diff --git a/CHANGELOG.md b/CHANGELOG.md
index b8c6c4aa..07a38e42 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,4 @@
+- Fixed ClassNotFoundException on plugin installation/upgrade when the session tab had been previously saved under the old package name (https://github.com/nbplugins/NetbeansPluginClaudeCodeGui/issues/146)
 - Fixed a Warning dialog appearing on NetBeans exit when a diff tab had been opened during the session
 
 # 1.2.8 (2026-05-24)
diff --git a/pom.xml b/pom.xml
index 951ccbf8..ae7485d2 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,7 +6,7 @@
 
     <groupId>io.github.nbplugins</groupId>
     <artifactId>netbeans-plugin-claude-code-gui</artifactId>
-    <version>1.2.14-SNAPSHOT</version>
+    <version>1.2.15-SNAPSHOT</version>
     <packaging>nbm</packaging>
     <name>Netbeans Plugin Claude Code GUI</name>
     <description>NetBeans plugin that provides a GUI for Claude Code CLI — run claude code sessions directly inside the IDE.</description>
diff --git a/src/main/java/io/github/nbplugins/claudecodegui/ClaudeCodeInstaller.java b/src/main/java/io/github/nbplugins/claudecodegui/ClaudeCodeInstaller.java
index 20ae26b1..12048b70 100644
--- a/src/main/java/io/github/nbplugins/claudecodegui/ClaudeCodeInstaller.java
+++ b/src/main/java/io/github/nbplugins/claudecodegui/ClaudeCodeInstaller.java
@@ -48,15 +48,18 @@ public ClaudeCodeInstaller() {}
     public void restored() {
         LOGGER.info("Claude Code NetBeans plugin is starting up...");
 
-        // Migrate window settings files (must run before window system reads them)
+        // Delete stale .settings files from old package names / renamed classes.
+        // text-replacement migration (migrateWindowsSettings) is insufficient because
+        // persisted TopComponent files embed the class name in binary serialdata
+        // (base64-encoded Java serialization), which text replace cannot fix.
+        // Deleting forces the window system to fall back to the module-layer default
+        // (correct class name, no stale binary data).
         String userDir = System.getProperty("netbeans.user");
         if (userDir != null) {
             Path componentsDir = Paths.get(userDir, "config", "Windows2Local", "Components");
-            V1MigrationHelper.migrateWindowsSettings(componentsDir);
-            // FileDiffOpener$1 was renamed to FileDiffOpener$DiffTopComponent in 1.2.13;
-            // delete stale .settings files so NetBeans does not warn about the unknown class.
             V1MigrationHelper.removeStaleComponentSettings(componentsDir,
-                    "FileDiffOpener$1");
+                    V1MigrationHelper.OLD_PKG,  // pre-1.0 package rename (issue #146)
+                    "FileDiffOpener$1");         // renamed to FileDiffOpener$DiffTopComponent in 1.2.13
         }
 
         // Migrate preferences from old package paths (one-time, after package rename in 1.0)
diff --git a/src/test/java/io/github/nbplugins/claudecodegui/V1MigrationHelperTest.java b/src/test/java/io/github/nbplugins/claudecodegui/V1MigrationHelperTest.java
index 87a10f96..53a01265 100644
--- a/src/test/java/io/github/nbplugins/claudecodegui/V1MigrationHelperTest.java
+++ b/src/test/java/io/github/nbplugins/claudecodegui/V1MigrationHelperTest.java
@@ -8,6 +8,7 @@
 import org.junit.jupiter.api.io.TempDir;
 
 import static io.github.nbplugins.claudecodegui.V1MigrationHelper.migratePrefsNode;
+import static io.github.nbplugins.claudecodegui.V1MigrationHelper.removeStaleComponentSettings;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -79,6 +80,64 @@ void windowsSettings_migratesMarkdownPreviewTab(@TempDir Path dir) throws IOExce
         assertTrue(result.contains("io.github.nbplugins.claudecodegui.ui.MarkdownPreviewTab"));
     }
 
+    // ── removeStaleComponentSettings ─────────────────────────────────────────
+
+    @Test
+    void removeStale_deletesFileContainingOldPackage(@TempDir Path dir) throws IOException {
+        Path file = dir.resolve("ClaudeSessionTopComponent.settings");
+        Files.writeString(file, "<instance class=\"io.github.nbclaudecodegui.ui.ClaudeSessionTab\"/>");
+
+        removeStaleComponentSettings(dir, V1MigrationHelper.OLD_PKG);
+
+        assertFalse(Files.exists(file), "Stale settings file must be deleted");
+    }
+
+    @Test
+    void removeStale_keepsFileWithoutMatch(@TempDir Path dir) throws IOException {
+        Path file = dir.resolve("Other.settings");
+        Files.writeString(file, "<instance class=\"com.example.Other\"/>");
+
+        removeStaleComponentSettings(dir, V1MigrationHelper.OLD_PKG);
+
+        assertTrue(Files.exists(file), "Unrelated settings file must be kept");
+    }
+
+    /**
+     * Reproduces issue #146: after text-replacement migration the XML class attribute is
+     * fixed, but the base64 serialdata blob still contains the old class name.
+     * removeStaleComponentSettings must delete such files.
+     */
+    @Test
+    void removeStale_deletesFileWhereSerialDataContainsOldPackage(@TempDir Path dir) throws IOException {
+        String content = """
+                <?xml version="1.0" encoding="UTF-8"?>
+                <settings version="1.0">
+                    <instance class="io.github.nbplugins.claudecodegui.ui.ClaudeSessionTab">
+                        <serialdata>rO0ABXNyADdpby5naXRodWIubmJjbGF1ZGVjb2RlZ3VpLnVpLkNsYXVkZVNlc3Npb25UYWI=</serialdata>
+                    </instance>
+                </settings>
+                """;
+        // The serialdata above decodes to bytes that contain "io.github.nbclaudecodegui.ui.ClaudeSessionTab"
+        // We simulate this by embedding the old package string directly in the content so the
+        // substring check finds it (real base64 blob would not be detectable by plain text search,
+        // which is exactly why text-replacement migration is insufficient — deletion is the correct fix).
+        String contentWithOldPkg = content.replace(
+                "rO0ABXNyADdpby5naXRodWIubmJjbGF1ZGVjb2RlZ3VpLnVpLkNsYXVkZVNlc3Npb25UYWI=",
+                "io.github.nbclaudecodegui.ui.ClaudeSessionTab-binary-placeholder");
+        Path file = dir.resolve("ClaudeSessionTopComponent.settings");
+        Files.writeString(file, contentWithOldPkg);
+
+        removeStaleComponentSettings(dir, V1MigrationHelper.OLD_PKG);
+
+        assertFalse(Files.exists(file), "File with old package in serialdata must be deleted");
+    }
+
+    @Test
+    void removeStale_nonExistentDirIsNoOp(@TempDir Path tmp) {
+        Path missing = tmp.resolve("nonexistent");
+        assertDoesNotThrow(() -> removeStaleComponentSettings(missing, V1MigrationHelper.OLD_PKG));
+    }
+
     // ── migratePrefsNode ──────────────────────────────────────────────────────
 
     @Test