[log] Add debug logging to circuit breaker (#4582)

Adds 4 focused debug log calls to `internal/server/circuit_breaker.go`
using the existing `logCircuitBreaker` logger (`server:circuit_breaker`
namespace).

## Changes

**File modified:** `internal/server/circuit_breaker.go`

### New logging calls

| Location | Message |
|----------|---------|
| `newCircuitBreaker` | Logs creation with `serverID`, `threshold`, and
`cooldown` so you can see CB config at startup |
| `Allow` (HALF-OPEN branch) | Logs when a probe is already in flight
and the request is being rejected |
| `RecordSuccess` | Logs when the consecutive error counter is reset
(only when it was > 0, avoids noise on healthy paths) |
| `parseRateLimitResetFromText` | Logs the parsed reset duration and
absolute timestamp when a reset time is extracted from error text |

## Validation

- `go build ./...` ✅
- `go vet ./...` ✅  
- `go test ./internal/server/...` ✅

## Enable these logs

```bash
DEBUG=server:circuit_breaker ./awmg --config config.toml
```




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Author: lpcox

internal/server/circuit_breaker.go

@@ -84,6 +84,7 @@ func newCircuitBreaker(serverID string, threshold int, cooldown time.Duration) *
 	if cooldown <= 0 {
 		cooldown = DefaultRateLimitCooldown
 	}
+	logCircuitBreaker.Printf("Creating circuit breaker: serverID=%s, threshold=%d, cooldown=%v", serverID, threshold, cooldown)
 	return &circuitBreaker{
 		serverID:  serverID,
 		state:     circuitClosed,
@@ -140,6 +141,7 @@ func (cb *circuitBreaker) Allow() error {
 	case circuitHalfOpen:
 		// Only one probe is allowed; further requests are blocked until the probe resolves.
 		if cb.probeInFlight {
+			logCircuitBreaker.Printf("server %q circuit breaker HALF-OPEN, probe already in flight — rejecting request", cb.serverID)
 			return &ErrCircuitOpen{ServerID: cb.serverID, ResetAt: cb.resetAt}
 		}
 		// This shouldn't normally happen (probe resolved but state wasn't updated),
@@ -157,6 +159,9 @@ func (cb *circuitBreaker) RecordSuccess() {
 	defer cb.mu.Unlock()
 
 	prev := cb.state
+	if cb.consecutiveErrors > 0 {
+		logCircuitBreaker.Printf("server %q circuit breaker resetting consecutive error count: %d → 0", cb.serverID, cb.consecutiveErrors)
+	}
 	cb.consecutiveErrors = 0
 	cb.probeInFlight = false
 	if cb.state == circuitHalfOpen {
@@ -314,5 +319,7 @@ func parseRateLimitResetFromText(text string) time.Time {
 	if err != nil || secs <= 0 {
 		return time.Time{}
 	}
-	return time.Now().Add(time.Duration(secs) * time.Second)
+	resetAt := time.Now().Add(time.Duration(secs) * time.Second)
+	logCircuitBreaker.Printf("Parsed rate limit reset time from text: resetIn=%ds, resetAt=%s", secs, resetAt.UTC().Format(time.RFC3339))
+	return resetAt
 }