review agent failed to dedupe: double-posted its summary comment after a retry: how to fix

TL;DR

The agent posts a fresh summary on every run without checking whether it already posted one. Make the summary idempotent: look for the bot's existing comment via a marker line, update it if found, and only create a new one if it is absent.

The error

review agent failed to dedupe: double-posted its summary comment after a retry: how to fix
(two identical "Review summary" comments from the bot on the same PR)

Steps

1. Give the summary a marker

Start the comment body with a distinctive first line the agent can search for, such as ## Review summary [bot-managed]. Expected output: every summary the bot posts is identifiable later.

2. List existing comments before posting

On each run, fetch the PR's comments and filter by the bot author plus the marker line. Expected output: the agent knows whether a summary already exists.

3. Update instead of create

If the marker is found, PATCH the existing comment with the new body. Only POST when no marked comment exists. Expected output: one summary comment that reflects the latest run.

4. Test the retry path

Trigger a retry on a test PR and confirm the outcome. Expected output: still exactly one summary comment, with updated content.

When to use

• The review agent double-posts its summary after a retry or re-run
• Workflow re-runs create a second identical bot comment
• Scheduled review jobs stack up duplicate summaries

When not to use

• Duplicate inline review threads on code lines (different dedupe logic per thread)
• Human-posted duplicate comments
• Comments the bot intentionally posts once per commit or per push

Tool compatibility

• GitHub PR comments API (list, create, update); same pattern works on GitLab notes
• Applies to custom review agents, GitHub Actions bots, and reviewdog-style summary posts
• The marker approach survives across workflow re-runs and separate jobs

Variant phrasings

bot posted two summaries after the workflow was re-run

Same fix. Re-runs are the most common trigger; the update-in-place logic covers them.

duplicate inline review comments from the agent

Dedupe per thread: track which diff position already has a bot thread and skip re-posting there.

agent posts a new summary on every push

Decide the intended behavior first. If one rolling summary is wanted, use the marker update. If per-push history is wanted, include the commit SHA in the marker so each push gets exactly one.

Why it happens

Retries re-execute the whole job from scratch, including the post-comment step, with no memory of the previous attempt. Without a check-then-update pattern, each attempt adds another comment. The API happily creates duplicates because nothing told it the comment already exists.

Edge cases

• Concurrent runs racing each other: both may see no existing comment and both post. Serialize the summary step or accept last-write-wins with a short lock.
• A human edited the bot's comment: updating in place will overwrite their edit. Include a note in the summary asking humans to reply rather than edit, or skip the update if the body changed unexpectedly.
• Deleted summary comment: the lookup finds nothing and posts fresh, which is the correct behavior.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_AXWsUxG1nNFXi-MSnVOapA