fix(ci): restore fork-safe token fallback on PR gates broken by #66373 (#66577)

#66373 swapped GITHUB_TOKEN -> AUTOFIX_BOT_PAT across the workflows. That
PAT is empty on fork PRs (forks get no repo secrets), which broke every
fork PR two ways:

1. detect-changes classified with the empty PAT -> the compare API failed
   all 3 retries -> the classifier failed open and force-enabled the
   ci_review lane on EVERY fork PR.
2. The ci-reviewed / mcp-catalog-reviewed label gates then read labels with
   the same empty PAT via a hard-failing retry step -> the job failed with
   no recovery a fork contributor could perform (they can't self-add the
   label; re-running can't fix it).

Restores the pre-#66373 fork-safe behavior without reverting the commit's
real improvements (job timeouts, per-file flake retry, network-install
retries):

- detect-changes + ci.yml: token falls back to the built-in read-only
  github.token when AUTOFIX_BOT_PAT is empty. On main it uses the PAT
  (authoritative); on forks it uses github.token, which can read the
  public compare endpoint. (An input `default:` only applies on omission,
  not on an empty passed value — hence the explicit `|| github.token`.)
- lint ci-review + supply-chain mcp-catalog gates: restore the inline
  `gh pr view ... || true` label read with the github.token fallback,
  dropping the hard-failing retry "Fetch PR labels" step. Graceful
  degrade to "label absent" on an API blip, same as before #66373.

Same-repo enforcement is unchanged (byte-identical logic; the PAT is still
used there). Fork PRs classify correctly and the gates read labels via the
read-only token exactly as they did before the regression.

.github/actions/detect-changes/action.yml

@@ -47,7 +47,12 @@ runs:
       id: classify
       shell: bash
       env:
-        GH_TOKEN: ${{ inputs.github-token }}
+        # Fall back to the built-in read-only token when the caller passes an
+        # empty value. Fork PRs get no repo secrets, so AUTOFIX_BOT_PAT is ""
+        # there, and an input `default:` only applies when the input is omitted,
+        # not when it's passed empty. Without this fallback the compare API
+        # fails on forks and the classifier fails open (every lane forced on).
+        GH_TOKEN: ${{ inputs.github-token || github.token }}
         REPO: ${{ github.repository }}
         EVENT_NAME: ${{ github.event_name }}
         BASE_SHA: ${{ github.event.pull_request.base.sha }}

.github/workflows/ci.yml

@@ -53,7 +53,9 @@ jobs:
         id: classify
         uses: ./.github/actions/detect-changes
         with:
-          github-token: ${{ secrets.AUTOFIX_BOT_PAT }}
+          # Forks get no repo secrets (AUTOFIX_BOT_PAT is empty); fall back to
+          # the built-in read-only token so classification still works there.
+          github-token: ${{ secrets.AUTOFIX_BOT_PAT || github.token }}
 
   # ─────────────────────────────────────────────────────────────────────
   # Lane-gated sub-workflows. Each runs in parallel after detect finishes.

.github/workflows/lint.yml

@@ -177,18 +177,19 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Fetch PR labels
-        id: pr-labels
-        uses: ./.github/actions/retry
-        env:
-          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT }}
-        with:
-          command: gh pr view "${{ github.event.pull_request.number }}" --json labels --jq '.labels[].name'
       - name: Require ci-reviewed label
         id: label-check
+        env:
+          # Read-only label lookup. Use the built-in GITHUB_TOKEN (present and
+          # read-only on forks) so the gate works on fork PRs; fall back to it
+          # when AUTOFIX_BOT_PAT is empty. `|| true` degrades an API blip to
+          # "label absent" rather than hard-failing the step.
+          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT || github.token }}
         run: |
           set -euo pipefail
-          if echo "${{ steps.pr-labels.outputs.stdout }}" | grep -Fxq 'ci-reviewed'; then
+          PR="${{ github.event.pull_request.number }}"
+          LABELS=$(gh pr view "$PR" --json labels --jq '.labels[].name' || true)
+          if echo "$LABELS" | grep -Fxq 'ci-reviewed'; then
             echo "reviewed=true" >> "$GITHUB_OUTPUT"
             echo "ci-reviewed label present."
             exit 0
@@ -203,7 +204,7 @@ jobs:
       - name: Post or update review warning
         if: steps.label-check.outputs.reviewed != 'true' && github.event.pull_request.head.repo.fork != true
         env:
-          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT }}
+          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT || github.token }}
         run: |
           set -euo pipefail
           PR="${{ github.event.pull_request.number }}"
@@ -251,7 +252,7 @@ jobs:
       - name: Update previous warning to passed
         if: steps.label-check.outputs.reviewed == 'true' && github.event.pull_request.head.repo.fork != true
         env:
-          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT }}
+          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT || github.token }}
         run: |
           set -euo pipefail
           PR="${{ github.event.pull_request.number }}"

.github/workflows/supply-chain-audit.yml

@@ -238,20 +238,18 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Fetch PR labels
-        id: pr-labels
-        uses: ./.github/actions/retry
-        env:
-          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT }}
-        with:
-          command: gh pr view "${{ github.event.pull_request.number }}" --json labels --jq '.labels[].name'
       - name: Require explicit MCP catalog review label
         env:
-          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT }}
+          # Read-only label lookup. Use the built-in GITHUB_TOKEN (present and
+          # read-only on forks) so the gate works on fork PRs; fall back to it
+          # when AUTOFIX_BOT_PAT is empty. `|| true` degrades an API blip to
+          # "label absent" rather than hard-failing the step.
+          GH_TOKEN: ${{ secrets.AUTOFIX_BOT_PAT || github.token }}
         run: |
           set -euo pipefail
           PR="${{ github.event.pull_request.number }}"
-          if echo "${{ steps.pr-labels.outputs.stdout }}" | grep -Fxq 'mcp-catalog-reviewed'; then
+          LABELS=$(gh pr view "$PR" --json labels --jq '.labels[].name' || true)
+          if echo "$LABELS" | grep -Fxq 'mcp-catalog-reviewed'; then
             echo "MCP catalog review label present."
             exit 0
           fi