feat(plot): auto backend tries jgd first when installed

In auto mode, the JGD socket server starts eagerly and R-side hooks
try jgd > httpgd > standard based on package availability. Users who
install the jgd R package get interactive plots with zero config.

r.plot.useHttpgd: true still forces httpgd for backward compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: grantmcdermott

R/profile.R

@@ -25,10 +25,10 @@ local({
 })
 
 if (requireNamespace("sess", quietly = TRUE)) {
-    plot_backend <- Sys.getenv("SESS_PLOT_BACKEND", "standard")
+    plot_backend <- Sys.getenv("SESS_PLOT_BACKEND", "auto")
     sess::connect(
         use_rstudioapi = as.logical(Sys.getenv("SESS_RSTUDIOAPI", "TRUE")),
-        use_httpgd = (plot_backend == "httpgd"),
-        use_jgd = (plot_backend == "jgd")
+        use_httpgd = (plot_backend %in% c("auto", "httpgd")),
+        use_jgd = (plot_backend %in% c("auto", "jgd"))
     )
 }

package.json

@@ -1841,8 +1841,7 @@
         "r.plot.useHttpgd": {
           "type": "boolean",
           "default": false,
-          "markdownDescription": "Use the httpgd-based plot viewer instead of the base VSCode-R plot viewer.\n\nRequires the `httpgd` R package version 1.2.0 or later.",
-          "markdownDeprecationMessage": "Use `#r.plot.backend#` instead."
+          "markdownDescription": "Use the httpgd-based plot viewer instead of the base VSCode-R plot viewer.\n\nRequires the `httpgd` R package version 1.2.0 or later.\n\n**Deprecated:** Use `#r.plot.backend#` instead. When `#r.plot.backend#` is `auto`, setting this to `true` forces httpgd."
         },
         "r.plot.backend": {
           "type": "string",
@@ -1854,12 +1853,12 @@
             "jgd"
           ],
           "markdownEnumDescriptions": [
-            "Automatic: uses httpgd if `#r.plot.useHttpgd#` is true, otherwise standard",
+            "Automatic: tries JGD first (if installed), then httpgd, then standard. Respects `#r.plot.useHttpgd#` if set.",
             "Standard static plot viewer (PNG/SVG)",
             "httpgd-based interactive plot viewer (requires `httpgd` R package)",
             "JGD-based interactive plot viewer (requires `jgd` R package)"
           ],
-          "markdownDescription": "Select the plot backend.\n\nWhen set to `auto`, the backend is determined by the legacy `#r.plot.useHttpgd#` setting."
+          "markdownDescription": "Select the plot backend.\n\nWhen set to `auto`, the best available backend is used (JGD if installed, then httpgd, then standard). Setting `#r.plot.useHttpgd#` to `true` forces httpgd."
         },
         "r.plot.jgd.historyLimit": {
           "type": "number",

src/extension.ts

@@ -203,8 +203,8 @@ export async function activate(context: vscode.ExtensionContext): Promise<apiImp
     // initialize plot manager
     globalPlotManager = plotViewer.initializePlotManager();
 
-    // Set JGD_SOCKET env var for R child processes when using JGD backend
-    if (plotViewer.resolveBackend() === 'jgd') {
+    // Set JGD_SOCKET env var for R child processes when JGD server is running
+    if (plotViewer.resolveBackend() === 'jgd' || plotViewer.resolveBackend() === 'auto') {
         const jgdVars = (globalPlotManager as plotViewer.CommonPlotManager).getJgdEnvVars();
         for (const [key, value] of Object.entries(jgdVars)) {
             context.environmentVariableCollection.replace(key, value);

src/plotViewer/index.ts

@@ -8,11 +8,11 @@ import { JgdManager } from './jgdViewer';
 import { extensionContext } from '../extension';
 import { config } from '../util';
 
-export function resolveBackend(): 'standard' | 'httpgd' | 'jgd' {
+export function resolveBackend(): 'auto' | 'standard' | 'httpgd' | 'jgd' {
     const explicit = config().get<string>('plot.backend', 'auto');
     if (explicit !== 'auto') return explicit as 'standard' | 'httpgd' | 'jgd';
     if (config().get<boolean>('plot.useHttpgd', false)) return 'httpgd';
-    return 'standard';
+    return 'auto';
 }
 
 const commands = [
@@ -56,8 +56,8 @@ export class CommonPlotManager implements PlotManager {
 
     get activeViewer(): PlotViewer | undefined {
         const backend = resolveBackend();
-        if (backend === 'jgd') {
-            return this.jgdManager.getViewer() || this.standardPlotViewer;
+        if (backend === 'jgd' || backend === 'auto') {
+            return this.jgdManager.getViewer() || this.httpgdManager.getRecentViewer() || this.standardPlotViewer;
         }
         return this.httpgdManager.getRecentViewer() || this.standardPlotViewer;
     }
@@ -128,7 +128,7 @@ export function initializePlotManager(): PlotManager {
     manager.initialize();
 
     const backend = resolveBackend();
-    if (backend === 'jgd') {
+    if (backend === 'jgd' || backend === 'auto') {
         manager.jgdManager.start();
     }
 

src/rTerminal.ts

@@ -204,7 +204,7 @@ export async function makeTerminalOptions(): Promise<vscode.TerminalOptions> {
             SESS_USE_HTTPGD: backend === 'httpgd' ? 'TRUE' : 'FALSE',
             SESS_PLOT_BACKEND: backend,
         };
-        if (backend === 'jgd') {
+        if (backend === 'jgd' || backend === 'auto') {
             const jgdVars = (globalPlotManager as CommonPlotManager)?.getJgdEnvVars() ?? {};
             Object.assign(termOptions.env, jgdVars);
         }