$ llm codec: reasoning asks and hosted tools stop crossing into Bedrock/Anthropic, as in 1.5.5

[MattJackson]

What. This restores 1.5.5 for two translations that made a request bill work 1.5.5 never billed.

1. Bedrock thinking (row-159 L2#2, HIGH).
   • Before: a foreign reasoning ask (reasoning_effort, Anthropic thinking, Gemini budget) was written as Claude additionalModelRequestFields.thinking on a Bedrock Claude lane. That billed thinking tokens, stripped temperature/topP/top_k, and downgraded a forced toolChoice.
   • Before: the Bedrock reader promoted additionalModelRequestFields thinking/reasoningConfig/output_config.effort, so a Bedrock caller's ask switched thinking on at a foreign lane.
   • 1.5.5 dropped every cross-protocol ask on Bedrock egress (v1.5.5 crates/busbar/src/proto/bedrock/writer.rs:139-146) and promoted none (reader.rs:678, reasoning: None).
   • Now: the ask is dropped with a warn and reported as reasoning. The native additionalModelRequestFields still round-trips verbatim on the same dialect. The one registered crossing (CHANGELOG 1.6.0), Converse's top-level outputConfig.effort, is unchanged.
2. Anthropic hosted tools (row-159 L2#3, HIGH).
   • Before: a hosted tool that crossed the seam (Responses web_search, Chat web_search_options, web fetch, code execution) was written as an Anthropic server tool. Anthropic ran the searches and the turn charged search_units through server_tool_use.web_search_requests.
   • 1.5.5 stripped hosted tools before the Anthropic writer (v1.5.5 crates/busbar/src/proto/anthropic/writer.rs:171-178).
   • Now: they are dropped with a warn and reported. An Anthropic caller's own server tools are still relayed byte for byte, because the writer runs only across dialects.

Why. BUSBAR-1.6.0.md THE LLM DIALECT FIDELITY RULE: byte moves are pre-approved, but "Billing never moves". §7 Money and #77 keep the money path at 1.5.5. Neither move has an accepted-differences entry or a CHANGELOG line; the CHANGELOG lists only outputConfig.effort for Bedrock.

RED-able tests (1.5.5 egress bytes, from the lines above):

• bedrock/tests/ir_slot_wiring_tests.rs::a_reasoning_ask_neither_reaches_nor_leaves_bedrock_as_in_1_5_5: covers every ask kind × caps × model family, plus every native spelling on the read side.
• bedrock/tests/ir_mapping_structured_tests.rs::{a_native_reasoning_ask_is_not_promoted_to_the_ir, a_foreign_reasoning_ask_is_dropped_on_bedrock_egress}: temperature, topP and top_k are kept.
• bedrock/tests/ir_round3_tests.rs::{item12_off_writes_no_thinking_on_any_lane, item8_a_word_ask_on_an_adaptive_lane_writes_no_thinking}.
• codec/tests/ir_seam_tests.rs::bedrock_thinking_is_written_for_no_lane_model.
• codec/tests/parked_rows_cross_dialect_tests.rs: an additionalModelRequestFields budget no longer overrides the registered effort word.
• anthropic/tests/ir_slot_wiring_tests.rs::hosted_tools_that_crossed_the_seam_are_dropped_on_anthropic_egress, plus the ANT-13 round trip.
• req_a2b_thinking_metadata.json returns to its bytes from before 91ba178 ({"additionalModelRequestFields":{"top_k":40},…}).

No ledger, oracle cell or ceiling changes (net −390 lines).

[MattJackson]

row 155 B2 (#974) edits crates/busbar-plane-llm/src/codec/bedrock/mod.rs at fn claims and the DECL quota_exceeded_status / auth_failure_status_and_kind rows; disjoint from this PR's hunks.