diff --git a/cli.py b/cli.py
index 0683838d8..c3f438690 100644
--- a/cli.py
+++ b/cli.py
@@ -9314,9 +9314,11 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
             return
 
         from hermes_cli.partial_compress import (
+            extract_compress_flags,
             parse_partial_compress_args,
             rejoin_compressed_head_and_tail,
             split_history_for_partial_compress,
+            summarize_compress_preview,
         )
 
         # Args after the command word (e.g. "/compress here 3" -> "here 3").
@@ -9326,9 +9328,42 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
             if len(_parts) > 1:
                 raw_args = _parts[1].strip()
 
+        # Strip --preview/--dry-run/--aggressive before positional parsing
+        # so the flags coexist with 'here [N]' / focus-topic forms.
+        raw_args, preview, aggressive = extract_compress_flags(raw_args)
         partial, keep_last, focus_topic = parse_partial_compress_args(raw_args)
         focus_topic = focus_topic or ""
 
+        if aggressive:
+            # LLM-free hard truncation is not supported: it would need its
+            # own transcript-persistence path outside the guarded
+            # _compress_context rotation machinery. Surface that instead of
+            # silently mis-parsing the flag as a focus topic.
+            print("(._.) --aggressive is not supported; use '/compress here [N]' "
+                  "to keep only recent exchanges, or /undo to drop turns.")
+            if not preview:
+                return
+
+        if preview:
+            from agent.model_metadata import estimate_request_tokens_rough
+            _sys_prompt = getattr(self.agent, "_cached_system_prompt", "") or ""
+            _tools = getattr(self.agent, "tools", None) or None
+            approx_tokens = estimate_request_tokens_rough(
+                self.conversation_history,
+                system_prompt=_sys_prompt,
+                tools=_tools,
+            )
+            report = summarize_compress_preview(
+                self.conversation_history,
+                partial,
+                keep_last,
+                focus_topic or None,
+                approx_tokens,
+            )
+            for line in report["lines"]:
+                print(f"🗜️  {line}")
+            return
+
         original_count = len(self.conversation_history)
         with self._busy_command("Compressing context..."):
             try:
diff --git a/gateway/slash_commands.py b/gateway/slash_commands.py
index 199e79294..341efb4b0 100644
--- a/gateway/slash_commands.py
+++ b/gateway/slash_commands.py
@@ -3044,13 +3044,44 @@ class GatewaySlashCommandsMixin:
         # Parse args: either a focus topic (full compress) or the
         # boundary-aware "here [N]" form (partial compress).
         from hermes_cli.partial_compress import (
+            extract_compress_flags,
             parse_partial_compress_args,
             rejoin_compressed_head_and_tail,
             split_history_for_partial_compress,
+            summarize_compress_preview,
         )
         _raw_args = (event.get_command_args() or "").strip()
+        # Strip --preview/--dry-run/--aggressive before positional parsing
+        # so the flags coexist with 'here [N]' / focus-topic forms.
+        _raw_args, _preview, _aggressive = extract_compress_flags(_raw_args)
         partial, keep_last, focus_topic = parse_partial_compress_args(_raw_args)
 
+        _agg_note = ""
+        if _aggressive:
+            # LLM-free hard truncation is not supported on this surface —
+            # it would need its own transcript-persistence branch outside
+            # the guarded _compress_context rotation machinery (#44794).
+            _agg_note = t("gateway.compress.aggressive_unsupported")
+            if not _preview:
+                return _agg_note
+
+        if _preview:
+            # Report what WOULD be compressed — no agent, no writes.
+            from agent.model_metadata import estimate_request_tokens_rough
+            _pv_msgs = [
+                {"role": m.get("role"), "content": m.get("content")}
+                for m in history
+                if m.get("role") in {"user", "assistant"} and m.get("content")
+            ]
+            approx_tokens = estimate_request_tokens_rough(_pv_msgs)
+            report = summarize_compress_preview(
+                _pv_msgs, partial, keep_last, focus_topic, approx_tokens
+            )
+            lines = [f"🗜️ {line}" for line in report["lines"]]
+            if _aggressive:
+                lines.append(_agg_note)
+            return "\n".join(lines)
+
         try:
             from run_agent import AIAgent
             from agent.manual_compression_feedback import summarize_manual_compression
diff --git a/hermes_cli/commands.py b/hermes_cli/commands.py
index fc8c0a1da..7a8775d26 100644
--- a/hermes_cli/commands.py
+++ b/hermes_cli/commands.py
@@ -88,8 +88,8 @@ COMMAND_REGISTRY: list[CommandDef] = [
                args_hint="<platform>", cli_only=True),
     CommandDef("branch", "Branch the current session (explore a different path)", "Session",
                aliases=("fork",), args_hint="[name]"),
-    CommandDef("compress", "Compress conversation context (add 'here [N]' to keep recent N turns)", "Session",
-               args_hint="[here [N] | focus topic]"),
+    CommandDef("compress", "Compress conversation context (add 'here [N]' to keep recent N turns; --preview shows what would happen)", "Session",
+               aliases=("compact",), args_hint="[here [N] | focus topic | --preview|--dry-run]"),
     CommandDef("rollback", "List or restore filesystem checkpoints", "Session",
                args_hint="[number]"),
     CommandDef("snapshot", "Create or restore state snapshots of Hermes config/state", "Session",
diff --git a/hermes_cli/partial_compress.py b/hermes_cli/partial_compress.py
index dc1115d9f..129a9fc6b 100644
--- a/hermes_cli/partial_compress.py
+++ b/hermes_cli/partial_compress.py
@@ -108,6 +108,95 @@ def parse_partial_compress_args(
     return False, DEFAULT_KEEP_LAST, text or None
 
 
+def extract_compress_flags(raw_args: str) -> Tuple[str, bool, bool]:
+    """Strip ``--preview``/``--dry-run``/``--aggressive`` flags from the
+    argument string after ``/compress`` (or its ``/compact`` alias).
