[codex] Require OpenCode inline suggested diffs

[seonghobae]

What changed

• Posts structured OpenCode REQUEST_CHANGES findings through GitHub review comments so each finding's suggested_diff is inside the inline review thread comment.
• Keeps PR-level review bodies and overview comments summary-only; they no longer carry fenced suggested diffs for actionable findings.
• Adds a diff-free fallback REQUEST_CHANGES body when GitHub rejects inline anchors, instead of silently approving or copying unanchored diffs into the overview.

Contract

Line-specific OpenCode findings with suggested_diff must publish as GitHub review comments with path, line, side: RIGHT, and a comment body containing the fenced diff. If the anchor cannot be created, the workflow leaves the diff out of the PR-level body and explains the anchor failure.

Validation

• git diff --check
• YAML parse for .github/workflows/opencode-review.yml
• no repo-local OpenCode contract test file exists; validated the workflow contract markers directly
• Inline-diff contract markers: comments payload exists, inline comment body contains #### Suggested diff, and format_request_changes_body() no longer contains a fenced diff block.

[github-actions]

OpenCode Review Overview

• Head SHA: 92919acefb5ff631467168550cabdbe82c51caf2
• Workflow run: 27899787279
• Workflow attempt: 1
• Gate result: APPROVE (exit 0)

[opencode-agent]

OpenCode Agent approved this PR.

The changes in the workflow file improve the handling of review threads and failed checks, with no evidence of security, privacy, or regression risks.

• Result: APPROVE
• Reason: No blockers or regressions found in the changes.
• Head SHA: 92919acefb5ff631467168550cabdbe82c51caf2
• Workflow run: 27899787279
• Workflow attempt: 1