tri mutate spec: guard and operator mutants of a .t27 spec, run through t27c gen + zig test #6993

Problem

tri mutate run perturbs numeric literals only. The mutation runs that found 6 test gaps and 2 dead lines in specs/queen/actors.t27 (#6963) and 2 more in its follow-up (#6971) mutated guards and operators -- dropping an if (...) { return ...; } line, >= -> >, == -> != -- from a hand-written throwaway pairs list in /tmp, at about 13 s per mutant. Every spec loop rewrites that list.

Change

tri mutate spec --file <spec.t27> [--fn <name>] [--max N] [--jobs N]: generates the mutants itself (drop a one-line guard, flip a comparison, and<->or, + 1 -> nothing), lowers each with t27c gen, runs zig test on it, and prints each survivor with its line, so a survivor is read as a dead line or a test gap. The file is never edited in place: mutants live in a temp dir. --fn limits the run to the lines of one function, so a loop tick mutates only what it changed.

Acceptance

• on specs/queen/actors.t27 at spec(queen): BEAM-style actors under the Queen's agents -- pids, mailboxes, links, monitors, supervisors (Closes #6963) #6966's head it reports 0 survivors among guard drops, and its count matches the hand list;
• a planted test gap (delete one assert of each_strategy_picks_its_own_children) is reported as a survivor -- the negative control;
• card specs/tools/tri/mutate.t27 lists the new action; tri inventory check green.

Foreign code: Rust in cli/tri/src/mutate.rs under the owner's standing owner-approved-foreign approval (2026-10-06). Built on the Railway lab, not the Mac.

Part of #6971.