+
+    Flags may appear anywhere and coexist with the positional forms
+    (``here [N]``, ``--keep N``, or a focus topic); the returned
+    remainder is what :func:`parse_partial_compress_args` should see.
+
+    Returns ``(remaining_args, preview, aggressive_requested)``:
+
+    * ``preview`` — True when ``--preview`` or ``--dry-run`` was given.
+      The caller must report what WOULD be compressed (message counts,
+      token estimate, boundary) and make **no changes**.
+    * ``aggressive_requested`` — True when ``--aggressive`` was given.
+      The current surfaces do not implement an LLM-free hard-truncate
+      path (it would need its own transcript-persistence branch outside
+      the guarded ``_compress_context`` rotation machinery), so callers
+      surface a "not supported" note instead of silently treating the
+      flag as a focus topic.
+    """
+    preview = False
+    aggressive = False
+    kept: List[str] = []
+    for tok in (raw_args or "").split():
+        low = tok.lower()
+        if low in ("--preview", "--dry-run", "--dryrun"):
+            preview = True
+        elif low == "--aggressive":
+            aggressive = True
+        else:
+            kept.append(tok)
+    return " ".join(kept), preview, aggressive
+
+
+def summarize_compress_preview(
+    history: List[Dict[str, Any]],
+    partial: bool,
+    keep_last: int,
+    focus_topic: Optional[str],
+    approx_tokens: int,
+) -> Dict[str, Any]:
+    """Build the ``/compress --preview`` report — pure, no side effects.
+
+    Shared by the CLI (``cli.py::_manual_compress``) and the gateway
+    (``gateway/slash_commands.py::_handle_compress_command``) so both
+    surfaces report the same numbers the real run would use.
+
+    Returns a dict with ``head_count``/``tail_count``/``lines`` where
+    ``lines`` is a ready-to-print list of report strings.
+    """
+    total = len(history)
+    head = list(history)
+    tail: List[Dict[str, Any]] = []
+    effective_partial = partial
+    if partial:
+        head, tail = split_history_for_partial_compress(history, keep_last)
+        if not tail:
+            # Same degenerate-split fallback the real run applies.
+            effective_partial = False
+            head, tail = list(history), []
+
+    lines = [
+        "Preview — no changes made.",
+        f"Would compress {len(head)} of {total} message(s) "
+        f"(~{approx_tokens:,} tokens currently in context).",
+    ]
+    if effective_partial:
+        lines.append(
+            f"Boundary: keeping the last {keep_last} exchange(s) "
+            f"({len(tail)} message(s)) verbatim."
+        )
+    elif partial:
+        lines.append(
+            "Boundary: 'here' split would keep everything — "
+            "falling back to full compression."
+        )
+    if focus_topic:
+        lines.append(f'Focus topic: "{focus_topic}"')
+    lines.append("Run the command again without --preview to apply.")
+
+    return {
+        "head_count": len(head),
+        "tail_count": len(tail),
+        "total": total,
+        "partial": effective_partial,
+        "lines": lines,
+    }
+
+
 def _coerce_keep(value: str) -> int:
     """Parse a keep-count token, clamping to [1, MAX_KEEP_LAST]."""
     try:
diff --git a/locales/af.yaml b/locales/af.yaml
index a29f97dbc..18dd53058 100644
--- a/locales/af.yaml
+++ b/locales/af.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Nie genoeg gesprek om saam te pers nie (ten minste 4 boodskappe nodig)."
     no_provider:           "Geen verskaffer opgestel nie -- kan nie saampers nie."
     nothing_to_do:         "Niks om saam te pers nie (die transkripsie is steeds heeltemal beskermde konteks)."
