What does this PR do?

Distinguishes expected shutdown/restart cancellation from genuine processing failure so Discord, Telegram, and Matrix adapters do not emit false terminal failure reactions during intentional gateway cancellation.

Related Issue

Fixes #6315
Related historical issue: #1414
Follow-up to PR #1427
Separate env/pairing hardening is tracked in PR #6956

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)
• 🎯 New skill (bundled or hub)

Changes Made

• updated cancellation classification in gateway/platforms/base.py so expected cancellation is not treated like an ordinary processing failure
• adjusted gateway/platforms/discord.py, gateway/platforms/telegram.py, and gateway/platforms/matrix.py to avoid false terminal failure reactions on expected cancellation
• added regression coverage in tests/gateway/test_base_topic_sessions.py, tests/gateway/test_discord_reactions.py, tests/gateway/test_matrix.py, and tests/gateway/test_telegram_reactions.py
• kept this branch limited to the restart-cancellation fix instead of bundling shared env/pairing hardening

How to Test

1. Run /Users/kennyxie/Documents/Code/clawspace/hermes-agent/.venv/bin/python -m pytest tests/gateway/test_discord_reactions.py tests/gateway/test_telegram_reactions.py tests/gateway/test_base_topic_sessions.py tests/gateway/test_gateway_shutdown.py tests/gateway/test_matrix.py -n0 -q
2. Trigger an expected self-restart or shutdown cancellation and confirm no false ❌ is emitted
3. Trigger a genuine delivery/processing failure and confirm failure reactions still appear

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 26.4

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

Screenshots / Logs

• /Users/kennyxie/Documents/Code/clawspace/hermes-agent/.venv/bin/python -m pytest tests/gateway/test_discord_reactions.py tests/gateway/test_telegram_reactions.py tests/gateway/test_base_topic_sessions.py tests/gateway/test_gateway_shutdown.py tests/gateway/test_matrix.py -n0 -q → 152 passed, 3 skipped