Three Signal adapter improvements that depend on the no-edit-mode
plumbing from the previous commit.
1. Native formatting (markdown -> Signal bodyRanges)
Signal renders markdown as literal characters (**bold**, `code`, #
heading), which looks broken. Added _markdown_to_signal(text) that
strips markdown syntax and emits Signal-native bodyRanges as
start:length:STYLE entries. Offsets are computed in UTF-16 code
units so non-BMP emoji stay aligned. Supports BOLD, ITALIC, STRIKE,
MONO, and headings mapped to BOLD. Fenced code and inline code are
handled; link syntax is unwrapped to visible text + URL.
Includes edge-case fixes reported previously:
- Bullet lists ("* item") no longer misidentified as italics
- URLs containing underscores no longer italicized around the dot
2. Reply-quote context
Parses dataMessage.quote on inbound messages and populates
MessageEvent.raw_message with sender + timestamp_ms. This lets the
gateway's existing [Replying to: "..."] injector (gateway/run.py)
work on Signal, matching Telegram/Matrix behavior.
3. Processing reactions
Overrides on_processing_start -> hourglass and on_processing_complete
-> checkmark via the sendReaction JSON-RPC using targetAuthor and
targetTimestamp pulled from raw_message. Uses the ProcessingOutcome
enum introduced in the previous commit.
Also sets SUPPORTS_MESSAGE_EDITING = False on SignalAdapter so the
no-edit streaming path activates.
Tests: 40+ new tests in tests/gateway/test_signal_format.py covering
markdown conversion, UTF-16 offset correctness with non-BMP emoji,
bullet-list and URL false-positive regressions, reply-quote extraction,
and reaction payload shape. Regression extensions to test_signal.py.
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