fix(slack): truncate inflated original_text in approval/confirm chat.update handlers (#53693)

[liuhao1024]

What does this PR do?

Fixes Slack approval and confirmation card updates failing with invalid_blocks: must be less than 3001 characters when the original command/prompt text contains HTML-sensitive characters (angle brackets, ampersands).

The send path (send_exec_approval, send_slash_confirm) already budget-truncates section text to 3000 chars or fewer. But the button click handlers (_handle_approval_action, _handle_slash_confirm_action) extract original_text from the interaction payload and rebuild updated_blocks verbatim. Slack re-escapes HTML entities in the payload (e.g. & for &, < for the left angle bracket), inflating the text past the 3000-char section-block limit, causing chat.update to fail silently while the approval itself has already resolved.

Related Issue

Fixes #53693

Type of Change

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

Changes Made

• plugins/platforms/slack/adapter.py: Cap original_text to 3000 chars after extraction from interaction payload in both _handle_approval_action and _handle_slash_confirm_action. This matches the send-path budget and prevents entity-inflation overflow.
• tests/gateway/test_slack_approval_buttons.py: Add test_truncates_inflated_original_text to both TestSlackApprovalAction and TestSlackSlashConfirmAction -- inject 3040-char inflated text and assert the chat.update section block stays at 3000 chars or fewer.

How to Test

1. Run python -m pytest tests/gateway/test_slack_approval_buttons.py -v -- all 28 tests should pass, including the 2 new truncation tests. Observed result: 28 passed in 2.63s.
2. On a Slack-connected Hermes instance, trigger a command approval with HTML-heavy content (e.g. execute_code with Python comparisons). Press "Allow Once" -- the card should update to show "Approved" without errors.
3. Check gateway logs for "Failed to update approval message" -- should not appear for the inflated-text case.

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/gateway/test_slack_approval_buttons.py -v 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

[teknium1]

Merged via #69317 — your commit was cherry-picked onto current main with your authorship preserved in git history: your approval/confirm original_text truncation was cherry-picked directly.

Thanks for the contribution!