+    aggressive_unsupported: "--aggressive word nie ondersteun nie; gebruik '/compress here [N]' om net onlangse uitruilings te behou, of /undo om beurte te verwyder."
     focus_line:            "Fokus: \"{topic}\""
     summary_failed:        "⚠️ Opsomming kon nie gegenereer word nie ({error}). {count} historiese boodskap(pe) is verwyder en met 'n plekhouer vervang; vroeëre konteks kan nie meer herstel word nie. Oorweeg om jou auxiliary.compression-modelopstelling na te gaan."
     aborted:               "⚠️ Kompressie gestaak ({error}). Geen boodskappe is laat val nie — die gesprek is onveranderd. Voer /compress uit om weer te probeer, /reset vir 'n skoon sessie, of kyk na jou auxiliary.compression-modelkonfigurasie."
diff --git a/locales/de.yaml b/locales/de.yaml
index db6174f42..fed360785 100644
--- a/locales/de.yaml
+++ b/locales/de.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Nicht genug Konversation zum Komprimieren (mindestens 4 Nachrichten erforderlich)."
     no_provider:           "Kein Anbieter konfiguriert — Komprimierung nicht möglich."
     nothing_to_do:         "Noch nichts zu komprimieren (das Transkript ist weiterhin vollständig geschützter Kontext)."
+    aggressive_unsupported: "--aggressive wird nicht unterstützt; verwende '/compress here [N]', um nur die letzten Austausche zu behalten, oder /undo, um Beiträge zu entfernen."
     focus_line:            "Fokus: \"{topic}\""
     summary_failed:        "⚠️ Zusammenfassungsgenerierung fehlgeschlagen ({error}). {count} historische Nachricht(en) wurden entfernt und durch einen Platzhalter ersetzt; früherer Kontext ist nicht mehr wiederherstellbar. Überprüfen Sie die Konfiguration des auxiliary.compression-Modells."
     aborted:               "⚠️ Komprimierung abgebrochen ({error}). Keine Nachrichten wurden entfernt — die Konversation ist unverändert. Führe /compress aus, um es erneut zu versuchen, /reset für eine neue Sitzung, oder prüfe deine auxiliary.compression-Modellkonfiguration."
diff --git a/locales/en.yaml b/locales/en.yaml
index 9a9bf2067..da2610be9 100644
--- a/locales/en.yaml
+++ b/locales/en.yaml
@@ -103,6 +103,7 @@ gateway:
     not_enough:            "Not enough conversation to compress (need at least 4 messages)."
     no_provider:           "No provider configured -- cannot compress."
     nothing_to_do:         "Nothing to compress yet (the transcript is still all protected context)."
+    aggressive_unsupported: "--aggressive is not supported; use '/compress here [N]' to keep only recent exchanges, or /undo to drop turns."
     focus_line:            "Focus: \"{topic}\""
     summary_failed:        "⚠️ Summary generation failed ({error}). {count} historical message(s) were removed and replaced with a placeholder; earlier context is no longer recoverable. Consider checking your auxiliary.compression model configuration."
     aborted:               "⚠️ Compression aborted ({error}). No messages were dropped — conversation is unchanged. Run /compress to retry, /reset for a clean session, or check your auxiliary.compression model configuration."
diff --git a/locales/es.yaml b/locales/es.yaml
index e23e53f56..518a4b793 100644
--- a/locales/es.yaml
+++ b/locales/es.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "No hay suficiente conversación para comprimir (se necesitan al menos 4 mensajes)."
     no_provider:           "No hay proveedor configurado — no se puede comprimir."
     nothing_to_do:         "Aún no hay nada que comprimir (la transcripción sigue siendo todo contexto protegido)."
+    aggressive_unsupported: "--aggressive no es compatible; usa '/compress here [N]' para conservar solo los intercambios recientes, o /undo para eliminar turnos."
     focus_line:            "Enfoque: \"{topic}\""
     summary_failed:        "⚠️ Falló la generación del resumen ({error}). Se eliminaron {count} mensaje(s) históricos y se reemplazaron por un marcador; el contexto anterior ya no se puede recuperar. Considera revisar la configuración del modelo auxiliary.compression."
     aborted:               "⚠️ Compresión abortada ({error}). No se eliminó ningún mensaje — la conversación está intacta. Ejecuta /compress para reintentar, /reset para una sesión limpia, o revisa la configuración de tu modelo auxiliary.compression."
diff --git a/locales/fr.yaml b/locales/fr.yaml
index 7fb48aaa6..f6730ccdb 100644
--- a/locales/fr.yaml
+++ b/locales/fr.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Conversation insuffisante pour la compression (au moins 4 messages nécessaires)."
     no_provider:           "Aucun fournisseur configuré — compression impossible."
     nothing_to_do:         "Rien à compresser pour l'instant (la transcription est encore entièrement du contexte protégé)."
