test(chat): add ContextUsageComponentsTest regression tests and clarify context tokens note

app/src/androidTest/java/com/m57/hermescontrol/ui/chat/components/ContextUsageComponentsTest.kt

@@ -0,0 +1,108 @@
+package com.m57.hermescontrol.ui.chat.components
+
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.filters.MediumTest
+import com.m57.hermescontrol.theme.HermesControlTheme
+import com.m57.hermescontrol.ui.chat.ContextBreakdown
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * Regression coverage for backend-reported context occupancy.
+ *
+ * Cumulative REST input-token accounting must never masquerade as the live
+ * context-window numerator when the backend has not reported context_used.
+ */
+@RunWith(AndroidJUnit4::class)
+@MediumTest
+class ContextUsageComponentsTest {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    @Test
+    fun chip_missingBackendOccupancy_doesNotShowFakeZeroPercent() {
+        composeTestRule.setContent {
+            HermesControlTheme {
+                ContextUsageChip(
+                    usedTokens = null,
+                    fullTokens = 128_000L,
+                )
+            }
+        }
+
+        composeTestRule
+            .onNodeWithText("— / 128k context")
+            .assertIsDisplayed()
+
+        composeTestRule
+            .onNodeWithText("0%")
+            .assertDoesNotExist()
+    }
+
+    @Test
+    fun chip_backendOccupancyAvailable_showsDeterminateUsage() {
+        composeTestRule.setContent {
+            HermesControlTheme {
+                ContextUsageChip(
+                    usedTokens = 64_000L,
+                    fullTokens = 128_000L,
+                )
+            }
+        }
+
+        composeTestRule
+            .onNodeWithText("64k / 128k context")
+            .assertIsDisplayed()
+
+        composeTestRule
+            .onNodeWithText("50%")
+            .assertIsDisplayed()
+    }
+
+    @Test
+    fun detailSheet_missingBackendOccupancy_doesNotUseCumulativeInputTokensAsNumerator() {
+        composeTestRule.setContent {
+            HermesControlTheme {
+                ContextDetailSheet(
+                    breakdown =
+                        ContextBreakdown(
+                            inputTokens = 12_300L,
+                            outputTokens = 2_000L,
+                            cacheReadTokens = 500L,
+                            cacheWriteTokens = 250L,
+                            reasoningTokens = 100L,
+                            messageCount = 4,
+                        ),
+                    usedTokens = null,
+                    fullTokens = 128_000L,
+                    onDismiss = {},
+                )
+            }
+        }
+
+        // The live numerator is unavailable, even though cumulative REST
+        // input-token accounting exists below in the detail breakdown.
+        composeTestRule
+            .onNodeWithText("—")
+            .assertIsDisplayed()
+
+        composeTestRule
+            .onNodeWithText("Context window usage unavailable")
+            .assertIsDisplayed()
+
+        // Cumulative accounting is still preserved as informational detail.
+        composeTestRule
+            .onNodeWithText("12.3k")
+            .assertIsDisplayed()
+
+        // Most important regression guard: null occupancy is not rendered as
+        // a determinate zero-percent context state.
+        composeTestRule
+            .onNodeWithText("0% of context window used")
+            .assertDoesNotExist()
+    }
+}