The compile is a UI load's biggest removable cost and the only half of it that can
be kept — running the chunks is what an addon *is*. Measured through the addon
harness's `--together` load of the player's own 91 addons, three passes:
```
no cache 4,788 chunks compiled 3,324 ms
cold 1,592 compiled, 3,196 from cache 1,482 ms
warm 0 compiled, 4,788 from cache 471 ms (+24 ms of keys)
```
**About 940 ms off every login and every `/reload`**, and the first load after an
addon changes pays only for the files that changed.
`benilla-config/cache/lua/`, one file per chunk, keyed by a hash of the chunk's
own bytes and its name. Both chunk paths go through it — `run_chunk_named` and the
XML loader's own runner, which is how the biggest files in the corpus arrive
(pfQuest's database is 33 MiB of `<Include>`d Lua).
It cannot go wrong quietly. A key is a property of the bytes, so an edited file is
a different entry and a stale one is never asked for; an entry that is truncated,
corrupt or from another Lua build fails `lua_undump`'s header check and the source
is parsed instead, so a bad entry costs the parse it meant to save. The dump keeps
its debug info — `debugstack` is an addon-facing verb and a stripped chunk would
lie about its own lines — which the test asserts by raising from a cached chunk
and demanding its file and line back. The folder is capped at 512 MiB (one load's
worth is 159 MiB) and emptied wholesale when it is over: a cache that needed an
eviction policy would need bookkeeping that costs more than it saves.
The first build of this looked like it worked and saved nothing, because
`ahash::AHasher::default()` is seeded per process: every session hashed the same
file to a different name, found nothing and rewrote the whole cache (4,776 entries,
477 MiB, a steady 1,592 misses a run). Fixed seeds, and the instrument that caught
it — `benilla_ui::script::chunk_cache_line()`, hits and misses with the time each
spent — stays, because "the cache is installed" and "the cache is working" turned
out to be different claims.
Verified: the harness's verdicts over all 91 addons are **identical** with the
cache and with `WOW_LUA_CACHE=0`, the full gate chain is green, and the
`WOW_DATA` failure sets are unchanged (benilla-app 270, benilla-formats 80).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn
gromandClaude Opus 5
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