$ llm plane: Bedrock InvokeModel (protocol: bedrock-invoke), the Anthropic dialect inside the invoke envelope (stacked on #841)

[MattJackson]

PARITY-SCOPE item 2. The owner's 2026-09-29 compat scope puts the "Bedrock InvokeModel dialect" in scope (BUSBAR-1.6.0.md l.4805; l.4810 "Anthropic-on-Bedrock InvokeModel chat only"; l.4835; E table l.5499 "no evidence found"). #841 is only the model-override seam. The design is ARCHITECT-approved 2026-10-14 with four conditions, each met below. Stacked on #841: DRAFT until #841 lands. It is $, so it lands alone (rule 15).

Design. InvokeModel takes Anthropic's own Messages body and answers with Anthropic's own body and events, so bedrock-invoke is the Anthropic dialect carried inside Bedrock's envelope, not a seventh dialect. A model selects it with models.<m>.protocol: bedrock-invoke on a Bedrock provider. exchange/invoke.rs owns the envelope:

• Target. /model/{model}/invoke, or /invoke-with-response-stream. It is encoded by the same wire_and_canonical_path the Converse target goes through.
• Body. A byte-level splice, never a re-serialization: model and stream are removed, anthropic_version: bedrock-2023-05-31 is stated, and the caller's anthropic-beta field moves to body anthropic_beta. The anthropic-version field and the dialect's static headers are not sent. A streamed request asks accept: application/vnd.amazon.eventstream.
• Relay. An Anthropic caller is RELAYED inside the envelope (dialect fidelity: same dialect, governed splices only). Other callers translate to Anthropic exactly as for an Anthropic provider.
• Streams. Each AWS event-stream chunk frame's base64 bytes is one Anthropic stream event. Transcoder re-frames it as that dialect's own SSE, the event JSON byte for byte, on the shared codec/eventstream.rs. A mid-stream exception frame or a malformed frame becomes the dialect's error event and ends the stream.
• Refusals. {message} plus x-amzn-ErrorType is restated as Anthropic's error envelope, with the exception mapped to its kind, before the failure judge reads it.
• Probes. A probe goes through the same envelope.
• Credential. root::door_steps::member_routes now falls back to the provider protocol's default style when the member's own protocol states none, so the model keeps its Bedrock provider's SigV4. No dialect is named.

Conditions (ARCHITECT 2026-10-14)

1. tests/dialect_self_contained.rs needs no exemption. Nothing under src/codec changed; the envelope lives in the plane's exchange adapter.
2. No ProtocolDecl change and no ABI change. The envelope is no declared protocol at all, so nothing needs a model_only flag: a provider cannot default to it because the kernel's provider sweep does not know the name.
3. The kernel reads nothing and names nothing. the_envelope_is_no_declared_protocol_and_the_1_5_5_list_is_unchanged pins DECLS to 1.5.5's six in order, which is the list BOOT-020 and validate_unknown_protocol_lists_only_the_configured_planes_dialects print. a_provider_never_defaults_to_the_envelope pins the plane's refusal.
4. 1.5.5 never served InvokeModel chat (E table l.5499), so this is new surface. It has a CHANGELOG Added line and no oracle cell.

REDs (busbar-plane-llm/tests/exchange_invoke.rs, plus the root's a_member_whose_protocol_states_no_default_style_rides_its_providers): lane resolution; the provider refusal; targets; relay inside the envelope (body members, beta flags, fields, accept); the whole-answer target; byte preservation of the body edit; stream re-framing at four chunkings; a mid-stream exception; refusal restatement; money: a streamed answer over the envelope meters the carried dialect's 11 in and 7 out through Reply, with the carried dialect's text/event-stream head; and the 1.5.5 protocol list.