`[ui-phases]` could say a window paid for 61 whole-graph derivations. It could not say which of the
forty-odd `touch_layout` sites asked for them, and that is the half a fix has to be aimed at.
Measured on the player's interface, one derivation costs ~15.5 ms — from two directions: the
derivation count explains total resolve time at r = +0.977 across twenty windows (solve count:
r = -0.33, so solves are free and derivations are everything), and 26 of 78 worst-single-call
figures over 1 ms land in the 15-16 ms bin across eleven unrelated handlers by six authors, two of
which fired exactly once for their whole window. Eleven handlers cannot each independently be
15.5 ms slow; it is one shared charge landing on whoever reads the graph first, which is also why
the same session shows `resolve` p99 at 14.4 ms and worst frames "mostly tick". One defect, two
accounts.
So `#[track_caller]` down the naming chain and a tally of `file:line`, printed in the report. Not a
backtrace: `WOW_LAYOUT_DERIVE_TRACE` already captures those and has to be rationed to `n` prints
because of what they cost. This is a `(&'static str, u32)` key off `Location::caller()`, cheap
enough to leave armed, and take-and-rearm so a window reports its own rows and a VM replaced by
`/rl` re-arms without anybody noticing it was replaced.
Also a `[churn]` window in tick_bench, which records a negative: a plate roster turning over 4-in-40
every ten frames costs **zero** derivations on the player's own interface. `sync_nameplates` pools
the plate frames, so a new key rewrites an existing plate and mints nothing. With `resolve_bench`'s
hover-sweep, tooltip-content and moving-region tests all asserting zero, four candidate triggers are
now ruled out offline and the live tally is what names the real one.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn
gromandClaude Opus 5
c1a56f98ab