A DM reply carries no guild_id, so the connector's egress guard cannot
resolve the owning tenant from metadata.guild_id and declines the send
with "discord egress declined: target not routed to an onboarded tenant"
— the bug behind "the bot never replies in DMs". Guild replies are
unaffected (they carry guild_id), which is why the guild path worked
end-to-end while DMs looked broken.
The connector now resolves a DM reply's tenant from the recipient's
author binding (gateway-gateway #67, resolveByUser keyed on
metadata.user_id) — the outbound counterpart to inbound Phase 7a
author-first resolution. But it needs the recipient user_id ON the
outbound action, and the adapter only re-attached guild_id
(_capture_scope/_with_scope), no-op for DMs (the docstring even said so).
This extends the adapter's inbound-scope capture: for a DM (no guild_id)
remember chat_id -> the authentic author user_id we observed, and
re-attach it as metadata.user_id on outbound. Guild capture is unchanged
and wins when present; user_id is the DM-only fallback. The id is the one
the connector observed inbound (never gateway-asserted), so the trust
invariant holds.
+4 unit tests (DM reply re-attaches user_id + no guild_id; unknown chat
invents nothing; explicit user_id preserved; guild reply never carries
user_id). Proved load-bearing (reverting the re-attach fails the DM
test). 144 relay tests pass, ruff clean.
Pairs with gateway-gateway #67 (the connector-side resolver). Together
they close the DM-reply egress gap end-to-end.
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