What does this PR do?

When clarify is called with multiple choices on platforms that don't support inline buttons (Mattermost, etc.), the default send_clarify in BasePlatformAdapter renders choices as a numbered text list. The user replies with a number or text, but the gateway's text-intercept never fires because awaiting_text remains False. The agent blocks for 10 minutes and then times out.

Root Cause

clarify_gateway.register() sets awaiting_text = not bool(choices) (line 95). When choices are provided, awaiting_text is False. get_pending_for_session() (line 178) only returns entries with awaiting_text == True, so the user's text reply is never matched.

The base send_clarify in gateway/platforms/base.py renders choices as text but never calls mark_awaiting_text(clarify_id) to flip the flag. Adapters with inline buttons (Telegram, Discord) override send_clarify and resolve via button callbacks -- they don't hit this code path.

Related Issue

N/A

Type of Change

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

Changes Made

• See commit messages for detailed changes

How to Test

1. Run pytest tests/ -q — all tests should pass
2. Verify the specific scenario described above is resolved

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 26.4.1

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 and workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A

Code Intelligence

GitNexus unavailable -- analysis skipped, grep-based fallback used.

• Verified: get_pending_for_session called from gateway/run.py:5871 and gateway/platforms/base.py:2899 -- both are text-intercept paths
• Verified: mark_awaiting_text called from gateway/platforms/telegram.py:2814 (button callback) -- confirms button platforms handle it separately
• Blast radius: LOW -- only affects the default send_clarify path; adapters with button overrides are unaffected

Fixes Bug: clarify multiple-choice text fallback never intercepts user reply on Mattermost #25567