diff --git a/.github/workflows/probe-cross-repo-token.yml b/.github/workflows/probe-cross-repo-token.yml
new file mode 100644
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--- /dev/null
+++ b/.github/workflows/probe-cross-repo-token.yml
@@ -0,0 +1,163 @@
+# Throwaway probe (#238 Phase 0): can a workflow GITHUB_TOKEN read ANOTHER
+# repository's Actions/Checks data when that repository is public?
+#
+# GitHub's docs never join the two axes this sits on. The installation-token
+# side says the token is "limited to the repository that contains your
+# workflow" and "cannot be granted access to repositories that the
+# installation was not granted access to"; the endpoint side says each of
+# these endpoints "can be used without authentication ... if only public
+# resources are requested". Nothing states the evaluation order, so #238's
+# receiver-side polling architecture rests on an unverified premise.
+#
+# A bare 200 is confounded: public Actions data is world-readable, so a 200
+# alone cannot distinguish "the token authorized me" from "the token was
+# ignored". Hence four arms, with a private-repo discriminator.
+#
+# Also captures x-ratelimit-remaining across two target repos, to settle
+# whether the 1,000 req/hr bucket is per-workflow-repo or per-target-repo.
+#
+# Closed unmerged; deleted with the probe branch.
+name: probe-cross-repo-token
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+permissions: {}
+
+jobs:
+  no-permissions:
+    name: GITHUB_TOKEN with permissions {}
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    permissions: {}
+    steps:
+      - name: Probe cross-repo reads
+        shell: bash
+        env:
+          PROBE_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -uo pipefail
+
+          BASE=https://api.github.com/repos/melodic-software
+          Q='actions/runs?per_page=1'
+
+          probe() {
+            local label="$1" auth="$2" url="$3"
+            local hdrs body code
+            hdrs="$(mktemp)"
+            body="$(mktemp)"
+            if [ "$auth" = yes ]; then
+              code="$(curl -sS -o "$body" -D "$hdrs" -w '%{http_code}' \
+                -H 'Accept: application/vnd.github+json' \
+                -H 'X-GitHub-Api-Version: 2022-11-28' \
+                -H "Authorization: Bearer ${PROBE_TOKEN}" \
+                "$url")" || code=curl-error
+            else
+              code="$(curl -sS -o "$body" -D "$hdrs" -w '%{http_code}' \
+                -H 'Accept: application/vnd.github+json' \
+                -H 'X-GitHub-Api-Version: 2022-11-28' \
+                "$url")" || code=curl-error
+            fi
+            echo "=== ${label}"
+            echo "    auth=${auth} http=${code}"
+            grep -iE '^(x-ratelimit-(limit|remaining|used|resource)|x-accepted-github-permissions):' \
+              "$hdrs" | tr -d '\r' | sed 's/^/    /' || true
+            if [ "$code" != 200 ]; then
+              echo "    body: $(head -c 200 "$body" | tr -d '\n')" || true
+            fi
+            rm -f "$hdrs" "$body"
+          }
+
+          probe "ARM A  unauth       -> PUBLIC  claude-code-plugins" no  "${BASE}/claude-code-plugins/${Q}"
+          probe "ARM B  GITHUB_TOKEN -> PUBLIC  claude-code-plugins" yes "${BASE}/claude-code-plugins/${Q}"
+          probe "ARM B2 GITHUB_TOKEN -> PUBLIC  standards"           yes "${BASE}/standards/${Q}"
+          probe "ARM C  GITHUB_TOKEN -> PRIVATE medley"              yes "${BASE}/medley/${Q}"
+          probe "ARM D  GITHUB_TOKEN -> OWN     ci-workflows"        yes "${BASE}/ci-workflows/${Q}"
+
+          echo "=== ARM E  full detection chain -> PUBLIC claude-code-plugins"
+          RUN_ID="$(curl -sS \
+            -H 'Accept: application/vnd.github+json' \
+            -H "Authorization: Bearer ${PROBE_TOKEN}" \
