📜 Description

ClientReportRecorder.recordLostEnvelopeItem counted discarded log and metric items by fully deserializing the envelope payload just to read getItems().size(). The item count is already carried in the envelope item header (item_count, set by SentryEnvelopeItem.fromLogs/fromMetrics and round-tripped through the disk cache), so this change reads it from the header instead of deserializing. Byte counts still come from the raw getData() bytes.

• Added SentryEnvelopeItemHeader.getItemCount().
• Log/metric branches of recordLostEnvelopeItem now use the header count; when it is absent (legacy/foreign envelopes) they fall back to 1 and never deserialize.
• Transactions are untouched — span counts are not stored in the header and that path isn't implicated.

💡 Motivation and Context

Under sustained rate limiting (e.g. transaction/span quota exhausted while logs.enabled=true), envelopes are discarded continuously via rate limiting → queue/cache overflow → send/network errors. Each discard ran a full JSON deserialization on the SentryAsyncConnection/SentryExecutorService threads. The gson reader's error-tolerant recovery machinery throws an exception per token, and Throwable.fillInStackTrace dominated the CPU profile — the cost then fed back into more queue overflow and more discards, pinning CPU cores in a busy-loop indefinitely. Delivery of non-rate-limited categories (errors) stopped, and the only workaround was disabling logs.

Reading the count from the header makes the discard path O(1) and allocation/exception-free.

Fixes GH-5830
Fixes JAVA-662

💚 How did you test it?

Unit tests in ClientReportTest:

• Existing log/metric count tests remain green (header count equals list size).
• New regression test: a log item whose payload would fail to deserialize is still counted from the header, and getLogs() is verified never to be called.
• New test for the null item_count fallback (counts as 1).

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

None.