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docs(desktop): correct leak-typing numbers on a real session

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Re-ran the leak harness on a populated session (Phaser thread) for both
unpatched and patched builds. The original 'listener leak' was transient
warm-up cost, not a steady-state leak — both versions show 0 listener
growth/round in steady state.

The load-bearing number is forced layouts per character:
  unpatched (HEAD~2):  7.02 layouts/char
  patched   (HEAD):    2.35 layouts/char  (3× fewer)

The patches reduce per-char forced-layout work to Blink's natural floor.
Document node count and heap are flat in both builds.
This commit is contained in:
Brooklyn Nicholson 2026-05-21 17:14:21 -05:00
parent a1b8631176
commit e18c233c1e
1 changed files with 22 additions and 19 deletions
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41
apps/desktop/scripts/profile-typing-lag.md
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@ -58,31 +58,34 @@ makes the path slow.
### Leak counters — `leak-typing.mjs`
Types N chars, clears, force-GCs, captures `Performance.getMetrics` deltas.
Reveals leaked event listeners, heap drift, document node growth, and
forced-layout counts.
Types N chars per round, clears, force-GCs, captures
`Performance.getMetrics` deltas. Reveals leaked event listeners, heap
drift, document node growth, and forced-layout counts.
```bash
node apps/desktop/scripts/leak-typing.mjs --rounds=6 --chars=200 --cps=50
# After clicking into a real session (e.g. via click-session.mjs):
node apps/desktop/scripts/leak-typing.mjs --rounds=8 --chars=200 --cps=50
```
Before patches (real run on this branch's previous tip):
```
heapUsedMB Δ/round=+0.06 /char=+0.0003
jsListeners Δ/round=+34.75 /char=+0.1737 ← LEAK
layoutCount Δ/round=+453.00 /char=+2.27
```
**Real-session numbers (Phaser thread, 8 rounds × 200 chars):**
After patches:
```
heapUsedMB Δ/round=+0.00 /char=+0.0000
jsListeners Δ/round=+0.00 /char=+0.0000 ← fixed
layoutCount Δ/round=+476.00 /char=+2.38
```
| | unpatched (HEAD~2) | patched (HEAD) |
|---|---|---|
| jsListeners growth/round | +0 | +0 |
| DOM nodes growth/round | +0 | +0 |
| heap growth/round | ~0 (V8 housekeeping) | ~0 |
| **forced layouts/char** | **7.02** | **2.35** (3× fewer) |
The listener leak is gone. The forced-layout count is unchanged because
~2 layouts/char is what Blink naturally does when a contentEditable grows
1px per character; not a JS-driven flush.
The forced-layout count is the load-bearing number — typing into a real
session was triggering ~7 layouts per character on the unpatched build
(scrollHeight reads + per-px CSS var writes + FadeText scrollWidth reads
all stacking up). After the patches it's down to ~2.35/char, which is
Blink's natural cost for a 1px/char-growing contentEditable and can't
be lowered further without architectural changes.
The initial "+35 listeners/round leak" I called out on the first
unpatched run turned out to be transient warm-up (popovers initializing,
etc.); steady-state listener growth was 0 both before and after.
### CPU profile + heap snapshot — `profile-typing.mjs`