feat(chat): surface per-model reasoning capabilities (#946) (#951)

Add ModelCapabilities (capabilities: Map<String, ModelCapabilities>?)
to ModelProvider matching backend /api/model/options shape
{model: {fast, reasoning, can_disable_reasoning}}. Nullable/defaulted
for backward compat with old backends (ignoreUnknownKeys+SnakeCase).

Chat composer: gate reasoning dropdown on can_disable_reasoning and
supportsReasoning — "None" disabled with "reasoning always on" hint
when can_disable==false, chip disabled with "No reasoning" when
reasoning==false. Missing keys offer full scale.

Sync currentModelCapabilities from cachedModelOptions on
SessionInfo, resume, preload/refresh, and optimistic /model swap;
clear on resetSessionState. Used by ComposerToolbar via ChatScreen.

Model picker: surface same hints in ModelPickerDialog (pinned+all)
and ModelScreen ProviderCard.

Verified: ktlintCheck OK, compileDebugKotlin OK (rerun-tasks).

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

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

@@ -760,6 +760,8 @@ fun ChatScreen(
                 reasoningLevel = state.reasoningLevel,
                 onModelTap = { viewModel.openModelPicker() },
                 onReasoningTap = { level -> viewModel.setReasoningLevel(level) },
+                canDisableReasoning = state.currentModelCapabilities?.can_disable_reasoning,
+                supportsReasoning = state.currentModelCapabilities?.reasoning,
             )
         }
 

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

@@ -12,6 +12,7 @@ import com.m57.hermescontrol.data.local.HermesDatabase
 import com.m57.hermescontrol.data.local.SlashUsageStore
 import com.m57.hermescontrol.data.model.Attachment
 import com.m57.hermescontrol.data.model.AttachmentSource
+import com.m57.hermescontrol.data.model.ModelCapabilities
 import com.m57.hermescontrol.data.model.ModelProvider
 import com.m57.hermescontrol.data.model.PinnedModel
 import com.m57.hermescontrol.data.model.SessionMessage
@@ -291,6 +292,9 @@ data class ChatUiState(
     val modelPickerLoading: Boolean = false,
     // Current session's active model label (provider/model), shown in the chip
     val currentSessionModel: String? = null,
+    // Per-model reasoning capabilities for the current session's model
+    // (issue #946). Null when unknown — UI offers full scale.
+    val currentModelCapabilities: ModelCapabilities? = null,
     // Reasoning effort level for the current session
     val reasoningLevel: String? = null,
     val terminalBackend: String? = null,
@@ -810,6 +814,7 @@ class ChatViewModel(
                             fullContextTokens = if (modelSwapped) null else state.fullContextTokens,
                         )
                     }
+                    syncCurrentModelCapabilities()
                     if (modelSwapped) {
                         // Issue #817: after a swap the REST model/info window is
                         // PROFILE-scoped and may describe the old model (e.g. a
@@ -1070,6 +1075,7 @@ class ChatViewModel(
                         terminalBackend = terminalBackend ?: it.terminalBackend,
                     )
                 }
+                syncCurrentModelCapabilities()
                 // Mirror the active runtime session id app-wide (issue #532).
                 ActiveSessionHolder.set(runtimeSessionId ?: sessionId, sessionId)
                 addSystemMessage("Session resumed")
@@ -1836,6 +1842,7 @@ class ChatViewModel(
             if (result is NetworkResult.Success) {
                 cachedModelOptions = result.data.providers.orEmpty()
                 _uiState.update { it.copy(modelPickerPinned = AuthManager.getPinnedModels()) }
+                syncCurrentModelCapabilities()
             }
         }
     }
@@ -1878,6 +1885,7 @@ class ChatViewModel(
                             modelPickerLoading = false,
                         )
                     }
+                    syncCurrentModelCapabilities()
                 }
 
                 is NetworkResult.Failure -> {
@@ -1932,6 +1940,7 @@ class ChatViewModel(
                 currentSessionModel = "$provider/$model",
             )
         }
+        syncCurrentModelCapabilities()
         // Model switch changes the context-window denominator — refetch it.
         fetchContextUsage()
         handleSlashCommand("/model $model --provider $provider --session")
@@ -1963,6 +1972,40 @@ class ChatViewModel(
         }
     }
 
+    fun getModelCapabilities(
+        providerSlug: String,
+        modelName: String,
+    ): ModelCapabilities? = cachedModelOptions.find { it.slug == providerSlug }?.capabilities?.get(modelName)
+
+    fun getCurrentModelCapabilities(): ModelCapabilities? {
+        val label = _uiState.value.currentSessionModel ?: return null
+        val idx = label.indexOf('/')
+        if (idx <= 0) return null
+        val provider = label.substring(0, idx)
+        val model = label.substring(idx + 1)
+        return getModelCapabilities(provider, model)
+    }
+
+    private fun syncCurrentModelCapabilities() {
+        val label = _uiState.value.currentSessionModel
+        val caps =
+            if (label == null) {
+                null
+            } else {
+                val idx = label.indexOf('/')
+                if (idx <= 0) {
+                    null
+                } else {
+                    val provider = label.substring(0, idx)
+                    val model = label.substring(idx + 1)
+                    cachedModelOptions.find { it.slug == provider }?.capabilities?.get(model)
+                }
+            }
+        _uiState.update { state ->
+            if (state.currentModelCapabilities != caps) state.copy(currentModelCapabilities = caps) else state
+        }
+    }
+
     fun switchSession(sessionId: String) {
         if (sessionId == _uiState.value.currentSessionId) return
 
