feat(gateway): show per-category context breakdown in /usage (#55204)

Channel users get the same context split the desktop popover shows
(PR #54907) — system prompt, tools, rules, skills, MCP, subagents,
memory, conversation — under the existing Context line in /usage.

Reuses agent.context_breakdown.compute_session_context_breakdown, so
there is no new tool and no new engine. The slices are estimates
(chars/4) and the block is labelled _(estimated)_; the headline
Context line keeps using the provider-measured last_prompt_tokens.
Rendering is fail-open: any engine error returns no breakdown and the
rest of /usage is unaffected.

- gateway/slash_commands.py: _context_breakdown_lines() helper + wire
  into _handle_usage_command
- locales/*.yaml: breakdown_header, breakdown_line, and 8 category
  labels across all 16 locales (parity gate)
- tests/gateway/test_usage_command.py: render + fail-open coverage

locales/af.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Koste: ingesluit"
     label_context:            "Konteks: {used} / {total} ({pct}%)"
     label_compressions:       "Saamperserings: {count}"
+    breakdown_header: "🧩 **Konteksverdeling** _(geskat)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Stelselopdrag"
+    breakdown_cat_tool_definitions: "Nutsmiddeldefinisies"
+    breakdown_cat_rules: "Reëls"
+    breakdown_cat_skills: "Vaardighede"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Subagent-definisies"
+    breakdown_cat_memory: "Geheue"
+    breakdown_cat_conversation: "Gesprek"
     header_session_info:      "📊 **Sessie-inligting**"
     label_messages:           "Boodskappe: {count}"
     label_estimated_context:  "Geskatte konteks: ~{count} tokens"

locales/de.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Kosten: inbegriffen"
     label_context:            "Kontext: {used} / {total} ({pct}%)"
     label_compressions:       "Kompressionen: {count}"
+    breakdown_header: "🧩 **Kontextaufschlüsselung** _(geschätzt)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "System-Prompt"
+    breakdown_cat_tool_definitions: "Tool-Definitionen"
+    breakdown_cat_rules: "Regeln"
+    breakdown_cat_skills: "Fähigkeiten"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Subagent-Definitionen"
+    breakdown_cat_memory: "Speicher"
+    breakdown_cat_conversation: "Konversation"
     header_session_info:      "📊 **Sitzungsinfo**"
     label_messages:           "Nachrichten: {count}"
     label_estimated_context:  "Geschätzter Kontext: ~{count} Tokens"

locales/en.yaml

@@ -344,6 +344,16 @@ gateway:
     label_cost_included:      "Cost: included"
     label_context:            "Context: {used} / {total} ({pct}%)"
     label_compressions:       "Compressions: {count}"
+    breakdown_header:         "🧩 **Context breakdown** _(estimated)_"
+    breakdown_line:           "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt:        "System prompt"
+    breakdown_cat_tool_definitions:     "Tool definitions"
+    breakdown_cat_rules:                "Rules"
+    breakdown_cat_skills:               "Skills"
+    breakdown_cat_mcp:                  "MCP"
+    breakdown_cat_subagent_definitions: "Subagent definitions"
+    breakdown_cat_memory:               "Memory"
+    breakdown_cat_conversation:         "Conversation"
     header_session_info:      "📊 **Session Info**"
     label_messages:           "Messages: {count}"
     label_estimated_context:  "Estimated context: ~{count} tokens"

locales/es.yaml

@@ -329,6 +329,16 @@ gateway:
     label_cost_included:      "Costo: incluido"
     label_context:            "Contexto: {used} / {total} ({pct}%)"
     label_compressions:       "Compresiones: {count}"
+    breakdown_header: "🧩 **Desglose del contexto** _(estimado)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Prompt del sistema"
+    breakdown_cat_tool_definitions: "Definiciones de herramientas"
+    breakdown_cat_rules: "Reglas"
+    breakdown_cat_skills: "Habilidades"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Definiciones de subagentes"
+    breakdown_cat_memory: "Memoria"
+    breakdown_cat_conversation: "Conversación"
     header_session_info:      "📊 **Información de la sesión**"
     label_messages:           "Mensajes: {count}"
     label_estimated_context:  "Contexto estimado: ~{count} tokens"

locales/fr.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Coût : inclus"
     label_context:            "Contexte : {used} / {total} ({pct}%)"
     label_compressions:       "Compressions : {count}"
+    breakdown_header: "🧩 **Répartition du contexte** _(estimée)_"
+    breakdown_line: "• {label} : ~{count} ({pct} %)"
+    breakdown_cat_system_prompt: "Invite système"
+    breakdown_cat_tool_definitions: "Définitions des outils"
+    breakdown_cat_rules: "Règles"
+    breakdown_cat_skills: "Compétences"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Définitions des sous-agents"
+    breakdown_cat_memory: "Mémoire"
+    breakdown_cat_conversation: "Conversation"
     header_session_info:      "📊 **Infos de session**"
     label_messages:           "Messages : {count}"
     label_estimated_context:  "Contexte estimé : ~{count} jetons"

