gh pr diff silently truncates multi-file PRs (max_lines=100)

[PLNech]

Summary

rtk gh pr diff calls compact_diff(&raw, 100) which silently drops output after 100 compacted lines. For multi-file PRs (3+ files with non-trivial changes), this truncates the diff without any signal to the caller — no exit code change, no stderr warning.

Impact

• Agents doing PR review receive incomplete diffs and miss findings in later files
• Silent truncation: agent has no signal to retry or fallback
• Workaround: gh pr view --json files,additions,deletions,body works but requires knowing about the limitation

Root cause

src/gh_cmd.rs:1070 — compact_diff(&raw, 100) hard-caps at 100 lines total output. This was likely inherited from the local git diff path where 100 lines is reasonable. PR diffs are structurally larger.

Fix

Raised max_lines from 100 to 500 in pr_diff(). Regression test added with synthetic 5-file PR diff asserting all files appear in output.

Fixed in commit 859143c on feature/agentic-fuzzing branch.

Upstream candidate

This is likely an upstream bug too (default value error, not a design choice). The compact_diff function's max_lines parameter was designed to be configurable per-caller, but pr_diff just used the same low default as local diffs. Could be a straightforward cherry-pick to rtk-ai/rtk.