fix: randomize the captured output delimiter

[MikeeI]

Summary

Captured stdout currently uses the fixed multiline delimiter EOF, although a remote command may legitimately emit EOF on a line by itself.
This change creates one randomized Bash-only delimiter per capture and uses it for both framing lines while retaining the streaming tee path.

Evidence

• entrypoint.sh on the current base frames every captured value with the literal line EOF.
• GitHub's multiline-string contract requires that the delimiter not occur on a line by itself within the value.
• The runner parser closes a multiline value when a line equals its delimiter.
• A controlled capture of vor\nEOF\nnach\n produced static framing in which the first EOF closes the value before nach.

Changes

• Generate one delimiter from eight underscore-separated Bash $RANDOM components for each capture invocation.
• Use the same quoted delimiter in the opening and closing GITHUB_OUTPUT lines.
• Keep the drone-ssh | tee pipeline, live logs, byte ordering, and public stdout output unchanged.

Risks and boundaries

• $RANDOM is seedable pseudo-randomness, not cryptographic entropy; this removes the deterministic collision but not every theoretical or adversarial collision.
• GitHub warns that delimiter framing cannot safely represent completely arbitrary content without buffering; this pull request intentionally preserves streaming.
• Nonzero-pipeline cleanup, output without a final newline, and stderr ownership remain unchanged and outside this correction.

Verification

• bash -n entrypoint.sh && shellcheck entrypoint.sh && git diff --check — passed.
• Controlled capture writes vor, EOF, and nach — one randomized framing pair encloses all three lines in order.
• Controlled executable exits 17 — the unchanged pipefail pipeline still returns 17.

I checked the relevant issues, comments, pull requests, discussions, releases, and capture history; this pull request is not a duplicate.

Disclosure

Investigated thoroughly with GPT-5.6 Codex (high reasoning effort), using Oh My Pi as the agent framework.

This report is not generic or unreviewed AI-generated output. Its claims were checked against the cited evidence, and it includes the relevant detail intended to help maintainers resolve the issue.

If reports like this are not useful to the project, please let me know and I will refrain from submitting similar ones. My intent is to help without wasting maintainer time or energy or discouraging their work.

Thank you for your work.