diff --git a/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/palette/AtmospherePresets.kt b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/palette/AtmospherePresets.kt
new file mode 100644
index 0000000..117791a
--- /dev/null
+++ b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/palette/AtmospherePresets.kt
@@ -0,0 +1,134 @@
+package link.socket.phosphor.palette
+
+import link.socket.phosphor.signal.AtmospherePattern
+import link.socket.phosphor.signal.AtmosphereState
+
+/**
+ * Canonical atmosphere presets for Lumos scene-global rendering.
+ *
+ * These presets use Socket-aligned default hues: 244-degree indigo,
+ * 197-degree cyan, 32-degree amber, and 280-degree purple. Consumers can
+ * construct their own [AtmosphereState] instances when a different palette or
+ * motion profile is needed.
+ */
+object AtmospherePresets {
+    val IDLE =
+        AtmosphereState(
+            primaryHue = 250f,
+            secondaryHue = 175f,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = 0.0f,
+            pattern = AtmospherePattern.LONGITUDE,
+            patternSpeed = 0.25f,
+            pulseAmplitude = 0.025f,
+            pulseFrequency = 0.30f,
+            rotationY = 0.14f,
+            rotationX = 0.0f,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+
+    val LISTENING =
+        AtmosphereState(
+            primaryHue = 195f,
+            secondaryHue = 270f,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = 0.0f,
+            pattern = AtmospherePattern.PLASMA,
+            patternSpeed = 1.15f,
+            pulseAmplitude = 0.06f,
+            pulseFrequency = 0.5f,
+            rotationY = 0.16f,
+            rotationX = 0.10f,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+
+    val THINKING =
+        AtmosphereState(
+            primaryHue = 244f,
+            secondaryHue = 185f,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = 0.0f,
+            pattern = AtmospherePattern.SPIRAL,
+            patternSpeed = 0.7f,
+            pulseAmplitude = 0.025f,
+            pulseFrequency = 0.45f,
+            rotationY = 0.45f,
+            rotationX = 0.10f,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+
+    val UNCERTAIN =
+        AtmosphereState(
+            primaryHue = 32f,
+            secondaryHue = 280f,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = 0.45f,
+            pattern = AtmospherePattern.SPIRAL,
+            patternSpeed = 1.0f,
+            pulseAmplitude = 0.06f,
+            pulseFrequency = 0.16f,
+            rotationY = 0.10f,
+            rotationX = 0.10f,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+
+    val READY =
+        AtmosphereState(
+            primaryHue = 249f,
+            secondaryHue = 197f,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = 0.0f,
+            pattern = AtmospherePattern.PULSE,
+            patternSpeed = 1.3f,
+            pulseAmplitude = 0.04f,
+            pulseFrequency = 0.5f,
+            rotationY = 0.20f,
+            rotationX = -0.20f,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+
+    val ALL: List<Pair<String, AtmosphereState>> =
+        listOf(
+            "idle" to IDLE,
+            "listening" to LISTENING,
+            "thinking" to THINKING,
+            "uncertain" to UNCERTAIN,
+            "ready" to READY,
+        )
+
+    /**
+     * Resolve a canonical preset by name, ignoring case.
+     */
+    fun byName(name: String): AtmosphereState? =
+        ALL.firstOrNull { (presetName, _) -> presetName.equals(name, ignoreCase = true) }?.second
+}
diff --git a/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmospherePattern.kt b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmospherePattern.kt
new file mode 100644
index 0000000..dee9b49
--- /dev/null
+++ b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmospherePattern.kt
@@ -0,0 +1,34 @@
+package link.socket.phosphor.signal
+
+import kotlinx.serialization.Serializable
+
+/**
+ * Scene-global pattern families used by [AtmosphereState].
+ *
+ * Patterns describe spatial variation in the renderer's atmosphere. Surface
+ * adapters can interpret each family with renderer-specific math while keeping
+ * a stable signal contract in common code.
+ */
+@Serializable
+enum class AtmospherePattern {
+    /** Horizontal-banded sine pattern around the vertical axis. */
+    LONGITUDE,
+
+    /** Vertical-banded sine pattern around the polar axis. */
+    LATITUDE,
+
+    /** Combined theta and phi sweep. */
+    SPIRAL,
+
+    /** Linear sweep along the Y axis. */
+    SCAN,
+
+    /** Three-axis noise sum. */
+    PLASMA,
+
+    /** Radial concentric rings from center. */
+    PULSE,
+
+    /** No pattern variation. */
+    SOLID,
+}
diff --git a/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereState.kt b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereState.kt
new file mode 100644
index 0000000..9f9b496
--- /dev/null
+++ b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereState.kt
@@ -0,0 +1,49 @@
+package link.socket.phosphor.signal
+
+import kotlinx.serialization.Serializable
+
+/**
+ * Scene-global visual parameter for renderer atmosphere.
