Two follow-ups to the V4.8.2 duplicate-fan-out fixes Prism filed.
1. `Inbox.acceptBridgeFrame(blob)` + shared 4096-entry msgId LRU.
The relay durably stores blobs and pushes them to every active
delivery channel; without a cross-channel ack the bridge frame
ran first and the next inbox-poll re-dispatched the same blob
~30 s later, tripping on consumed prekeys. Bridge consumers now
plumb pushed frames through `acceptBridgeFrame`, which shares
the dedup gate + ack path with `pollOnce`. Whichever channel
delivers first wins; the other acks-and-skips. Inbox records
the msgId before the ack so a parallel poll can't observe an
in-flight ack window.
2. `Shade.aliasSession(oldLabel, newLabel)`. First-contact forces
the receiver to label the new session by the relay's sender
fingerprint hint (`fp:<senderfp>`); the post-decrypt plaintext
typically announces the peer's real address. Aliasing moves
session, trusted identity, peer-verification, and identity-
version under the canonical label. Holds the per-peer mutex on
both labels (lexicographic order) so concurrent crypto ops can't
observe a half-moved state. Refuses to overwrite an existing
session at the new label.
Wire change: `IncomingMessage.expiresAt?` now surfaces the relay's
expiry so receivers can pass bridge frames straight to
`acceptBridgeFrame` without inventing a TTL.
Tests cover bridge-then-poll, poll-then-bridge, aliasSession happy
path, refuse-to-overwrite, and same-label no-op.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>