chat: optional per-chat agent so one session can mix agents

clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/Actions.generated.cs

@@ -129,6 +129,8 @@ public ActionType(string value)
 
     public static readonly ActionType ChatConfigChanged = new ActionType("chat/configChanged");
 
+    public static readonly ActionType ChatMoved = new ActionType("chat/moved");
+
     public static readonly ActionType ChatInputRequested = new ActionType("chat/inputRequested");
 
     public static readonly ActionType ChatInputAnswerChanged = new ActionType("chat/inputAnswerChanged");
@@ -1180,7 +1182,7 @@ public sealed record SessionChatUpdatedAction
 
     /// <summary>Mutable summary fields that changed; omitted fields are unchanged.
     ///
-    /// Identity fields (`resource`) never change and MUST be omitted by
+    /// Identity fields (`resource`, `provider`) never change and MUST be omitted by
     /// senders; receivers SHOULD ignore them if present.</summary>
     public required PartialChatSummary Changes { get; init; }
 }
@@ -2092,10 +2094,10 @@ public sealed record ChatIsArchivedChangedAction
 /// <summary>Config values set on a chat changed.
 ///
 /// Merges `config` into the chat's
-/// {@link ChatConfigState | `ChatState.config`} overlay, or replaces the
-/// overlay when `replace` is `true`. Only properties with `chatMutable: true`
-/// in the session's config schema may be set. To reset a property to the
-/// session's value, replace the overlay with one that omits the property.</summary>
+/// {@link ChatConfigState | `ChatState.config`} values, or replaces them when
+/// `replace` is `true`; keys missing after a replace take their property's
+/// `default`. Only properties with `chatMutable: true` in
+/// the effective schema may be set.</summary>
 public sealed record ChatConfigChangedAction
 {
     public ActionType Type { get; init; } = ActionType.ChatConfigChanged;
@@ -2108,6 +2110,31 @@ public sealed record ChatConfigChangedAction
     public bool? Replace { get; init; }
 }
 
+/// <summary>The chat moved to another session.
+///
+/// Dispatched by the host on the moved chat's channel after a cross-session
+/// `moveChat`. `provider` and `schema` are the chat's
+/// {@link ChatState.provider | `provider`} and
+/// {@link ChatConfigState.schema | `config.schema`} relative to the new
+/// session; absent clears them. `ChatState` has no session field, so the
+/// reducer does not store `session`; it tells subscribers which session now
+/// owns the chat.</summary>
+public sealed record ChatMovedAction
+{
+    public ActionType Type { get; init; } = ActionType.ChatMoved;
+
+    /// <summary>The new owning session URI.</summary>
+    public required string Session { get; init; }
+
+    /// <summary>The chat's provider in the new session; absent clears it.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; init; }
+
+    /// <summary>The chat's config schema in the new session; absent clears it.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public SessionConfigSchema? Schema { get; init; }
+}
+
 /// <summary>A session requested input from the user.
 ///
 /// Creates an unresolved {@link InputRequestResponsePart} in the active turn,
@@ -2782,6 +2809,12 @@ public sealed record PartialChatSummary
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public ChatInteractivity? Interactivity { get; init; }
 
+    /// <summary>Agent provider ID backing this chat. See {@link ChatState.provider}.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; init; }
+
     /// <summary>The subset of the session's working directories this chat uses.
     /// See {@link ChatState.workingDirectories} for the full semantics.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
@@ -2897,6 +2930,7 @@ public StateActionConverter()
         ["chat/isReadChanged"] = typeof(ChatIsReadChangedAction),
         ["chat/isArchivedChanged"] = typeof(ChatIsArchivedChangedAction),
         ["chat/configChanged"] = typeof(ChatConfigChangedAction),
+        ["chat/moved"] = typeof(ChatMovedAction),
         ["chat/inputRequested"] = typeof(ChatInputRequestedAction),
         ["chat/inputAnswerChanged"] = typeof(ChatInputAnswerChangedAction),
         ["chat/inputCompleted"] = typeof(ChatInputCompletedAction),

clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/Commands.generated.cs

@@ -485,6 +485,14 @@ public sealed record InitializeResult
     /// Stability: 1.0 - Early development.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public TcpConnectionsCapability? TcpConnections { get; init; }
+
+    /// <summary>Present when chats in one session may be backed by different agents
+    /// (see {@link CreateChatParams.provider} and {@link ChatState.provider}).
+    /// Clients MUST NOT send `CreateChatParams.provider` without it.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public MultipleChatProvidersCapability? MultipleChatProviders { get; init; }
 }
 
 /// <summary>Identifies a protocol implementation — the software (and build) on one end
@@ -614,6 +622,13 @@ public sealed record AutomationCustomizationsCapability
 {
 }
 
