fix(report-failure): name the trigger a stranded outage row points at

[tend-agent]

Problem

The Trigger column of a tend-outage row is the only pointer back to the work a failed run stranded. It goes blank for the one trigger where that pointer matters most, and prints #null when a field is missing.

repository_dispatch is unhandled. tend-mention relays review events through a secretless job that re-posts them as a repository_dispatch, so the handle job runs on that event and the PR number arrives as client_payload.pr rather than in a pull_request object. The if/elif chain has no branch for it, so every failure on the relay path records Trigger: N/A — and a relayed review is exactly the case a maintainer can't recover from the run alone, since tend-review fires only on pull_request_target and never retries. This path is in constant use: gh api "repos/max-sixty/tend/actions/runs?event=repository_dispatch" returns a steady stream of tend-mention runs.

workflow_run names no run. The ci-fix path hardcodes REF="CI fix for workflow run", discarding workflow_run.id — the id of the CI failure the job was dispatched to fix.

Missing fields render as null. jq -r '.issue.number' prints the literal string null when the field is absent, so the cell reads #null rather than falling back to N/A.

Solution

Add a repository_dispatch branch reading client_payload.pr, link the upstream run id in the workflow_run branch, and give every extraction // empty plus a ${VAR:+…} guard so an absent field leaves the cell blank (rendered as N/A by the existing ${REF:-N/A}) instead of #null.

Testing

shared/steps/ has no shell test harness — shellcheck via pre-commit is the only automated gate, and it passes on the changed file. So the block was exercised directly: the REF logic was sliced out of the script (between the # Build a one-line reference comment and TIMESTAMP=) and sourced under crafted GITHUB_EVENT_PATH payloads, before and after.

Before, on origin/main:

repository_dispatch  -> N/A
workflow_run         -> CI fix for workflow run
issues (no number)   -> #null

After:

relayed review               -> #815
relay w/o pr                 -> N/A
ci-fix                       -> CI fix for [run 30795510450](https://github.com/max-sixty/tend/actions/runs/30795510450)
ci-fix w/o id                -> CI fix for workflow run
PR event                     -> #821
PR event w/o number          -> N/A
issue comment                -> #808
issue w/o number             -> N/A
schedule                     -> N/A

Adding a real harness for shared/steps/ is worth considering separately — three of the recent outage-path fixes have all landed in scripts nothing can test — but that is a bigger change than this fix warrants, so it is not bundled here.

Scope

Separate from the other two open changes on this path, and textually disjoint from both. #818 names the cause of a failure (in claude/action.yaml); #809 dedups rows across matrix legs (in the EXISTING branch of this same script, lines 49+). This one fixes what the row points at, in the REF block at lines 19–29.