+    aggressive_unsupported: "--aggressive n'est pas pris en charge ; utilisez '/compress here [N]' pour ne conserver que les échanges récents, ou /undo pour supprimer des tours."
     focus_line:            "Focus : \"{topic}\""
     summary_failed:        "⚠️ Échec de la génération du résumé ({error}). {count} message(s) historique(s) ont été supprimés et remplacés par un espace réservé ; le contexte antérieur n'est plus récupérable. Vérifiez la configuration du modèle auxiliary.compression."
     aborted:               "⚠️ Compression interrompue ({error}). Aucun message n'a été supprimé — la conversation est inchangée. Lancez /compress pour réessayer, /reset pour une nouvelle session, ou vérifiez la configuration de votre modèle auxiliary.compression."
diff --git a/locales/ga.yaml b/locales/ga.yaml
index 5ca740fca..26ede56fd 100644
--- a/locales/ga.yaml
+++ b/locales/ga.yaml
@@ -92,6 +92,7 @@ gateway:
     not_enough:            "Níl go leor comhrá le dlúthú (teastaíonn 4 theachtaireacht ar a laghad)."
     no_provider:           "Níl aon soláthraí cumraithe — ní féidir dlúthú."
     nothing_to_do:         "Níl aon rud le dlúthú fós (tá an traschríbhinn fós uile mar chomhthéacs cosanta)."
+    aggressive_unsupported: "Ní thacaítear le --aggressive; úsáid '/compress here [N]' chun na malartuithe is déanaí amháin a choinneáil, nó /undo chun sealanna a scriosadh."
     focus_line:            "Fócas: \"{topic}\""
     summary_failed:        "⚠️ Theip ar ghiniúint achoimre ({error}). Baineadh {count} teachtaireacht stairiúil agus cuireadh ionadaí ina n-áit; níl an comhthéacs roimhe seo in-aisghabhála a thuilleadh. Smaoinigh ar an gcumraíocht auxiliary.compression a sheiceáil."
     aborted:               "⚠️ Cuireadh deireadh leis an dlúthú ({error}). Níor baineadh aon teachtaireacht — tá an comhrá gan athrú. Rith /compress chun é a thriail arís, /reset le haghaidh seisiún glan, nó seiceáil do chumraíocht samhla auxiliary.compression."
diff --git a/locales/hu.yaml b/locales/hu.yaml
index 02a877724..b98272b9f 100644
--- a/locales/hu.yaml
+++ b/locales/hu.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Nincs elég beszélgetés a tömörítéshez (legalább 4 üzenet kell)."
     no_provider:           "Nincs konfigurált szolgáltató — nem lehet tömöríteni."
     nothing_to_do:         "Még nincs mit tömöríteni (a teljes átirat még védett kontextus)."
+    aggressive_unsupported: "A --aggressive nem támogatott; használd a '/compress here [N]' parancsot, hogy csak a legutóbbi váltásokat tartsd meg, vagy a /undo parancsot körök törléséhez."
     focus_line:            "Fókusz: \"{topic}\""
     summary_failed:        "⚠️ Az összefoglaló generálása sikertelen ({error}). {count} korábbi üzenet eltávolítva és helykitöltővel helyettesítve; a korábbi kontextus már nem helyreállítható. Érdemes ellenőrizni az auxiliary.compression modell konfigurációját."
     aborted:               "⚠️ Tömörítés megszakítva ({error}). Egyetlen üzenet sem lett eldobva — a beszélgetés változatlan. Futtass /compress parancsot az újrapróbálkozáshoz, /reset egy új munkamenethez, vagy ellenőrizd az auxiliary.compression modell konfigurációt."
diff --git a/locales/it.yaml b/locales/it.yaml
index d3bff53b5..5f0711e84 100644
--- a/locales/it.yaml
+++ b/locales/it.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Conversazione insufficiente da comprimere (servono almeno 4 messaggi)."
     no_provider:           "Nessun provider configurato — impossibile comprimere."
     nothing_to_do:         "Niente da comprimere per ora (la trascrizione è ancora tutta contesto protetto)."
+    aggressive_unsupported: "--aggressive non è supportato; usa '/compress here [N]' per conservare solo gli scambi recenti, oppure /undo per rimuovere i turni."
     focus_line:            "Focus: \"{topic}\""
     summary_failed:        "⚠️ Generazione del riepilogo non riuscita ({error}). {count} messaggio/i storico/i sono stati rimossi e sostituiti con un segnaposto; il contesto precedente non è più recuperabile. Considera di controllare la configurazione del modello auxiliary.compression."
     aborted:               "⚠️ Compressione interrotta ({error}). Nessun messaggio è stato eliminato — la conversazione è invariata. Esegui /compress per riprovare, /reset per una nuova sessione, o controlla la configurazione del modello auxiliary.compression."
