ruling: phase0-comrak-002 (mimalloc) ACCEPTED, scoped to the comrak CLI workload

Human ruling on the needs-human-review allocator swap (+4.6%, CI
[+3.3%,+5.8%]): accepted as a real win for the measured comrak CLI
single-stream markdown-render workload, explicitly not a blanket
mimalloc mandate. Ledger row stays needs-human-review (append-only);
the ruling is documented in results/rulings/phase0-comrak-002.md and
reflected in the case study.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

results/rulings/phase0-comrak-002.md

@@ -0,0 +1,44 @@
+# Human ruling — `phase0-comrak-002` (mimalloc allocator swap)
+
+**Ruling: ACCEPTED, scoped to the measured workload.**
+**Ruled by:** project owner (repo maintainer), recorded 2026-07-12.
+**Ledger row:** `phase0-comrak-002` remains `needs-human-review` (the
+append-only ledger records what the *pipeline* decided; this document is
+the human decision layered on top).
+
+## What was measured
+
+Swapping comrak's global allocator to
+[mimalloc](https://github.com/microsoft/mimalloc):
+
+- **Speedup: 1.046 median, 95% CI [1.033, 1.058]** (+4.6%) on the comrak
+  CLI rendering the pinned Pro Git corpus (11.0 MB markdown, single
+  stream), interleaved A/B vs a pristine-rebuilt baseline.
+- Byte-identical golden replay. The pipeline routed it to
+  `needs-human-review` per SPEC §8 because a global allocator swap is a
+  behavioral change no single benchmark can fully clear.
+
+## The ruling and its scope
+
+**Accepted** as a real, CI-significant win **for the comrak CLI's
+single-stream markdown-render workload** — the workload measured, on the
+calibrated hardware in `results/calibration/`.
+
+This is explicitly **not** a blanket "always link mimalloc" mandate:
+
+- The upside (+4.6%) is genuine but modest; it does not justify making
+  mimalloc a default across unrelated targets or workloads without their
+  own measurement.
+- The comrak CLI on this workload is single-threaded, which is what makes
+  the ruling low-risk here — the concurrency/fragmentation concerns SPEC
+  §8 flags are minimal for a short-lived, single-stream CLI process. A
+  long-running or heavily-multithreaded comrak *library* embedding would
+  need its own review before inheriting this.
+
+## Why this is the honest resolution
+
+The `needs-human-review` tier exists precisely to force this judgment
+instead of letting a green benchmark auto-ship a global behavioral
+change. The judgment: yes for the measured CLI workload, with the scope
+written down so the number can't be over-generalized later. The tier did
+its job; the win is real; the ruling is bounded.