contract, connector: a listener's protocol offer is the entry's offer for its accepting side (INBOUND-LISTEN)

[MattJackson]

This PR is the INBOUND-LISTEN piece of step 36, per the ARCHITECT ruling of 2026-10-14. That ruling rejected hard-coding the listener's offer in the root.

The append

LocateIn gains a pre-tag tail: accept: u32 and _accept_reserved: u32. Its size goes from 152 to 160.

• accept = 1: asks the framer for the protocol offer (ALPN) that an ACCEPTING listener it frames makes. The target may be empty.
• accept = 0: the dial offer, unchanged. Every caller builds LocateIn zeroed, so no existing caller changes.

Why

The ALPN offer is the framer's on both sides (BUSBAR-1.6.0.md l.477-478), but the two sides differ. v1.5.5's client offered h2, http/1.1, while its listener offered http/1.1 alone (v1.5.5 crates/busbar/src/tls.rs:242).

What the connector does with it

• framer::accept_offer reads the accepting side's offer.
• Connector::listen secures a need's listener with that offer, never with the entry's registered dial offer.
• An entry that refuses the question offers nothing.

RED

connector_tests::a_listener_offers_the_entrys_accept_offer_not_its_dial_offer checks three things:

• the entry answers its dial offer and its accept offer differently;
• a TLS client offering h2, http/1.1 to the need's listener agrees on http/1.1;
• the listener does not use the server config's own pinned offer.

Other files

• The layout golden, its record list and the C header move with the append. The header is hand-written in the generator's format, and preflight's abi-header --write diff judges it.
• The hunks are disjoint from contract: an emit carries the answer's status on an accepted stream's head (INBOUND-LISTEN, l.4913) #1012's EmitIn append, and git merge-tree shows the two merging cleanly.

[MattJackson]

Rule 20 note from #1030 (row 155): disjoint hunks in busbar_plugin.h, abi-layout.golden, layout_golden.rs (OnPieceOut gains tap_fault at 181; _fault_reserved moves to 182, plus BB_PLANE_TAP_FAULT_* consts after UNITS_FLOOR). A test merge is clean.