fix(sessions): reject blank SQLite branch names

[jbeckwith-oai]

Summary

Reject empty and whitespace-only names before AdvancedSQLiteSession creates or switches to a branch. Both creation methods now reject names that delete_branch() cannot remove, while preserving automatic naming with None and exact padded names.

The fix adds a two-line guard, updates the method docstrings, and covers both creation entry points. Existing stored branches are unchanged.

Test plan

• All six new regression cases fail without the guard and pass with it.
• AdvancedSQLiteSession tests: 160 passed, including automatic and padded branch-name coverage.
• Full verification: formatting, lint, mypy, and Pyright passed; 10,858 tests passed and 60 skipped, including configured native-macOS sandbox exclusions.
• Independent implementation review completed with no actionable findings; final diff matches the reviewed content.

Issue number

Fixes #5178

Checks

• I've added new tests, if relevant
• I've run .agents/skills/code-change-verification/scripts/run.sh
• I've confirmed all verification steps pass
• I've completed an independent Codex code review before submitting this PR

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-25T21:54:06.301958Z	fb5e288	PR opened
🔒 Security Review	✅ Completed 2026-09-25T21:54:47.674715Z	fb5e288	PR opened

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