fix: harden persistence, concurrency, and memory export

[Da7-Tech]

What changed

• merge concurrent edges per directional pair, preserve reinforcement deltas, and serialize daily edge decay under the graph lock
• make atomic replacement complete short writes with unique O_EXCL temp files and directory fsync
• harden graph/journal repair, provenance reads, CLI validation, deterministic ranking, and hot-memory tie-breaking
• treat exported memories as quoted data, escape guard markers, and add explicit privacy guidance
• replace the stale competitor scorecard with a neutral scope comparison and align every benchmark/documentation claim with measured behavior
• update pinned GitHub Actions and clean benchmark temp directories

Root cause and impact

The 6.2.7 save path merged whole edge adjacency maps, so concurrent links or stale writers could lose one direction or erase a fresh boost. Several durability and provenance paths also trusted single-write completion, a bounded journal tail, or structurally valid-but-hostile state more than the public guarantees allowed. Agent export did not clearly separate remembered data from instructions.

This change closes those gaps while preserving the one-file, stdlib-only design and existing graph format.

Validation

• 213/213 unit tests on Python 3.14 and Python 3.11
• full fuzz: 420/420 adversarial cases
• recall benchmark: recall@1 and recall@5 = 1.00 at 100 and 1,000 nodes
• multilingual: 24/24; competing-distractor discrimination: 12/12
• 180-day soak: 15/15 core survival, 0/256 stale junk, 7/8 hot core slots
• mutation sample: 47/120 killed (39%), survivors printed and triaged
• concurrency stress: 20/20 repeated rounds
• end-to-end install/export smoke from paths containing spaces
• checksum: b3e944ce9103bd5e353e09a12f434721cb274bc919326361039104889c6c5e03