Convert pasted thread links into composer pills

[brsbl]

Human comments

What was wrong

The shared composer treated pasted thread URLs as ordinary text instead of resolving them into existing thread mentions.

What changed

• Bare same-origin thread URLs become title pills; Undo restores the original URLs.
• Code, quotes, authored links, foreign URLs, and query/fragment destinations remain literal; paste without formatting bypasses conversion.
• One editor-owned collection tracks pending pastes, using Tiptap change ranges. Deadline, cancellation, and undo behavior are preserved.
• CLI and Plugin Guide document the existing equivalent mention representation.

How you verified

• Remote CI passed at 08261de44e, including builds, typechecks, lint, bundle budgets, and Linux/Windows tests.
• Chrome for Testing 151: conversion, two-step undo/redo, mixed HTML protection, plain-paste bypass, and restored drafts.
• Slop Cop at 08261de44e: security and performance clear; architecture and correctness share one P2 follow-up below. No P0/P1.

The 19 lifecycle, 14 parser, and 156 shared-composer tests pass remotely. Clipboard payloads use browser ClipboardEvents; native clipboard shortcut dispatch was unavailable. Real keyboard-handler regression tests cover Cmd/Ctrl+Shift+V. User QA remains pending.

P2 follow-up: mixed HTML pasted immediately after an existing word can shift clipboard protection indexes and convert a code URL. Preserve paste-relative occurrence identity or skip when contextual filtering changes correspondence. See paste filtering.

Screenshots use identical fixture data and route at 2× density. Before: 75308f4076; after: 08261de44e.

Composer	Before	After
Wide, 1440 × 900
Compact, 390 × 844

BB-Thread-ID: thr_xeaa8vnrt2

AGENT GENERATED

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