refactor(tui): yazi-style Miller columns, clipboard, debug tracing

[engalar]

Summary

• Refactor TUI to yazi-style Miller columns with tab-based navigation, async preview, and borderless UI
• Add clipboard copy support and NDSL/MDL format switching in overlay
• Add content-aware column widths with soft wrap and preview on drill-in
• Add debug trace logging via MXCLI_TUI_DEBUG=1 environment variable
• Fix animation issues: forward animTickMsg to miller, remove column-width animation for instant transitions

Test plan

• Run mxcli tui -p <project.mpr> and verify Miller column navigation works
• Test Tab key switches between columns
• Test clipboard copy (y key) in overlay view
• Test NDSL/MDL switch in overlay
• Test MXCLI_TUI_DEBUG=1 mxcli tui -p <project.mpr> produces trace output
• Verify column widths adapt to content without animation glitches

🤖 Generated with Claude Code

[ako]

Code Review: refactor(tui): yazi-style Miller columns, clipboard, debug tracing

Overview

Major TUI rewrite (29 files, +4024/-1561 lines) moving from a 2-panel layout to yazi-inspired Miller columns with tabs, async preview, and clipboard support. The old model.go, layout.go, and panels/ directory are deleted and replaced with app.go, miller.go, column.go, preview.go, tab.go, and supporting files.

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Critical Issues

1. itoa() is broken for numbers >= 10 (tui/tab.go)

func itoa(n int) string {
    return string(rune('0'+n%10)) + ""
}

For n=12 this returns "2", not "12". Use strconv.Itoa(n).

2. LoadTreeMsg always loads into the active tab (race condition, tui/app.go)

When a cross-project tab is created via PickerDoneMsg, a LoadTreeMsg is dispatched async. If the user switches tabs before it arrives, the handler updates the wrong tab. The message should carry a tab ID.

3. String truncation corrupts multi-byte characters (tui/column.go)

label = label[:contentWidth-2]

Byte-level slicing on strings containing emoji icons (from icons.go) will produce invalid UTF-8. Use lipgloss.Truncate() or rune-aware truncation.

4. View() mutations on value receivers are silently discarded (tui/miller.go)

View() has a value receiver and calls m.parent.SetSize(...), m.current.SetSize(...). These mutations are lost on the copy. Same issue with viewZen(). This works by accident because bubbletea re-renders frequently, but it's fragile and wasteful.

5. PreviewEngine goroutines leak on tab close and app quit

• PreviewEngine.cancelFunc is never called on app exit — only CloseTrace() is called
• When a tab is closed via W, its PreviewEngine (and any in-flight exec.CommandContext subprocesses) are never cancelled
• Should add a Close() method to PreviewEngine and call it on tab close + app quit

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Moderate Issues

6. ~315 lines of dead code in tui/keys.go

DefaultListKeys(), DefaultOverlayKeys(), DefaultCompareKeys(), DefaultTabKeys(), DefaultGlobalKeys() and their key map types are defined but never used anywhere. All key handling uses raw msg.String() comparisons. This entire file should either be integrated or removed.

7. Dead code in tui/tab.go and tui/miller.go

• NavState type is defined but unused
• MillerFocusPreview constant exists but focus is never set to it
• GoBack() and ToggleZen() exported methods are never called

8. CloseTrace() doesn't reset traceActive (tui/trace.go)

A Trace() call after CloseTrace() would attempt to write to a closed file.

9. //nolint:govet suppression (tui/miller.go)

func (m MillerView) handleMouse(msg tea.MouseMsg) (MillerView, tea.Cmd) { //nolint:govet

Suppresses the legitimate vet warning about value receiver semantics instead of fixing the underlying issue.

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Minor Issues

10. Magic numbers scattered throughout

• millerH := a.height - 3 — magic 3 for chrome height
• Column width thresholds: 80, 50, 30, 35, 25, 15, 8 in columnWidths()
• Scroll step 3 hardcoded in multiple mouse handlers

11. openDiagram — temp files never cleaned up, WriteString error ignored

Pre-existing issue but worth noting. Also nodeType and elkJSON are interpolated into HTML without sanitization (low risk since it's a local file).

12. tabbar.go — rebuildZones() in SetTabs() is redundant

View() clears and rebuilds zones from scratch, making the earlier call unnecessary.

13. Plan docs included in PR

docs/plans/2026-03-22-bson-ndsl-format.md (463 lines) and docs/plans/2026-03-23-tui-yazi-refactor-design.md (376 lines) are implementation plans. Consider whether these belong in the repo long-term or should be removed before merge.

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What Looks Good

• The overall architecture (Miller columns, async preview with caching + cancellation, tab system) is well-designed
• Clipboard implementation correctly uses stdin pipe (no command injection) with OSC 52 fallback for remote sessions
• sync.Once protection on trace initialization
• Preview cache prevents redundant mxcli subprocess spawns
• Clean separation of concerns across the new files

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Recommendation

Request changes — fix the critical bugs (#1-5) and remove dead code (#6-7) before merging. The value-receiver-mutation pattern (#4) is the most architecturally concerning issue and could cause subtle rendering bugs.

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