feat(chat): /resume and /history open the session history tab (issue #864) (#876)

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

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatScreen.kt

@@ -74,6 +74,7 @@ import androidx.lifecycle.compose.LocalLifecycleOwner
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.repeatOnLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
+import com.m57.hermescontrol.HistoryScreen
 import com.m57.hermescontrol.NavigationController
 import com.m57.hermescontrol.R
 import com.m57.hermescontrol.data.model.Attachment
@@ -193,6 +194,15 @@ fun ChatScreen(
         }
     }
 
+    // /resume · /history (issue #864): open the session history tab so the
+    // user picks a past session — client-side, no gateway round-trip.
+    LaunchedEffect(state.openHistoryRequested) {
+        if (state.openHistoryRequested) {
+            NavigationController.navigateTo(HistoryScreen)
+            viewModel.consumeOpenHistoryRequest()
+        }
+    }
+
     // Arm + trigger older-message paging when the user scrolls near the top.
     // Before prepending, capture the anchor (first visible message id + offset)
     // so the same content stays under the reader's eye after the insert

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -279,6 +279,9 @@ data class ChatUiState(
     // #865). Empty until the local store loads; commands without recorded
     // usage keep their catalog order.
     val slashUsageCounts: Map<String, Int> = emptyMap(),
+    // Transient nav request from /resume and /history (issue #864): the
+    // screen consumes it by navigating to the history tab, then clears it.
+    val openHistoryRequested: Boolean = false,
     // In-session model picker (issue #589) — surfaced when the user types /model
     // (or taps the top-bar model chip). Mirror of the global model screen's
     // picker, but the selection hot-swaps the CURRENT session via the slash path.
@@ -1435,6 +1438,13 @@ class ChatViewModel(
                 openUpdateConfirm()
             }
 
+            is SlashResult.OpenHistory -> {
+                // Client-side: open the session history tab so the user can
+                // pick a past session to resume (issue #864) — no gateway
+                // round-trip (the backend slash worker can't answer /resume).
+                _uiState.update { it.copy(openHistoryRequested = true) }
+            }
+
             is SlashResult.RpcDispatch -> {
                 dispatchViaRpc(command)
             }
@@ -3231,6 +3241,11 @@ class ChatViewModel(
         _uiState.update { it.copy(backgroundCompleteMessage = null) }
     }
 
+    /** Consume the /resume · /history navigation request (issue #864). */
+    fun consumeOpenHistoryRequest() {
+        _uiState.update { it.copy(openHistoryRequested = false) }
+    }
+
     // ── Approval flow ───────────────────────────────────────────────────
 
     private fun handleApprovalRequest(event: WsEvent.ApprovalRequest) {

app/src/main/java/com/m57/hermescontrol/ui/chat/SlashCommandDispatcher.kt

@@ -31,6 +31,7 @@ class SlashCommandDispatcher {
             "/fork", "/branch" -> SlashResult.SessionBranch
             "/model" -> SlashResult.ModelSwitch
             "/update" -> SlashResult.Update
+            "/resume", "/history" -> SlashResult.OpenHistory
             else -> SlashResult.RpcDispatch
         }
     }
@@ -71,4 +72,12 @@ sealed class SlashResult {
      * after 45s (issue #862).
      */
     data object Update : SlashResult()
+
+    /**
+     * Open the session history tab client-side (issue #864). /resume and
+     * /history are CLI-flavored interactive commands the mobile gateway path
+     * can't answer usefully — same class of problem as /update (#862). The
+     * user picks a past session from history and resumes it from there.
+     */
+    data object OpenHistory : SlashResult()
 }