+ *
+ * AtmosphereState describes the global environment through which rendered
+ * light propagates. It is not a per-agent state; [AgentVisualState] remains the
+ * per-agent counterpart for position, activity, and phase progress.
+ *
+ * @property primaryHue Primary hue in degrees, expected in 0..360.
+ * @property secondaryHue Secondary hue in degrees, expected in 0..360.
+ * @property saturation Color saturation, expected in 0..1.
+ * @property lightness Color lightness, expected in 0..1.
+ * @property bipolarStrength Two-pole color strength; values greater than zero enable bipolar color mode.
+ * @property pattern Spatial pattern family.
+ * @property patternSpeed Temporal scale for pattern movement.
+ * @property pulseAmplitude Radial scale modulation amplitude.
+ * @property pulseFrequency Radial scale modulation rate in Hz.
+ * @property rotationY Continuous spin rate around the Y axis.
+ * @property rotationX Continuous spin rate around the X axis.
+ * @property surfaceBump Surface deformation amplitude.
+ * @property noise Per-voxel position jitter scale.
+ * @property voxelGap Voxel scale-down amount used by renderers that show lattice gaps.
+ * @property ySquash Vertical squash ratio.
+ * @property resolution Lattice resolution.
+ * @property glow Renderer-interpreted atmospheric glow intensity.
+ */
+@Serializable
+data class AtmosphereState(
+    val primaryHue: Float,
+    val secondaryHue: Float,
+    val saturation: Float,
+    val lightness: Float,
+    val bipolarStrength: Float,
+    val pattern: AtmospherePattern,
+    val patternSpeed: Float,
+    val pulseAmplitude: Float,
+    val pulseFrequency: Float,
+    val rotationY: Float,
+    val rotationX: Float,
+    val surfaceBump: Float,
+    val noise: Float,
+    val voxelGap: Float,
+    val ySquash: Float,
+    val resolution: Int,
+    val glow: Float,
+)
diff --git a/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereTransition.kt b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereTransition.kt
new file mode 100644
index 0000000..8307645
--- /dev/null
+++ b/phosphor-core/src/commonMain/kotlin/link/socket/phosphor/signal/AtmosphereTransition.kt
@@ -0,0 +1,58 @@
+package link.socket.phosphor.signal
+
+import kotlinx.serialization.Serializable
+
+/**
+ * Diagnostic snapshot for a transition between two atmosphere states.
+ *
+ * The transition carries both raw time progress and eased progress so renderer
+ * integrations can report exactly which interpolation input produced the
+ * current state. Preset names are nullable because either endpoint may be a
+ * caller-constructed [AtmosphereState].
+ *
+ * Default preset transition table planned for AtmosphereChoreographer:
+ *
+ * | From -> To | Duration (s) | Easing |
+ * | --- | ---: | --- |
+ * | idle -> listening | 0.6 | eager |
+ * | idle -> thinking | 0.8 | easeOut |
+ * | idle -> uncertain | 1.4 | easeInOut |
+ * | idle -> ready | 1.1 | overshoot |
+ * | listening -> idle | 0.9 | easeInOut |
+ * | listening -> thinking | 0.75 | settled |
+ * | listening -> uncertain | 1.5 | easeInOut |
+ * | listening -> ready | 1.05 | overshoot |
+ * | thinking -> idle | 1.0 | easeInOut |
+ * | thinking -> listening | 0.65 | eager |
+ * | thinking -> uncertain | 1.65 | easeInOut |
+ * | thinking -> ready | 0.95 | overshoot |
+ * | uncertain -> idle | 1.15 | easeInOut |
+ * | uncertain -> listening | 0.6 | easeInOut |
+ * | uncertain -> thinking | 0.65 | easeInOut |
+ * | uncertain -> ready | 0.95 | easeInOut |
+ * | ready -> idle | 1.5 | easeInOut |
+ * | ready -> listening | 0.65 | eager |
+ * | ready -> thinking | 0.85 | settled |
+ * | ready -> uncertain | 1.7 | easeInOut |
+ * | default fallback | 1.1 | easeInOut |
+ *
+ * @property from Starting atmosphere state.
+ * @property to Target atmosphere state.
+ * @property fromPresetName Preset name for [from], or null when [from] is not a known preset.
