fix(ci): use GITHUB_TOKEN installation auth + model fallback for Copilot workflows

.github/workflows/copilot-design-pass.yml

@@ -125,13 +125,17 @@ jobs:
           printf '%s' "$FULL_PROMPT" > "$RUNNER_TEMP/full-prompt.txt"
 
           set +e
-          RESULT=$(COPILOT_GITHUB_TOKEN="$GITHUB_TOKEN" timeout 840 copilot \
-            -f "$RUNNER_TEMP/full-prompt.txt" \
-            -s \
-            --no-ask-user \
-            --model claude-opus-4.8 \
-            --allow-all 2>/dev/null)
-          EXIT_CODE=$?
+          MODELS="${COPILOT_MODELS:-claude-opus-4.8 claude-opus-4.6 gpt-5-mini}"
+          RESULT=""; EXIT_CODE=1
+          for MODEL in $MODELS; do
+            RESULT=$(timeout 840 copilot --yolo \
+              -f "$RUNNER_TEMP/full-prompt.txt" \
+              --model "$MODEL" 2>/dev/null)
+            EXIT_CODE=$?
+            [ $EXIT_CODE -eq 0 ] && [ -n "$RESULT" ] && break
+            echo "::warning::Copilot model $MODEL failed (exit $EXIT_CODE) — trying next"
+            RESULT=""; EXIT_CODE=1
+          done
           set -e
 
           if [ $EXIT_CODE -ne 0 ] || [ -z "$RESULT" ]; then

.github/workflows/copilot-flake-review.yml

@@ -138,9 +138,15 @@ jobs:
 
           TASK="The following tests are flaky (passed and failed across multiple runs). Fix them according to the system prompt guidelines. Flake report: $REPORT"
 
-          COPILOT_GITHUB_TOKEN="$GITHUB_TOKEN" copilot \
-            -p "$TASK" \
-            -s --no-ask-user --model claude-opus-4.8 --allow-all || true
+          MODELS="${COPILOT_MODELS:-claude-opus-4.8 claude-opus-4.6 gpt-5-mini}"
+          for MODEL in $MODELS; do
+            set +e
+            timeout 600 copilot --yolo -p "$TASK" --model "$MODEL"
+            CODE=$?
+            set -e
+            [ $CODE -eq 0 ] && break
+            echo "::warning::Copilot model $MODEL failed (exit $CODE) — trying next"
+          done || true
 
       - name: Check for changes and create PR
         env:

.github/workflows/copilot-investigate.yml

@@ -49,9 +49,20 @@ jobs:
 
           TASK="Investigate issue #${ISSUE_NUMBER} in repo ${{ github.repository }}. Title: ${ISSUE_TITLE}. Body: ${ISSUE_BODY}. Search the codebase to find relevant files. Check git log for recent changes. Post your investigation notes as a comment on the issue using: gh issue comment ${ISSUE_NUMBER} --body-file /tmp/investigation.md"
 
-          COPILOT_GITHUB_TOKEN="$GITHUB_TOKEN" copilot \
-            -p "$TASK" \
-            -s --no-ask-user --model claude-opus-4.8 --allow-all
+          # GITHUB_TOKEN installation auth (org-billed) + ordered model fallback.
+          MODELS="${COPILOT_MODELS:-claude-opus-4.8 claude-opus-4.6 gpt-5-mini}"
+          SUCCESS=0
+          for MODEL in $MODELS; do
+            set +e
+            timeout 600 copilot --yolo -p "$TASK" --model "$MODEL"
+            CODE=$?
+            set -e
+            if [ $CODE -eq 0 ]; then SUCCESS=1; break; fi
+            echo "::warning::Copilot model $MODEL failed (exit $CODE) — trying next"
+          done
+          # Fail the step if every model failed, so the "investigated" label is not
+          # applied to an issue that never received an investigation comment.
+          [ $SUCCESS -eq 1 ] || { echo "::error::All Copilot models failed — no investigation posted"; exit 1; }
 
       - name: Add investigated label
         env: