feat: add flag to disable workspace agent context sync (#28522)

cli/testdata/coder_server_--help.golden

@@ -55,6 +55,13 @@ OPTIONS:
           the workspace serves malicious JavaScript. This is recommended for
           security purposes if a --wildcard-access-url is configured.
 
+      --disable-workspace-agent-context-sync bool, $CODER_DISABLE_WORKSPACE_AGENT_CONTEXT_SYNC
+          Stop persisting workspace agent context snapshots (instructions,
+          skills, and MCP state used for pinned chat context). When set, coderd
+          rejects agent context pushes as unimplemented and agents stop sending
+          them; chats cannot pin workspace context. Use this to shed the
+          database write load of context sync on large deployments.
+
       --disable-workspace-sharing bool, $CODER_DISABLE_WORKSPACE_SHARING
           Disable workspace sharing. Workspace ACL checking is disabled and only
           owners can have ssh, apps and terminal access to workspaces. Access

cli/testdata/server-config.yaml.golden

@@ -566,6 +566,13 @@ disableWorkspaceSharing: false
 # their chats.
 # (default: <unset>, type: bool)
 disableChatSharing: false
+# Stop persisting workspace agent context snapshots (instructions, skills, and MCP
+# state used for pinned chat context). When set, coderd rejects agent context
+# pushes as unimplemented and agents stop sending them; chats cannot pin workspace
+# context. Use this to shed the database write load of context sync on large
+# deployments.
+# (default: <unset>, type: bool)
+disableWorkspaceAgentContextSync: false
 # These options change the behavior of how clients interact with the Coder.
 # Clients include the Coder CLI, Coder Desktop, IDE extensions, and the web UI.
 client: