Zotero 9.0.x: ItemPane custom-section icons missing (TypeError in itemPaneSection.js setL10nID)

Bug description

In Zotero 9.0.4 / 9.0.5 / 9.0.6, plugin-provided sections in the main window ItemPane are rendered by calling setL10nID() / setL10nArgs() during element initialization, before the element is upgraded — this._section is still undefined. The base class then throws:

TypeError: can't access property "dataset", this._section is undefined
    setL10nID chrome://zotero/content/elements/itemPaneSection.js:288

The exception propagates out of renderCustomSections() (itemDetails.js) and aborts section registration, so the plugin's ItemPane sidebar icon is silently missing. Reproduced with llm-for-zotero 3.8.31 on Zotero 9.0.6 (Windows 11): the "LLM Assistant" icon never appears in the main-window ItemPane sidebar, while the plugin itself loads fine (the standalone Ctrl+Shift+L window works).

This looks like a regression from the 9.0 refactor of itemPaneSection.js — pre-9.0 the setters only touched DOM properties.

Steps to reproduce

1. Install Zotero 9.0.6 and any plugin that registers an ItemPane section (e.g. llm-for-zotero 3.8.31).
2. Open the main window and select an item.
3. The plugin's icon is missing from the ItemPane sidebar.
4. Check the error console: the TypeError above is logged once per section registration.

Expected behavior

Plugin ItemPane icons render as in Zotero 7/8.

Proposed fix

Cache the l10n values when not initialized, exactly like the existing registerSectionIcon() method does; init() already replays both cached values after upgrade:

     setL10nID(l10nId) {
+      if (!this.initialized) {
+        this._sectionL10nId = l10nId;
+        return;
+      }
       this._section.dataset.l10nId = l10nId;
       this._sectionL10nId = l10nId;
     }

     setL10nArgs(l10nArgs) {
+      if (!this.initialized) {
+        this._sectionL10nArgs = l10nArgs;
+        return;
+      }
       this._section.dataset.l10nArgs = l10nArgs;
       this._sectionL10nArgs = l10nArgs;
     }

This patch is verified working on 9.0.6 (icons + LLM chat panel functional afterwards); one-click script and full repro at https://github.com/kebogan/zotero-item-pane-patch

Environment

• Zotero 9.0.6 (also confirmed present in 9.0.4 / 9.0.5 sources)
• Windows 11
• llm-for-zotero 3.8.31 (any section-registering plugin is affected)