Summary

Combined PR that adds three related improvements enabling first-class Signal support:

1. send_file tool — agents can attach files to outgoing platform messages
2. No-edit-mode streaming — gateway streaming path for platforms without a message-edit API
3. Signal adapter native formatting, reply quotes, and reactions — consumes the no-edit path

The three are shipped together because #3 depends on the SUPPORTS_MESSAGE_EDITING / ProcessingOutcome plumbing introduced in #2, and #1 is the natural companion for attachment-capable platforms like Signal.

Commit 1 — feat(tools): send_file tool for platform attachment uploads

Why: There was no first-class way for an agent to attach a file (image, PDF, audio) to an outgoing platform message — you had to hack the path into the prompt.

What: New tools/send_file_tool.py resolves the active adapter from conversation context and calls adapter.send(..., attachments=[path]). Includes path validation, size limits, and MIME sniffing. Auto-discovered by tools/registry.py.

Tests: 28 new tests in tests/tools/test_send_file_tool.py.

Risk: Low — pure addition.

Commit 2 — feat(gateway): no-edit-mode streaming for platforms without message edit API

Why: Signal (and some other transports) have no outbound message-edit API, so the existing streaming loop that repeatedly edits a placeholder message fails silently and leaves a trailing ▉ cursor visible in clients.

What:

• BasePlatformAdapter.SUPPORTS_MESSAGE_EDITING: bool = True class attr (adapters that can't edit override to False).
• ProcessingOutcome enum for on_processing_start/on_processing_complete hook return values.
• StreamConsumerConfig.no_edit_mode: bool = False + wiring in gateway/run.py (no_edit_mode=not _adapter_supports_edit).
• stream_consumer.py no-edit branch flushes on paragraph breaks (\n\n) above a minimum buffer plus segment/done/commentary events, instead of time-interval edits.

All edit-mode platforms (Telegram, Matrix, Discord) default True and take the original code path unchanged — the new branch is effectively dead code for them.

Tests: 23 new tests in tests/gateway/test_stream_consumer_no_edit.py, plus regression extensions to test_stream_consumer.py.

Risk: Medium — touches the gateway hot path.

Regression matrix

Commit 3 — feat(gateway/signal): native formatting, reply quotes, and reactions

Why: Signal messages from Hermes currently show literal **bold**, `code`, # heading. Inbound reply-quote context is ignored. Reactions (✅ on completion) never fire.

What — three sub-features on the same adapter:

3a. Markdown → Signal bodyRanges

New _markdown_to_signal(text) -> (plain, styles) 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, headings → BOLD, fenced/inline code, link unwrapping.

Includes two previously-reported regression fixes:

• Bullet lists (* item) no longer misidentified as italics
• URLs containing underscores no longer italicized around the dot

3b. Reply-quote extraction

Parses dataMessage.quote and populates MessageEvent.raw_message with sender + timestamp_ms. Lets the gateway's existing [Replying to: "..."] injector work on Signal, matching Telegram/Matrix behavior.

3c. Processing reactions

Overrides on_processing_start → ⏳ and on_processing_complete → ✅ via sendReaction RPC, using targetAuthor/targetTimestamp from raw_message. Uses the ProcessingOutcome enum from commit 2.

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 (markdown conversion, UTF-16 offset correctness with non-BMP emoji, bullet-list and URL false-positive regressions, reply-quote extraction, reaction payload shape) + regression extensions to test_signal.py.

Risk: Medium-High — biggest patch in this PR. Feature is opt-in in the sense that only Signal users experience it.

Test plan

Automated (all green locally)

source venv/bin/activate
python -m pytest \
  tests/tools/test_send_file_tool.py \
  tests/gateway/test_stream_consumer.py \
  tests/gateway/test_stream_consumer_no_edit.py \
  tests/gateway/test_signal.py \
  tests/gateway/test_signal_format.py \
  -v

Result: 275 passed on the combined scope.

Manual Signal verification checklist

Against a real Signal test account:

• Code block rendering — ask "write me a python hello world in a code block" → monospace render, no literal backticks
• Bullet list, no italic false positive — ask "give me a bulleted list of 3 kitchen utensils" → * renders as bullet, not italic
• URL preservation — ask "summarize https://example.com/foo_bar_baz" → URL intact, no italicization around underscores or dot
• Reply-quote context — quote-reply one of Hermes' messages with "what did you mean?" → response references the quoted text
• Reaction lifecycle — send message, observe ⏳ on start and ✅ on completion, then the reply
• Emoji + formatting UTF-16 offsets — message with 👋 and **bold** → bold range correct across the non-BMP emoji

Files changed

Modified (6):

• gateway/platforms/base.py
• gateway/platforms/signal.py
• gateway/run.py
• gateway/stream_consumer.py
• tests/gateway/test_signal.py
• tests/gateway/test_stream_consumer.py

New (4):

• tests/gateway/test_signal_format.py
• tests/gateway/test_stream_consumer_no_edit.py
• tests/tools/test_send_file_tool.py
• tools/send_file_tool.py

Notes for reviewers

• Happy to split into three separate PRs if preferred — each commit stands on its own.
• Signal bodyRanges UTF-16 offset math is the highest-risk area; the dedicated tests (test_utf16_offset_*) are worth focused review.
• The no-edit-mode branch in stream_consumer.py is guarded by self._no_edit_mode and is dead code on edit-capable adapters.