diff --git a/locales/ja.yaml b/locales/ja.yaml
index 7bce7e41e..02d4df8ef 100644
--- a/locales/ja.yaml
+++ b/locales/ja.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "圧縮するための会話が不十分です (少なくとも 4 件のメッセージが必要)。"
     no_provider:           "プロバイダーが構成されていません — 圧縮できません。"
     nothing_to_do:         "まだ圧縮するものがありません (トランスクリプトはすべて保護されたコンテキストのままです)。"
+    aggressive_unsupported: "--aggressive はサポートされていません。'/compress here [N]' で直近のやり取りだけを残すか、/undo でターンを削除してください。"
     focus_line:            "フォーカス: \"{topic}\""
     summary_failed:        "⚠️ 要約の生成に失敗しました ({error})。{count} 件の履歴メッセージが削除され、プレースホルダーに置き換えられました。以前のコンテキストは復元できません。auxiliary.compression モデルの設定を確認してください。"
     aborted:               "⚠️ 圧縮が中止されました ({error})。メッセージは削除されていません — 会話はそのままです。再試行するには /compress、新しいセッションを開始するには /reset を実行するか、auxiliary.compression モデル設定を確認してください。"
diff --git a/locales/ko.yaml b/locales/ko.yaml
index 9fcce0d9a..5404ec36c 100644
--- a/locales/ko.yaml
+++ b/locales/ko.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "압축할 대화가 충분하지 않습니다 (최소 4개의 메시지가 필요합니다)."
     no_provider:           "구성된 제공자가 없습니다 -- 압축할 수 없습니다."
     nothing_to_do:         "아직 압축할 내용이 없습니다 (대화 내용이 모두 보호된 컨텍스트입니다)."
+    aggressive_unsupported: "--aggressive는 지원되지 않습니다. '/compress here [N]'으로 최근 대화만 유지하거나 /undo로 턴을 삭제하세요."
     focus_line:            "초점: \"{topic}\""
     summary_failed:        "⚠️ 요약 생성에 실패했습니다 ({error}). 과거 메시지 {count}개가 제거되어 자리표시자로 대체되었으며, 이전 컨텍스트는 더 이상 복구할 수 없습니다. auxiliary.compression 모델 설정을 확인해 보세요."
     aborted:               "⚠️ 압축이 중단되었습니다 ({error}). 메시지가 삭제되지 않았으며 대화는 그대로 유지됩니다. 다시 시도하려면 /compress를 실행하거나, 새 세션을 시작하려면 /reset을 사용하거나, auxiliary.compression 모델 설정을 확인하세요."
diff --git a/locales/pt.yaml b/locales/pt.yaml
index a406e3de7..ee9b95bb9 100644
--- a/locales/pt.yaml
+++ b/locales/pt.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Não há conversa suficiente para comprimir (são necessárias pelo menos 4 mensagens)."
     no_provider:           "Nenhum fornecedor configurado — não é possível comprimir."
     nothing_to_do:         "Ainda não há nada para comprimir (a transcrição continua a ser todo o contexto protegido)."
+    aggressive_unsupported: "--aggressive não é suportado; usa '/compress here [N]' para manter apenas as trocas recentes, ou /undo para remover turnos."
     focus_line:            "Foco: \"{topic}\""
     summary_failed:        "⚠️ Falha ao gerar o resumo ({error}). {count} mensagem(ns) histórica(s) foram removidas e substituídas por um marcador; o contexto anterior já não pode ser recuperado. Considera verificar a configuração do modelo auxiliary.compression."
     aborted:               "⚠️ Compressão abortada ({error}). Nenhuma mensagem foi removida — a conversa está inalterada. Executa /compress para tentar de novo, /reset para uma sessão nova, ou verifica a configuração do modelo auxiliary.compression."
diff --git a/locales/ru.yaml b/locales/ru.yaml
index 995335b28..3628f1e25 100644
--- a/locales/ru.yaml
+++ b/locales/ru.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Недостаточно беседы для сжатия (нужно минимум 4 сообщения)."
     no_provider:           "Провайдер не настроен — сжатие невозможно."
     nothing_to_do:         "Пока нечего сжимать (стенограмма всё ещё полностью является защищённым контекстом)."
+    aggressive_unsupported: "--aggressive не поддерживается; используйте '/compress here [N]', чтобы сохранить только недавние обмены, или /undo, чтобы удалить ходы."
     focus_line:            "Фокус: \"{topic}\""
     summary_failed:        "⚠️ Не удалось сгенерировать сводку ({error}). {count} историч. сообщений было удалено и заменено заполнителем; предыдущий контекст больше нельзя восстановить. Проверьте конфигурацию модели auxiliary.compression."
     aborted:               "⚠️ Сжатие прервано ({error}). Сообщения не были удалены — разговор не изменился. Запустите /compress для повторной попытки, /reset для новой сессии или проверьте конфигурацию модели auxiliary.compression."
diff --git a/locales/tr.yaml b/locales/tr.yaml
index 5e67a951e..32f1d6b72 100644
--- a/locales/tr.yaml
+++ b/locales/tr.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Sıkıştırmak için yeterli konuşma yok (en az 4 mesaj gerekli)."
     no_provider:           "Yapılandırılmış sağlayıcı yok — sıkıştırılamıyor."
     nothing_to_do:         "Henüz sıkıştırılacak bir şey yok (transkript hâlâ tamamen korunan bağlam)."