+/// <summary>Presence capability for {@link InitializeResult.multipleChatProviders}.
+///
+/// Stability: 1.0 - Early development.</summary>
+public sealed record MultipleChatProvidersCapability
+{
+}
+
 /// <summary>Re-establishes a dropped connection. The server replays missed actions or
 /// provides fresh snapshots.</summary>
 public sealed record ReconnectParams
@@ -1015,6 +1030,19 @@ public sealed record CreateChatParams
     /// <summary>Client-selected initial display title for the new chat.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public string? Title { get; init; }
+
+    /// <summary>Agent provider ID for the new chat. Absent means the session's provider.
+    ///
+    /// Requires {@link InitializeResult.multipleChatProviders}. Hosts reject with
+    /// `InvalidParams` a provider that is not in the root state's `agents` or
+    /// whose agent does not advertise `multipleChats`. Forks and side chats
+    /// (`source` present) continue the source chat's history, so they always use
+    /// the source chat's agent: absent means that agent, and a different value is
+    /// rejected. Agent capability checks for this request use the chat's agent.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; init; }
 }
 
 /// <summary>Disposes a chat and cleans up server-side resources.</summary>
@@ -1079,6 +1107,19 @@ public sealed record ChatMoveToNewSessionDestination
 /// Rejection leaves ownership, catalog order, chat state, and root summaries
 /// unchanged.
 ///
+/// A moved chat keeps its agent. After the move the host reports
+/// {@link ChatState.provider | `provider`} on the chat whenever it differs from
+/// the destination session's provider, including when the chat had none
+/// because it matched its old session. Hosts MAY refuse, as an unsupported
+/// destination, a move they cannot support, such as one that changes whether
+/// the chat's agent matches its session's.
+///
+/// A moved chat's `config.values` move with it unchanged. If a move changes
+/// whether the chat needs its own `config.schema`, the host sets or clears it,
+/// or refuses the move as an unsupported destination. After a cross-session
+/// move the host dispatches `chat/moved` on the chat's channel with its new
+/// session, `provider` and `config.schema`.
+///
 /// On success every moved chat keeps its URI, state, and immutable
 /// `ChatOrigin`. The host commits ownership and catalog order before publishing
 /// `session/chatRemoved`, `session/chatAdded`, `session/chatsReordered`, and

clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/JsonSerializerContext.generated.cs

@@ -154,6 +154,7 @@ namespace Microsoft.AgentHostProtocol;
 [JsonSerializable(typeof(ChatIsArchivedChangedAction))]
 [JsonSerializable(typeof(ChatIsReadChangedAction))]
 [JsonSerializable(typeof(ChatMovableChangedAction))]
+[JsonSerializable(typeof(ChatMovedAction))]
 [JsonSerializable(typeof(ChatMoveDestination))]
 [JsonSerializable(typeof(ChatMoveDestinationKind))]
 [JsonSerializable(typeof(ChatMoveToNewSessionDestination))]
@@ -286,6 +287,7 @@ namespace Microsoft.AgentHostProtocol;
 [JsonSerializable(typeof(ModelSelection))]
 [JsonSerializable(typeof(MoveChatParams))]
 [JsonSerializable(typeof(MoveChatResult))]
+[JsonSerializable(typeof(MultipleChatProvidersCapability))]
 [JsonSerializable(typeof(MultipleChatsCapability))]
 [JsonSerializable(typeof(MultipleWorkingDirectoriesCapability))]
 [JsonSerializable(typeof(OtlpExportLogsParams))]

clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/State.generated.cs

@@ -2365,6 +2365,12 @@ public sealed class ChatSummary
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public ChatInteractivity? Interactivity { get; set; }
 
+    /// <summary>Agent provider ID backing this chat. See {@link ChatState.provider}.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; set; }
+
     /// <summary>The subset of the session's working directories this chat uses.
     /// See {@link ChatState.workingDirectories} for the full semantics.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
@@ -2492,6 +2498,17 @@ public sealed class ChatState
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public ChatInteractivity? Interactivity { get; set; }
 
+    /// <summary>Agent provider ID backing this chat. Absent means the session's
+    /// {@link SessionMetadata.provider | `provider`}; hosts set it when it
+    /// differs. The chat's agent never changes, but `provider` is reported
+    /// relative to its session, so `chat/moved` may set or clear it. Like
+    /// `resource`, it is omitted from `session/chatUpdated` changes. Forks and
+    /// side chats use the source chat's agent.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; set; }
+
     /// <summary>The subset of the session's
     /// {@link SessionState.workingDirectories | `workingDirectories`} that this
     /// chat's agent has tool access to. Every entry MUST be present in the owning
@@ -2536,9 +2553,7 @@ public sealed class ChatState
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public List<CanvasReference>? Canvases { get; set; }
 
