feat: adopt side-questions via prompt.btw and /btw command in Chat (fixes #1015) (#1026)

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

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

@@ -478,6 +478,40 @@ class ChatViewModelTest {
             verify { HermesWsClient.send(WsMethods.SESSION_INTERRUPT, any(), any()) }
         }
 
+    @Test
+    fun testSlashCommand_btw_dispatchesPromptBtw_andSetsBtwState() =
+        runTest {
+            val (viewModel, sessionId) = createViewModelWithSession()
+
+            every {
+                HermesWsClient.request(WsMethods.PROMPT_BTW, any(), any())
+            } returns
+                CompletableDeferred(
+                    mapOf("task_id" to "btw_123456"),
+                )
+
+            viewModel.sendMessage("/btw which file was that in?")
+            advanceUntilIdle()
+
+            val btw = viewModel.uiState.value.btwState
+            assertNotNull(btw)
+            assertEquals("which file was that in?", btw?.question)
+            assertEquals("btw_123456", btw?.taskId)
+            assertTrue(btw?.isLoading == true)
+            verify {
+                HermesWsClient.request(
+                    WsMethods.PROMPT_BTW,
+                    mapOf("session_id" to sessionId, "text" to "which file was that in?"),
+                    any(),
+                )
+            }
+            // Ensure transcript messages were NOT polluted with the side question
+            assertTrue(
+                viewModel.uiState.value.messages
+                    .none { it.content.contains("which file was that in?") },
+            )
+        }
+
     // ── Slash usage ranking (issue #865) ────────────────────────────────────
 
     @Test

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

@@ -535,6 +535,43 @@ class ChatWsEventReducerTest {
         assertEquals("💾 Self-improvement review: Skill 'android-ci' patched", msg.content)
     }
 
+    @Test
+    fun testBtwComplete_updatesBtwState() {
+        val state =
+            ChatUiState(
+                currentSessionId = "session-1",
+                btwState =
+                    BtwUiState(
+                        question = "what model?",
+                        isLoading = true,
+                    ),
+            )
+        val event =
+            WsEvent.BtwComplete(
+                taskId = "btw_123456",
+                question = "what model?",
+                text = "This conversation uses Gemini 3.7.",
+                sessionId = "session-1",
+            )
+
+        val result =
+            ChatWsEventReducer.reduce(
+                state = state,
+                streamingState = StreamingState(),
+                event = event,
+                currentSessionId = "session-1",
+            )
+
+        val btw = result.state.btwState
+        org.junit.Assert.assertNotNull(btw)
+        assertEquals("btw_123456", btw?.taskId)
+        assertEquals("what model?", btw?.question)
+        assertEquals("This conversation uses Gemini 3.7.", btw?.answer)
+        assertEquals(false, btw?.isLoading)
+        // Zero messages appended to transcript!
+        assertEquals(0, result.state.messages.size)
+    }
+
     // ── Issue #771: reasoning survives a tool call (regression) ────────────
     //
     // Real gateway capture for `run echo hi` (reasoning model):

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

@@ -74,6 +74,14 @@ class SlashCommandDispatcherTest {
         assertEquals(SlashResult.OpenHistory, dispatcher.dispatch("/History"))
     }
 
+    @Test
+    fun `btw routes to SideQuestion`() {
+        assertEquals(SlashResult.SideQuestion("what model is this?"), dispatcher.dispatch("/btw what model is this?"))
+        assertEquals(SlashResult.SideQuestion("what model is this?"), dispatcher.dispatch("/BTW what model is this?"))
+        assertEquals(SlashResult.SideQuestion(""), dispatcher.dispatch("/btw"))
+        assertEquals(SlashResult.SideQuestion(""), dispatcher.dispatch("/btw   "))
+    }
+
     @Test
     fun `NEW uppercase still routes to NewSession`() {
         // Dispatcher lower-cases before matching, so case must not matter.