+    aggressive_unsupported: "--aggressive desteklenmiyor; yalnızca son alışverişleri tutmak için '/compress here [N]' kullanın veya turları silmek için /undo kullanın."
     focus_line:            "Odak: \"{topic}\""
     summary_failed:        "⚠️ Özet oluşturma başarısız ({error}). {count} geçmiş mesaj kaldırılıp yer tutucuyla değiştirildi; önceki bağlam artık kurtarılamaz. auxiliary.compression model yapılandırmanızı kontrol edin."
     aborted:               "⚠️ Sıkıştırma iptal edildi ({error}). Hiçbir mesaj silinmedi — konuşma değişmedi. Tekrar denemek için /compress, temiz bir oturum için /reset komutunu çalıştırın veya auxiliary.compression model yapılandırmanızı kontrol edin."
diff --git a/locales/uk.yaml b/locales/uk.yaml
index 8e9123450..af43c7e8d 100644
--- a/locales/uk.yaml
+++ b/locales/uk.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "Недостатньо розмови для стиснення (потрібно щонайменше 4 повідомлення)."
     no_provider:           "Постачальника не налаштовано — неможливо стиснути."
     nothing_to_do:         "Поки що немає що стискати (стенограма все ще є повністю захищеним контекстом)."
+    aggressive_unsupported: "--aggressive не підтримується; використовуйте '/compress here [N]', щоб зберегти лише останні обміни, або /undo, щоб видалити ходи."
     focus_line:            "Фокус: \"{topic}\""
     summary_failed:        "⚠️ Не вдалося згенерувати зведення ({error}). {count} історичних повідомлень було видалено та замінено заповнювачем; попередній контекст більше не можна відновити. Перевірте конфігурацію моделі auxiliary.compression."
     aborted:               "⚠️ Стиснення скасовано ({error}). Жодне повідомлення не було видалено — розмова не змінилася. Виконайте /compress, щоб повторити спробу, /reset для нової сесії, або перевірте конфігурацію моделі auxiliary.compression."
diff --git a/locales/zh-hant.yaml b/locales/zh-hant.yaml
index 1190e23d0..3f34fd263 100644
--- a/locales/zh-hant.yaml
+++ b/locales/zh-hant.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "對話內容不足，無法壓縮（至少需要 4 則訊息）。"
     no_provider:           "未設定提供方 — 無法壓縮。"
     nothing_to_do:         "目前沒有可壓縮的內容（對話記錄仍全部為受保護的上下文）。"
+    aggressive_unsupported: "不支援 --aggressive；請使用 '/compress here [N]' 只保留最近的對話，或使用 /undo 刪除回合。"
     focus_line:            "聚焦：\"{topic}\""
     summary_failed:        "⚠️ 摘要產生失敗（{error}）。{count} 則歷史訊息已被移除並以佔位符取代；先前的上下文已無法復原。建議檢查 auxiliary.compression 模型設定。"
     aborted:               "⚠️ 壓縮已中止 ({error})。未刪除任何訊息 — 對話保持不變。執行 /compress 重試，執行 /reset 開始新工作階段，或檢查你的 auxiliary.compression 模型設定。"
diff --git a/locales/zh.yaml b/locales/zh.yaml
index e8444394a..6183612b5 100644
--- a/locales/zh.yaml
+++ b/locales/zh.yaml
@@ -88,6 +88,7 @@ gateway:
     not_enough:            "对话内容不足，无法压缩（至少需要 4 条消息）。"
     no_provider:           "未配置提供方 — 无法压缩。"
     nothing_to_do:         "暂无可压缩内容（对话记录仍全部为受保护上下文）。"
+    aggressive_unsupported: "不支持 --aggressive；请使用 '/compress here [N]' 只保留最近的对话，或使用 /undo 删除回合。"
     focus_line:            "聚焦：\"{topic}\""
     summary_failed:        "⚠️ 摘要生成失败（{error}）。{count} 条历史消息已被移除并替换为占位符；之前的上下文已无法恢复。建议检查 auxiliary.compression 模型配置。"
     aborted:               "⚠️ 压缩已中止 ({error})。未删除任何消息 — 对话保持不变。运行 /compress 重试，运行 /reset 开始新会话，或检查你的 auxiliary.compression 模型配置。"
diff --git a/scripts/release.py b/scripts/release.py
index 0c5a481e9..21af630ce 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -45,6 +45,7 @@ ACP_REGISTRY_MANIFEST = REPO_ROOT / "acp_registry" / "agent.json"
 
 # Auto-extracted from noreply emails + manual overrides
 AUTHOR_MAP = {
+    "louis@letsfive.io": "Mibayy",  # PR #3243 salvage (/compact alias + preview/aggressive flags for /compress)
     "ai-lab@foxmail.com": "CrazyBoyM",  # PR #55828 salvage (image_gen openai-codex: wire image-to-image / reference-image editing via Codex Responses input_image parts; magic-byte + read-guard + 25MB-cap + clamp-to-16 hardening)
     "r0gersm1th@users.noreply.github.com": "r0gersm1th",  # PR #3219 salvage (whatsapp bridge: resolve LID sender IDs to phone numbers in the message payload so phone-based allowlists match; commit authored by collaborator r0gersm1th, PR by @ajmeese7)
     "louis@letsfive.io": "Mibayy",  # PR #3296 salvage (status: provider label honors config.yaml model.base_url, not just OPENAI_BASE_URL env)
diff --git a/tests/cli/test_compress_flags.py b/tests/cli/test_compress_flags.py
new file mode 100644
index 000000000..be7ddcc0c
--- /dev/null
+++ b/tests/cli/test_compress_flags.py
@@ -0,0 +1,155 @@
+"""Tests for /compress --preview/--dry-run/--aggressive flags and the
+/compact alias (PR #3243 salvage).
