feat(channel,runtime): 批次2 后端 — 消息级角色归属进上下文 + IM 私聊随主会话角色 + 渠道级绑定

按 design/22 §2/§3/§4.4/§7（3/4/5）。
- ①「消息级角色归属」进入模型上下文（批次 1 只做存储+DTO）：历史消息的发送角色现在对模型可见，且**不把系统元数据塞进用户正文**（design/11 §10 红线）
- ② IM owner 私聊镜像解析出的角色 = **主会话绑定的角色**（§7-3）
- ③ 渠道级绑定：ChannelAccount 加 personaId（channels.json 读写/校验/脱敏沿用既有约定）+ 角色解析优先级 **会话 > 渠道 > 默认** + **群聊/陌生人强制默认角色**（§7-4）；admin 渠道配置端点支持 personaId
- Docs/api-client 版本 +1
- 验收：go build/vet/test 全绿 + linux/darwin 交叉编译

internal/runtime/loop/memory.go

@@ -36,16 +36,7 @@ type asyncExtractor interface {
 // project memory is injected so no owner-sensitive memory leaks to a group or
 // stranger.
 func (l *Loop) injectMemory(ctx context.Context, messages []model.Message) []model.Message {
-	personaID := l.personaFor(ctx)
-	if l.retriever == nil || personaID == "" {
-		return messages
-	}
-	env := sessionEnvFrom(ctx)
-	block, err := l.retrieveMemoryBlock(ctx, env, personaID, queryFromMessages(messages))
-	if err != nil {
-		l.log.Warn("memory inject", "error", err, "env", env.ActorEnv)
-		return messages
-	}
+	block := l.memoryBlock(ctx, messages)
 	if block == "" {
 		return messages
 	}
@@ -55,6 +46,25 @@ func (l *Loop) injectMemory(ctx context.Context, messages []model.Message) []mod
 	return out
 }
 
+// memoryBlock renders the round's memory block, or "" when there is nothing to
+// inject (no retriever/persona, a retrieval error, or no relevant memory). It is
+// split out from injectMemory because the assembly places other leading blocks
+// between the memory block and the conversation (the role context of design/22
+// §7-5), so it needs the block itself rather than a pre-prefixed slice.
+func (l *Loop) memoryBlock(ctx context.Context, messages []model.Message) string {
+	personaID := l.personaFor(ctx)
+	if l.retriever == nil || personaID == "" {
+		return ""
+	}
+	env := sessionEnvFrom(ctx)
+	block, err := l.retrieveMemoryBlock(ctx, env, personaID, queryFromMessages(messages))
+	if err != nil {
+		l.log.Warn("memory inject", "error", err, "env", env.ActorEnv)
+		return ""
+	}
+	return block
+}
+
 // retrieveMemoryBlock returns the memory injection block for env and the turn's
 // role. The owner-full env keeps the pre-existing Inject behavior. The restricted
 // env (group chat / stranger) injects only project-scope memory (人人可读, not
@@ -105,9 +115,17 @@ func formatMemoryBlock(results []memory.Result, marker string) string {
 // re-injects the persona's relevant long-term memory — retrieval is re-run every
 // round from the current conversation, not cached from the first turn, so it
 // supports cross-round refresh — folds in the per-session working-memory summary
-// when present, and applies the optional TransformContext hook last so a caller
-// can project/filter what the model actually sees. It returns the input unchanged
+// when present, renders the role/speaker attribution of the conversation (design/22
+// §7-5), and applies the optional TransformContext hook last so a caller can
+// project/filter what the model actually sees. It returns the input unchanged
 // when nothing is configured.
+//
+// The existing order is preserved exactly: the leading blocks are the per-round
+// time, the working-memory summary and the memory block, in that order; the role
+// declaration sits right after them (immediately before the conversation it
+// describes) and the speaker boundary notes are inserted into the conversation
+// itself. A conversation with no speaker label renders no attribution at all, so
+// every single-role path keeps the prompt it had before multi-character support.
 func (l *Loop) assembleContext(ctx context.Context, messages []model.Message, round int) []model.Message {
 	var leading []model.Message
 	// Per-round "current time" so the model naturally knows the wall clock (not a
@@ -122,11 +140,16 @@ func (l *Loop) assembleContext(ctx context.Context, messages []model.Message, ro
 			leading = append(leading, model.TextMessage(model.RoleSystem, "工作记忆: "+s))
 		}
 	}
-	leading = append(leading, l.injectMemory(ctx, messages)...)
-
-	out := leading
+	if block := l.memoryBlock(ctx, messages); block != "" {
+		leading = append(leading, model.TextMessage(model.RoleSystem, block))
+	}
+	decl, ok, view := l.attributeConversation(ctx, messages)
+	if ok {
+		leading = append(leading, decl)
+	}
+	out := append(leading, view...)
 	if l.transformContext != nil {
-		out = l.transformContext(ctx, leading, round)
+		out = l.transformContext(ctx, out, round)
 	}
 	return out
 }