R3-3 tool half: t27c run-record reports the independence level from independence.t27 #7600

Part of epic #6655, Round 3 item R3-3. The contract specs/verified/independence.t27 landed in #7516 (#7497). That issue names the tool half as a later slice: "generated Rust in t27c and thin glue reading three receipts". This is that slice.

Goal

t27c run-record reports whether a run's three placements are independent evidence, judged by independence.t27. Today it reports authentication (FRESH) and the die level (NAMED), but not whether the three placements ran on distinct dies.

Boundary

• bootstrap/gen/rust/verified/independence.rs: t27c gen-rust specs/verified/independence.t27, never hand-edited.
• bootstrap/src/main.rs: the #[path] module line.
• bootstrap/src/service.rs: run-record glue only.
• bootstrap/tests/signed_receipt_reader.rs: tests and the drift check.
• Hand-written foreign code stays inside the own-language budget: at most 40 lines per file and 80 per diff.
• No change to independence.t27 or any other spec. No gate files. No exit-code change: independence is reported, not yet required.

User Scenarios & Testing

• Given three FRESH, DIE_NAMED receipts naming three distinct dies under one key, run-record prints Independence: INDEP_DIES.
• Given three such receipts naming one die, it prints INDEP_NONE with first missing INDEP_SHARED_DIE (5).
• Given v1 receipts with no DNA, it prints first missing INDEP_DIE_UNNAMED (3).
• The verifier has no roster, so every key is ROSTER_NONE and INDEP_OPERATORS is never printed.

Requirements

• FR-1: the decision is indep_first_missing / indep_level from the generated Rust; the glue only parses the receipts' device_dna and key_id hex and passes them in.
• FR-2: the checked-in Rust is byte-identical to t27c gen-rust specs/verified/independence.t27, pinned by the existing drift test.

Success Criteria

• cargo test --release -p t27c --test signed_receipt_reader passes, including independence_needs_three_distinct_dies.
• cargo test --release -p t27c --test run_record_reader passes.
• A mutant that zeroes the parsed DNA fails independence_needs_three_distinct_dies.
• lefthook run pre-push passes: own-language and foreign-budget.