fix: fall back to search page when homepage lacks ondemand.s

[gnuhpc]

Problem

X redesigned its homepage (x.com) to use a new React Router (TSR) architecture. The new homepage no longer contains the ondemand.s file reference in its HTML, causing ClientTransaction initialization to fail. Without a valid transaction ID, endpoints that require the x-client-transaction-id header (like SearchTimeline) return HTTP 404.

Related issues: #78, #73, #69

This PR complements #79 (which sends auth cookies with the homepage request) — but even with cookies, the redesigned homepage still lacks ondemand.s.

Root Cause

The _ensure_client_transaction() method fetches https://x.com and calls get_ondemand_file_url() to find the ondemand.s JS file. Since the homepage redesign, this file reference is gone, so get_ondemand_file_url() returns None (after PR #79's fix) or crashes with AttributeError (before).

However, the search page (https://x.com/search?q=AI&f=live) has NOT been redesigned — it still uses the legacy responsive-web/client-web/ frontend and contains the ondemand.s file reference (232 occurrences in the HTML).

Fix

Add a fallback in _ensure_client_transaction(): if the homepage does not contain ondemand.s, automatically fetch the search page and use it for ClientTransaction initialization.

ondemand_url = get_ondemand_file_url(response=home_page_response)
if not ondemand_url:
    # Fall back to search page (still uses legacy frontend)
    search_page = cffi_session.get(
        "https://x.com/search?q=AI&f=live",
        headers=ct_headers, timeout=10,
    )
    search_response = bs4.BeautifulSoup(search_page.content, "html.parser")
    ondemand_url = get_ondemand_file_url(response=search_response)
    if not ondemand_url:
        raise ValueError("Failed to extract ondemand file URL from homepage and search page")
    home_page_response = search_response
    home_page = search_page

Verification

• ClientTransaction initializes successfully via search page fallback
• twitter search "AI" returns results (was 404)
• Transaction IDs are generated correctly
• CT cache saves the search page HTML for subsequent requests
• All other commands (post, quote, feed, user-posts) continue to work

Note

This PR only modifies _ensure_client_transaction() — a minimal, focused change. The search page fallback is also documented in the XClientTransaction project (see PR #44 and #45).