fix(pretty): prefer details.patch over details.diff for edit tool rendering

[iamxeph]

Problem

When diffSplit: true is enabled, the edit tool diff never renders in side-by-side mode and silently falls back to a unified diff. Similarly, word-level diff emphasis and line-number gutters fail to activate for edit results, degrading to plain line-colored output.

Root Cause

In pi's core edit tool (packages/coding-agent/src/core/tools/edit.ts), EditToolDetails explicitly provides two diff representations:

export interface EditToolDetails {
	/** Display-oriented diff of the changes made */
	diff: string;
	/** Standard unified patch of the changes made */
	patch: string;
	firstChangedLine?: number;
}

When executing an edit:

const diffResult = generateDiffString(baseContent, newContent);
const patch = generateUnifiedPatch(path, baseContent, newContent);
return {
	content: [...],
	details: { diff: diffResult.diff, patch, firstChangedLine: diffResult.firstChangedLine },
};

extensions/pretty.ts previously read only result.details.diff (the display-oriented diff which lacks @@ hunk headers). Because details.diff does not contain @@ hunk headers, the inHunk state in both src/split.ts (parseRows) and src/diff.ts remained false across all lines. Consequently:

• buildSplit treated every line as an unparsed full row, failing to split into columns.
• colorizeDiff skipped paired word-diff analysis and line-number gutter formatting.

Solution

• Added extractEditDiff(result) in extensions/pretty.ts to prefer details.patch when available, falling back to details.diff.
• With details.patch (the standard unified patch) consumed, buildSplit and colorizeDiff receive the expected hunk headers, allowing side-by-side split rendering, word-level emphasis, and line gutters to work as originally designed without altering any core parser logic.

Verification

• Added integration tests in test/wire.test.ts:
  • edit result prefers details.patch over details.diff (verifies split view separator │ is present when diffSplit is on)
  • edit result falls back to details.diff when details.patch is absent
• Ran bun run typecheck: clean (0 errors).
• Ran bun test: all 124 tests passed (0 failed).
• Verified interactively in pi: side-by-side split diff and word-level emphasis render cleanly.