fix(review-pr): add verification checklist for multi-line suggestions (#1608)

## Summary

- Replaces the vague "minimize the range" instruction for multi-line
suggestions with a concrete 4-step verification checklist
- Addresses the root cause of #1607: the bot constructs suggestion
ranges that are wider than the replacement text, silently deleting
correct code when applied

## Root cause analysis

Investigated all three known cases:

1. **#1310** (PR #1309): `start_line: 18, line: 22` — 5-line range
replaced with fewer lines, deleting the `git-wt` fallback branch
2. **#1326** (PR #1322): `start_line: 289, line: 291` — range included a
closing ` ``` ` fence that GitHub consumed as the suggestion's own
delimiter
3. **#1598**: `start_line: 93, line: 127` — 35-line range replaced with
a shorter rewrite, deleting the `gh issue view` code block

Common thread: the bot sets a line range covering more content than it
intends to replace. The replacement text is shorter, so the surplus
lines are silently deleted. The existing instruction ("minimize the
range") didn't give the bot a way to verify correctness.

## Fix

The new checklist requires the bot to:
1. **Read the exact lines** in the range before posting
2. **Verify no silent deletions** — every line must appear in the
replacement or be intentionally removed
3. **Cap range at ~10 lines** — larger suggestions should be split or
pushed as commits
4. **Avoid spanning markdown fences** — prevents delimiter collision

## Test plan

- [ ] Review a PR with a multi-line suggestion opportunity and verify
the bot follows the checklist
- [ ] Verify the bot splits or commits changes larger than ~10 lines
instead of using a suggestion

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: worktrunk-bot <254187624+worktrunk-bot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: worktrunk-bot

.claude/skills/review-pr/SKILL.md

@@ -276,8 +276,22 @@ array indices to object keys, which GitHub rejects.
 - If a review has both suggestions and prose observations, put the suggestions
   as inline comments and the prose in the review body.
 - Multi-line suggestions: set `start_line` and `line` to define the range.
-  **Minimize the range** — only include lines that actually need changing. A
-  range that's too wide can delete correct code adjacent to the fix.
+  GitHub **replaces** every line in that range with the suggestion content — any
+  line in the range that isn't reproduced in the replacement is **deleted**.
+
+  **Before posting any multi-line suggestion, verify it:**
+
+  1. **Read the exact lines** `start_line` through `line` from the diff hunk.
+  2. **Diff mentally**: every line in that range must either appear (possibly
+     modified) in the replacement text, or be a line you intend to delete. If
+     any line would be silently dropped, **shrink the range** or include the
+     line in the replacement.
+  3. **Cap the range at ~10 lines.** Larger suggestions are error-prone and hard
+     to review. For changes spanning more than 10 lines, split into multiple
+     suggestions or push a fix commit instead.
+  4. **Never span markdown fences.** If the range includes a `` ``` `` line,
+     GitHub's suggestion parser may consume it as a delimiter, corrupting the
+     result. Either shrink the range to avoid the fence or push a commit.
 
 ### 5. Monitor CI