perf: stop leaking React trees on repeated injection mutations

[guanbinrui]

Summary

Follow-up to #12432, which fixed this class of React-tree leak for injectAvatar and the tips buttons on x.com. The remaining injection points that build a React tree inside an onNodeMutation / onTargetChanged handler had the same bug: a mutation of the watched element (lazy image src swaps, hover states, feed virtualization reusing nodes) re-runs the handler, which attaches a fresh shadow-root sibling + React tree without tearing down the previous one. Over a long scroll session this accumulates orphaned DOM nodes / shadow roots / React roots — each with its own data-fetching hooks — until navigation.

Changes

Area	Fix
facebook / minds / instagram injection/Avatar/index.tsx	Call remove() before re-creating the DOMProxy, mirroring the twitter.com fix from #12432.
twitter.com/injection/MaskIcon.tsx — injectMaskIconToPostTwitter	post.author refines several times as parsing completes and re-fires on every onNodeMutation of the tweet, so each add() stacked another DOMProxy shadow sibling + <Icon> React root (visible as duplicated Mask icons on posts). Reuse a single proxy, tear down the previous tree first, and release the post.author subscription on signal abort.
twitter.com/injection/MaskIcon.tsx — injectMaskUserBadgeAtTwitter (_ helper)	check() re-ran on every mutation and re-called attachReactTreeWithContainer with the same shadow key, which the mounter rejects with a console.error on every floating-bio-card hover while also clobbering remover to a no-op. Attach once; remove() / onRemove reset the guard so a genuinely re-added element still re-attaches.
site-adaptor-infra/ui.ts — startPostListener	The per-post AbortController wired a listener onto the page-lifetime signal on every post set and never removed it, so every post scrolled past left a permanent listener (and its retained controller). Pass { signal: abort.signal } so it drops when the post unmounts.

Behavior

Output values are unchanged; only the redundant / leaked work is removed.

Test plan

• Scroll a busy x.com timeline for a while with devtools open — no console.error from attachReactTreeToMountedRoot, no duplicate Mask icons on posts whose author re-parses, DOM node / listener count stays flat.
• Hover profile bio cards on x.com repeatedly — Mask badge still appears once, no console spam.
• Facebook / Instagram / Minds feeds — avatar injection still works, no shadow-root pile-up.

🤖 Generated with Claude Code

https://claude.ai/code/session_013SLkuieqJXCMg1xoL98jij