fix: balance Telegram HTML chunks

[IceCodeNew]

Summary

• split Telegram HTML by parsed visible characters instead of raw payload offsets
• close and reopen active formatting tags so every chunk is independently valid HTML
• preserve newline characters at preferred split boundaries
• cover nested tags, entities, adjacent tags, and line boundaries with regression tests

Root cause

The previous splitter only avoided cutting inside the text of a tag or entity. It did not track open tags across chunk boundaries, so long formatted content could produce an unclosed tag in one request and an orphaned closing tag in the next, causing Telegram Bot API rejection.

Validation

• mise exec -- uv run --with pytest --with pytest-cov -- pytest --cov --cov-branch --cov-report=xml (546 passed; misses and partials unchanged)
• prek run --all-files
• CodeRabbit CLI review against master (0 findings after one valid newline-preservation fix)

Summary by CodeRabbit

• Bug Fixes

  • Improved Telegram message splitting to respect visible-character limits while preserving valid HTML formatting in every message.
  • Prevented messages from being split inside HTML tags or entities.
  • Preserved leading line breaks when content is divided.
  • Daily briefings exceeding Telegram’s limit now fail instead of being split.
  • Authority forecasts are delivered independently and may be safely split across multiple formatted messages.

• Documentation

  • Clarified Telegram delivery and message-sizing behavior.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2246050b-fc31-4c4b-8418-63098568d821

📥 Commits

Reviewing files that changed from the base of the PR and between 65ce112 and db6d2a8.

📒 Files selected for processing (3)

• docs/design.md
• tests/test_publishers.py
• weather_briefing/publishers.py

📝 Walkthrough

Walkthrough

Telegram publisher message splitting now uses an HTML parser to enforce visible-character limits and produce independently valid HTML chunks. Tests cover tags, entities, nesting, and newlines, while design documentation specifies the delivery behavior.

Changes

Telegram HTML chunking

Layer / File(s)	Summary
Parser-driven HTML chunking weather_briefing/publishers.py	_split_message now delegates to _TelegramHTMLChunker, which counts visible characters, tracks open tags, and closes formatting tags in each chunk.
Chunking validation and delivery contract tests/test_publishers.py, docs/design.md	Tests validate balanced HTML and entity splitting, and the design documentation describes visible-character counting and independently valid Telegram requests.

Estimated code review effort: 3 (Moderate) | ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly captures the main change: making Telegram HTML chunks balanced and valid.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/balance-telegram-html-chunks

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.63%. Comparing base (04fa7be) to head (db6d2a8).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #42   +/-   ##
=======================================
  Coverage   99.62%   99.63%           
=======================================
  Files          38       38           
  Lines        5944     5980   +36     
  Branches      323      325    +2     
=======================================
+ Hits         5922     5958   +36     
  Misses         15       15           
  Partials        7        7           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@weather_briefing/publishers.py`:
- Around line 269-273: Update _finish_chunk to avoid appending or emitting a
chunk when the accumulated content has zero visible characters, including
trailing empty markup such as an empty nested tag. Preserve the existing
closing-tag and open-tag state handling for chunks containing visible text, and
ensure empty markup is not sent as a separate request.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 67b7debc-4b8f-4f02-b291-99c2dba6cd40

📥 Commits

Reviewing files that changed from the base of the PR and between 04fa7be and 65ce112.

📒 Files selected for processing (3)

• docs/design.md
• tests/test_publishers.py
• weather_briefing/publishers.py