fix(tools): point email home-channel error at EMAIL_HOME_ADDRESS

The no-home-channel error for send_message derived the env var name
generically as <PLATFORM>_HOME_CHANNEL, producing EMAIL_HOME_CHANNEL for
the email platform. But gateway/config.py reads EMAIL_HOME_ADDRESS, so a
user following the error's guidance would set a variable that is never
consulted. Add a per-platform override map so the email hint names the
variable actually read; all other platforms keep the generic hint.

tests/tools/test_send_message_tool.py

@@ -1256,6 +1256,54 @@ class TestParseTargetRefEmail:
         assert _parse_target_ref("slack", "user@example.com")[2] is False
 
 
+class TestEmailHomeChannelErrorHint:
+    """The no-home-channel error for email points at the real env var.
+
+    Email reads its home channel from EMAIL_HOME_ADDRESS (gateway/config.py),
+    not the generic EMAIL_HOME_CHANNEL. The error guidance must name the
+    variable that is actually consulted so users who follow it succeed.
+    """
+
+    def test_email_error_names_email_home_address(self):
+        email_cfg = SimpleNamespace(enabled=True, token="", extra={})
+        config = SimpleNamespace(
+            platforms={Platform.EMAIL: email_cfg},
+            get_home_channel=lambda _platform: None,
+        )
+        with patch("gateway.config.load_gateway_config", return_value=config), \
+             patch("tools.interrupt.is_interrupted", return_value=False):
+            result = json.loads(
+                send_message_tool(
+                    {
+                        "action": "send",
+                        "target": "email",
+                        "message": "hi",
+                    }
+                )
+            )
+        assert "EMAIL_HOME_ADDRESS" in result["error"]
+        assert "EMAIL_HOME_CHANNEL" not in result["error"]
+
+    def test_non_email_platform_keeps_generic_home_channel_hint(self):
+        telegram_cfg = SimpleNamespace(enabled=True, token="***", extra={})
+        config = SimpleNamespace(
+            platforms={Platform.TELEGRAM: telegram_cfg},
+            get_home_channel=lambda _platform: None,
+        )
+        with patch("gateway.config.load_gateway_config", return_value=config), \
+             patch("tools.interrupt.is_interrupted", return_value=False):
+            result = json.loads(
+                send_message_tool(
+                    {
+                        "action": "send",
+                        "target": "telegram",
+                        "message": "hi",
+                    }
+                )
+            )
+        assert "TELEGRAM_HOME_CHANNEL" in result["error"]
+
+
 class TestSendDiscordThreadId:
     """_send_discord uses thread_id when provided."""
 

tools/send_message_tool.py

@@ -44,6 +44,11 @@ _E164_TARGET_RE = re.compile(r"^\s*\+(\d{7,15})\s*$")
 # an explicit target for the email platform, not fall through to channel-name
 # resolution which has no way to resolve a raw address.
 _EMAIL_TARGET_RE = re.compile(r"^\s*[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\s*$")
+# Most platforms read their home channel from "<PLATFORM>_HOME_CHANNEL", but a
+# few diverge. Email reads EMAIL_HOME_ADDRESS (see gateway/config.py), so the
+# generic "<PLATFORM>_HOME_CHANNEL" hint would point users at a variable that is
+# never read. Map the exceptions so the error guidance is actually actionable.
+_HOME_CHANNEL_ENV_OVERRIDES = {"email": "EMAIL_HOME_ADDRESS"}
 _IMAGE_EXTS = {".jpg", ".jpeg", ".png", ".webp", ".gif"}
 _VIDEO_EXTS = {".mp4", ".mov", ".avi", ".mkv", ".3gp"}
 _AUDIO_EXTS = {".ogg", ".opus", ".mp3", ".wav", ".m4a", ".flac"}
@@ -269,10 +274,13 @@ def _handle_send(args):
             chat_id = home.chat_id
             used_home_channel = True
         else:
+            home_env = _HOME_CHANNEL_ENV_OVERRIDES.get(
+                platform_name, f"{platform_name.upper()}_HOME_CHANNEL"
+            )
             return json.dumps({
                 "error": f"No home channel set for {platform_name} to determine where to send the message. "
                 f"Either specify a channel directly with '{platform_name}:CHANNEL_NAME', "
-                f"or set a home channel via: hermes config set {platform_name.upper()}_HOME_CHANNEL <channel_id>"
+                f"or set a home channel via: hermes config set {home_env} <channel_id>"
             })
 
     duplicate_skip = _maybe_skip_cron_duplicate_send(platform_name, chat_id, thread_id)