fix(telegram): truncate mid-stream overflow instead of splitting

[liuhao1024]

What does this PR do?

Fixes an infinite message duplication loop in the Telegram adapter when streamed content exceeds the 4096 UTF-16 code-unit limit. During streaming (finalize=False), the pre-flight overflow check unconditionally called _edit_overflow_split, which spawned continuation messages and updated the active message_id. On the next token, the full accumulated text (still > 4096) was edited to the new message, triggering another split — creating an infinite chain of duplicate replies.

The fix: when finalize=False and content exceeds the limit, truncate the preview to 4000 code-units (safe margin below 4096) and fall through to the normal edit path. The real split only happens when finalize=True (stream complete).

Related Issue

Fixes #48648

Type of Change

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

Changes Made

• gateway/platforms/telegram.py: In edit_message(), when finalize=False and content exceeds MAX_MESSAGE_LENGTH, truncate to 4000 code-units instead of calling _edit_overflow_split. The split path is preserved for finalize=True.
• tests/gateway/test_telegram_overflow_truncation.py: 3 regression tests — mid-stream truncation, finalize-True split, and under-limit passthrough.

How to Test

1. Run python -m pytest tests/gateway/test_telegram_overflow_truncation.py -v — all 3 tests should pass
2. On Telegram: start a streaming response that grows past 4096 chars. Before this fix, you'd see infinite nested replies. After: the preview truncates at 4000 chars and the final message splits cleanly.

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

⚠️ GitNexus unavailable — grep-based fallback used.

• Analyzed: gateway/platforms/telegram.py::edit_message (callers: stream_consumer, gateway run.py)
• Blast radius: LOW — only affects mid-stream overflow path; finalize-True and under-limit paths unchanged
• Related patterns: _edit_overflow_split at L2804 handles chunked delivery on finalize; this fix defers to it

[teknium1]

Closing as superseded by #51736 (merged to main in 73a20a6ad), which fixed #48648 by gating the overflow split on finalize. Your fix targeted gateway/platforms/telegram.py, which no longer exists — the Telegram adapter was relocated to plugins/platforms/telegram/adapter.py in a bundled-plugin refactor, so the change landed there instead. The salvaged PR (#50408 by @Tranquil-Flow) hit the current path. Thanks for the fix and the report — credited in the issue.