What does this PR do?

Fixes two bugs in the WeChat (weixin) message delivery path:

1. MEDIA tag leaks for common file types

BasePlatformAdapter.extract_media() regex whitelist was missing .md, .json, .yaml, .yml, .toml, .log. When MEDIA:/path/to/file.md was used, the regex did not match → the MEDIA tag appeared as raw text on WeChat/Feishu/Telegram etc. instead of the file being routed through document-upload paths.

Fix: Added md|json|yaml|yml|toml|log to the regex alternation (single-line change). All other parts of the pattern (path wrapping, quote/backtick stripping, trailing-delimiter lookahead, [[audio_as_voice]] / [[as_document]] directives) are unchanged.

2. No retry on session/rate-limit errors

send_weixin_direct() fallback path returned immediately on errors like ret=-2 (rate limit) or errcode=-14 (session timeout) without any retry or context_token refresh. After gateway restart, stale context_tokens caused persistent failures.

Fix: Added a retry loop (up to 2 attempts) that clears the stale context_token before retrying. On session errors, the retry sends without a context token (tokenless fallback), with a 3-second backoff between attempts.

Related Issue

Closes #32601

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)

Changes Made

• gateway/platforms/base.py — extend the MEDIA tag regex alternation with md|json|yaml|yml|toml|log (+1/-1 lines)
• gateway/platforms/weixin.py — add retry loop in send_weixin_direct() fallback path for session/rate-limit errors (+29/-5 lines)
• tests/gateway/test_platform_base.py — add parametrized test test_media_tag_accepts_text_config_extensions covering each new extension (+13 lines)

How to Test

# Test the regex fix (20 tests: 14 existing + 6 new parametrized)
python3 -m pytest tests/gateway/test_platform_base.py -v -k TestExtractMedia

# Test the retry logic
python3 -m pytest tests/gateway/test_weixin.py -v

Manual verification

• Sent .md, .json, .yaml, .yml, .toml, .log files via MEDIA: tag → all delivered correctly
• Restarted gateway → verified retry fires and uses tokenless fallback
• Existing file types (.txt, .pdf, .png) still work correctly

Checklist

Code

• I have read the Contributing Guide
• My commit messages follow Conventional Commits (fix(weixin): ...)
• I searched for existing PRs to make sure this is not a duplicate
• My PR contains only changes related to this fix (no unrelated commits)
• I have run focused tests for the touched code and all pass
• I have added tests for my changes
• I have tested on my platform: macOS 15.x

Documentation & Housekeeping

• I have updated relevant documentation — N/A (regex-internal + retry-internal change)
• I have updated cli-config.yaml.example if I added/changed config keys — N/A
• I have updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — N/A
• I have considered cross-platform impact — regex matches absolute (/...) and tilde (~/...) paths consistently with the existing pattern; no Windows-path coupling
• I have updated tool descriptions/schemas if I changed tool behavior — N/A

Related / Positioning

Issue #32601 lists two bugs. Both are addressed in this single PR because:

Keeping these together makes sense because they were discovered together in a real deployment scenario (WeChat delivery path), and the retry logic in bug 2 is the fallback path that fires when file delivery (which bug 1 affects) hits transient errors.

This PR is part of a cluster of MEDIA regex fixes. Compared to siblings:

• fix(gateway): sync MEDIA regex extension allowlist with SUPPORTED_DOCUMENT_TYPES #29609 (dynamic allowlist from SUPPORTED_DOCUMENT_TYPES) — preferable long-term, but this PR also fixes the WeChat retry issue which fix(gateway): sync MEDIA regex extension allowlist with SUPPORTED_DOCUMENT_TYPES #29609 does not cover
• fix(weixin): MEDIA tag regex now covers .md, .json, .yaml, .yml, .toml, .log #32611, fix(gateway): accept text/config extensions in MEDIA tag regex #32751 (closed) — same regex fix, without retry logic
• The retry fix in weixin.py is orthogonal to whichever regex approach lands, and can be cherry-picked independently