fix(discord): retry standalone send on 429 rate-limit instead of dropping chunks

[liuhao1024]

What does this PR do?

Adds 429 rate-limit retry logic to the standalone Discord send path (_standalone_send), preventing multi-chunk messages from being silently truncated when a rate limit is hit mid-delivery.

Related Issue

Fixes #44468

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• plugins/platforms/discord/adapter.py: Add _standalone_parse_retry_after() helper to extract retry_after from Discord 429 JSON responses. Wrap both the text POST and per-media POST in _standalone_send with a retry loop (3 attempts, honouring retry_after with 0.5s floor and 10s cap).
• tests/tools/test_send_message_tool.py: Add TestStandaloneParseRetryAfter (5 unit tests for the parser) and TestSendDiscord429Retry (4 integration tests covering retry-on-429, exhausted retries, missing retry_after, and non-429 error paths).

How to Test

1. Run pytest tests/tools/test_send_message_tool.py::TestStandaloneParseRetryAfter tests/tools/test_send_message_tool.py::TestSendDiscord429Retry -v — all 9 tests should pass.
2. Run pytest tests/tools/test_send_message_tool.py -v — all 142 tests should pass (no regressions).
3. Run pytest tests/e2e/test_discord_adapter.py -v — all 6 tests should pass.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Code Intelligence

• Analyzed: plugins/platforms/discord/adapter.py::_standalone_send (callers: 1 via standalone_sender_fn registry entry, flows: send_message_tool._send_to_platform → entry.standalone_sender_fn)
• Blast radius: LOW — changes are confined to the standalone send path; the live adapter path is unaffected
• Related patterns: Mirrors the existing retry pattern in _send_telegram_message_with_retry() and the adapter's _extract_discord_retry_after() / _is_discord_rate_limit() helpers

[tonydwb]

Code Review Summary

Verdict: Approved

Bug Fix - Looks Good

• plugins/platforms/discord/adapter.py — Adds retry logic for 429 rate-limit responses in the standalone send path, using Discord's retry_after field (floored at 0.5s, capped at 10s, max 3 attempts).
• Handles 429 for both text messages and media uploads.
• Clean retry-after parsing with proper error handling.

Testing

• tests/tools/test_send_message_tool.py — Comprehensive test coverage:
  • TestStandaloneParseRetryAfter: 5 tests for the parsing function
  • TestSendDiscord429Retry: 4 tests for the retry behavior (success, exhausted retries, no retry_after, non-429)

Code Quality

• No security concerns.
• Well-structured retry loop with clear logging.

---

Reviewed by Hermes Agent

[alt-glitch]

Duplicate of #44488 — same Discord 429 retry (honoring retry_after) on the standalone send path (plugins/platforms/discord/adapter.py) to stop dropping multi-chunk messages (#44468). #44488 is the earliest-open canonical.

[liuhao1024]

Closing as duplicate of #44488 by @AIalliAI, which implements the same Discord 429 retry fix (honoring retry_after in the standalone send path). That PR was opened earlier (2026-06-11T21:25Z) with the same approach and adapter file.