+ * @property toPresetName Preset name for [to], or null when [to] is not a known preset.
+ * @property progressLinear Time-based progress, expected in 0..1.
+ * @property progressEased Easing-adjusted progress, expected in 0..1.
+ * @property easingName Easing identifier used for diagnostics.
+ * @property durationSeconds Transition duration in seconds.
+ */
+@Serializable
+data class AtmosphereTransition(
+    val from: AtmosphereState,
+    val to: AtmosphereState,
+    val fromPresetName: String?,
+    val toPresetName: String?,
+    val progressLinear: Float,
+    val progressEased: Float,
+    val easingName: String,
+    val durationSeconds: Float,
+)
diff --git a/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/palette/AtmospherePresetsTest.kt b/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/palette/AtmospherePresetsTest.kt
new file mode 100644
index 0000000..7be1b44
--- /dev/null
+++ b/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/palette/AtmospherePresetsTest.kt
@@ -0,0 +1,134 @@
+package link.socket.phosphor.palette
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+import link.socket.phosphor.signal.AtmospherePattern
+import link.socket.phosphor.signal.AtmosphereState
+
+class AtmospherePresetsTest {
+    @Test
+    fun `IDLE preset references are equal by value`() {
+        assertEquals(AtmospherePresets.IDLE, AtmospherePresets.IDLE)
+    }
+
+    @Test
+    fun `byName returns expected atmosphere state case-insensitively`() {
+        assertEquals(AtmospherePresets.UNCERTAIN, AtmospherePresets.byName("uncertain"))
+        assertEquals(AtmospherePresets.UNCERTAIN, AtmospherePresets.byName("UnCeRtAiN"))
+    }
+
+    @Test
+    fun `byName returns null for unknown preset`() {
+        assertNull(AtmospherePresets.byName("unknown"))
+    }
+
+    @Test
+    fun `ALL contains five canonical presets`() {
+        assertEquals(5, AtmospherePresets.ALL.size)
+        assertEquals(
+            listOf("idle", "listening", "thinking", "uncertain", "ready"),
+            AtmospherePresets.ALL.map { (name, _) -> name },
+        )
+    }
+
+    @Test
+    fun `canonical presets use locked prototype parameters`() {
+        assertEquals(
+            listOf(
+                "idle" to
+                    state(
+                        primaryHue = 250f,
+                        secondaryHue = 175f,
+                        bipolarStrength = 0.0f,
+                        pattern = AtmospherePattern.LONGITUDE,
+                        patternSpeed = 0.25f,
+                        pulseAmplitude = 0.025f,
+                        pulseFrequency = 0.30f,
+                        rotationY = 0.14f,
+                        rotationX = 0.0f,
+                    ),
+                "listening" to
+                    state(
+                        primaryHue = 195f,
+                        secondaryHue = 270f,
+                        bipolarStrength = 0.0f,
+                        pattern = AtmospherePattern.PLASMA,
+                        patternSpeed = 1.15f,
+                        pulseAmplitude = 0.06f,
+                        pulseFrequency = 0.5f,
+                        rotationY = 0.16f,
+                        rotationX = 0.10f,
+                    ),
+                "thinking" to
+                    state(
+                        primaryHue = 244f,
+                        secondaryHue = 185f,
+                        bipolarStrength = 0.0f,
+                        pattern = AtmospherePattern.SPIRAL,
+                        patternSpeed = 0.7f,
+                        pulseAmplitude = 0.025f,
+                        pulseFrequency = 0.45f,
+                        rotationY = 0.45f,
+                        rotationX = 0.10f,
+                    ),
+                "uncertain" to
+                    state(
+                        primaryHue = 32f,
+                        secondaryHue = 280f,
+                        bipolarStrength = 0.45f,
+                        pattern = AtmospherePattern.SPIRAL,
+                        patternSpeed = 1.0f,
+                        pulseAmplitude = 0.06f,
+                        pulseFrequency = 0.16f,
+                        rotationY = 0.10f,
+                        rotationX = 0.10f,
+                    ),
+                "ready" to
+                    state(
+                        primaryHue = 249f,
+                        secondaryHue = 197f,
+                        bipolarStrength = 0.0f,
+                        pattern = AtmospherePattern.PULSE,
+                        patternSpeed = 1.3f,
+                        pulseAmplitude = 0.04f,
+                        pulseFrequency = 0.5f,
+                        rotationY = 0.20f,
+                        rotationX = -0.20f,
+                    ),
+            ),
+            AtmospherePresets.ALL,
+        )
+    }
+