+
+Covers the pure helpers in ``hermes_cli.partial_compress`` plus alias
+resolution in the command registry. The CLI and gateway surfaces both
+route through these helpers, so the flag semantics are pinned here once.
+"""
+
+from hermes_cli.commands import COMMANDS, resolve_command
+from hermes_cli.partial_compress import (
+    DEFAULT_KEEP_LAST,
+    extract_compress_flags,
+    parse_partial_compress_args,
+    summarize_compress_preview,
+)
+
+
+def _history(n_pairs: int) -> list[dict[str, str]]:
+    h: list[dict[str, str]] = []
+    for i in range(n_pairs):
+        h.append({"role": "user", "content": f"u{i}"})
+        h.append({"role": "assistant", "content": f"a{i}"})
+    return h
+
+
+# ── /compact alias resolution ─────────────────────────────────────────
+
+
+def test_compact_resolves_to_compress():
+    cmd = resolve_command("compact")
+    assert cmd is not None
+    assert cmd.name == "compress"
+    assert "compact" in cmd.aliases
+
+
+def test_compact_alias_with_slash():
+    cmd = resolve_command("/compact")
+    assert cmd is not None and cmd.name == "compress"
+
+
+def test_compact_listed_in_flat_commands():
+    assert "/compact" in COMMANDS
+    assert "alias for /compress" in COMMANDS["/compact"]
+
+
+def test_compress_args_hint_documents_preview():
+    cmd = resolve_command("compress")
+    assert cmd is not None
+    assert "--preview" in (cmd.args_hint or "")
+
+
+# ── extract_compress_flags ────────────────────────────────────────────
+
+
+def test_no_flags_passthrough():
+    rest, preview, aggressive = extract_compress_flags("here 3")
+    assert rest == "here 3"
+    assert preview is False
+    assert aggressive is False
+
+
+def test_preview_flag_stripped():
+    rest, preview, aggressive = extract_compress_flags("--preview")
+    assert rest == ""
+    assert preview is True
+    assert aggressive is False
+
+
+def test_dry_run_is_preview():
+    for form in ("--dry-run", "--dryrun", "--DRY-RUN"):
+        _, preview, _ = extract_compress_flags(form)
+        assert preview is True, form
+
+
+def test_aggressive_flag_detected():
+    rest, preview, aggressive = extract_compress_flags("--aggressive")
+    assert rest == ""
+    assert preview is False
+    assert aggressive is True
+
+
+def test_flags_coexist_with_here_form():
+    rest, preview, aggressive = extract_compress_flags("--preview here 4")
+    assert rest == "here 4"
+    assert preview is True
+    partial, keep, focus = parse_partial_compress_args(rest)
+    assert partial is True and keep == 4 and focus is None
+
+
+def test_flags_coexist_with_focus_topic():
+    rest, preview, _ = extract_compress_flags("database schema --dry-run")
+    assert rest == "database schema"
+    assert preview is True
+    partial, _, focus = parse_partial_compress_args(rest)
+    assert partial is False and focus == "database schema"
+
+
+def test_aggressive_dry_run_combo():
+    rest, preview, aggressive = extract_compress_flags("--aggressive --dry-run")
+    assert rest == ""
+    assert preview is True and aggressive is True
+
+
+def test_empty_args():
+    rest, preview, aggressive = extract_compress_flags("")
+    assert rest == "" and preview is False and aggressive is False
+
+
+# ── summarize_compress_preview ────────────────────────────────────────
+
+
+def test_preview_full_compress_counts():
+    hist = _history(5)
+    report = summarize_compress_preview(hist, False, DEFAULT_KEEP_LAST, None, 1234)
+    assert report["head_count"] == 10
+    assert report["tail_count"] == 0
+    assert report["total"] == 10
+    assert report["partial"] is False
+    joined = "\n".join(report["lines"])
+    assert "no changes made" in joined.lower()
+    assert "10 of 10" in joined
+    assert "1,234" in joined
+
+
+def test_preview_partial_boundary_counts():
+    hist = _history(5)
+    report = summarize_compress_preview(hist, True, 2, None, 999)
+    # Keeping last 2 exchanges = 4 tail messages, 6 head messages.
