store: Stdlib-only YAML frontmatter parsing for markdown memory files

graph/solutions/stdlib-only-yaml-frontmatter-parsing-for-markdown-memory-fil-312bc2.md

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+---
+id: 312bc25f-1d4c-4a17-8ea6-3516d9e952a2
+type: solution
+title: "Stdlib-only YAML frontmatter parsing for markdown memory files"
+tags: [cognitive-memory, python, architecture, stdlib]
+importance: 0.7
+confidence: 0.8
+created: "2026-02-13T17:39:51.592359+00:00"
+updated: "2026-02-13T17:39:51.592359+00:00"
+---
+
+Built a complete YAML frontmatter parser/serializer using only Python stdlib (re module + manual parsing). Key design decisions:
+
+- Parse frontmatter between --- markers with regex
+- Handle nested lists (relations) and simple key-value pairs
+- Slugify titles with 6-char UUID suffix for unique filenames
+- Keep _index.json as derived cache (rebuilt from files via reindex)
+- Keep _state.json for mutable data (access counts, decay scores) 
+- Git-track markdown files but gitignore _index.json and _state.json
+
+The decay model uses: importance × e^(-0.03 × days_since_access) × log2(access_count + 1) × type_weight
+Half-life is ~23 days. Type weights range from 0.8 (error/general) to 1.3 (decision).
+
+Content preview (first 200 chars) stored in _index.json enables zero-file-I/O search for recall and search commands.