skills(running-in-ci): cover the joint case of $GITHUB_REPOSITORY + ! in a comment body

[tend-agent]

Problem

tend-triage run 25295135366 on max-sixty/worktrunk shipped a public comment (issue #2564 comment 4367561809) with two simultaneous corruption signals:

1. A markdown link with literal ${GITHUB_REPOSITORY} that did not interpolate: [src/main.rs:1300](https://github.com/${GITHUB_REPOSITORY}/blob/main/src/main.rs#L1300). The link is broken — clicks 404.
2. Literal \! backslash-bang corruption on debug_assert\! and bail\! (Rust syntax that should render as debug_assert! / bail!).

Session-log inspection confirmed the bot used gh issue comment 2564 --body "$(cat <<'EOF' ... EOF)". The single-quoted heredoc form fails on both axes: the bash preprocessor's ! → \! rewrite still fires (it operates at the string level before bash parses the heredoc), and ${GITHUB_REPOSITORY} does not expand (single-quoted heredoc disables interpolation).

Why the existing guidance didn't catch it

running-in-ci already has two relevant warnings:

• The $GITHUB_REPOSITORY paragraph offers two ways to fix unexpanded variables: unquoted <<EOF or the Write tool.
• The ! paragraph mandates the Write tool when the body contains an exclamation mark.

Neither paragraph addresses the joint case — when a body contains both a ! and a ${GITHUB_REPOSITORY} reference. Unquoted <<EOF fixes the variable but not the ! (preprocessor still mangles). Write-tool composition fixes the ! but not the variable (Write does not interpolate). The bot picked single-quoted <<'EOF', which fails both.

The ! rule says "use Write tool"; the URL rule offers Write tool as an alternative — but neither tells the bot how to embed $GITHUB_REPOSITORY in a Write-tool-composed file. So when both gotchas applied at once, neither rule's recipe was complete.

Fix

One sentence added to the $GITHUB_REPOSITORY paragraph: when the body contains a ! (Write mandatory), write an OWNER_REPO placeholder into the file and substitute via sed -i "s|OWNER_REPO|$GITHUB_REPOSITORY|g" /tmp/body.md before gh ... --body-file. Plus an explicit warning that single-quoted <<'EOF' with both a ! and ${GITHUB_REPOSITORY} in the body fails on both counts.

The sed recipe is preprocessor-safe: $GITHUB_REPOSITORY is owner/repo (no !), and the sed command itself contains no ! (uses | as delimiter because / appears in the value).

Gate assessment

• Confidence: Critical — clearly wrong public output (broken markdown link + visible backslash escapes shown to a community reporter). 1 occurrence sufficient per Gate 1.
• Magnitude: Targeted fix to existing guidance, one sentence added. Normal evidence bar.
• Structural vs stochastic: Structural. The same conditions reproduce — the existing guidance offers Write-tool and unquoted-heredoc as alternatives without addressing the joint case. A bot facing a body with both ! and ${GITHUB_REPOSITORY} will plausibly pick <<'EOF' again.
• Recurrence history: 4 prior \!-shipping incidents in the last month's evidence gist (issue #2309 comment, PR #2359 title, PR #2361 title, the <\!-- HTML-comment case). The ${GITHUB_REPOSITORY} non-expansion case is new this run. Both gates pass.

Evidence

• Bot comment: Flaky: test_prune_skips_unmerged on Windows — Permission denied reading .git/config from background subprocess worktrunk#2564 (comment)
• Triage run: https://github.com/max-sixty/worktrunk/actions/runs/25295135366
• Evidence gist (this month): https://gist.github.com/9675d1510da32c68a68c1d45137b21e0
• Prior \! shipping incident write-up: tend PR #318