-    /// <summary>Configuration values set on this chat, applied over the owning session's
-    /// {@link SessionState.config | `SessionState.config`}. See
-    /// {@link ChatConfigState}.</summary>
+    /// <summary>This chat's configuration. See {@link ChatConfigState}.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public ChatConfigState? Config { get; set; }
 
@@ -3343,6 +3358,12 @@ public sealed record SessionChatSummary
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public ChatInteractivity? Interactivity { get; init; }
 
+    /// <summary>Agent provider ID backing this chat. See {@link ChatState.provider}.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Provider { get; init; }
+
     /// <summary>Current chat status, matching {@link ChatSummary.status}.
     ///
     /// Includes the activity bits and the orthogonal {@link SessionStatus.IsRead}
@@ -3464,8 +3485,8 @@ public sealed record SessionConfigPropertySchema
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public bool? SessionMutable { get; init; }
 
-    /// <summary>When `true`, the property may be set per chat with `chat/configChanged`.
-    /// The chat's value overrides the session's value for that chat only.</summary>
+    /// <summary>When `true`, the property may be changed per chat with
+    /// `chat/configChanged`, affecting only that chat.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public bool? ChatMutable { get; init; }
 }
@@ -3497,16 +3518,30 @@ public sealed class SessionConfigState
     public required Dictionary<string, JsonElement> Values { get; set; }
 }
 
-/// <summary>Configuration values set on a chat: an overlay on the owning session's
-/// {@link SessionState.config | `SessionState.config`}.
+/// <summary>A chat's configuration. `values` holds the chat's `chatMutable` properties
+/// of the effective schema. For a chat without its own `schema`, other
+/// properties are session-wide and come from the session's config; a chat with
+/// its own `schema` does not use the session's config. It does not inherit
+/// from the session: a chat's `values` change only through
+/// `chat/configChanged` on the chat.
 ///
-/// It carries only the chat's own values; the session's config schema
-/// applies. The effective config of a chat is the session's values with
-/// these values applied over them. Only properties with `chatMutable: true`
-/// in the session's config schema can be set on a chat.</summary>
+/// Only `chatMutable` properties can be changed with `chat/configChanged`;
+/// hosts reject other keys. Hosts set the initial `values` when they create
+/// the chat. When the session has a config, hosts set `config` on every chat.</summary>
 public sealed class ChatConfigState
 {
-    /// <summary>Config values set on this chat, keyed by property id</summary>
+    /// <summary>Config schema for this chat's `chatMutable` properties. Absent means the
+    /// session's schema. Hosts set it, as the chat's own schema, when the chat's
+    /// {@link ChatState.provider | `provider`} differs from the session's; when
+    /// present, clients use it instead of the session's schema.
+    ///
+    /// Stability: 1.0 - Early development.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public SessionConfigSchema? Schema { get; set; }
+
+    /// <summary>The chat's values for the `chatMutable` properties of the effective
+    /// schema, keyed by property id. A missing key takes that property's
+    /// `default`.</summary>
     public required Dictionary<string, JsonElement> Values { get; set; }
 }
 

clients/dotnet/src/AgentHostProtocol/Generated/ActionMetadata.generated.cs

@@ -127,6 +127,9 @@ public static bool TryGetActionType(object action, out ActionType actionType)
             case ChatMovableChangedAction value:
                 actionType = value.Type;
                 return true;
+            case ChatMovedAction value:
+                actionType = value.Type;
+                return true;
             case ChatPendingMessageRemovedAction value:
                 actionType = value.Type;
                 return true;

clients/dotnet/src/AgentHostProtocol/Reducers.cs

@@ -1144,6 +1144,17 @@ public static ReduceOutcome ApplyToChat(ChatState state, StateAction action)
                 state.Config ??= new ChatConfigState { Values = chatValues };
                 state.Config.Values = chatValues;
                 return ReduceOutcome.Applied;
+            case ChatMovedAction a:
+                state.Provider = a.Provider;
+                if (state.Config is not null)
+                {
+                    state.Config.Schema = a.Schema;
+                }
+                else if (a.Schema is not null)
+                {
+                    state.Config = new ChatConfigState { Schema = a.Schema, Values = new Dictionary<string, JsonElement>() };
+                }
+                return ReduceOutcome.Applied;
         }
 
         return ReduceOutcome.OutOfScope;

