fix: validate JSON before parsing deployment summary output

[defangdevs]

Summary

• defang services --json can exit 0 while printing non-JSON to stdout (seen: a version-string-like line ahead of the JSON array). The summary step's jq calls then fail under set -e, turning an already-successful deployment into a failed job.
• Validate the captured output with jq empty before trusting it, falling back to [] on either a non-zero exit code or invalid JSON — matching the existing fallback comment's intent.

This is live-breaking right now: both Deploy Sample to aws BYOC and Deploy Sample to gcp BYOC in DefangLabs/defang-mvp's CLI Smoketests failed on the new "Deployment summary" step after this action's main picked up #54, even though the actual deployments succeeded and services came up healthy. That failure cascades into DefangLabs/defang's "Go package" workflow going red on main via the smoketest trigger.

Related: DefangLabs/defang-mvp Actions run https://github.com/DefangLabs/defang-mvp/actions/runs/32288618542

Test plan

• CI on this PR passes
• Re-run (or wait for next) defang-mvp smoketest run against defang-github-action@main to confirm the summary step no longer fails when defang services --json output is unparseable

[coderabbitai]

Important

• 🔍 Trigger review

This repository does not receive automatic reviews because it has fewer than 10 stars.

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Run ID: 13b2ddc2-8e91-463c-98ab-f67423a8dafb

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[defangdevs]

Heads up: this is now recurring on every push to defang@main, not a one-off. A second push (run https://github.com/DefangLabs/defang/actions/runs/32289380925) just hit the same failure via https://github.com/DefangLabs/defang-mvp/actions/runs/32290325677 — both aws and gcp smoketests deployed fine and failed only at the summary step with the same jq: parse error / exit code 5.

Since defang-mvp pins this action to @main (floating), every defang main push will keep going red until this merges. CI here is green — happy to have this reviewed/merged whenever convenient.

[lionello]

@defangdevs this sounds like a CLI bug

[defangdevs]

Root cause landed upstream: DefangLabs/defang#2225 (merged 2026-08-19T23:39:46Z) fixes term.Println/Print* writing human-readable/debug output to stdout even in --json mode — that's what was corrupting defang services --json under DEFANG_DEBUG=1 and breaking this step's jq parse.

This PR's defensive "validate JSON before parsing, fall back to []" change is still good hardening independent of that fix (any future stray stdout write, from this CLI or a future one, would otherwise silently break deployment summaries again). Happy to merge as-is, or close if you'd rather rely solely on the upstream fix — your call.

[defangdevs]

Another live instance of this bug: DefangLabs/defang main run https://github.com/DefangLabs/defang/actions/runs/32313014805 failed via cascading smoketest https://github.com/DefangLabs/defang-mvp/actions/runs/32315433846 (AWS BYOC). AWS deploy itself succeeded (84 resources, service healthy) but the summary step's jq crashed on non-JSON defang services --json output, exit 5 — same failure mode this PR fixes.