gen-rust: a string parameter lowers to &'static str, so every host must leak its input #7449

Problem

t27c gen-rust lowers every string / str / []const u8 type to &'static str. That covers parameters too (bootstrap/src/compiler.rs:28328 and :28350). Generated code can only be called with a string that lives for the whole process, so a host that reads text at run time has to leak it first.

There are two callers today, and both do this:

• bootstrap/src/main.rs:7418 (t27c asm, t27a MVP: TRI-27 assembler/disassembler with a round-tripping field table (T735, T736) #6507): Box::leak(read_t27a_input(input)?.into_boxed_str()).
• cli/tri/src/mutate.rs, the mutate census glue for tri mutate census: one table and one exit code for a directory of specs #7433: one Box::leak of each spec's stdout before calling census::is_summary_line / summary_adds_up / count_at.

For a short-lived CLI process the leak costs nothing. But any long-running host (the Queen, a server, a loop over many inputs) has two bad choices: leak without bound, or hand-write the rule again in Rust. The only-t27 rule exists to prevent the second.

Expected

• A function parameter of type string lowers to &str, with an elided lifetime.
• A pub const NAME : str = "..." keeps &'static str.
• A function that returns a string slice of a parameter would need a named lifetime. If gen-rust cannot express that yet, it should refuse loudly rather than emit 'static.

Acceptance

• t27c gen-rust specs/tri/mutate/census.t27 emits pub fn is_summary_line(line: &str) -> bool and pub fn after_count(line: &str, at: usize, tail: &str) -> usize.
• With the regenerated files, the Box::leak in cli/tri/src/mutate.rs (census) and the one in bootstrap/src/main.rs (t27c asm) can be removed. Both crates still build: cargo build -p tri -p t27c.
• tools/l2_regen_check.py stays green: the generated files under gen/rust/ and bootstrap/gen/rust/ are regenerated in the same change.

Notes

• The fix is in bootstrap/src/compiler.rs, which moves FROZEN_HASH, so it lands through the owner's path.
• Found while wiring tri mutate census: one table and one exit code for a directory of specs #7433 slice 2b.

Boundary

• specs/tri/mutate/census.t27
• bootstrap/src/compiler.rs
• bootstrap/src/main.rs
• cli/tri/src/mutate.rs
• tools/l2_regen_check.py

User Scenarios

• Given a .t27 spec declares a function parameter of type string, when t27c gen-rust compiles it, then the generated Rust function signature uses &str with an elided lifetime instead of &'static str.
• Given a .t27 spec declares a pub const NAME : str = "...", when t27c gen-rust compiles it, then the generated Rust constant keeps type &'static str.
• Given a .t27 spec declares a function that returns a string slice derived from a parameter, when t27c gen-rust cannot express the required named lifetime, then compilation fails with a clear error rather than emitting 'static.

Requirements

• FR-001: Function parameters of type string / str / []const u8 MUST lower to &str with an elided lifetime in generated Rust code.
• FR-002: pub const declarations of type str with string literals MUST continue to lower to &'static str.
• FR-003: If a function returns a string slice tied to a parameter lifetime and gen-rust cannot express the required named lifetime, the compiler MUST emit a diagnostic error and stop rather than generate 'static.
• FR-004: The generated files under gen/rust/ and bootstrap/gen/rust/ MUST be regenerated in the same change so that tools/l2_regen_check.py passes.
• FR-005: After regeneration, the Box::leak calls in bootstrap/src/main.rs (for t27c asm) and cli/tri/src/mutate.rs (for census) MUST be removable while both crates still build with cargo build -p tri -p t27c.