[konlue]

Fixes #8156.

Problem

With retryStrategy = failover the circuit breaker recorded the outcome of the whole logical request against the initial upstream's key: DividePlugin.forwardWithCircuitBreaker wrapped the entire downstream chain (failover retries and body write-back included) with recordOutcome(response, initialKey). A successful failover therefore credited the failed upstream with a success, clearing its consecutive failures — the breaker never opened and the upstream kept receiving initial traffic. The failover target recorded its own outcome (DefaultRetryStrategy.resend), but the initial attempt had no immediate failure record.

Change

• The divide plugin publishes the initial attempt's breaker key onto the exchange (UpstreamCircuitBreaker.INITIAL_BREAKER_KEY) when retries are possible.
• AbstractHttpClientPlugin.execute wraps the initial attempt with recordOutcome(response, initialKey): a headers-stage failure (5xx, connect errors, timeouts) is recorded immediately, even when a failover follows; a success is credited only when no failover happens. CURRENT-policy retries record per attempt as well.
• The divide-level whole-chain recording is removed when retries are possible; with zero retries the terminal recording stays, so the no-retry behavior is unchanged.
• Half-open probes are unchanged and mutually exclusive: probe requests forbid retries and are recorded exclusively by the probe path.
• Compatibility: an attempt's outcome is judged at the response-header stage — where the issue's reproduction path (503, connect errors) fails. Body-stage errors are no longer attributed to the initial upstream when retries are possible.

Tests

• InitialAttemptBreakerAttributionTest drives the real execute() with a per-host stubbed doRequest and the real breaker singleton.
• Repeated initial failures with no failover target open the initial upstream's breaker.
• A fails / B succeeds on every request: after the threshold, A's breaker is open even though every logical request succeeded, and B's breaker stays closed.
• A succeeded initial attempt clears its own consecutive failures.

Verification

shenyu-plugin-httpclient: 166/166
shenyu-plugin-divide: 158/158
shenyu-plugin-base: 357/357

Checkstyle clean on the three touched modules.