feat(mindmachine): implement Android MVP app scaffold, session flows, safety gating, and tests

app/src/test/java/com/mindmachine/mvp/SessionValidatorTest.kt

@@ -0,0 +1,46 @@
+package com.mindmachine.mvp
+
+import com.mindmachine.mvp.domain.SessionMode
+import com.mindmachine.mvp.domain.VisualPattern
+import com.mindmachine.mvp.domain.SessionConfig
+import com.mindmachine.mvp.session.SessionValidator
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class SessionValidatorTest {
+    private val valid = SessionConfig(
+        presetId = "relax",
+        durationSec = 600,
+        mode = SessionMode.AUDIO_VISUAL,
+        visualPatternType = VisualPattern.PULSE,
+        blinkFrequencyHz = 6f,
+        intensityPercent = 50,
+        carrierFrequencyHz = 200f,
+        binauralDifferenceHz = 6f,
+    )
+
+    @Test
+    fun valid_with_headset_passes() {
+        assertNull(SessionValidator.validate(valid, headsetAvailable = true))
+    }
+
+    @Test
+    fun audio_without_headset_is_blocked() {
+        val error = SessionValidator.validate(valid, headsetAvailable = false)
+        assertEquals("Stereo headphones are required for binaural audio. Connect headphones or switch to Visual-only.", error)
+    }
+
+    @Test
+    fun visual_only_without_headset_passes() {
+        assertNull(SessionValidator.validate(valid.copy(mode = SessionMode.VISUAL_ONLY), headsetAvailable = false))
+    }
+
+    @Test
+    fun out_of_range_values_are_blocked() {
+        assertEquals("Duration must be 1 to 30 minutes.", SessionValidator.validate(valid.copy(durationSec = 59), true))
+        assertEquals("Blink frequency must be 1.0 to 20.0 Hz.", SessionValidator.validate(valid.copy(blinkFrequencyHz = 21f), true))
+        assertEquals("Carrier frequency must be 80 to 400 Hz.", SessionValidator.validate(valid.copy(carrierFrequencyHz = 79f), true))
+        assertEquals("Binaural difference must be 0.5 to 20 Hz.", SessionValidator.validate(valid.copy(binauralDifferenceHz = 0.1f), true))
+    }
+}