t27o: the oracle samples texts that never reach a match arm, so text predicates pass vacuously #9102

Part of the t27o epic (see #8998). Found by the dogfood run of tri t27o on bootstrap/src/compiler.rs (see #9090, see #9093).

The oracle passes a text parameter the same fixed samples every time: "", "a", "abc", "0", "42", "0x1f", "a b" and "-7". compiler.rs is full of predicates that match a type name or an operator. For every one of them, all 8 vectors reach the default arm. Of the 15 compiler.rs helpers that t27o converted, the 7 with a text parameter all have only default-arm vectors:

• zig_uint_bits, int_value_bits, int_rank and is_integer_type_suffix;
• compound_binop, is_icarus_builtin and has_empty_operand.

So "oracle-equivalent" says nothing about the arms. A body with every arm but the default deleted passes the same 8 asserts. In #9093 the port had to add 26 hand-picked vectors per function (from the Rust, on the lab) before the tests meant anything.

User Scenarios

• Given fn int_rank(ty: &str) -> u32 { match ty.trim() { "u8" | "i8" => 8, ..., _ => 0 } }, when tri t27o --oracle writes the harness, then the samples for ty include every string literal the body compares ty (or a value derived from it) against, those literals with surrounding whitespace, and the fixed samples.
• Given a predicate over bytes (matches!(b[i], b'+' | b'-' | ...)), when the harness samples a text parameter, then the samples include texts that contain those byte literals.
• Given a converted body with one arm deleted, when tri t27o --check runs, then a test oracle_* block FAILs.

Requirements

• FR-001: The oracle harness MUST add, for each text parameter, the string literals of the body's match arms, == comparisons and starts_with / ends_with / contains arguments, each alone and wrapped in one space, plus the body's byte and char literals as one-byte texts.
• FR-002: For integer parameters it MUST add the integer literals the body compares against, and those values plus and minus one.
• FR-003: The number of samples MUST stay bounded (at most 64 per parameter), and the choice MUST be deterministic.

Success Criteria

• tri t27o --check on a file holding compiler.rs's compound_binop writes an oracle_compound_binop test with at least one assert whose expected value is not null.
• tri t27o --check on the same file, with the "/=" arm deleted from the Rust copy and the converted spec built from the unmodified Rust, exits non-zero.

Boundary

• specs/tools/t27o/rust_convert.t27
• gen/rust/tools/t27o/rust_convert.rs
• .trinity/seals/t27o_T27oRust.json