fix(ci): the same-scope batching gate counts Refs, so any umbrella reference exempts a single-issue PR #16795

What happens

scripts/check_pr_issue_batching.py exists because the batching rule "was documented in CLAUDE.md and checked by nothing" (.github/workflows/pr-issue-validation.yml). Its stated intent: "This is not a ban on single-issue PRs; it requires the author to say why one stands alone."

It does not require that in practice. check() returns early:

issues = referenced_issues(body)
if len(issues) >= 2:
    return True, f"Batched: references {len(issues)} issues (...)."

and _REFERENCE counts refs and part of alongside the closing keywords:

r"(?:resolves|closes|fixes|refs|references|part of)\s+..."

So a PR with Closes #A plus Refs #B scores as two issues and is reported as "Batched", with no rationale ever required. That is not an edge case: linking the umbrella is exactly what ~/.claude/docs/issue-decomposition.md tells every child PR to do, so the common, correct shape silently exempts itself from the gate.

Evidence

• PR feat(kb): accept spreadsheet, presentation and OpenDocument uploads (#16775) #16788 is a single-issue PR (Closes #16775, Refs #16772 — the umbrella). Check same-scope batching reports SUCCESS.
• My other two, security(kb): sanitize every knowledge-base write at the store_fact chokepoint (#16770) #16781 (Closes #16770, Refs #16777) and feat(documents): verify ZIP-based office and ODF formats by content (#16773) #16783 (Closes #16773, Refs #16772), have the same shape.
• None of the three carried a Single-issue rationale: line when they passed. I have since added one to each by hand — the gate did not ask.

Why it matters

The gate reads as enforcing something it does not, which is worse than an absent check: a reviewer seeing "Check same-scope batching ✓" reasonably concludes the author justified standing alone. Guards must distinguish satisfied from not examined.

Options

1. Count only the closing keywords (resolves|closes|fixes) toward "batched" — a Refs/part of link is context, not a second delivered issue. Most precise, and matches what "batched" means everywhere else in the process (Closes #A, #B).
2. Keep counting them, but require the rationale whenever a PR closes exactly one issue, regardless of how many it references.

Both fixes are in one function. (1) also makes the check's own message truthful: #16788 is not "batched", and saying so is the defect.

Acceptance criteria

• A PR closing one issue and referencing an umbrella requires a Single-issue rationale: line.
• A genuinely batched PR (Closes #A, #B) still passes with no rationale.
• The script's unit tests cover the umbrella-reference shape, which is the one that regressed.

Found during

Cross-checking my own PRs after autobot-ai-01 mentioned adding a rationale line that mine had passed without.