diff --git a/app/src/androidTest/java/com/m57/hermescontrol/ui/chat/components/ReasoningCardTest.kt b/app/src/androidTest/java/com/m57/hermescontrol/ui/chat/components/ReasoningCardTest.kt
new file mode 100644
index 00000000..494509c1
--- /dev/null
+++ b/app/src/androidTest/java/com/m57/hermescontrol/ui/chat/components/ReasoningCardTest.kt
@@ -0,0 +1,74 @@
+package com.m57.hermescontrol.ui.chat.components
+
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import androidx.compose.ui.test.performScrollTo
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.filters.MediumTest
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * Regression tests for the ReasoningCard "Show full" crash (issue #882).
+ *
+ * Inside a LazyColumn item the main axis is unbounded, so a verticalScroll
+ * measured with an infinite max height throws
+ * IllegalStateException ("Vertically scrollable component was measured with an
+ * infinity maximum height constraints"). The old implementation passed
+ * `heightIn(max = Dp.Unspecified)` once "Show full" was tapped, which lifted
+ * the cap entirely and reproduced exactly that crash.
+ */
+@RunWith(AndroidJUnit4::class)
+@MediumTest
+class ReasoningCardTest {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    /** Long enough to overflow the ~40%-of-screen collapsed cap (~22 lines). */
+    private val longReasoning =
+        buildString {
+            repeat(60) { index -> appendLine("reasoning line $index") }
+        }
+
+    private fun renderInLazyColumn(reasoningText: String) {
+        composeTestRule.setContent {
+            LazyColumn {
+                item(key = "reasoning") {
+                    ReasoningCard(reasoningText = reasoningText)
+                }
+            }
+        }
+    }
+
+    @Test
+    fun showFull_insideLazyColumn_doesNotCrash() {
+        renderInLazyColumn(longReasoning)
+
+        // Expand the card.
+        composeTestRule.onNodeWithTag("reasoning_card").performClick()
+        composeTestRule.onNodeWithText("Show full").assertIsDisplayed()
+
+        // "Show full" lifts the cap — must NOT crash the layout pass.
+        composeTestRule.onNodeWithText("Show full").performClick()
+        // The card now grows taller than the viewport, so the toggle button
+        // sits below the fold — scroll it into view before asserting/clicking.
+        composeTestRule.onNodeWithText("Show less").performScrollTo().assertIsDisplayed()
+        composeTestRule.onNodeWithText("Show less").performClick()
+
+        // And back down again.
+        composeTestRule.onNodeWithText("Show full").performScrollTo().assertIsDisplayed()
+    }
+
+    @Test
+    fun shortReasoning_noOverflow_noShowFullButton() {
+        renderInLazyColumn("short reasoning")
+
+        composeTestRule.onNodeWithTag("reasoning_card").performClick()
+        composeTestRule.onNodeWithText("Show full").assertDoesNotExist()
+    }
+}
diff --git a/app/src/main/java/com/m57/hermescontrol/ui/chat/components/MessageCards.kt b/app/src/main/java/com/m57/hermescontrol/ui/chat/components/MessageCards.kt
index 31b28909..2d6dfd40 100644
--- a/app/src/main/java/com/m57/hermescontrol/ui/chat/components/MessageCards.kt
+++ b/app/src/main/java/com/m57/hermescontrol/ui/chat/components/MessageCards.kt
@@ -73,7 +73,6 @@ import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.text.withStyle
-import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import com.m57.hermescontrol.R
@@ -176,19 +175,26 @@ fun ReasoningCard(
             }
             AnimatedVisibility(visible = expanded) {
                 Column {
-                    Column(
+                    Text(
+                        text = reasoningText,
+                        style = MaterialTheme.typography.bodySmall.copy(fontFamily = FontFamily.Monospace),
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                         modifier =
                             Modifier
-                                .heightIn(max = if (fullHeight) Dp.Unspecified else capHeight)
-                                .verticalScroll(scrollState),
-                    ) {
-                        Text(
-                            text = reasoningText,
-                            style = MaterialTheme.typography.bodySmall.copy(fontFamily = FontFamily.Monospace),
-                            color = MaterialTheme.colorScheme.onSurfaceVariant,
-                            modifier = Modifier.padding(top = 4.dp),
-                        )
-                    }
+                                .padding(top = 4.dp)
+                                .then(
+                                    if (!fullHeight) {
+                                        // Capped at ~40% of the screen with internal scroll.
+                                        Modifier.heightIn(max = capHeight).verticalScroll(scrollState)
+                                    } else {
+                                        // "Show full": render the whole trace at natural height.
+                                        // A scrollable must NEVER be measured with an infinite
+                                        // max height — inside a LazyColumn item (unbounded main
+                                        // axis) that combination throws IllegalStateException.
+                                        Modifier
+                                    },
+                                ),
+                    )
                     if (isStreaming) {
                         ReasoningPulsingDot(modifier = Modifier.padding(top = 6.dp))
                     }