locales/ga.yaml

@@ -336,6 +336,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Costas: san áireamh"
     label_context:            "Comhthéacs: {used} / {total} ({pct}%)"
     label_compressions:       "Dlúthuithe: {count}"
+    breakdown_header: "🧩 **Miondealú comhthéacs** _(measta)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Leid an chórais"
+    breakdown_cat_tool_definitions: "Sainmhínithe uirlisí"
+    breakdown_cat_rules: "Rialacha"
+    breakdown_cat_skills: "Scileanna"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Sainmhínithe fo-ghníomhairí"
+    breakdown_cat_memory: "Cuimhne"
+    breakdown_cat_conversation: "Comhrá"
     header_session_info:      "📊 **Eolas Seisiúin**"
     label_messages:           "Teachtaireachtaí: {count}"
     label_estimated_context:  "Comhthéacs measta: ~{count} comhartha"

locales/hu.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Költség: belefoglalva"
     label_context:            "Kontextus: {used} / {total} ({pct}%)"
     label_compressions:       "Tömörítések: {count}"
+    breakdown_header: "🧩 **Kontextus-bontás** _(becsült)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Rendszerüzenet"
+    breakdown_cat_tool_definitions: "Eszközdefiníciók"
+    breakdown_cat_rules: "Szabályok"
+    breakdown_cat_skills: "Készségek"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Alügynök-definíciók"
+    breakdown_cat_memory: "Memória"
+    breakdown_cat_conversation: "Beszélgetés"
     header_session_info:      "📊 **Munkamenet-információ**"
     label_messages:           "Üzenetek: {count}"
     label_estimated_context:  "Becsült kontextus: ~{count} token"

locales/it.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Costo: incluso"
     label_context:            "Contesto: {used} / {total} ({pct}%)"
     label_compressions:       "Compressioni: {count}"
+    breakdown_header: "🧩 **Suddivisione del contesto** _(stimata)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Prompt di sistema"
+    breakdown_cat_tool_definitions: "Definizioni degli strumenti"
+    breakdown_cat_rules: "Regole"
+    breakdown_cat_skills: "Competenze"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Definizioni dei subagenti"
+    breakdown_cat_memory: "Memoria"
+    breakdown_cat_conversation: "Conversazione"
     header_session_info:      "📊 **Info sessione**"
     label_messages:           "Messaggi: {count}"
     label_estimated_context:  "Contesto stimato: ~{count} token"

locales/ja.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "コスト: 含まれています"
     label_context:            "コンテキスト: {used} / {total} ({pct}%)"
     label_compressions:       "圧縮回数: {count}"
+    breakdown_header: "🧩 **コンテキスト内訳** _(推定)_"
+    breakdown_line: "• {label}: 約{count} ({pct}%)"
+    breakdown_cat_system_prompt: "システムプロンプト"
+    breakdown_cat_tool_definitions: "ツール定義"
+    breakdown_cat_rules: "ルール"
+    breakdown_cat_skills: "スキル"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "サブエージェント定義"
+    breakdown_cat_memory: "メモリ"
+    breakdown_cat_conversation: "会話"
     header_session_info:      "📊 **セッション情報**"
     label_messages:           "メッセージ数: {count}"
     label_estimated_context:  "推定コンテキスト: ~{count} トークン"

locales/ko.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "비용: 포함됨"
     label_context:            "컨텍스트: {used} / {total} ({pct}%)"
     label_compressions:       "압축: {count}"
+    breakdown_header: "🧩 **컨텍스트 분석** _(추정치)_"
+    breakdown_line: "• {label}: 약 {count} ({pct}%)"
+    breakdown_cat_system_prompt: "시스템 프롬프트"
+    breakdown_cat_tool_definitions: "도구 정의"
+    breakdown_cat_rules: "규칙"
+    breakdown_cat_skills: "스킬"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "서브에이전트 정의"
+    breakdown_cat_memory: "메모리"
+    breakdown_cat_conversation: "대화"
     header_session_info:      "📊 **세션 정보**"
     label_messages:           "메시지: {count}"
     label_estimated_context:  "예상 컨텍스트: 약 {count} 토큰"

