feat: add durable safe retries with uncertainty tracking and SDK examples

internal/storage/mysql/migrations/000005_safe_retry.up.sql

@@ -0,0 +1,13 @@
+-- 安全重试保留跨尝试的不确定效果，旧迁移及旧操作摘要保持不变。
+ALTER TABLE pulse_tasks
+    ADD COLUMN effect_uncertain BOOLEAN NOT NULL DEFAULT FALSE COMMENT '曾有已授权执行的效果尚未核实，重试与耗尽不清除，仅权威成功或核查可解除',
+    ADD CONSTRAINT ck_task_effect_uncertain CHECK (effect_uncertain IN (0,1) AND (effect_uncertain=FALSE OR state NOT IN ('SUCCEEDED','FAILED','CANCELLED')));
+UPDATE pulse_tasks SET effect_uncertain=TRUE WHERE state='NEEDS_REVIEW';
+ALTER TABLE pulse_attempts
+    ADD COLUMN retryable BOOLEAN NOT NULL DEFAULT FALSE COMMENT 'Worker 明确失败时声明可安全重试，不用于未知效果或证明实际已安排重试',
+    ADD CONSTRAINT ck_attempt_retryable CHECK (retryable IN (0,1) AND (retryable=FALSE OR state='FAILED'));
+ALTER TABLE pulse_attempt_evidence
+    ADD COLUMN retryable BOOLEAN NOT NULL DEFAULT FALSE COMMENT '原失败报告的安全重试声明，证据本身不触发重试',
+    ADD CONSTRAINT ck_evidence_retryable CHECK (retryable IN (0,1) AND (retryable=FALSE OR outcome='FAILED'));
+ALTER TABLE pulse_attempt_receipts
+    ADD KEY ix_result_receipt(namespace_id,attempt_id,operation,request_digest) COMMENT '同一结果换消息身份重报时读取原始已应用回执';