# Phase 78-1: Inline Slots Fixed Mode (C3/C4/C5/C6) — Results

## Goal

Remove per-operation ENV gate overhead for C3/C4/C5/C6 inline slots by caching the enable decisions at a single boundary (`bench_profile` refresh), while keeping Box Theory properties:

- Single boundary
- Reversible via ENV
- Fail-fast (no mid-run toggling assumptions)
- Minimal observability (perf + throughput)

## Change Summary

- New box: `core/box/tiny_inline_slots_fixed_mode_box.{h,c}`
  - ENV: `HAKMEM_TINY_INLINE_SLOTS_FIXED=0/1` (default `0`)
  - When enabled, caches:
    - `HAKMEM_TINY_C3_INLINE_SLOTS`
    - `HAKMEM_TINY_C4_INLINE_SLOTS`
    - `HAKMEM_TINY_C5_INLINE_SLOTS`
    - `HAKMEM_TINY_C6_INLINE_SLOTS`
  - Hot path uses `tiny_c{3,4,5,6}_inline_slots_enabled_fast()`.

- Integration boundary:
  - `core/bench_profile.h`: calls `tiny_inline_slots_fixed_mode_refresh_from_env()` after preset `putenv` defaults.

- Hot path call sites migrated:
  - `core/box/tiny_front_hot_box.h`
  - `core/box/tiny_legacy_fallback_box.h`
  - `core/front/tiny_c{3,4,5,6}_inline_slots.h`

## A/B Method

- Same binary A/B (layout-safe): `scripts/run_mixed_10_cleanenv.sh`
- Workload: Mixed SSOT, `ITERS=20000000`, `WS=400`, `RUNS=10`
- Toggle:
  - Baseline: `HAKMEM_TINY_INLINE_SLOTS_FIXED=0`
  - Treatment: `HAKMEM_TINY_INLINE_SLOTS_FIXED=1`

## Results (10-run)

Computed via AWK summary:

- Baseline (FIXED=0): mean `54.54M ops/s`, CV `0.51%`
- Treatment (FIXED=1): mean `55.80M ops/s`, CV `0.57%`
- Delta: `+2.31%` ✅

Decision: **GO** (exceeds +1.0% threshold).

## Promotion

For Mixed preset/cleanenv SSOT alignment:

- `core/bench_profile.h`: `HAKMEM_TINY_INLINE_SLOTS_FIXED=1` default
- `scripts/run_mixed_10_cleanenv.sh`: `HAKMEM_TINY_INLINE_SLOTS_FIXED=1` default

Rollback:

```sh
export HAKMEM_TINY_INLINE_SLOTS_FIXED=0
```