fix(hookify): replace hand-rolled YAML parser + fix new_text field on Write

[adelaidasofia]

Summary

Two silent bugs discovered via a full regression harness (39 test cases across all hookify rules):

Bug 1 — config_loader.py: hand-rolled YAML parser double-escapes backslashes

The custom parser in extract_frontmatter stripped surrounding quotes but did not process YAML escape sequences. In double-quoted YAML, \\d means one backslash + d (i.e. \d, a regex digit class). The old parser stored the raw characters between the quotes — two backslashes + d — so the compiled regex pattern matched a literal \d string instead of a digit.

Impact: Any hookify rule using \d, \w, \s, \b, or \[ in a double-quoted pattern: value silently never fired. The rule loaded without error; the condition just always returned False.

Fix: Replace the 85-line hand-rolled parser with yaml.safe_load + a YAMLError guard. Four lines.

Side-effect / authoring note: Unquoted YAML patterns starting with [ (e.g. pattern: [A-Z].*) are now correctly rejected as YAML flow sequences — this was always invalid YAML that the old parser accidentally tolerated. Rule authors must single-quote such patterns: pattern: '[A-Z].*'. This is standard YAML practice.

Bug 2 — rule_engine.py: new_text field on Write returns empty string

_extract_field('new_text', 'Write', tool_input) called tool_input.get('new_string', ''). The Write tool stores its content under content, not new_string (that's Edit). So any rule with field: new_text on a file event silently never fired when the tool was Write.

Fix: One-line change — fall back to content when new_string is absent, matching the existing behaviour of field: content.

Test plan

• Regression harness: 39 test cases covering positive + negative for every active rule — 39/39 pass after these fixes (was 36/39 before)
• session-close-sonnet-check (uses \d{8} pattern) — was silently broken, now fires correctly
• warn-exclamation-marks (uses [A-Z] pattern, single-quoted after authoring fix) — fires correctly
• block-em-dash, warn-external-prose-humanizer — verified with Write tool using field: new_text
• No regressions on rules that were already working

🤖 Generated with Claude Code