From 034d30895f8e5f41c000ff5bec6dd29a22208ff3 Mon Sep 17 00:00:00 2001
From: Local Dev <dev@localhost>
Date: Tue, 8 Sep 2026 19:14:29 +0200
Subject: [PATCH] fix(theseus/addons): captureTab skips addon-owned tabs
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Reported: the Screenshot dropdown produces a blank white PNG "every time".
Verified end-to-end via CDP: the FIRST capture on a real page (silentmode.st)
worked (221 KB, real pixels). Every capture after that came back as a
uniform-white 1920×899 PNG (~24 KB, all bytes 255/255/255/255 confirmed by
canvas getImageData in the editor tab).

Root cause: api.captureTab reads activeTab(), which after the first successful
run is the editor.html tab the add-on just opened. CDP Page.captureScreenshot
on the editor's own tab happily snapshots its still-blank canvas, and the
addon writes that white PNG into scratch → opens a new editor showing it →
next re-capture snapshots THAT editor → all-white feedback loop.

Fix: track the last active tab that isn't an add-on-owned page (or the
Settings tab) in setActive(), and have captureTab fall back to it when the
current active tab has an addonId or settings flag. Last resort: the first
non-addon non-settings tab in the list. If none exists, throw a clear "open
a page you'd like to shoot first" error instead of returning white pixels.

No new capability; no manifest change; addons keep calling
api.captureTab({mode}) exactly as before. Ships in the next Theseus release.
---
 main.js | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/main.js b/main.js
index 2ff2e932..71bba569 100644
--- a/main.js
+++ b/main.js
@@ -1534,8 +1534,24 @@ function initAddons() {
     //   region   — run the caller-supplied overlay source in the tab, wait
     //              for a rect (or null = cancel), then capturePage(rect).
     captureTab: async (opts, addonId) => {
-      const t = activeTab();
+      // Prefer the currently-active tab, BUT if that's an add-on-owned page
+      // (e.g. the screenshot editor is already up when the user re-picks a
+      // mode from the dropdown), fall back to the most-recently-active real
+      // tab. Otherwise a second capture snapshots the editor's still-blank
+      // canvas and every follow-up produces a white PNG.
+      let t = activeTab();
+      if (t && (t.addonId || t.settings)) {
+        const fallback = tabById(lastCapturableTabId);
+        if (fallback && !fallback.addonId && !fallback.settings) t = fallback;
+        else {
+          // Last resort: any non-addon non-settings tab in the list.
+          t = tabs.find((x) => !x.addonId && !x.settings) || t;
+        }
+      }
       if (!t) throw new Error("no active tab");
+      if (t.addonId || t.settings) {
+        throw new Error("no capturable tab — open a page you'd like to shoot first");
+      }
       const wc = t.view.webContents;
       const host = t?.prov?.host || (() => { try { return new URL(wc.getURL()).host; } catch { return ""; } })();
       const mode = String(opts?.mode || "visible");
@@ -1686,6 +1702,11 @@ const tabs = [];       // { id, view, title, url, prov }
 let activeId = null, tabSeq = 0;
 const tabById = (id) => tabs.find((t) => t.id === id);
 const activeTab = () => tabById(activeId);
+// The most-recently-active non-addon tab. captureTab falls back to this when
+// the currently-active tab is an add-on-owned page (e.g. the screenshot
+// editor itself) — otherwise a re-triggered capture snapshots the editor's
+// still-blank canvas instead of the page the user actually wants to shoot.
+let lastCapturableTabId = null;
 
 // Provenance goes to BOTH the top chrome (registry badge + site-info panel) and
 // the bottom status line, so the resolver detail lives on the bottom bar.
@@ -2018,6 +2039,10 @@ function setActive(id) {
   if (target) target.view.setVisible(true);
   for (const t of tabs) if (t.id !== id) t.view.setVisible(false);
   const t = activeTab();
+  // Track the last active tab that isn't an add-on-owned page so captureTab
+  // has a sensible fallback when the user re-triggers the dropdown from
+  // inside (say) the screenshot editor.
+  if (t && !t.addonId && !t.settings) lastCapturableTabId = t.id;
   if (t?.prov) pushNav(t.prov);
   chrome.webContents.send("bcnr-offer", t?.bcnrOffer ? { host: t.bcnrOffer.host, tld: t.bcnrOffer.tld, registry: REGISTRY } : null);
   emitTabs();