Fix UI-TARS scroll parsing (scroll actions were silently dropped)

[jiayuww]

Problem

uitars_parser (in src/open_apps/agent/utils.py) never translated scroll
actions into BrowserGym scroll(dx, dy) calls. The raw model string was passed
through unchanged, and since it isn't a valid BrowserGym action signature, the
scroll silently failed. Every UI-TARS-family model (UI-TARS, and any model
routed through this parser) effectively could not scroll.

Click and type are translated correctly, so any eval dominated by click/type
never surfaced this — it only bites tasks that require scrolling.

How to reproduce

UI-TARS-1.5 emits scroll actions in this exact form (verified across real run
trajectories — 59 scroll steps sampled, e.g. scroll(direction='down', point='(612,455)'),
scroll(direction='down', point='(1022, 666)'), scroll(direction='up', point='(1920,536)')):

from open_apps.agent.utils import flexible_parser

resp = "<think>scroll to see more</think><action>scroll(direction='down', point='(612,455)')</action>"
print(flexible_parser(resp)["action"])

Before this PR this prints:

scroll(direction='down', point='(612,455)')     # unchanged — NOT a valid scroll(dx, dy) call

The string reaches BrowserGym as-is; scroll expects positional scroll(dx, dy),
not direction=/point= kwargs, so the action fails / no-ops. Click and type in
the same trajectory translate fine, which is why this stayed hidden.

Root cause

The two scroll branches had mutually exclusive conditions, so neither body
ever executed:

# scroll(direction='down', point='(906,509)') -> scroll(dx, dy)
if result["action"].startswith("scroll(direction=d"):          # gate: char after '=' must be 'd'  -> NO quote
    direction = re.findall(
        r"scroll\(direction='(.*?)', point='\((\d+),(\d+)\)'\)", # regex: requires direction='...'  -> a quote
        result["action"])
    ...

• The startswith("scroll(direction=d") gate requires the character right after
  = to be d (i.e. scroll(direction=down…, no quote).
• The regex requires direction='…' (i.e. with a quote).

No string can satisfy both at once, so the branch is dead code (same for the
up branch).

What we changed

Replaced the two dead branches with a single tolerant parse that:

1. matches any scroll(...) action,
2. extracts the direction (down/up/left/right) and the first two
   integers regardless of quoting/whitespace, and
3. emits an axis-aligned BrowserGym delta — down/right positive,
   up/left negative (a "scroll down" no longer also moves horizontally).

This also adds left/right, which the old code never handled.

if result["action"].startswith("scroll("):
    dir_match = re.search(
        r"direction\s*=\s*['\"]?(down|up|left|right)",
        result["action"],
        re.IGNORECASE,
    )
    nums = re.findall(r"-?\d+", result["action"])
    if dir_match and len(nums) >= 2:
        direction = dir_match.group(1).lower()
        x, y = int(nums[0]), int(nums[1])
        if direction == "down":
            dx, dy = 0, y
        elif direction == "up":
            dx, dy = 0, -y
        elif direction == "right":
            dx, dy = x, 0
        else:
            dx, dy = -x, 0
        result["action"] = f"scroll({dx}, {dy})"

Before / after (what the model emits -> parsed action)

model output	before (broken)	after (this PR)
scroll(direction='down', point='(612,455)')	scroll(direction='down', point='(612,455)') (invalid)	scroll(0, 455)
scroll(direction='up', point='(1920,536)')	scroll(direction='up', point='(1920,536)') (invalid)	scroll(0, -536)
scroll(direction='right', point='(300,400)')	(unchanged / dropped)	scroll(300, 0)
scroll(direction='left', point='(300,400)')	(unchanged / dropped)	scroll(-300, 0)

Click/type are unchanged:

model output	parsed action
click(point='(100,200)')	mouse_click(x=100, y=200)
type(content='hello\n')	keyboard_type(text='hello\n')

Tests

Adds tests/test_uitars_parser.py — 6 tests covering all four scroll
directions, whitespace tolerance in the point, and click/type regressions.
All pass.

Notes

• Coordinates are passed through as-is (raw pixels), matching the existing
  click-translation behavior.
• The scroll magnitude uses the point's coordinate on the scroll axis. This is a
  heuristic (the point marks where to scroll, while BrowserGym scroll takes a
  delta), but it scrolls the correct direction by a bounded amount instead of
  failing outright. Happy to switch to a fixed step size if maintainers prefer.

[marksibrahim]

Great catch Jiayu! This looks great