clients/go/ahp/reducers.go

@@ -858,6 +858,14 @@ func ApplyActionToChat(state *ahptypes.ChatState, action ahptypes.StateAction) R
 			state.Config.Values[k] = v
 		}
 		return ReduceOutcomeApplied
+	case *ahptypes.ChatMovedAction:
+		state.Provider = a.Provider
+		if state.Config != nil {
+			state.Config.Schema = a.Schema
+		} else if a.Schema != nil {
+			state.Config = &ahptypes.ChatConfigState{Schema: a.Schema, Values: map[string]json.RawMessage{}}
+		}
+		return ReduceOutcomeApplied
 	}
 	return ReduceOutcomeOutOfScope
 }

clients/go/ahptypes/actions.generated.go

@@ -71,6 +71,7 @@ const (
 	ActionTypeChatIsReadChanged                   ActionType = "chat/isReadChanged"
 	ActionTypeChatIsArchivedChanged               ActionType = "chat/isArchivedChanged"
 	ActionTypeChatConfigChanged                   ActionType = "chat/configChanged"
+	ActionTypeChatMoved                           ActionType = "chat/moved"
 	ActionTypeChatInputRequested                  ActionType = "chat/inputRequested"
 	ActionTypeChatInputAnswerChanged              ActionType = "chat/inputAnswerChanged"
 	ActionTypeChatInputCompleted                  ActionType = "chat/inputCompleted"
@@ -224,7 +225,7 @@ type SessionChatUpdatedAction struct {
 	Chat URI `json:"chat"`
 	// Mutable summary fields that changed; omitted fields are unchanged.
 	//
-	// Identity fields (`resource`) never change and MUST be omitted by
+	// Identity fields (`resource`, `provider`) never change and MUST be omitted by
 	// senders; receivers SHOULD ignore them if present.
 	Changes PartialChatSummary `json:"changes"`
 }
@@ -877,10 +878,10 @@ type ChatIsArchivedChangedAction struct {
 // Config values set on a chat changed.
 //
 // Merges `config` into the chat's
-// {@link ChatConfigState | `ChatState.config`} overlay, or replaces the
-// overlay when `replace` is `true`. Only properties with `chatMutable: true`
-// in the session's config schema may be set. To reset a property to the
-// session's value, replace the overlay with one that omits the property.
+// {@link ChatConfigState | `ChatState.config`} values, or replaces them when
+// `replace` is `true`; keys missing after a replace take their property's
+// `default`. Only properties with `chatMutable: true` in
+// the effective schema may be set.
 type ChatConfigChangedAction struct {
 	Type ActionType `json:"type"`
 	// Config values to set on the chat
@@ -889,6 +890,25 @@ type ChatConfigChangedAction struct {
 	Replace *bool `json:"replace,omitempty"`
 }
 
+// The chat moved to another session.
+//
+// Dispatched by the host on the moved chat's channel after a cross-session
+// `moveChat`. `provider` and `schema` are the chat's
+// {@link ChatState.provider | `provider`} and
+// {@link ChatConfigState.schema | `config.schema`} relative to the new
+// session; absent clears them. `ChatState` has no session field, so the
+// reducer does not store `session`; it tells subscribers which session now
+// owns the chat.
+type ChatMovedAction struct {
+	Type ActionType `json:"type"`
+	// The new owning session URI.
+	Session URI `json:"session"`
+	// The chat's provider in the new session; absent clears it.
+	Provider *string `json:"provider,omitempty"`
+	// The chat's config schema in the new session; absent clears it.
+	Schema *SessionConfigSchema `json:"schema,omitempty"`
+}
+
 // A session requested input from the user.
 //
 // Creates an unresolved {@link InputRequestResponsePart} in the active turn,
@@ -1872,6 +1892,7 @@ func (*ChatDraftChangedAction) isStateAction()                    {}
 func (*ChatIsReadChangedAction) isStateAction()                   {}
 func (*ChatIsArchivedChangedAction) isStateAction()               {}
 func (*ChatConfigChangedAction) isStateAction()                   {}
+func (*ChatMovedAction) isStateAction()                           {}
 func (*ChatInputRequestedAction) isStateAction()                  {}
 func (*ChatInputAnswerChangedAction) isStateAction()              {}
 func (*ChatInputCompletedAction) isStateAction()                  {}
@@ -2209,6 +2230,12 @@ func (u *StateAction) UnmarshalJSON(data []byte) error {
 			return err
 		}
 		u.Value = &value
+	case "chat/moved":
+		var value ChatMovedAction
+		if err := json.Unmarshal(data, &value); err != nil {
+			return err
+		}
+		u.Value = &value
 	case "chat/inputRequested":
 		var value ChatInputRequestedAction
 		if err := json.Unmarshal(data, &value); err != nil {