row 155 B1a: DEFAULT_PROTOCOL leaves busbar-kernel; the 1.5.5 refusals of the provider dialect keys are pinned

[MattJackson]

Row 155 B1, first slice (B1a). Not a money ($) change. Not run locally: per the lane rules there is no cargo build/test/clippy/xtask on the laptop, only cargo fmt. ModernCI is the proof.

What

• DEFAULT_PROTOCOL = "anthropic" and default_protocol() are deleted from busbar-kernel (config/providers.rs:112). ProviderCfg::protocol becomes #[serde(default)]: an omitted key is empty, and the kernel fills in no dialect.
  • Governing lines:
    • BUSBAR-1.6.0.md Part 2 ci: close the gaps the 1.5.3 release found, at the root #49: "Core/kernel contains zero plane-instance literals ... and zero transport-protocol/scheme literals".
    • Part 0 THE DESIGN §4: "A plane receives, at open, the dialect fields of the providers it references and resolves model → dialect itself; the kernel checks no dialect".
    • Part 2 #1: "Core names ZERO plane types".
  • The omitted-key default is the llm plane's own (busbar-plane-llm exchange::shaping::DEFAULT_PROTOCOL).
• No customer-visible byte moves.
  • Only a direct ProviderCfg parse ever reached the kernel default, and only tests do that.
  • The catalog's ProviderDef::protocol is required (1.5.5 too, and pinned below), so every resolved provider carries the catalog's dialect.
  • config-schema.snapshot.json is unchanged: it already records ProviderCfg.protocol as optional: true.
• Pins for the coordinator's validation guard. The dialect keys' refusals must stay byte-identical to 1.5.5 in text, order, field path and boot-time stage. crates/busbar-kernel/src/config/tests/provider_refusal_pins.rs pins each 1.5.5 refusal of protocol, error_map, path and path_base that no oracle cell or test already pinned:
  • the deployment invalid-type sentences, each at its own line/column;
  • the catalog missing field \protocol``;
  • the composed-destination refusals base_url+path and base_url+path_base (v1.5.5 crates/busbar/src/config_validate/mod.rs:406 and :430), in order.
  • Already pinned elsewhere, so not repeated: BOOT-020 (unknown protocol), BOOT-022 (StatusClass), BOOT-026..029 (leading /), BOOT-122 (catalog protocol type) and NEUT-U-providers (unknown key).

RED

config::tests::an_omitted_provider_protocol_names_no_dialect_in_the_kernel. On base, an omitted protocol: read the kernel's dialect name; after this PR it is empty.

Rows drained (before → after)

• qa/c1-literals.toml: finding c1-literals:literal · crates/busbar-kernel/src/config/providers.rs · anthropic: 1 → struck.
• qa/construction.toml kernel known_sites: crates/busbar-kernel/src/config/providers.rs :: anthropic: 1 → struck.
• scripts/plane-grep-gate.sh ALLOWLIST: anthropic|crates/busbar-kernel/src/config/providers.rs|DEFAULT_PROTOCOL: 2 rows → 1. The row would now suppress nothing and fail the dead-row check.
• plane-purity frozen-wire pragmas in busbar-kernel: the production one (providers.rs) and its test-scope twin (serde_default_fns_return_their_documented_constants) are deleted.

The B1 field split (lane design; not all in this PR)

• Core-owned, typed in the kernel: base_url, api_key (SecretRef), health, allow_metadata_hosts, and the outbound-auth binding auth, token_url, scope, subject.
• Provisionally core-owned, pending the ARCHITECT ruling: path and path_base. The boot destination guard composes base_url+path and base_url+path_base (config_validate/mod.rs:2281-2335).
• Plane-shaped, carried by core as an opaque table the llm plane parses: protocol (core reads it only as an opaque word through contract MODEL_PROTOCOL_KEYS for the auth default style, #50), error_map, organization, project, max_output_key, anthropic_adaptive_thinking, native_structured_output, model_capabilities.

What follows (not this PR)

• B1b, the resolved-side table. Two blockers:
  • ProviderCfg's protocol, error_map, path and path_base are in the v1.5.3 config-schema baseline. Removing them is an additive-only RED that needs owner waivers or a new resolved type; this is with the ARCHITECT.
  • Every resolved-side reader routes through crates/busbar/src/root/door_steps.rs (kernel_sections, provider_routes). That file is edited by the open row 155: the door path serves budget on_exhaust: downgrade as 1.5.5 did ($, ahead of #824) #833, row 155 (L1#3): a model's protocol override reaches the llm plane and is served, fail-closed (#51) #841, row 166 PR1: secret resolve takes a config-time proof (ConfigScope) and the config-scope gate #863 and row 74 F25: a lane base URL's userinfo is stripped, never dialled, sent or printed, as 1.5.5 did #876 (queue rule 20).
• B1c, the grammar. It waits for the ARCHITECT's ruling on the seam: a neutral shape descriptor parsed in-stream, or the frozen structs kept as they are.

Shared-file note

crates/busbar-kernel/src/config/tests/tests.rs is also touched by #900 (and draft #571). The hunks are disjoint: lines 1-10, around 1440-1580, and around 2240.