order listed here.
+    let scripted = [
+        // Two players join in the same tick.
+        (
+            0,
+            Command::Join {
+                key: [1; 16],
+                name: "Ada".to_owned(),
+            },
+        ),
+        (
+            0,
+            Command::Join {
+                key: [2; 16],
+                name: "Grace".to_owned(),
+            },
+        ),
+        // Player 0 hits the outcrop origin three times, five ticks apart.
+        // The third hit breaks the rock and gives a stone.
+        (
+            2,
+            Command::Dig {
+                player: PlayerId(0),
+                pos: origin,
+            },
+        ),
+        (
+            7,
+            Command::Dig {
+                player: PlayerId(0),
+                pos: origin,
+            },
+        ),
+        (
+            12,
+            Command::Dig {
+                player: PlayerId(0),
+                pos: origin,
+            },
+        ),
+        // Player 1 hits the tile to the right of the origin once.
+        (
+            20,
+            Command::Dig {
+                player: PlayerId(1),
+                pos: right_of_origin,
+            },
+        ),
+        // Player 1 leaves and returns with a name of 40 bytes, which the
+        // world shortens to 32.
+        (
+            30,
+            Command::Leave {
+                player: PlayerId(1),
+            },
+        ),
+        (
+            40,
+            Command::Join {
+                key: [2; 16],
+                name: "ä".repeat(20),
+            },
+        ),
+    ];
+    let mut ticks = vec![Vec::new(); 60];
+    for (tick, command) in scripted {
+        ticks[tick].push(command);
+    }
+    ticks
+}
+
+/// Covers the map generator, the map encoding (terrain numbers, byte order of
+/// width and height) and the snapshot header.
+#[test]
+fn the_starting_snapshot_is_unchanged() {
+    let actual = fnv1a64(&World::new(SEED).to_snapshot());
+    assert_eq!(
+        actual, 0x1b78_d996_1586_fbf1,
+        "the starting world or the snapshot format changed; if saves are \
+         affected, raise SNAPSHOT_VERSION in core/src/snapshot.rs; then \
+         update this value"
+    );
+}
+
+/// Covers the rules of joining, leaving and digging, the shortening of names
+/// and the encoding of players.
+#[test]
+fn the_frozen_session_ends_in_the_same_state() {
+    let mut world = World::new(SEED);
+    for commands in frozen_script(&world) {
+        world.step(&commands);
+    }
+    assert_eq!(
+        world.state_hash(),
+        0xc304_43df_fc74_dcfc,
+        "the rules or the snapshot format changed; old recordings no longer \
+         verify; if saves are affected, raise SNAPSHOT_VERSION in \
+         core/src/snapshot.rs; then update this value"
+    );
+}
+
+/// Covers the recording header and layout and the wire format of commands.
+#[test]
+fn the_recording_format_is_unchanged() {
+    let mut world = World::new(SEED);
+    let mut recording = Recording::start(&world);
+    for commands in frozen_script(&world) {
+        recording.push_tick(&commands);
+        world.step(&commands);
+    }
+    assert_eq!(
+        fnv1a64(&recording.to_bytes(&world)),
+        0x2312_5a7d_d8ef_5ae0,
+        "the recording or command format changed; raise RECORDING_VERSION in \
+         core/src/replay.rs; then update this value"
+    );
+}
diff --git a/core/tests/world.rs b/core/tests/world.rs
index ae70c04..b839f5d 100644
--- a/core/tests/world.rs
+++ b/core/tests/world.rs
@@ -2,7 +2,9 @@ use grovewright_core::command::Command;
 use grovewright_core::inventory::ITEM_STONE;
 use grovewright_core::map::{Pos, Terrain};
 use grovewright_core::mapgen::{outcrop_origin, spawn_pos};
-use grovewright_core::player::{PlayerId, PlayerKey, MAX_KNOWN_PLAYERS, MAX_ONLINE_PLAYERS};
+use grovewright_core::player::{
+    PlayerId, PlayerKey, MAX_KNOWN_PLAYERS, MAX_NAME_BYTES, MAX_ONLINE_PLAYERS,
+};
 use grovewright_core::world::{Event, World, DIG_COOLDOWN_TICKS, TICKS_PER_SECOND};
 
 fn key(n: u8) -> PlayerKey {
@@ -112,6 +114,28 @@ fn a_returning_player_can_change_their_name() {
     assert_eq!(world.player(id).unwrap().name, "Neuer Name");
 }
 
+#[test]
+fn overlong_names_are_stored_shortened_on_both_join_paths() {
+    let mut world = World::new(1);
+    world.step(&[Command::Join {
+        key: key(1),
+        name: "ä".repeat(20),
+    }]);
+    assert_eq!(world.player(PlayerId(0)).unwrap().name, "ä".repeat(16));
+
+    world.step(&[Command::Leave {
+        player: PlayerId(0),
+    }]);
+    world.step(&[Command::Join {
+        key: key(1),
+        name: "x".repeat(MAX_NAME_BYTES + 10),
+    }]);
+    assert_eq!(
+        world.player(PlayerId(0)).unwrap().name,
+        "x".repeat(MAX_NAME_BYTES)
+    );
+}
+
 #[test]
 fn a_fifth_online_player_is_refused() {
     let mut world = World::new(1);