probe: #205 workflow-token dispatch evidence (temporary branch)

Authorized in !213 #6254: one dispatch of release-exercise.yml under
${{ github.token }}, body {"ref":"main"} with no inputs, actions: write
granted explicitly. Branch is deleted once the code is recorded on #205.

Refs #205

.github/workflows/token-dispatch-probe.yml

@@ -0,0 +1,42 @@
+# TEMPORARY PROBE — #205's workflow-token evidence, authorized by andres in
+# !213 #6254. Lives only on probe/205-token-dispatch; the branch is deleted
+# once the status code is recorded on #205.
+#
+# The one question: does a dispatch POST succeed under ${{ github.token }} on
+# this instance? Every prior measurement used a PAT, and the two identities
+# demonstrably differ here (#192: DELETE labels -> 500 for the workflow token,
+# 204 for a PAT). Target and terms per the authorization: release-exercise.yml
+# (dry wiring, doors push-gated so a dispatch skips them), body exactly
+# {"ref":"main"} with NO inputs — it declares none, and an input-contract
+# refusal would masquerade as a token failure.
+name: token dispatch probe
+on:
+  push:
+    branches: [probe/205-token-dispatch]
+
+permissions:
+  actions: write        # the write under test, granted explicitly (#6254)
+  contents: read
+
+jobs:
+  probe:
+    runs-on: ubuntu-latest
+    steps:
+      - name: dispatch release-exercise.yml as the workflow token
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: |
+          out="$(mktemp)"
+          code="$(curl -sS -o "$out" -w '%{http_code}' -X POST \
+            -H "Authorization: Bearer $GITHUB_TOKEN" \
+            -H 'Content-Type: application/json' \
+            -d '{"ref":"main"}' \
+            "$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/actions/workflows/release-exercise.yml/dispatches")"
+          echo "probe: POST .../release-exercise.yml/dispatches as github.token -> HTTP $code"
+          echo "probe: response body: $(tr -d '\n' <"$out")"
+          if [ "$code" = "204" ]; then
+            echo "probe: the workflow token CAN dispatch on this instance."
+          else
+            echo "probe: NON-204 under the workflow token — a finding in its own right (#205)."
+            exit 1
+          fi