fix: incorrect nested iframe xpaths

[seanmcguire12]

why

• incorrect/broken xpaths for nested iframes with siblings meant act often failed on websites where the HTML follows this pattern
• getAccessibilityTreeWithFrames() populates an internal map: seg: Map<Frame | null, string>
• for every iframe it visits, the map stores the frameXpath the XPath segment (/html/body/iframe[2], …) pointing from that iframe’s parent document to the iframe element itself
• previously, the map key was the parent frame: seg.set(snapshot.parentFrame, snapshot.frameXpath);
• if a website contains 2+ sibling iframes, the first siblings frameXpath would get overwritten/lost

what changed

• keyed the seg map by the frame itself so that siblings are no longer overwritten

test plan

• added an eval that has nested iframes with siblings

[changeset-bot]

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Latest commit: 7b5d562

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[greptile-apps]

Greptile Summary

This PR fixes a critical bug in the XPath generation system for nested iframes. The core issue was that when multiple sibling iframes existed on a page, the XPath mapping would incorrectly overwrite previous siblings' paths, causing act() operations to fail. This was due to using the parent frame as the key in the internal seg map.

The fix changes the seg map to be keyed by the frame itself rather than its parent frame, ensuring each iframe's XPath information is preserved independently. This is a robust solution that maintains the integrity of the XPath hierarchy while fixing the sibling iframe issue.

The changes include:

• Modified lib/a11y/utils.ts to use frame instead of parentFrame as map key
• Added a new required frame field to FrameSnapshot interface
• Added a new eval test case 'nested_iframes_2' to validate the fix

Confidence score: 5/5

1. This PR is very safe to merge as it fixes a clear bug without introducing new complexity
2. The score is 5 because the change is well-isolated, includes tests, and fixes a clear logical error in the original implementation
3. While all changes look good, pay special attention to lib/a11y/utils.ts as it contains the core fix

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[MrHaikuSwan]

@seanmcguire12 = 🐐