docs: warn that press_key/fill_input double-inserts characters on newer Chrome

[blaircullen]

What

Adds a field-tested gotcha to SKILL.md: press_key (and therefore fill_input, which calls it per character) double-inserts every character on newer Chrome.

Repro

new_tab("about:blank")
js("document.body.innerHTML='<input id=t>';document.querySelector('#t').focus();")
for ch in "abc": press_key(ch)
js("(()=>document.querySelector('#t').value)()")   # -> "aabbcc"   (expected "abc")

Confirmed on HeadlessChrome 149.0.0.0. Real-world symptom: a login filled via fill_input sent mm33mmeeddiiaa for m3media and the site returned "Invalid username or password" — looked like a credential problem, was actually doubled input.

Root cause

press_key dispatches keyDown with a text field and a separate char event:

cdp("Input.dispatchKeyEvent", type="keyDown", **base, **({"text": text} if text else {}))
if text and len(text) == 1:
    cdp("Input.dispatchKeyEvent", type="char", text=text, ...)

On newer Chrome the keyDown carrying text already inserts the character, so the explicit char event inserts it a second time. (On older builds keyDown(text) apparently didn't auto-insert, so the pair produced a single insert — hence it worked before.)

This PR

Documentation only — adds the symptom, root cause, and a native-value-setter workaround for controlled inputs.

Suggested real fix (not in this PR)

Make press_key insert exactly once on all Chrome versions — either drop text from the keyDown and let the char event do the insert, or send rawKeyDown + char. Happy to follow up with the code change + a regression test if you'd prefer it in the same PR.

🤖 Generated with Claude Code

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[browser-harness-review]

✅ Skill review passed

Reviewed 1 file(s) — no findings.