test(plot): install sess Suggests so svglite path is tested

remotes::install_local() defaults to dependencies=NA, which installs
only Depends/Imports/LinkingTo. After svglite was moved from Imports to
Suggests (04ebd7d), the build stopped installing it, so the plot_latest
handler fell back to png and the session test's strict svglite assertion
failed on CI.

Pass dependencies=TRUE to the build's install_local call, matching
R CMD check semantics so optional (Suggests) functionality is exercised.
Also branch the test assertion on svglite availability so it stays
correct whether or not svglite is present.

Author: grantmcdermott

package.json

@@ -2017,7 +2017,7 @@
   "scripts": {
     "vscode:prepublish": "node esbuild.js --production",
     "changelog": "npx git-cliff v2.8.5.. -o",
-    "build": "node esbuild.js && Rscript -e \"remotes::install_local('sess', force=TRUE)\"",
+    "build": "node esbuild.js && Rscript -e \"remotes::install_local('sess', dependencies=TRUE, force=TRUE)\"",
     "watch": "node esbuild.js --watch",
     "clean": "rimraf out",
     "pretest": "npm run clean && tsc -p ./",

src/test/suite/session.test.ts

@@ -138,6 +138,11 @@ suite('Session Communication', () => {
         sandbox.stub(util, 'getRterm').resolves(rPath);
         sandbox.stub(util, 'promptToInstallSessPackage').resolves();
 
+        // svglite is a Suggests (optional) dependency of the sess package, so it may or
+        // may not be present. Detect it before stubbing so the format assertions below
+        // can verify the correct code path (SVG when installed, png fallback otherwise).
+        const svgliteInstalled = (await util.getRPackageVersion('svglite')) !== undefined;
+
         const result = await rTerminal.createRTerm(true);
         assert.ok(result);
         await waitFor(() => session.activeSession, 15000, 200);
@@ -175,7 +180,14 @@ suite('Session Communication', () => {
         }, 15000, 500);
 
         assert.ok(svgliteResp && svgliteResp.data, 'svglite data should be returned');
-        assert.strictEqual(svgliteResp.format, 'svglite', 'format should be svglite');
+        // svglite is an optional (Suggests) dependency of the sess package. When it is
+        // installed the handler renders SVG; otherwise it falls back to png. Assert the
+        // path that actually applies to this environment so both branches are tested.
+        if (svgliteInstalled) {
+            assert.strictEqual(svgliteResp.format, 'svglite', 'format should be svglite when svglite is installed');
+        } else {
+            assert.strictEqual(svgliteResp.format, 'png', 'format should fall back to png when svglite is not installed');
+        }
 
         // Reset history to ensure we track the next plot if we were to recreate the panel
         // Wait, since panel is reused, we shouldn't reset history if we just want it to pass,