@@ -2167,6 +2210,7 @@ class ChatViewModel(
                 showModelPicker = false,
                 modelPickerLoading = false,
                 currentSessionModel = null,
+                currentModelCapabilities = null,
                 reasoningLevel = null,
                 terminalBackend = null,
                 usedContextTokens = null,

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

@@ -89,6 +89,8 @@ fun ChatInputBar(
     reasoningLevel: String? = null,
     onModelTap: () -> Unit = {},
     onReasoningTap: (String?) -> Unit = {},
+    canDisableReasoning: Boolean? = null,
+    supportsReasoning: Boolean? = null,
 ) {
     // Allow sending while the agent is mid-turn or awaiting approval: the
     // gateway's prompt.submit busy-input policy queues it as the next turn
@@ -319,6 +321,8 @@ fun ChatInputBar(
                     onReasoningSelected = onReasoningTap,
                     onMicTap = onMicTap,
                     modifier = Modifier.testTag("chat_composer_toolbar"),
+                    canDisableReasoning = canDisableReasoning,
+                    supportsReasoning = supportsReasoning,
                 )
 
                 // Attachment dropdown (anchored to the attach button in ComposerToolbar)

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

@@ -41,6 +41,11 @@ import com.m57.hermescontrol.R
  * Layout: [📎 attach] [model chip] [←spacer→] [🧠 reasoning] [🎙 mic]
  *
  * The reasoning chip opens a dropdown menu to pick a level (instead of cycling).
+ * When [canDisableReasoning] is false the "None" level is disabled with a
+ * "reasoning always on" hint (issue #946). Absent key (null) means no
+ * restriction is known — full scale offered.
+ * When [supportsReasoning] is false the model takes no reasoning parameter
+ * and the chip is disabled.
  */
 @Composable
 fun ComposerToolbar(
@@ -53,8 +58,12 @@ fun ComposerToolbar(
     onReasoningSelected: (String?) -> Unit,
     onMicTap: () -> Unit,
     modifier: Modifier = Modifier,
+    canDisableReasoning: Boolean? = null,
+    supportsReasoning: Boolean? = null,
 ) {
     var showReasoningMenu by remember { mutableStateOf(false) }
+    val reasoningDisabledForModel = supportsReasoning == false
+    val canDisable = canDisableReasoning
 
     Row(
         modifier =
@@ -105,9 +114,15 @@ fun ComposerToolbar(
             FilterChip(
                 selected = reasoningLevel != null,
                 onClick = { showReasoningMenu = true },
+                enabled = !reasoningDisabledForModel,
                 label = {
                     Text(
-                        text = buildReasoningLabel(reasoningLevel),
+                        text =
+                            if (reasoningDisabledForModel) {
+                                "No reasoning"
+                            } else {
+                                buildReasoningLabel(reasoningLevel)
+                            },
                         style = MaterialTheme.typography.bodySmall,
                         maxLines = 1,
                         overflow = TextOverflow.Ellipsis,
@@ -129,6 +144,22 @@ fun ComposerToolbar(
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
                     modifier = Modifier.padding(horizontal = 12.dp, vertical = 6.dp),
                 )
+                if (canDisable == false) {
+                    Text(
+                        text = "reasoning always on",
+                        style = MaterialTheme.typography.labelSmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.7f),
+                        modifier = Modifier.padding(horizontal = 12.dp, vertical = 2.dp),
+                    )
+                }
+                if (reasoningDisabledForModel) {
+                    Text(
+                        text = "no reasoning parameter for this model",
+                        style = MaterialTheme.typography.labelSmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.7f),
+                        modifier = Modifier.padding(horizontal = 12.dp, vertical = 2.dp),
+                    )
+                }
                 HorizontalDivider()
                 val allLevels =
                     listOf(
@@ -142,6 +173,8 @@ fun ComposerToolbar(
                         "ultra" to "Ultra",
                     )
                 allLevels.forEach { (level, label) ->
+                    val isNone = level == "none"
+                    val noneDisabled = isNone && (canDisable == false || reasoningDisabledForModel)
                     DropdownMenuItem(
                         text = {
                             Text(
@@ -153,10 +186,10 @@ fun ComposerToolbar(
                                         null
                                     },
                                 color =
-                                    if (reasoningLevel == level) {
-                                        MaterialTheme.colorScheme.primary
-                                    } else {
-                                        MaterialTheme.colorScheme.onSurface
+                                    when {
+                                        noneDisabled -> MaterialTheme.colorScheme.onSurface.copy(alpha = 0.38f)
+                                        reasoningLevel == level -> MaterialTheme.colorScheme.primary
+                                        else -> MaterialTheme.colorScheme.onSurface
                                     },
                             )
                         },
@@ -164,6 +197,7 @@ fun ComposerToolbar(
                             showReasoningMenu = false
                             onReasoningSelected(level)
                         },
+                        enabled = !noneDisabled && !reasoningDisabledForModel,
                     )
                 }
             }