fix(previewer): use Snacks.image for image preview when buffer is already loaded

[shy-robin]

Summary

When an image file is already open in a buffer (via nvim-tree, fzf-lua, etc.), previewing the same image in fzf-lua again results in a blank preview window.

Root cause: When entry.bufnr is set and loaded, the previewer copies buffer lines to a temp buffer (nvim_buf_get_lines → nvim_buf_set_lines). However, Snacks.image sets the image buffer's filetype to "image" with empty/placeholder content — copying these lines produces a blank preview, and attach_snacks_image_buf is never reached (it's in the else branch).

Fix: Detect image buffers (filetype == "image") early in the entry.bufnr branch and delegate to attach_snacks_image_buf instead of copying lines.

Steps to reproduce

1. Use fzf-lua to find an image file → preview works ✓
2. Open the image into a buffer
3. Use fzf-lua to preview the same image again → blank preview ✗ (fixed)

Test plan

• Preview image not yet loaded → works
• Open image to buffer, then preview again → works (was blank before fix)
• Non-image buffers still preview normally via line copying
• No regression for inline image rendering in markdown previews

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved preview handling for image files to display them correctly instead of rendering as text.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e0e04fa3-9d00-41e9-bbb4-bf33063d33ab

📥 Commits

Reviewing files that changed from the base of the PR and between c9e7b7b and e4cb715.

📒 Files selected for processing (1)

• lua/fzf-lua/previewer/builtin.lua

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📝 Walkthrough

Walkthrough

A conditional check is added to handle image buffers specially in the preview population logic. When an entry buffer is loaded and contains image data, the code now routes through attach_snacks_image_buf with a temporary buffer instead of copying buffer lines, with early return on success or fallthrough to existing behavior on failure.

Changes

Cohort / File(s)	Summary
Image Buffer Preview Handling lua/fzf-lua/previewer/builtin.lua	Added conditional logic to detect and handle image buffers using attach_snacks_image_buf instead of standard buffer line copying; falls back to existing behavior if attachment fails.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 ✨ A rabbit hops through preview land,
Where images now beautifully stand,
With Snacks attached, no lines to copy,
The code stays clean, the buffers snappy!
Hop along, dear dev, all is grand! 🖼️

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the main change: fixing image preview behavior by using Snacks.image when an image buffer is already loaded, which is the core issue addressed in this pull request.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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