fix: use --sandbox danger-full-access for Codex review mode

[wesm]

Summary

• Switch Codex review mode from --sandbox read-only to --sandbox danger-full-access to fix CI reviews failing on large diffs
• The bwrap sandbox (used by both read-only and workspace-write modes) blocks loopback networking, causing git commands to fail with bwrap: loopback: Failed RTM_NEWADDR: Operation not permitted — this makes Codex unable to inspect diffs, so reviews report the code is inaccessible
• workspace-write has the same bwrap loopback bug (openai/codex#15496), so danger-full-access is the only working option
• Update review_guidelines to document the rationale so security reviewers don't flag it
• Update scripts/changelog.sh to match

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (1d6acd4)

Verdict: Changes are not ready as-is due to 2 medium-severity regressions in Codex review execution.

Medium

• internal/agent/codex.go:141, internal/agent/codex.go:183, scripts/changelog.sh:85
  The change assumes any Codex binary that exposes --sandbox also supports --sandbox none. The current detection only checks for the flag itself, and the changelog script does not validate support at all, so some CLI versions may now fail at runtime when invoked with none.
  Suggested fix: probe specifically for --sandbox none support, then fall back to the prior mode or another compatible path when unsupported.

• internal/agent/codex.go:141, internal/agent/codex.go:210, scripts/changelog.sh:85
  Changing review-mode execution from read-only to none removes the previous protection against background review jobs mutating the user’s working checkout. That also reintroduces the risk of interfering with concurrent local git activity, including lock contention.
  Suggested fix: keep review runs effectively read-only by using an isolated temp clone/worktree or a sandbox mode that permits the required git reads without allowing filesystem writes.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)

[roborev-ci]

roborev: Combined Review (dc742d8)

Verdict: Changes introduce a high-severity regression by removing read-only guarantees from review execution, plus a medium-severity blast-radius increase in changelog generation.

High

• internal/agent/codex.go:144
  Switching non-agentic review mode from --sandbox read-only to --sandbox danger-full-access removes the enforced guarantee that review runs cannot modify the user’s checkout. Because this path is used for automated review jobs, a prompt-following or misbehaving Codex run can now edit files, create index.lock, or otherwise leave the repo dirty during what is supposed to be a read-only review.
  Suggested fix: Preserve a non-mutating execution path for reviews, or isolate the full-access workaround to a temporary clone/worktree or only the specific environment that requires it.

Medium

• scripts/changelog.sh:85
  The changelog helper now also runs Codex with danger-full-access, even though this flow only needs to read the prompt and write the generated output file. That unnecessarily broadens the blast radius of release tooling by allowing arbitrary edits to the current checkout as a side effect of generating notes.
  Suggested fix: Keep changelog generation read-only, or run the full-access invocation from an isolated temporary directory.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)