diff --git a/docs/concepts/agent-workspace.md b/docs/concepts/agent-workspace.md
index 2b0ea5924..edf43e889 100644
--- a/docs/concepts/agent-workspace.md
+++ b/docs/concepts/agent-workspace.md
@@ -16,6 +16,8 @@ sessions.
 resolve relative paths against the workspace, but absolute paths can still reach
 elsewhere on the host unless sandboxing is enabled. If you need isolation, use
 [`agent.sandbox`](/gateway/sandboxing) (and/or per‑agent sandbox config).
+When sandboxing is enabled and `workspaceAccess` is not `"rw"`, tools operate
+inside a sandbox workspace under `~/.clawdbot/sandboxes`, not your host workspace.
 
 ## Default location
 
diff --git a/docs/gateway/configuration.md b/docs/gateway/configuration.md
index abad5bb7a..3125780b4 100644
--- a/docs/gateway/configuration.md
+++ b/docs/gateway/configuration.md
@@ -1473,6 +1473,7 @@ Controls session scoping, idle expiry, reset triggers, and where the session sto
 
 Fields:
 - `mainKey`: direct-chat bucket key (default: `"main"`). Useful when you want to “rename” the primary DM thread without changing `agentId`.
+  - Sandbox note: `agent.sandbox.mode: "non-main"` uses this key to detect the main session. Any session key that does not match `mainKey` (groups/channels) is sandboxed.
 - `agentToAgent.maxPingPongTurns`: max reply-back turns between requester/target (0–5, default 5).
 - `sendPolicy.default`: `allow` or `deny` fallback when no rule matches.
 - `sendPolicy.rules[]`: match by `provider`, `chatType` (`direct|group|room`), or `keyPrefix` (e.g. `cron:`). First deny wins; otherwise allow.
diff --git a/docs/gateway/sandboxing.md b/docs/gateway/sandboxing.md
index 7f2e6ba24..93a629bbe 100644
--- a/docs/gateway/sandboxing.md
+++ b/docs/gateway/sandboxing.md
@@ -31,6 +31,8 @@ Not sandboxed:
 - `"off"`: no sandboxing.
 - `"non-main"`: sandbox only **non-main** sessions (default if you want normal chats on host).
 - `"all"`: every session runs in a sandbox.
+Note: `"non-main"` is based on `session.mainKey` (default `"main"`), not agent id.
+Group/channel sessions use their own keys, so they count as non-main and will be sandboxed.
 
 ## Scope
 `agent.sandbox.scope` controls **how many containers** are created:
diff --git a/docs/gateway/troubleshooting.md b/docs/gateway/troubleshooting.md
index 7d663ccae..43b636892 100644
--- a/docs/gateway/troubleshooting.md
+++ b/docs/gateway/troubleshooting.md
@@ -122,6 +122,19 @@ or state drift because only one workspace is active.
 **Fix:** keep a single active workspace and archive/remove the rest. See
 [Agent workspace](/concepts/agent-workspace#legacy-workspace-folders).
 
+### Main chat running in a sandbox workspace
+
+Symptoms: `pwd` or file tools show `~/.clawdbot/sandboxes/...` even though you
+expected the host workspace.
+
+**Why:** `agent.sandbox.mode: "non-main"` keys off `session.mainKey` (default `"main"`).
+Group/channel sessions use their own keys, so they are treated as non-main and
+get sandbox workspaces.
+
+**Fix options:**
+- If you want host workspaces for an agent: set `routing.agents.<id>.sandbox.mode: "off"`.
+- If you want host workspace access inside sandbox: set `workspaceAccess: "rw"` for that agent.
+
 ### "Agent was aborted"
 
 The agent was interrupted mid-response.
diff --git a/docs/multi-agent-sandbox-tools.md b/docs/multi-agent-sandbox-tools.md
index 58d47cee7..d17ee98f2 100644
--- a/docs/multi-agent-sandbox-tools.md
+++ b/docs/multi-agent-sandbox-tools.md
@@ -252,6 +252,15 @@ The global `agent.workspace` and `agent.sandbox` are still supported for backwar
 
 ---
 
+## Common Pitfall: "non-main"
+
+`sandbox.mode: "non-main"` is based on `session.mainKey` (default `"main"`),
+not the agent id. Group/channel sessions always get their own keys, so they
+are treated as non-main and will be sandboxed. If you want an agent to never
+sandbox, set `routing.agents.<id>.sandbox.mode: "off"`.
+
+---
+
 ## Testing
 
 After configuring multi-agent sandbox and tools:
diff --git a/docs/start/getting-started.md b/docs/start/getting-started.md
index 4104da617..d523ba71c 100644
--- a/docs/start/getting-started.md
+++ b/docs/start/getting-started.md
@@ -19,6 +19,23 @@ Recommended path: use the **CLI onboarding wizard** (`clawdbot onboard`). It set
 
 If you want the deeper reference pages, jump to: [Wizard](/start/wizard), [Setup](/start/setup), [Pairing](/start/pairing), [Security](/gateway/security).
 
+Sandboxing note: `agent.sandbox.mode: "non-main"` uses `session.mainKey` (default `"main"`),
+so group/channel sessions are sandboxed. If you want the main agent to always
+run on host, set an explicit per-agent override:
+
+```json
+{
+  "routing": {
+    "agents": {
+      "main": {
+        "workspace": "~/clawd",
+        "sandbox": { "mode": "off" }
+      }
+    }
+  }
+}
+```
+
 ## 0) Prereqs
 
 - Node `>=22`