diff --git a/.github/workflows/publish-to-pypi.yml b/.github/workflows/publish-to-pypi.yml
index 57ec82e..28860e4 100644
--- a/.github/workflows/publish-to-pypi.yml
+++ b/.github/workflows/publish-to-pypi.yml
@@ -24,6 +24,9 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+    outputs:
+      # The notify job replies in the start notice's thread.
+      slack-ts: ${{ steps.slack-start.outputs.ts }}
 
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -34,6 +37,7 @@ jobs:
 
       # Non-fatal: Slack being down must not block the release.
       - name: Notify Slack (start)
+        id: slack-start
         if: ${{ vars.SLACK_CHANNEL_ID != '' }}
         continue-on-error: true
         uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0
@@ -121,6 +125,13 @@ jobs:
     if: ${{ !cancelled() && vars.SLACK_CHANNEL_ID != '' }}
     runs-on: ubuntu-latest
 
+    env:
+      # Notices reply in the start notice's thread, quoted so YAML keeps the ts a
+      # string. Without a start notice (its post failed or never ran) this is null,
+      # which the Slack client drops, and they post to the channel. Failures are
+      # also broadcast to the channel; success stays in the thread.
+      THREAD_TS: ${{ needs.build.outputs.slack-ts && format('"{0}"', needs.build.outputs.slack-ts) || 'null' }}
+
     steps:
       - name: Notify Slack (checks failed)
         if: ${{ needs.pre-publish-checks.result == 'failure' }}
@@ -144,6 +155,8 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
+            reply_broadcast: ${{ env.THREAD_TS != 'null' }}
             text: >-
               *plain-parser*: Build of `${{ github.ref_name }}` FAILED :x:. Nothing was published to PyPI.
               See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.
@@ -157,6 +170,8 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
+            reply_broadcast: ${{ env.THREAD_TS != 'null' }}
             text: >-
               *plain-parser*: Uploading `${{ github.ref_name }}` to the GitHub Release FAILED :x:. Nothing was published to PyPI.
               See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.
@@ -170,6 +185,8 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
+            reply_broadcast: ${{ env.THREAD_TS != 'null' }}
             text: >-
               *plain-parser*: Publishing `${{ github.ref_name }}` to PyPI FAILED :x:.
               See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.
@@ -195,6 +212,7 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
             text: >-
               *plain-parser*: pre-release `${{ github.ref_name }}` published to PyPI :test_tube:.
               Normal installs are unaffected — try it with `pip install --pre plain-parser==${{ steps.version.outputs.version }}`.
@@ -208,6 +226,23 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
             text: >-
               *plain-parser*: `${{ github.ref_name }}` published to PyPI :white_check_mark:.
               Install with `pip install --upgrade plain-parser`.
+
+      # Success also puts a ✅ on the start notice, so the result shows in the
+      # channel without another message. Needs the app's reactions:write scope.
+      # Non-fatal: the result is already posted, and a re-run gets already_reacted.
+      - name: Notify Slack (✅ on the start notice)
+        if: ${{ needs.publish-to-pypi.result == 'success' && env.THREAD_TS != 'null' }}
+        continue-on-error: true
+        uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0
+        with:
+          method: reactions.add
+          token: ${{ secrets.SLACK_BOT_TOKEN }}
+          errors: true
+          payload: |
+            channel: ${{ vars.SLACK_CHANNEL_ID }}
+            timestamp: ${{ env.THREAD_TS }}
+            name: white_check_mark