Fix underflow in flat storage RowIterator after a clear.

[vorporeal]

Description

Fixes the crash reported in Sentry issue WARP-CLIENT-BETA-STABLE-7TK6.

When flat storage had discarded prior scrollback, clearing all rows and then resizing rebuilt an empty row index with a zero content offset while the underlying content buffer retained its absolute offset. Materializing the next row could then underflow while indexing content and panic in RowIterator::next.

This preserves the existing absolute content offset when rebuilding an empty index and adds a regression test covering truncate-front, clear, resize, push, and row materialization.

Linked Issue

• Sentry: WARP-CLIENT-BETA-STABLE-7TK6

Testing

• Verified the new regression test fails before the fix in release mode with the expected range start index ... out of range for slice of length 1024 panic.
• cargo nextest run --manifest-path /Users/david/src/warp-2/Cargo.toml -p warp_terminal -E 'test(test_clear_after_truncate_front_then_resize_and_push_does_not_panic)'
• cargo nextest run --release --manifest-path /Users/david/src/warp-2/Cargo.toml -p warp_terminal -E 'test(test_clear_after_truncate_front_then_resize_and_push_does_not_panic)'
• cargo fmt --manifest-path /Users/david/src/warp-2/Cargo.toml -p warp_terminal -- --check

Manual validation and screenshots are not included because this fixes an internal flat-storage invariant that is directly reproduced by the unit regression test.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

Changelog Entries for Stable

CHANGELOG-BUG-FIX: Fixed a crash that could occur after clearing and resizing a terminal with scrollback.

Co-Authored-By: Oz oz-agent@warp.dev

[vorporeal]

• Fix underflow in flat storage RowIterator after a clear. #12085 👈 (View in Graphite)
• master

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[oz-for-oss]

@vorporeal

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[oz-for-oss]

Overview

This PR updates flat storage index rebuilding to preserve the absolute content offset when resizing an empty index after scrollback truncation and clear, and adds a focused regression test for the crash path.

Concerns

• No blocking correctness, security, or spec-alignment concerns found in the reviewed diff.

Verdict

Found: 0 critical, 0 important, 0 suggestions

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