fix: preserve a distinct backup path for *.original.md inputs

[shaun0927]

Problem

PR #150 added automatic backup creation for memory_compress_file, but there is one filename shape where that contract breaks.

For inputs already ending in *.original.md, resolveBackupPath() returns the same path as the input file, so the function writes the backup and then immediately overwrites that same path with the compressed content.

Fix

Keep the existing behavior for ordinary Markdown files:

• notes.md -> notes.original.md

But make already-suffixed inputs produce a distinct backup path:

• notes.original.md -> notes.original.backup.md

This keeps the diff narrow and preserves the existing naming convention for the common case while making the advertised backup behavior true for *.original.md inputs.

Verification

• npm test -- test/compress-file.test.ts
• npm run build

Regression coverage added

New test case:

• notes.original.md writes its backup to notes.original.backup.md
• the backup contains the original Markdown
• the input file contains the compressed Markdown

[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: fd7cb9d8-078a-4976-b8eb-440126a8d82a

📥 Commits

Reviewing files that changed from the base of the PR and between 1bdeaad and 471ccbc.

📒 Files selected for processing (2)

• src/functions/compress-file.ts
• test/compress-file.test.ts

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📝 Walkthrough

Walkthrough

The resolveBackupPath() function in compress-file is updated to generate backup filenames conditionally: if the input filename ends with .original, it appends .backup instead of .original, preventing overwrites. A test case validates this behavior.

Changes

Cohort / File(s)	Summary
Backup Path Logic src/functions/compress-file.ts	Updated resolveBackupPath() to append .backup when basename ends with .original; otherwise append .original. Prevents duplicate .original suffix collisions.
Backup Path Test test/compress-file.test.ts	Added test case for files already ending in .original.md, verifying backup writes to .original.backup.md and original input receives compressed content.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 When .original comes to call,
We append .backup instead of all,
No overwrites shall befall,
The test hops through with ease and thrall,
A fix both simple and quite small!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly summarizes the main change: modifying backup path generation for files already ending with .original.md to produce distinct backups instead of collisions.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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