+    assert report["head_count"] == 6
+    assert report["tail_count"] == 4
+    assert report["partial"] is True
+    joined = "\n".join(report["lines"])
+    assert "last 2 exchange" in joined
+
+
+def test_preview_partial_degenerate_falls_back_to_full():
+    hist = _history(2)  # keep_last=5 would swallow everything
+    report = summarize_compress_preview(hist, True, 5, None, 100)
+    assert report["partial"] is False
+    assert report["head_count"] == 4
+    joined = "\n".join(report["lines"])
+    assert "falling back to full compression" in joined
+
+
+def test_preview_includes_focus_topic():
+    hist = _history(4)
+    report = summarize_compress_preview(hist, False, DEFAULT_KEEP_LAST, "db schema", 50)
+    assert 'Focus topic: "db schema"' in "\n".join(report["lines"])
+
+
+def test_preview_is_side_effect_free():
+    hist = _history(4)
+    before = [dict(m) for m in hist]
+    summarize_compress_preview(hist, True, 1, None, 10)
+    assert hist == before
diff --git a/tests/gateway/test_compress_preview.py b/tests/gateway/test_compress_preview.py
new file mode 100644
index 000000000..62eeda06d
--- /dev/null
+++ b/tests/gateway/test_compress_preview.py
@@ -0,0 +1,120 @@
+"""Tests for gateway /compress --preview/--dry-run/--aggressive flags
+(PR #3243 salvage).
+
+The preview path must return a report WITHOUT building an agent or
+touching the transcript; --aggressive must return an explanatory
+message rather than being mis-parsed as a focus topic.
+"""
+
+from datetime import datetime
+from unittest.mock import MagicMock
+
+import pytest
+
+from gateway.config import GatewayConfig, Platform, PlatformConfig
+from gateway.platforms.base import MessageEvent
+from gateway.session import SessionEntry, SessionSource, build_session_key
+
+
+def _make_source() -> SessionSource:
+    return SessionSource(
+        platform=Platform.TELEGRAM,
+        user_id="u1",
+        chat_id="c1",
+        user_name="tester",
+        chat_type="dm",
+    )
+
+
+def _make_event(text: str) -> MessageEvent:
+    return MessageEvent(text=text, source=_make_source(), message_id="m1")
+
+
+def _make_history(n_pairs: int = 3) -> list[dict[str, str]]:
+    h: list[dict[str, str]] = []
+    for i in range(n_pairs):
+        h.append({"role": "user", "content": f"u{i}"})
+        h.append({"role": "assistant", "content": f"a{i}"})
+    return h
+
+
+def _make_runner(history: list[dict[str, str]]):
+    from gateway.run import GatewayRunner
+
+    runner = object.__new__(GatewayRunner)
+    runner.config = GatewayConfig(
+        platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="***")}
+    )
+    session_entry = SessionEntry(
+        session_key=build_session_key(_make_source()),
+        session_id="sess-1",
+        created_at=datetime.now(),
+        updated_at=datetime.now(),
+        platform=Platform.TELEGRAM,
+        chat_type="dm",
+    )
+    runner.session_store = MagicMock()
+    runner.session_store.get_or_create_session.return_value = session_entry
+    runner.session_store.load_transcript.return_value = history
+    runner.session_store.rewrite_transcript = MagicMock()
+    runner.session_store.update_session = MagicMock()
+    runner.session_store._save = MagicMock()
+    runner._session_db = None
+    return runner
+
+
+@pytest.mark.asyncio
+async def test_preview_reports_without_mutating():
+    runner = _make_runner(_make_history(3))
+    result = await runner._handle_compress_command(_make_event("/compress --preview"))
+    assert "no changes made" in result.lower()
+    assert "6 of 6" in result
+    runner.session_store.rewrite_transcript.assert_not_called()
+    runner.session_store.update_session.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_dry_run_alias_matches_preview():
+    runner = _make_runner(_make_history(3))
+    result = await runner._handle_compress_command(_make_event("/compress --dry-run"))
+    assert "no changes made" in result.lower()
+    runner.session_store.rewrite_transcript.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_preview_with_here_boundary():
+    runner = _make_runner(_make_history(4))
+    result = await runner._handle_compress_command(
+        _make_event("/compress --preview here 2")
+    )
+    assert "last 2 exchange" in result
+    assert "4 of 8" in result
+    runner.session_store.rewrite_transcript.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_aggressive_returns_unsupported_note_without_mutating():
+    runner = _make_runner(_make_history(3))
+    result = await runner._handle_compress_command(
+        _make_event("/compress --aggressive")
+    )
+    assert "--aggressive is not supported" in result
+    runner.session_store.rewrite_transcript.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_aggressive_dry_run_shows_preview_plus_note():
+    runner = _make_runner(_make_history(3))
+    result = await runner._handle_compress_command(
+        _make_event("/compress --aggressive --dry-run")
+    )
+    assert "no changes made" in result.lower()
+    assert "--aggressive is not supported" in result
+    runner.session_store.rewrite_transcript.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_preview_still_requires_enough_history():
+    runner = _make_runner(_make_history(1))  # only 2 messages
+    result = await runner._handle_compress_command(_make_event("/compress --preview"))
+    assert "not enough" in result.lower()