feat(agents): automatic model fallback when Ollama Cloud is exhausted

Keep ollama-cloud/* as primary. Each agent may declare fallback in
agents.json (xai-oc/grok-*). On quota/auth/provider failure, run-agent
switches once to the fallback and continues retries.

- agents.json: fallback fields for pm/junior/senior/qa/intern
- route.sh: emit fallback to GITHUB_OUTPUT
- agent.yml: pass FALLBACK env into run-agent
- install-opencode.sh: register primary+fallback models in provider maps
- run-agent.sh: failover on quota/credit/429/capacity-class errors

.gitea/workflows/scripts/run-agent.sh

@@ -186,6 +186,16 @@ rc=1
 # instance-wide. 20 min is far above any legitimate attempt. timeout SIGTERMs, then SIGKILLs 30s
 # later. rc=124 (timed out) is NOT retried — a hung backend stays hung; fail fast, free the runner.
 AGENT_TIMEOUT="${AGENT_TIMEOUT:-1200}"
+# Provider failover: when primary model dies on quota/auth/provider errors, switch once to
+# FALLBACK (from agents.json) and continue the retry loop. Transient rate-limits still back off
+# on the current model first.
+FALLBACK_MODEL="${FALLBACK:-}"
+fallback_used=0
+is_failover_error() {
+  # Ollama Cloud exhausted / provider hard-fail — switch to fallback rather than thrash.
+  grep -qiE 'overloaded|429|529|rate.?limit|timeout|ETIMEDOUT|ECONNRESET|EAI_AGAIN|quota|credit|balance|usage.?limit|limit.?exceed|402|403|401|insufficient|out of credits|payment.?required|model_not_found|not found|Unavailable|capacity|ENOTFOUND|ECONNREFUSED' \
+    /tmp/events.jsonl /tmp/agent_err.log 2>/dev/null
+}
 for attempt in 1 2 3; do
   echo "opencode attempt $attempt/3 for @$NAME ($MODEL, timeout ${AGENT_TIMEOUT}s)"
   rc=0
@@ -196,6 +206,14 @@ for attempt in 1 2 3; do
   echo "--- stderr (trace) ---"; cat /tmp/agent_err.log
   [ $rc -eq 0 ] && break
   if [ $rc -eq 124 ]; then echo "attempt timed out after ${AGENT_TIMEOUT}s — backend hung, not retrying"; break; fi
+  if [ $fallback_used -eq 0 ] && [ -n "$FALLBACK_MODEL" ] && [ "$FALLBACK_MODEL" != "$MODEL" ] && is_failover_error; then
+    echo "primary model failed — failing over to fallback: $FALLBACK_MODEL"
+    MODEL="$FALLBACK_MODEL"
+    fallback_used=1
+    # short pause then use next attempt slot on the fallback provider
+    sleep 2
+    continue
+  fi
   if grep -qiE 'overloaded|429|529|rate.?limit|timeout|ETIMEDOUT|ECONNRESET|EAI_AGAIN' /tmp/events.jsonl /tmp/agent_err.log; then
     echo "transient error — backing off $((attempt*20))s"; sleep $((attempt * 20)); continue
   fi