Required floor reports the eval-frame call memo's process-wide hits and misses

[gunbai-bot]

An instrument for the follow-up PR that changes the eval-frame call memo's key. That change must be judged on the FULL floor (deep-deer-663's parent, 2026-10-01), and the floor had no reading of this memo:

• The per-context counters (eval_call_memo_counters) die with each context.
• The process-level absorb that used to aggregate them was deleted as write-only; see the release_process_caches_at_exit doc.

Seed admission receipt: hand-written v1 seed Rust, admitted under gunbc.v1_maintenance_standing v1_seed_standing (DESIGN §3 purpose test). It serves the v2 self-host program: it is the reading by which the eval-memo keying change (#12934) is judged on the full floor. It adds observability only, with no gate and no new growth surface.

Change

• Counters: process-wide atomic hits and misses, maintained at the same two points as the per-context counters (eval_call_memo_get hit, eval_call_memo_put miss), so the two cannot disagree about what a hit is.
• Receipt line: claim_executor prints required-floor: eval_call_memo hits=<h> misses=<m> beside the existing compile_dag_rust_emit_check_memo and compile_dag_diagnostic_census_memo receipts, one line each, as those are.

This PR's own CI floor run is the BEFORE reading for the memo-key PR. Both runs report through this one instrument, so the numbers are cited from the runs, never transcribed (DESIGN §6).

Evidence: cargo clippy -p v1-compiler --all-targets -- -D warnings is clean (remote).

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