Verify-before-send helper: assert draft shows body once + URL once on own line

[Trace824]

Summary

Before clicking the post/reply button, automation has no first-class check that the Draft.js compose field contains the intended body exactly once and the URL exactly once on its own line. A small verify helper would catch double/replace/caret bugs before publish.

Repro

• Context: x.com compose after multi-step type/insert.
• Steps:
  1. Build draft via body insert + URL append.
  2. Read compose text (execute_js / read helpers).
  3. Click [data-testid=tweetButtonInline] or reply button without structural assert.
• Observed: doubled or mangled drafts can be published; failures only noticed after the fact.

Code pointers (verified against /workspace/FSB)

• extension/site-guides/social/twitter.js — tweetButtonInline, tweetTextarea_0, reply button selectors (~L47–143).
• extension/content/actions.js — draft editable resolve / text read surfaces; likely area to add verify_draft or export a shared assert used by tools.
• mcp/src/tools/manual.ts — tool registration pattern for a new optional helper.

Proposed fix

Add a lightweight helper (content or MCP-facing) that reads compose text from the resolved editable and asserts: body substring once, URL once, URL preceded by newline (or on last line). Fail closed before click on tweet button.

Acceptance / regression

• Helper fails on doubled body or mid-line URL; passes on well-formed draft.
• Integrates with existing selectors in twitter.js site guide.

Owner

extension (helper); mcp-server if exposed as a tool

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Priority: P2 · Owner: extension

[LakshmanTurlapati]

Fixed in #143: type_text now verifies the rendered text (line breaks included) exactly once, and the X guide adds author, account and single-click checks around posting.