[codex] Preserve DECCOLM width on row resizes

[forketyfork]

what changed

• Preserve the active 80/132-column DECCOLM width when Architect's target column count has not changed.
• Let row-only updates resize the VT rows without resetting the DECCOLM width.
• Update VT pixel metadata on pixel-only layout updates.
• Send DEC 2048 resize reports with the VT model's logical rows/columns and the latest pixel fields.
• Add regression coverage for row-only and pixel-only layout changes, plus the architecture note.

why

The previous preservation check depended on the whole PTY winsize staying unchanged. A row-only or pixel-only layout update changed the winsize, so Architect resized ghostty-vt back to the computed grid/full column count and broke DECCOLM layouts like the vttest cursor movement table. DEC 2048 reports also need to describe the preserved VT model, not the PTY layout width.

checks

• zig build test
• zig build
• just lint

[chatgpt-codex-connector]

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[Copilot]

Pull request overview

Adjusts Architect’s terminal resize pipeline to keep ghostty-vt’s active DECCOLM (80/132) column mode stable across row-only and pixel-only layout updates, preventing unintended reflows when the layout’s target column count hasn’t changed.

Changes:

• Refines DECCOLM preservation to depend on layout column-target changes (not full winsize equality), allowing row-only resizes without resetting DECCOLM width.
• Updates ghostty-vt pixel metadata on pixel-only layout updates and ensures in-band (DEC 2048) reports still reflect new pixel geometry.
• Adds regression tests for row-only and pixel-only layout changes, and updates the architecture documentation to match the behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/app/layout.zig	Updates resize decision logic to preserve DECCOLM width across row/pixel-only changes; adds pixel-metadata update path and regression tests.
docs/ARCHITECTURE.md	Clarifies the terminal resize/DECCOLM preservation behavior in the architecture invariants section.

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