feat(signal): add author-aware native reply quotes

[poisdahl]

Summary

Add native Signal reply quotes end to end using the displayed-message timestamp and actual sender identity.

This supersedes #30453. Its core idea and original commit are preserved with @xyanglu's authorship, while the implementation is rebuilt for current main and fixes the group-chat author bug identified in review. Addresses the outbound-quote slice of #39043.

Why

signal-cli requires quoteAuthor whenever quoteTimestamp is present. A Signal group destination is not the author of the quoted message, so using chat_id can fail the send RPC. Edited envelopes also have a fresh event timestamp and a distinct editMessage.targetSentTimestamp for the displayed/original message.

Changes

• preserve normal inbound data-message timestamp as the event/dedupe identity, with envelope fallback
• keep edited events distinct while retaining targetSentTimestamp as the native quote/reaction anchor
• prefer Signal ACI / sourceUuid as quote author, with sourceNumber fallback
• emit quoteTimestamp and quoteAuthor atomically, or safely fall back to an unquoted send if either value is invalid
• preserve the latest native anchor through debounce, separate busy bursts, and /steer queue fallbacks
• cover text, images, documents, voice/video, and multi-image sends
• quote only the first chunk when a long text reply is split into multiple Signal messages
• correct the Signal guide's obsolete version-fallback claim and retain contributor attribution

Validation

Refreshed onto main@fef0e16fe on 2026-09-08; exact head 25d09c66de. Native quote metadata and upstream's durable route metadata are both preserved. MessageEvent imports follow the current owner module.

• scripts/run_tests.sh tests/gateway/test_signal.py tests/gateway/test_queue_command.py — 87 passed, 0 failed
• scripts/run_tests.sh tests/gateway/test_kanban_routed_transport.py tests/gateway/test_kanban_route_anchor_capture.py — 6 passed, 0 failed
• Ruff on changed Python files and git diff --check against current main: clean
• Fresh GitHub CI, Docs, Nix, Docker amd64/arm64, macOS, and Windows checks all succeeded

Scope and related work

This PR does not implement outbound edits, remote delete, read receipts, or arbitrary agent/MCP reply operations.

• feat(signal): add timestamp edits and opt-in tool progress #34561 is complementary outbound edit/progress and send-ID work and overlaps several files
• feat(signal): add policy-aware read receipts #67495 is the policy-aware read-receipt PR and has a direct Signal-envelope interaction with this branch
• remote delete should follow the final timestamp/revision ownership contract rather than being stacked here

Merge sequencing with #67495

Whichever of #67495 and this PR lands second must be rebased and revalidated on the merged Signal envelope path.

The combined implementation must preserve separate timestamp meanings for edits:

• read receipts target the fresh nested data-message/event timestamp
• quote and reaction anchoring target editMessage.targetSentTimestamp
• the merged raw metadata must retain feat(signal): add policy-aware read receipts #67495's sender_uuid and is_note_to_self fields as well as this PR's native anchor

Do not collapse receipt identity and displayed-message anchoring into one raw timestamp field.

[teknium1]

Thanks for rebuilding the quote path around the current Signal adapter. The premise is confirmed on current main: gateway/platforms/signal.py:749 constructs inbound events without message_id, gateway/platforms/base.py:115 therefore has no Signal reply anchor, and gateway/platforms/signal.py:1055-1095 does not translate reply_to into Signal RPC quote fields.

The proposed flow is appropriately scoped: it preserves the sender identity already retained as user_id_alt / user_id (gateway/platforms/signal.py:709-718), emits timestamp and author atomically, and follows existing metadata propagation across text and attachment delivery paths (gateway/platforms/base.py:5097-5103, 5128-5133, 5185-5224). No blocking implementation issue was identified from the diff.

Automated hermes-sweeper review.

[alt-glitch]

This was generated by AI during triage.

Related to #30453 and the #39043 Signal capability umbrella. This is a current-main salvage that adds the group-safe quoteAuthor mechanism, so it is not marked duplicate.