mask-risc tests: count allocations per thread in borrowed_alloc and oracle_alloc

[AdaWorldAPI]

Problem

borrowed_alloc failed in the Rust Tests test job on #1349's head (run 37450481656):

the borrowed arena allocated 900 bytes across ten row counts

#1349 did not touch mask-risc.

Cause

The test measures allocations with a process-global AtomicUsize. libtest keeps its own threads running while the test body runs, and those threads can allocate while the measured window is open. no_alloc.rs had already recorded the same contamination at 790 bytes.

I reproduced it locally with CI's -C target-cpu=x86-64-v3, so this is not a SIMD-tier issue. The unchanged binary failed 1 run in 300 under CPU load (6 × yes).

Fix

borrowed_alloc.rs and oracle_alloc.rs now use the thread-local Cell counter that fused_ternlog.rs, fused_terminal.rs and program_collapse.rs already use. Every measured window runs on the test thread, so counting only that thread is exact. The module docs that described the counter as process-global are updated.

Verification

• Under the same load: 0 failures in 300 runs of each binary.
• The counter still catches real allocations: an 8-byte allocation planted inside borrowed_alloc's measured window turns the test red (80 bytes reported). Both existing can-it-fire probes are unchanged and pass.
• Gates: cargo test, clippy -D warnings and fmt are clean for lance-graph-mask-risc.

Scope: test-only; no library code changes.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MHMvKHLhM6xwRswKY4s6vY

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Reviewing files that changed from the base of the PR and between 3290a9c and 6cf5947.

📒 Files selected for processing (2)

• crates/lance-graph-mask-risc/tests/borrowed_alloc.rs
• crates/lance-graph-mask-risc/tests/oracle_alloc.rs

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(requestId: dc2696fa-3079-401c-ae5e-e1e3d059cbe6)

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Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T10:58:01.678070Z	6cf5947	Draft marked ready

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