diff --git a/.github/workflows/trunk-impacted-targets.yml b/.github/workflows/trunk-impacted-targets.yml
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+# Uploads this PR's impacted targets to Trunk so the parallel merge queue can
+# schedule it. Trunk needs an impacted-targets upload to place a PR into a lane;
+# without one, fork PRs never enter the queue and have to be merged by hand (see
+# PR #2819).
+#
+# The upload authenticates with the org API token (x-api-token) on internal PRs.
+# Fork PR workflow runs do NOT receive repo secrets — GitHub withholds them from
+# `pull_request` runs originating in a fork — so for forks we authenticate with
+# the workflow run id instead (x-forked-workflow-run-id). Trunk verifies the run
+# id belongs to a live fork-PR workflow whose head SHA matches the payload.
+# Ref: https://docs.trunk.io/merge-queue/optimizations/parallel-queues/api#handling-forked-pull-requests
+#
+# SECURITY: this MUST stay on the `pull_request` trigger, never
+# `pull_request_target`. `pull_request_target` would hand repo secrets to code
+# from untrusted forks ("pwn request"). The fork path deliberately needs no
+# secret, so the plain `pull_request` trigger is sufficient and safe.
+name: Trunk Impacted Targets
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
+
+concurrency:
+  # Supersede in-flight uploads when the PR head moves; the last upload per head
+  # SHA wins on Trunk's side anyway. Key on the PR number, not head_ref: fork
+  # PRs frequently share a source branch name (many are opened from `main`), and
+  # keying on head_ref would put two such PRs in one group where one cancels the
+  # other's upload — leaving that head SHA without the upload it needs to enter
+  # the queue.
+  group: trunk-impacted-targets-${{ github.event.pull_request.number || github.head_ref || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  upload:
+    runs-on: ubuntu-latest
+    # Reads only the event payload and talks out to Trunk — no repo write or PR
+    # API access needed.
+    permissions:
+      contents: read
+    env:
+      IS_FORK: ${{ github.event.pull_request.head.repo.full_name != github.repository }}
+      RUN_ID: ${{ github.run_id }}
+      REPO_OWNER: ${{ github.repository_owner }}
+      REPO_NAME: ${{ github.event.repository.name }}
+      PR_NUMBER: ${{ github.event.pull_request.number }}
+      # Head SHA (not the synthetic merge commit): it matches the workflow run's
+      # head_sha, which is what Trunk checks when verifying a fork upload.
+      PR_SHA: ${{ github.event.pull_request.head.sha }}
+      TARGET_BRANCH: ${{ github.event.pull_request.base.ref }}
+      TRUNK_API_TOKEN: ${{ secrets.TRUNK_API_TOKEN }}
+    steps:
+      - name: Upload impacted targets to Trunk
+        # Not continue-on-error: a silent failure here is exactly what kept fork
+        # PRs out of the queue, so surface upload problems loudly. --retry rides
+        # out transient Trunk/network blips.
+        run: |
+          set -euo pipefail
+
+          # We report "ALL" — every target — which is always correct: it can
+          # never under-report and let the queue merge conflicting PRs in
+          # parallel. It yields no parallelism benefit, but it gets every PR
+          # (forks included) into the queue. To actually parallelise, replace
+          # "ALL" with a computed target-name list (e.g. derived from the
+          # dorny/paths-filter outputs in test.yml) once the queue's target
+          # names are defined; see the Trunk bazel-action reference impl.
+          payload="$(jq -n \
+            --arg host "github.com" \
+            --arg owner "$REPO_OWNER" \
+            --arg name "$REPO_NAME" \
+            --argjson number "$PR_NUMBER" \
+            --arg sha "$PR_SHA" \
+            --arg targetBranch "$TARGET_BRANCH" \
+            '{repo: {host: $host, owner: $owner, name: $name}, pr: {number: $number, sha: $sha}, targetBranch: $targetBranch, impactedTargets: "ALL"}')"
+
+          if [ "$IS_FORK" = "true" ]; then
+            echo "Fork PR — authenticating with x-forked-workflow-run-id ($RUN_ID)"
+            auth_header="x-forked-workflow-run-id: $RUN_ID"
+          else
+            echo "Internal PR — authenticating with x-api-token"
+            auth_header="x-api-token: $TRUNK_API_TOKEN"
+          fi
+
+          curl --fail --silent --show-error --retry 3 --retry-all-errors \
+            -X POST "https://api.trunk.io/v1/setImpactedTargets" \
+            -H "Content-Type: application/json" \
+            -H "$auth_header" \
+            --data "$payload"