Adds Task 1.6: a backward-cursor paginator in base.py, a message-type
normalizer in parsers.py, and the WeChat chat-message scraper in wechat.py.
- app/scraper/parsers.py: normalize_wechat_type() maps 1 -> "text",
-2 -> "divider", everything else -> "unknown". Total (never raises);
unknown codes pass through so no real message is silently dropped.
- app/scraper/base.py: paginate_by_cursor() generic async generator. Takes
a fetch(cursor) -> (rows, next_cursor, has_more) coroutine; advances the
cursor and stops on has_more=False OR an empty page (defensive). Same
RateLimiter integration as paginate_by_page.
- app/scraper/wechat.py: scrape_wechat_messages() wraps
POST /wechatweb/msg/chats. Body is form-encoded (NOT JSON) — content-type
is overridden per request to application/x-www-form-urlencoded via the
YunkeClient.post(headers=...) override hook. Pages backward by setting
end = data.end - 1 each batch, repeats until hasLast=false. Drops any
record whose type/messageType is -2 (date divider UI chrome). Yields
normalized dicts (snake_case Message columns + channel="wechat" +
raw_json); the raw type code is preserved on raw_json for the
persistence layer (Task 1.7).
Tests: 13 new (10 parser parametrized + 3 scraper). respx-mocked
msg/chats with two backward pages — asserts [m1, m2, m3] yielded (the -2
divider dropped), full field mapping vs the live-capture names, the
content-type is form-encoded (not JSON), and the 2nd request body's
end == E1 - 1 (proving the backward cursor advance).
Co-Authored-By: Claude <noreply@anthropic.com>
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