fix(xhs): recover homepage search submission

[IRONICBo]

Summary

• recover Xiaohongshu homepage searches when typing succeeds but Enter does not trigger navigation
• re-locate the submit affordance after the query is entered instead of reusing the pre-input coordinate
• recognize the current .single-line-search-btn inside its .textarea-container
• keep the strict result-page guard so homepage feed cards cannot be reported as search results
• document the homepage composer lifecycle and result-route invariant in the XHS knowledge file

Production evidence

An Axiom failure on v0.5.5 showed the requested query present in the input while the browser remained on /explore. The run observed 32 homepage feed cards, returned zero search cards, and reported Search did not transition to a valid Xiaohongshu result page.

A second historical failure had the same shape: the requested query and suggestion panel were visible, but unrelated homepage cards remained underneath and no result route was entered.

Root cause

The homepage AI composer mounts or re-renders its visible submit button only after text is entered. submit_search measured the button before typing, so its fallback reused a missing or stale coordinate. When Xiaohongshu also ignored the synthetic Enter event, the query remained in the homepage input until the strict transition check correctly rejected the page.

Implementation

• add .single-line-search-btn to the explicit submit selector list
• scope submit lookup to the closest .textarea-container to avoid the hidden duplicate composer
• refresh searchInput after an unsuccessful Enter and click the live post-typing submit control
• preserve the latest post-click transition state for failure diagnostics

Validation

• cargo test -p socai-core --lib — 99 passed, 0 failed, 2 ignored
• cargo test -p socai-cli — 6 passed, 0 failed
• node --check core/src/sites/xhs/page_scripts.js
• git diff --check
• real logged-in homepage search for 内容策划 招聘 上海 entered /search_result_ai, preserved the exact query, and returned 10 requested cards
• four additional normal searches entered valid result pages
• deterministic fault injection blocked the first Enter: before the fix the page stayed on /explore with 30 homepage cards and zero results; after the fix click_refreshed_search_button entered the result page and returned 8 requested cards

No new Rust test function was added, following the repository engineering rule; the dynamic browser behavior was validated against the live logged-in Xiaohongshu DOM and with the controlled Enter-failure path.

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[IRONICBo]