+    private fun state(
+        primaryHue: Float,
+        secondaryHue: Float,
+        bipolarStrength: Float,
+        pattern: AtmospherePattern,
+        patternSpeed: Float,
+        pulseAmplitude: Float,
+        pulseFrequency: Float,
+        rotationY: Float,
+        rotationX: Float,
+    ): AtmosphereState =
+        AtmosphereState(
+            primaryHue = primaryHue,
+            secondaryHue = secondaryHue,
+            saturation = 0.85f,
+            lightness = 0.60f,
+            bipolarStrength = bipolarStrength,
+            pattern = pattern,
+            patternSpeed = patternSpeed,
+            pulseAmplitude = pulseAmplitude,
+            pulseFrequency = pulseFrequency,
+            rotationY = rotationY,
+            rotationX = rotationX,
+            surfaceBump = 0.10f,
+            noise = 0.20f,
+            voxelGap = 0.05f,
+            ySquash = 0.95f,
+            resolution = 10,
+            glow = 1.0f,
+        )
+}
diff --git a/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/signal/AtmosphereStateTest.kt b/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/signal/AtmosphereStateTest.kt
new file mode 100644
index 0000000..ae80513
--- /dev/null
+++ b/phosphor-core/src/commonTest/kotlin/link/socket/phosphor/signal/AtmosphereStateTest.kt
@@ -0,0 +1,96 @@
+package link.socket.phosphor.signal
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlinx.serialization.json.Json
+
+class AtmosphereStateTest {
+    @Test
+    fun `AtmosphereState supports JSON serialization`() {
+        val state =
+            AtmosphereState(
+                primaryHue = 244f,
+                secondaryHue = 197f,
+                saturation = 0.85f,
+                lightness = 0.6f,
+                bipolarStrength = 0.25f,
+                pattern = AtmospherePattern.PLASMA,
+                patternSpeed = 1.15f,
+                pulseAmplitude = 0.06f,
+                pulseFrequency = 0.5f,
+                rotationY = 0.16f,
+                rotationX = 0.1f,
+                surfaceBump = 0.1f,
+                noise = 0.2f,
+                voxelGap = 0.05f,
+                ySquash = 0.95f,
+                resolution = 10,
+                glow = 1.0f,
+            )
+
+        val json = Json { encodeDefaults = true }
+        val encoded = json.encodeToString(AtmosphereState.serializer(), state)
+        val decoded = json.decodeFromString(AtmosphereState.serializer(), encoded)
+
+        assertEquals(state, decoded)
+    }
+
+    @Test
+    fun `AtmosphereTransition supports JSON serialization`() {
+        val transition =
+            AtmosphereTransition(
+                from =
+                    AtmosphereState(
+                        primaryHue = 250f,
+                        secondaryHue = 175f,
+                        saturation = 0.85f,
+                        lightness = 0.6f,
+                        bipolarStrength = 0f,
+                        pattern = AtmospherePattern.LONGITUDE,
+                        patternSpeed = 0.25f,
+                        pulseAmplitude = 0.025f,
+                        pulseFrequency = 0.3f,
+                        rotationY = 0.14f,
+                        rotationX = 0f,
+                        surfaceBump = 0.1f,
+                        noise = 0.2f,
+                        voxelGap = 0.05f,
+                        ySquash = 0.95f,
+                        resolution = 10,
+                        glow = 1f,
+                    ),
+                to =
+                    AtmosphereState(
+                        primaryHue = 249f,
+                        secondaryHue = 197f,
+                        saturation = 0.85f,
+                        lightness = 0.6f,
+                        bipolarStrength = 0f,
+                        pattern = AtmospherePattern.PULSE,
+                        patternSpeed = 1.3f,
+                        pulseAmplitude = 0.04f,
+                        pulseFrequency = 0.5f,
+                        rotationY = 0.2f,
+                        rotationX = -0.2f,
+                        surfaceBump = 0.1f,
+                        noise = 0.2f,
+                        voxelGap = 0.05f,
+                        ySquash = 0.95f,
+                        resolution = 10,
+                        glow = 1f,
+                    ),
+                fromPresetName = "idle",
+                toPresetName = "ready",
+                progressLinear = 0.5f,
+                progressEased = 0.72f,
+                easingName = "overshoot",
+                durationSeconds = 1.1f,
+            )
+
+        val json = Json { encodeDefaults = true }
+        val encoded = json.encodeToString(AtmosphereTransition.serializer(), transition)
+        val decoded = json.decodeFromString(AtmosphereTransition.serializer(), encoded)
+
+        assertEquals(transition, decoded)
+    }
+}