+            "${BASE}/claude-code-plugins/${Q}" | jq -r '.workflow_runs[0].id // empty')" || true
+          echo "    run_id=${RUN_ID:-<none>}"
+          if [ -n "${RUN_ID:-}" ]; then
+            CR_URL="$(curl -sS \
+              -H 'Accept: application/vnd.github+json' \
+              -H "Authorization: Bearer ${PROBE_TOKEN}" \
+              "${BASE}/claude-code-plugins/actions/runs/${RUN_ID}/jobs" \
+              | jq -r '.jobs[0].check_run_url // empty')" || true
+            echo "    check_run_url=${CR_URL:-<none>}"
+            if [ -n "${CR_URL:-}" ]; then
+              probe "ARM E  GITHUB_TOKEN -> PUBLIC  check-run annotations" yes "${CR_URL}/annotations"
+            fi
+          fi
+
+  actions-checks-read:
+    name: GITHUB_TOKEN with actions+checks read
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    permissions:
+      actions: read
+      checks: read
+    steps:
+      - name: Probe cross-repo reads
+        shell: bash
+        env:
+          PROBE_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -uo pipefail
+
+          BASE=https://api.github.com/repos/melodic-software
+          Q='actions/runs?per_page=1'
+
+          probe() {
+            local label="$1" auth="$2" url="$3"
+            local hdrs body code
+            hdrs="$(mktemp)"
+            body="$(mktemp)"
+            if [ "$auth" = yes ]; then
+              code="$(curl -sS -o "$body" -D "$hdrs" -w '%{http_code}' \
+                -H 'Accept: application/vnd.github+json' \
+                -H 'X-GitHub-Api-Version: 2022-11-28' \
+                -H "Authorization: Bearer ${PROBE_TOKEN}" \
+                "$url")" || code=curl-error
+            else
+              code="$(curl -sS -o "$body" -D "$hdrs" -w '%{http_code}' \
+                -H 'Accept: application/vnd.github+json' \
+                -H 'X-GitHub-Api-Version: 2022-11-28' \
+                "$url")" || code=curl-error
+            fi
+            echo "=== ${label}"
+            echo "    auth=${auth} http=${code}"
+            grep -iE '^(x-ratelimit-(limit|remaining|used|resource)|x-accepted-github-permissions):' \
+              "$hdrs" | tr -d '\r' | sed 's/^/    /' || true
+            if [ "$code" != 200 ]; then
+              echo "    body: $(head -c 200 "$body" | tr -d '\n')" || true
+            fi
+            rm -f "$hdrs" "$body"
+          }
+
+          probe "ARM A  unauth       -> PUBLIC  claude-code-plugins" no  "${BASE}/claude-code-plugins/${Q}"
+          probe "ARM B  GITHUB_TOKEN -> PUBLIC  claude-code-plugins" yes "${BASE}/claude-code-plugins/${Q}"
+          probe "ARM B2 GITHUB_TOKEN -> PUBLIC  standards"           yes "${BASE}/standards/${Q}"
+          probe "ARM C  GITHUB_TOKEN -> PRIVATE medley"              yes "${BASE}/medley/${Q}"
+          probe "ARM D  GITHUB_TOKEN -> OWN     ci-workflows"        yes "${BASE}/ci-workflows/${Q}"
+
+          echo "=== ARM E  full detection chain -> PUBLIC claude-code-plugins"
+          RUN_ID="$(curl -sS \
+            -H 'Accept: application/vnd.github+json' \
+            -H "Authorization: Bearer ${PROBE_TOKEN}" \
+            "${BASE}/claude-code-plugins/${Q}" | jq -r '.workflow_runs[0].id // empty')" || true
+          echo "    run_id=${RUN_ID:-<none>}"
+          if [ -n "${RUN_ID:-}" ]; then
+            CR_URL="$(curl -sS \
+              -H 'Accept: application/vnd.github+json' \
+              -H "Authorization: Bearer ${PROBE_TOKEN}" \
+              "${BASE}/claude-code-plugins/actions/runs/${RUN_ID}/jobs" \
+              | jq -r '.jobs[0].check_run_url // empty')" || true
+            echo "    check_run_url=${CR_URL:-<none>}"
+            if [ -n "${CR_URL:-}" ]; then
+              probe "ARM E  GITHUB_TOKEN -> PUBLIC  check-run annotations" yes "${CR_URL}/annotations"
+            fi
+          fi