CI - Ping PR author directly if checks fail (#3671)

# Description of Changes

When a merged PR fails checks, ping the PR author as well.

# API and ABI breaking changes

None. CI only.

# Expected complexity level and risk

2

# Testing

Demo message (not on an actual PR merge):
<img width="508" height="202" alt="image"
src="https://github.com/user-attachments/assets/69c16cf8-cad3-4744-8054-ea2b2d74cee0"
/>

---------

Co-authored-by: John Detter <4099508+jdetter@users.noreply.github.com>
Co-authored-by: Zeke Foppa <bfops@users.noreply.github.com>

Author: bfops

.github/workflows/discord-posts.yml

@@ -27,6 +27,7 @@ jobs:
           PR_NUMBER: ${{ github.event.pull_request.number }}
           PR_URL: ${{ github.event.pull_request.html_url }}
           MENTION_ON_FAILURE: ${{ secrets.DEV_OPS_ROLE_ID }}
+          DISCORD_USER_MAP: ${{ secrets.DISCORD_USER_MAP }}
         run: |
           message="PR merged: [(#${PR_NUMBER}) ${PR_TITLE}](<${PR_URL}>)"
           # Note that anything besides success is treated as a failure (e.g. if the check did not run at all, or if it is still pending).
@@ -39,6 +40,18 @@ jobs:
               ' |
               jq -r '"\(.workflow) / \(.name): \(.state)"'
           )"
+
+          # Lookup PR author's Discord ID from the provided JSON map (if any)
+          author_discord_id="$(
+            jq -r \
+              --arg u "${{ github.event.pull_request.user.login }}" \
+              'try .[$u] catch empty' \
+              <<<"${DISCORD_USER_MAP}"
+          )"
+          if [ -z "${author_discord_id}" ]; then
+            echo "Warning: PR author not found not found in USER_LOOKUP_JSON"
+          fi
+
           message+=$'\n'
           if [[ -z "${FAILED_CHECKS}" ]]; then
             message+='All checks passed.'
@@ -47,7 +60,11 @@ jobs:
             message+=$'\n'
             # This uses special Discord syntax for pinging a particular role.
             # Note the '&' - this is the difference between pinging a *role* and pinging a *person*.
-            message+=" (cc <@&${MENTION_ON_FAILURE}>)"
+            message+=" (cc <@&${MENTION_ON_FAILURE}>"
+            if [[ -n "${author_discord_id}" ]]; then
+              message+=" <@${author_discord_id}>"
+            fi
+            message+=")"
           fi
           # Use `jq` to construct the json data blob in the format required by the webhook.
           data="$(jq --null-input --arg msg "$message" '.content=$msg')"