Skip missing upstream branches in scheduled build

[qu0b]

Summary

The hourly Scheduled workflow has been failing on every run because branches.yaml lists branches that don't (yet) exist on the upstream repo — most recently geth/bal-devnet-7. Each failure also pings Discord, so the signal-to-noise on real breakages is poor.

Root cause

process_commits in .github/workflows/scheduled.yml already detects a missing upstream ref via the GitHub API and logs:

[LINE:28] Error fetching commit hash for ethereum/go-ethereum#bal-devnet-7, skipping.

…but the downstream loops still iterate over every config in config.yaml. For the missing entry:

1. COMMIT_HASH comes back empty.
2. The Docker Hub check queries the malformed image ethpandaops/geth:bal-devnet-7- (trailing dash).
3. That tag (unsurprisingly) doesn't exist, so the entry is classified as "needs build" and added to the deploy matrix.
4. The deploy job fails at actions/checkout with A branch or tag with the name 'bal-devnet-7' could not be found.

Confirmed against the latest run (gh run 26026938948).

Fix

Two narrow changes inside the check job:

• Docker Hub existence loop — continue when COMMIT_HASH is empty/null. Avoids wasted Docker Hub queries against malformed tags.
• Build-config generation loop — same skip, plus a ::warning:: annotation and a row appended to $GITHUB_STEP_SUMMARY (under a ## Skipped builds (upstream ref missing) heading written once).

The workflow stays green, the Discord notification step (if: cancelled() || failure()) no longer fires for missing-branch noise, and every skipped branch is plainly visible on the run page.

Self-healing

No state is persisted. The moment the branch is pushed upstream, the GitHub API returns a SHA on the next hourly cron → COMMIT_HASH is non-empty → the skip branch isn't taken → Docker Hub reports the proper <tag>-<sha> image missing → the build runs and pushes normally. No manual intervention needed when the branch reappears.

Test plan

• Trigger gh workflow run scheduled.yml after merge.
• Confirm the run is green even though geth/bal-devnet-7 is still missing upstream.
• Confirm a ::warning:: annotation appears on the run page for the missing entry.
• Confirm the run summary contains a Skipped builds (upstream ref missing) table listing the geth row (and any others).
• Confirm an existing branch (e.g. geth/master) still builds normally if its image is missing on Docker Hub.
• Confirm no Discord notification fires for the skipped entries.

[qu0b-reviewer]

🤖 qu0b-reviewer

The PR is clean — the two guards (Docker Hub check loop and config-generation loop) correctly skip configs whose upstream ref process_commits failed to resolve, with graceful/no-op fallback paths throughout. The SKIPPED_HEADER_WRITTEN sentinel for the summary table is correct (no double-header, no output on zero skips).

Looks good. 🦋

---

_{Reviewed @ d9bda370
"All non-trivial abstractions, to some degree, are leaky." — Joel Spolsky}