feat(chat): support /undo command with transcript reload and composer prefill (#1051)

app/src/test/java/com/m57/hermescontrol/ui/chat/ChatViewModelTest.kt

@@ -896,6 +896,45 @@ class ChatViewModelTest {
             assertEquals("openai/gpt-4o", viewModel.uiState.value.currentSessionModel)
         }
 
+    @Test
+    fun testUndoCommand_dispatchesAndPrefillsComposer() =
+        runTest {
+            val (viewModel, sessionId) = createViewModelWithSession()
+
+            every {
+                HermesWsClient.request(
+                    WsMethods.COMMAND_DISPATCH,
+                    mapOf("name" to "undo", "arg" to "2", "session_id" to sessionId),
+                    any(),
+                )
+            } returns
+                CompletableDeferred(
+                    mapOf(
+                        "type" to "prefill",
+                        "message" to "undone user message",
+                        "notice" to "↶ Undid 2 turns",
+                    ),
+                )
+
+            viewModel.sendMessage("/undo 2")
+            advanceUntilIdle()
+
+            // Prefill text is staged in UI state
+            assertEquals("undone user message", viewModel.uiState.value.pendingPrefillText)
+            // Notice is displayed as system message with rewind target feedback
+            assertTrue(
+                viewModel.uiState.value.messages
+                    .any { it.content.contains("↶ Undid 2 turns") && it.content.contains("undone user message") },
+            )
+            // Verify slash usage was recorded
+            assertEquals(1, viewModel.uiState.value.slashUsageCounts["/undo"])
+
+            // Consume prefill text
+            viewModel.consumePendingPrefill()
+            advanceUntilIdle()
+            assertNull(viewModel.uiState.value.pendingPrefillText)
+        }
+
     // ── Connection / init tests ──────────────────────────────────────────────
 
     @Test

app/src/test/java/com/m57/hermescontrol/ui/chat/SlashCommandDispatcherTest.kt

@@ -82,6 +82,14 @@ class SlashCommandDispatcherTest {
         assertEquals(SlashResult.SideQuestion(""), dispatcher.dispatch("/btw   "))
     }
 
+    @Test
+    fun `undo routes to Undo`() {
+        assertEquals(SlashResult.Undo(""), dispatcher.dispatch("/undo"))
+        assertEquals(SlashResult.Undo("2"), dispatcher.dispatch("/undo 2"))
+        assertEquals(SlashResult.Undo("3"), dispatcher.dispatch("/UNDO 3"))
+        assertEquals(SlashResult.Undo(""), dispatcher.dispatch("/Undo"))
+    }
+
     @Test
     fun `NEW uppercase still routes to NewSession`() {
         // Dispatcher lower-cases before matching, so case must not matter.

app/src/test/java/com/m57/hermescontrol/ui/chat/fakes/FakeChatMessageDao.kt

@@ -27,6 +27,10 @@ class FakeChatMessageDao : ChatMessageDao {
         messageList.forEach { messages[it.id] = it }
     }
 
+    override suspend fun deleteMessagesForSession(sessionId: String) {
+        messages.values.removeAll { it.sessionId == sessionId }
+    }
+
     /** Direct access for test setup — bypasses the suspend modifier. */
     fun addMessageDirect(message: ChatMessageEntity) {
         messages[message.id] = message