Add OTLP payload byte-size chunking to Agent365Exporter

[alexlu4250]

A365 OTLP traces endpoint enforces a 1 MB request body limit. The exporter previously batched by span count (512) with no byte-level enforcement, so batches of gen-AI spans could exceed 1 MB and get rejected (403/502/500).

This adds two layers of defense:

• Heuristic span size estimator (EstimateActivityBytes) with generous over-estimation

• Byte-size chunking (ChunkBySize) that splits per-identity batches into sub-batches under MaxPayloadBytes (default 900 KB, configurable via Agent365ExporterOptions)

• All-or-nothing semantics: if any chunk fails, the entire batch fails and the BatchExportProcessor retries

Per-span truncation (250 KB cap in ExportFormatter) already existed; this complements it at the batch level.

Mirrors Agent365-nodejs PR #237 (commit e05b3b6a).

Work item: AB#37660995

[github-actions]

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Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

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[Copilot]

Pull request overview

Adds byte-size-aware batching to the Agent365 OTLP/HTTP exporter to reduce the risk of exceeding the A365 ~1 MB request body limit (especially with large gen-AI spans), complementing existing per-span truncation.

Changes:

• Introduces heuristic OTLP span byte-size estimation (estimate_span_bytes / estimate_value_bytes) and generic chunking (chunk_by_size) with a default max payload of 900 KB.
• Updates _Agent365Exporter.export() to chunk per (tenantId, agentId) group and send multiple requests with all-or-nothing semantics per group.
• Adds unit + end-to-end style tests validating estimation, chunking invariants, truncation behavior, and exporter multi-request behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
tests/observability/core/exporters/test_payload_chunking.py	Adds coverage for estimator/chunker utilities and exporter multi-request chunking behavior.
.../observability/core/exporters/utils.py	Adds payload sizing constants, byte estimators, and a generic chunk_by_size helper.
.../observability/core/exporters/agent365_exporter.py	Chunks exports by estimated payload bytes and sends multiple POSTs per identity group.

[alexlu4250]

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