Post-1.0 code-shrink backlog (deferred from 2026-06-18 security review)

[laulpogan]

Deferred code-shrink candidates from the 2026-06-18 full security-review + shrink pass. Held until after the 1.0 soak — these touch security-critical relay/pairing hot paths, and refactoring them now would reset soak confidence on exactly the files that matter most. All are behaviour-preserving extractions; ship them once 1.0 is out.

The low-risk peripheral dedups from that pass already landed in #337 (parse_body_arg, hex_exact::<N>). The relay DoS-ceiling fixes landed in #336.

Relay (src/relay_server.rs)

• post_event + handle_intro share identical size/quota/dedup/slot-insertion logic (~30 LOC). Extract a common post_event_internal helper. Highest care — both are on the live relay ingest path.
• well_known_agent_card_a2a + well_known_agent share nick-parse → handle-lookup → 404 (~25 LOC). Extract the shared lookup; the two differ only in response envelope shape.

Pairing (src/pair_invite.rs)

• send_pair_drop_ack repeats the self relay/slot/token resolution-with-fallback logic also present in maybe_consume_pair_drop and send.rs::attempt_deliver (3 sites, ~40 LOC). Centralize into one resolver. Trust-adjacent — needs the pairing integration tests as the safety net.

Trivial single-use inlines (low value, evaluate individually)

These were skipped on "no single-use abstraction" grounds; only take the ones that genuinely improve clarity:

• agent_card::max_schema_version (~20 LOC, one caller) — simplify or inline
• agent_card::build_agent_card ↔ trust::add_self_to_trust JSON object overlap (~15)
• signing.rs [u8;32] validate+copy pattern (~15)
• enc/wire_x25519 context_info length-prefix framing helper (~6); nonce-init pattern (~5)
• platform.rs line-matching parse helpers (~8); read_wire_home_from_pid env-line parse (~6); parent_pid parse (~5)
• same_machine::local_fingerprint (~5); trust::now_iso inline (~4); org_membership::keypair test helper (~4)
• config.rs atomic-write-with-lock / lock-path helpers (~8)
• group.rs invalidate_signature (epoch++ / sig.clear) (~2)

Context

• Full review: 5 subsystems, 28 agents, 19/23 findings adversarially refuted as false positives.
• Total nominal LOC if all taken: ~209 (the 4 peripheral dedups, ~14 LOC, already shipped in refactor: dedup wire-send body parsing + collapse hex32/hex64 to a generic #337).

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