fix(i18n): clarify /model switch applies to current and future sessions (#1368) (#1373)

The /model confirmation copy used wording ('New sessions will use this model')
that misled users into thinking the current session still ran on the old
model and that they needed /new to see the switch take effect. In reality
cmdModel preserves the agent session id and re-invokes the runtime with
--resume <id> --model <new>, so the new model is live immediately for the
current turn and persists for all future sessions.

Updated MsgModelChanged in all 5 languages (en, zh-CN, zh-TW, ja, es) to
explicitly state 'this session and all future sessions will use it'.
Added CHANGELOG Fixed entry under Unreleased.

Co-authored-by: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -24,6 +24,14 @@
 
 - **core**: prevent same-name file attachments from overwriting each other. `SaveFilesToDisk` now scopes files by message ID, keeps duplicate names distinct within one message, and uses an atomic no-overwrite fallback for legacy callers without a message ID (#1552).
 
+## Unreleased
+
+### Fixed
+- **/model switch confirmation copy**: `MsgModelChanged` now explicitly states the
+  new model applies to the current session and all future sessions, removing the
+  misleading "new sessions" wording that made users think they needed `/new` to
+  see the change take effect (#1368).
+
 ## v1.3.3 (2026-06-15)
 
 First stable release of the 1.3.3 series. Stabilizes the v1.3.3-beta.1 → v1.3.3-beta.5

core/i18n.go

@@ -2202,11 +2202,11 @@ var messages = map[MsgKey]map[Language]string{
 		LangSpanish:            "Modelo actual: %s",
 	},
 	MsgModelChanged: {
-		LangEnglish:            "Model switched to `%s`. New sessions will use this model.",
-		LangChinese:            "模型已切换为 `%s`，新会话将使用此模型。",
-		LangTraditionalChinese: "模型已切換為 `%s`，新會話將使用此模型。",
-		LangJapanese:           "モデルを `%s` に切り替えました。新しいセッションで使用されます。",
-		LangSpanish:            "Modelo cambiado a `%s`. Las nuevas sesiones usarán este modelo.",
+		LangEnglish:            "Model switched to `%s`. This session and all future sessions will use it.",
+		LangChinese:            "模型已切换为 `%s`，当前会话与后续会话均使用此模型。",
+		LangTraditionalChinese: "模型已切換為 `%s`，當前會話與後續會話均使用此模型。",
+		LangJapanese:           "モデルを `%s` に切り替えました。このセッションと今後のセッションで使用されます。",
+		LangSpanish:            "Modelo cambiado a `%s`. Esta sesión y las futuras usarán este modelo.",
 	},
 	MsgModelChangeFailed: {
 		LangEnglish:            "❌ Failed to change model: %v",