pr-comment: pipe changes payload via stdin to avoid jq ARG_MAX failure

[reuvenharrison]

Summary

The pr-comment entrypoint built its JSON payload by passing the diff content as a jq --argjson changes "$changes" value. For specs whose changelog runs into the multi-megabyte range, the JSON string exceeds the OS argument-length limit (ARG_MAX, typically 2 MB on Linux), and jq aborts with:

/entrypoint.sh: line N: jq: Argument list too long

This happens after the script has printed the free ::notice:: review URL but before the POST to oasdiff-service, so the customer sees a /review?... notice in their action log, no PR comment from oasdiff[bot], and assumes the Pro workflow swap had no effect. Silent failure under set -e because the notice line has already been printed and the workflow step exit code propagates without an obvious "this is the cause" pointer.

Fix

Pipe $changes through stdin instead. printf is a shell builtin in POSIX /bin/sh / busybox ash, so the variable is never on argv and ARG_MAX is irrelevant. The jq filter changes $changes to . (the implicit stdin input), and the -n (null-input) flag is dropped since jq now consumes real input.

-payload=$(jq -n \
+payload=$(printf '%s' "$changes" | jq \
     --arg token "$github_token" \
     ...
-    --argjson changes "$changes" \
-    '{... changes: $changes}')
+    '{... changes: .}')

The other --arg values (token, owner/repo, SHAs, file paths) are short and stay on the command line unchanged.

Regression test

A new job pr_comment_handles_large_payload in .github/workflows/test.yaml stubs oasdiff to emit a ~4 MB synthetic changelog (two entries with 2 MB of filler each, well above the 2 MB Linux ARG_MAX ceiling) and asserts the entrypoint reaches the "No oasdiff-token provided" skip without aborting. If someone later reverts to --argjson changes "$changes", the synthetic payload trips ARG_MAX on the runner and the test fails with a specific error message pointing at the cause.

Follows the same stub-oasdiff-on-PATH pattern as the existing pr_comment_tolerates_oasdiff_fail_on and pr_comment_aborts_on_oasdiff_real_failure jobs.

Test plan

• bash -n pr-comment/entrypoint.sh clean
• YAML parser accepts the workflow file
• Synthetic 2 MB / 5000-change payload locally constructs a valid JSON object via the new stdin path
• On merge, the new CI job confirms the multi-MB path works end-to-end via the stubbed entrypoint

Discovered by

A Pro customer trying to set up the pr-comment workflow on a multi-thousand-endpoint spec. Their action log surfaced the exact jq: Argument list too long error from line 89; the fix shape was unambiguous from there.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

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