claude-code-chat-browser: YAML escape fix — handle colons, hashes, tabs, bool literals in frontmatter export

[clean6378-max-it]

Calendar Day

Wednesday, July 2, 2026 (PR 2 of 2)

Planned Effort

3 story points (Medium–High) — sprint item #6

Companion PR: Wednesday PR 1 (SessionMetadataDict #9) — independent; can land in either order.

Problem

The _escape_yaml() helper in utils/md_exporter.py does not handle several YAML-special characters and patterns:

• Colons followed by space (: ) — interpreted as key-value separator, corrupts frontmatter
• Hash/pound signs (#) — interpreted as inline comments, truncates values
• Tab characters — YAML spec forbids tabs for indentation
• YAML boolean literals (true, false, yes, no, on, off) — unquoted values parsed as booleans

Session titles and project paths from Claude Code regularly contain colons (e.g. C:\Users\..., Fix: handle edge case) and hashes. The resulting YAML frontmatter is malformed and fails to parse in downstream consumers.

Goal

One merged PR that makes exported YAML frontmatter round-trip cleanly through yaml.safe_load() for all real-world session metadata inputs, using always-double-quote scalars as the primary fix.

Scope

Touch points

• utils/md_exporter.py — _escape_yaml(): always double-quote YAML scalar values in frontmatter; escape internal " as \"; use block scalar (| or >) for multiline values
• tests/ — test_yaml_frontmatter_roundtrip: extract YAML between --- delimiters, yaml.safe_load(), assert dict matches original metadata
• tests/ — Hypothesis @given(st.text()) property test for round-trip fidelity

Out of scope

• Changes to Markdown body export format
• JS YAML parser compatibility tests (Python round-trip is sufficient)

Acceptance Criteria

• _escape_yaml() produces valid YAML for values containing : , #, \t, and boolean literals
• Double quotes within values escaped as \" before wrapping
• Multiline values use YAML block scalar syntax
• Exported frontmatter round-trips through yaml.safe_load()
• Hypothesis property-based test asserts round-trip fidelity
• Existing export tests pass with properly escaped output
• Full pytest, mypy --strict, and ruff pass
• PR approved by at least 1 reviewer

Verification

cd C:\Users\Jasen\CppAliance\claude-code-chat-browser
.\.venv\Scripts\Activate.ps1
pytest tests/ -k yaml -q
pytest -q

Manual: export session with title Fix: handle edge case — confirm frontmatter parses via yaml.safe_load().