diff --git a/gateway/cwd_placeholder.py b/gateway/cwd_placeholder.py
new file mode 100644
index 00000000000..f102595e337
--- /dev/null
+++ b/gateway/cwd_placeholder.py
@@ -0,0 +1,49 @@
+"""Resolve gateway ``terminal.cwd`` placeholder values to ``TERMINAL_CWD``.
+
+When ``terminal.cwd`` is unset or a placeholder (``.``, ``auto``, ``cwd``),
+the gateway must not blindly map host ``Path.home()`` into container backends.
+Docker with workspace mounting still needs an explicit host path signal
+(``MESSAGING_CWD`` or an absolute config path) for ``terminal_tool`` to map
+``/host/project`` → ``/workspace``.
+"""
+
+from __future__ import annotations
+
+CWD_PLACEHOLDERS = frozenset({".", "auto", "cwd"})
+
+
+def _truthy_env(value: str | None) -> bool:
+    return (value or "").strip().lower() in {"true", "1", "yes"}
+
+
+def resolve_placeholder_terminal_cwd(
+    *,
+    configured_cwd: str,
+    terminal_backend: str,
+    messaging_cwd: str | None,
+    docker_mount_cwd_to_workspace: bool,
+    home_fallback: str,
+) -> str | None:
+    """Return the ``TERMINAL_CWD`` value to set, or ``None`` to leave it unset.
+
+    Cases:
+      - **local** + placeholder → ``MESSAGING_CWD`` or ``home_fallback``
+      - **docker** + placeholder + mount on + host ``MESSAGING_CWD`` → host path
+        (for ``terminal_tool`` ``/workspace`` mapping)
+      - **docker** + placeholder + mount off → ``None`` (sandbox default)
+      - other non-local backends + placeholder → ``None``
+    """
+    if configured_cwd and configured_cwd not in CWD_PLACEHOLDERS:
+        return configured_cwd
+
+    backend = (terminal_backend or "local").strip().lower()
+    if backend == "local":
+        messaging = (messaging_cwd or "").strip()
+        return messaging or home_fallback
+
+    if backend == "docker" and docker_mount_cwd_to_workspace:
+        messaging = (messaging_cwd or "").strip()
+        if messaging and messaging not in CWD_PLACEHOLDERS:
+            return messaging
+
+    return None
diff --git a/gateway/run.py b/gateway/run.py
index 7736474e591..b08650d08ac 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -1660,16 +1660,27 @@ os.environ["HERMES_EXEC_ASK"] = "1"
 
 # Set terminal working directory for messaging platforms.
 # config.yaml terminal.cwd is the canonical source (bridged to TERMINAL_CWD
-# by the config bridge above).  When it's unset or a placeholder, default
-# to home directory.  MESSAGING_CWD is accepted as a backward-compat
-# fallback (deprecated — the warning above tells users to migrate).
+# by the config bridge above).  Placeholder values are resolved per-backend —
+# see gateway/cwd_placeholder.py for the three-case contract (local vs docker
+# mount-off vs docker mount-on).  MESSAGING_CWD is a backward-compat fallback.
+from gateway.cwd_placeholder import CWD_PLACEHOLDERS, resolve_placeholder_terminal_cwd
+
 _configured_cwd = os.environ.get("TERMINAL_CWD", "")
-if not _configured_cwd or _configured_cwd in {".", "auto", "cwd"}:
-    if os.environ.get("TERMINAL_ENV", "").strip().lower() == "ssh":
+if not _configured_cwd or _configured_cwd in CWD_PLACEHOLDERS:
+    _resolved_cwd = resolve_placeholder_terminal_cwd(
+        configured_cwd=_configured_cwd,
+        terminal_backend=os.environ.get("TERMINAL_ENV", ""),
+        messaging_cwd=os.getenv("MESSAGING_CWD"),
+        docker_mount_cwd_to_workspace=os.getenv(
+            "TERMINAL_DOCKER_MOUNT_CWD_TO_WORKSPACE", "false"
+        ).lower()
+        in {"true", "1", "yes"},
+        home_fallback=str(Path.home()),
+    )
+    if _resolved_cwd is None:
         os.environ.pop("TERMINAL_CWD", None)
     else:
-        _fallback = os.getenv("MESSAGING_CWD") or str(Path.home())
-        os.environ["TERMINAL_CWD"] = _fallback
+        os.environ["TERMINAL_CWD"] = _resolved_cwd
 
 from gateway.config import (
     ChannelOverride,