bug(critical): silent truncation causes data loss — LLM takes decisions on incomplete diffs #827

User report

I did a diff between 2 large files (+1000 lines of data/yaml) and asked Claude for a summary.
RTK truncated the diff, Claude didn't tell me or didn't notice.
I made important decisions based on this diff that I can't undo (very frustrating).
Claude confirmed the next day that RTK had truncated the data.
I lost trust, I don't have time for this, I'm uninstalling.

Root cause

rtk diff silently truncates output at 3 levels:

1. Max 50 changes shown (.take(50)) — no warning to LLM
2. Lines truncated at 70-80 chars — content silently cut
3. No machine-readable truncation marker — LLM cannot detect data loss

Same pattern exists in rtk git diff, rtk read, and potentially other commands.

Impact

• P0 severity: Users make irreversible decisions on incomplete data
• Trust killer: Once bitten, users uninstall RTK
• LLM blind spot: Claude/Copilot cannot tell the user that data was truncated

Proposed fix

Short term (must-fix)

Add a clear, machine-readable truncation warning at the end of any truncated output:

[warn] Output truncated: showing 50/847 changes. Run `diff file1 file2` for full output.

This lets the LLM:

1. Tell the user the diff is incomplete
2. Suggest running the raw command for full output
3. Avoid making decisions on partial data

Long term

• Add --full flag to disable truncation for critical commands (diff, read)
• Consider making rtk diff of large files pass through to raw diff with a warning
• Tee integration: save full output to disk, print hint

Affected commands

Related

• BUG: file size returned by RTK is truncated #822 — file size returned by RTK is truncated
• diff reports "Files are identical" when lines differ by only a few characters #781 — diff reports files identical when they differ
• Signal truncation in git diff, git log, and json filters #621 — signal truncation in git diff/log

Priority

P0 — This is a trust and safety issue. Users who experience silent data loss will uninstall RTK permanently.