diff --git a/.github/workflows/publish-to-pypi.yml b/.github/workflows/publish-to-pypi.yml
index cd800291..223ef34a 100644
--- a/.github/workflows/publish-to-pypi.yml
+++ b/.github/workflows/publish-to-pypi.yml
@@ -14,6 +14,9 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: write
+    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
@@ -23,6 +26,7 @@ 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
@@ -93,6 +97,13 @@ 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 (build failure)
         if: ${{ needs.build.result == 'failure' }}
@@ -103,6 +114,8 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
+            reply_broadcast: ${{ env.THREAD_TS != 'null' }}
             text: >-
               *Codeplain Client*: Build of `${{ github.ref_name }}` FAILED :x:. Nothing was published to PyPI.
               See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.
@@ -116,6 +129,8 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
+            reply_broadcast: ${{ env.THREAD_TS != 'null' }}
             text: >-
               *Codeplain Client*: Publishing `${{ github.ref_name }}` to PyPI FAILED :x:.
               See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.
@@ -141,6 +156,7 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
             text: >-
               *Codeplain Client*: pre-release `${{ github.ref_name }}` published to PyPI :test_tube:.
               Normal installs are unaffected — try it with `pip install --pre codeplain==${{ steps.version.outputs.version }}`.
@@ -154,10 +170,27 @@ jobs:
           errors: true
           payload: |
             channel: ${{ vars.SLACK_CHANNEL_ID }}
+            thread_ts: ${{ env.THREAD_TS }}
             text: >-
               *Codeplain Client*: `${{ github.ref_name }}` published to PyPI :white_check_mark:.
               Install with `pip install --upgrade codeplain`.
 
+      # 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
+
   # Release pipelines to be turned on only after the rest of the infrastructure
   # is ready.
   #
@@ -165,7 +198,7 @@ jobs:
   # # keeps its minimal permissions and no checkout.
   # linear-release:
   #   name: Record release in Linear
-  #   needs: publish-to-pypi
+  #   needs: [build, publish-to-pypi]
   #   runs-on: ubuntu-latest
   #
   #   permissions:
@@ -192,6 +225,9 @@ jobs:
   #     # outcome — `failure()` would never fire.
   #     - name: Notify Slack (release not recorded)
   #       if: ${{ steps.linear.outcome == 'failure' && vars.SLACK_CHANNEL_ID != '' }}
+  #       env:
+  #         # See the notify job.
+  #         THREAD_TS: ${{ needs.build.outputs.slack-ts && format('"{0}"', needs.build.outputs.slack-ts) || 'null' }}
   #       uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0
   #       with:
   #         method: chat.postMessage
@@ -199,6 +235,7 @@ jobs:
   #         errors: true
   #         payload: |
   #           channel: ${{ vars.SLACK_CHANNEL_ID }}
+  #           thread_ts: ${{ env.THREAD_TS }}
   #           text: >-
   #             *Codeplain Client*: `${{ github.ref_name }}` is on PyPI, but recording it in Linear FAILED :warning:.
   #             See <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|the run log>.