Summary

• Retry transient Telegram text-send failures in the direct send path.
• Honor retry_after when present and retry common 429/5xx responses with backoff.
• Keep timeout-like errors non-retried to avoid duplicate delivery risk.

Root cause

The gateway adapter already has retry handling for transient Telegram delivery failures, but the direct send_message Telegram path only retried parse-mode failures. A single transient 502 or 429 could therefore fail an otherwise valid delivery.

Changes

• Added a small retry helper around Telegram send_message calls used by the direct send path.
• Reused it for both formatted text and plain-text fallback sends.
• Added regression coverage for a 502 followed by a successful retry.

Validation

• python -m pytest tests/tools/test_send_message_tool.py::TestSendTelegramHtmlDetection::test_transient_bad_gateway_retries_text_send -q -n0 (failed before the code change, passed after)
• python -m pytest tests/tools/test_send_message_tool.py::TestSendTelegramHtmlDetection -q -n0
• python -m pytest tests/tools/test_send_message_tool.py -q -n0
• python -m py_compile tools/send_message_tool.py tests/tools/test_send_message_tool.py
• git diff --check

Refs #8844