locales/pt.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Custo: incluído"
     label_context:            "Contexto: {used} / {total} ({pct}%)"
     label_compressions:       "Compressões: {count}"
+    breakdown_header: "🧩 **Detalhamento do contexto** _(estimado)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Prompt do sistema"
+    breakdown_cat_tool_definitions: "Definições de ferramentas"
+    breakdown_cat_rules: "Regras"
+    breakdown_cat_skills: "Habilidades"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Definições de subagentes"
+    breakdown_cat_memory: "Memória"
+    breakdown_cat_conversation: "Conversa"
     header_session_info:      "📊 **Informações da sessão**"
     label_messages:           "Mensagens: {count}"
     label_estimated_context:  "Contexto estimado: ~{count} tokens"

locales/ru.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Стоимость: включено"
     label_context:            "Контекст: {used} / {total} ({pct}%)"
     label_compressions:       "Сжатий: {count}"
+    breakdown_header: "🧩 **Разбивка контекста** _(оценка)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Системный промпт"
+    breakdown_cat_tool_definitions: "Определения инструментов"
+    breakdown_cat_rules: "Правила"
+    breakdown_cat_skills: "Навыки"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Определения субагентов"
+    breakdown_cat_memory: "Память"
+    breakdown_cat_conversation: "Разговор"
     header_session_info:      "📊 **Информация о сеансе**"
     label_messages:           "Сообщений: {count}"
     label_estimated_context:  "Ориентировочный контекст: ~{count} токенов"

locales/tr.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Maliyet: dahil"
     label_context:            "Bağlam: {used} / {total} ({pct}%)"
     label_compressions:       "Sıkıştırmalar: {count}"
+    breakdown_header: "🧩 **Bağlam dökümü** _(tahmini)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Sistem istemi"
+    breakdown_cat_tool_definitions: "Araç tanımları"
+    breakdown_cat_rules: "Kurallar"
+    breakdown_cat_skills: "Beceriler"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Alt aracı tanımları"
+    breakdown_cat_memory: "Bellek"
+    breakdown_cat_conversation: "Konuşma"
     header_session_info:      "📊 **Oturum Bilgisi**"
     label_messages:           "Mesajlar: {count}"
     label_estimated_context:  "Tahmini bağlam: ~{count} token"

locales/uk.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "Вартість: включено"
     label_context:            "Контекст: {used} / {total} ({pct}%)"
     label_compressions:       "Стиснень: {count}"
+    breakdown_header: "🧩 **Розбивка контексту** _(оцінка)_"
+    breakdown_line: "• {label}: ~{count} ({pct}%)"
+    breakdown_cat_system_prompt: "Системний промпт"
+    breakdown_cat_tool_definitions: "Визначення інструментів"
+    breakdown_cat_rules: "Правила"
+    breakdown_cat_skills: "Навички"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "Визначення субагентів"
+    breakdown_cat_memory: "Пам'ять"
+    breakdown_cat_conversation: "Розмова"
     header_session_info:      "📊 **Інформація про сеанс**"
     label_messages:           "Повідомлень: {count}"
     label_estimated_context:  "Орієнтовний контекст: ~{count} токенів"

locales/zh-hant.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "費用：已包含"
     label_context:            "上下文：{used} / {total}（{pct}%）"
     label_compressions:       "壓縮次數：{count}"
+    breakdown_header: "🧩 **上下文明細** _(估算)_"
+    breakdown_line: "• {label}：約 {count} ({pct}%)"
+    breakdown_cat_system_prompt: "系統提示詞"
+    breakdown_cat_tool_definitions: "工具定義"
+    breakdown_cat_rules: "規則"
+    breakdown_cat_skills: "技能"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "子代理定義"
+    breakdown_cat_memory: "記憶"
+    breakdown_cat_conversation: "對話"
     header_session_info:      "📊 **工作階段資訊**"
     label_messages:           "訊息數：{count}"
     label_estimated_context:  "預估上下文：~{count} 個 token"

locales/zh.yaml

@@ -332,6 +332,16 @@ Future messages in this room will use that transcript until `/reset` or another
     label_cost_included:      "费用：已包含"
     label_context:            "上下文：{used} / {total}（{pct}%）"
     label_compressions:       "压缩次数：{count}"
+    breakdown_header: "🧩 **上下文明细** _(估算)_"
+    breakdown_line: "• {label}：约 {count} ({pct}%)"
+    breakdown_cat_system_prompt: "系统提示词"
+    breakdown_cat_tool_definitions: "工具定义"
+    breakdown_cat_rules: "规则"
+    breakdown_cat_skills: "技能"
+    breakdown_cat_mcp: "MCP"
+    breakdown_cat_subagent_definitions: "子代理定义"
+    breakdown_cat_memory: "记忆"
+    breakdown_cat_conversation: "对话"
     header_session_info:      "📊 **会话信息**"
     label_messages:           "消息数：{count}"
     label_estimated_context:  "估计上下文：~{count} 个令牌"