fix(memory): atomic save + per-line parse guard against corruption (#1481)

[ZhangJing-gugugaga]

Problem

Two defects in the memory server (issue #1481, "Memory MCP JSON Parsing Error - All Tools Failing") combine to make every tool fail on startup whenever the memory file is even slightly malformed:

1. saveGraph overwrote the file in place with fs.writeFile. A process crash during the write left a truncated last JSONL line — producing an invalid file.
2. loadGraph parsed each JSONL line inside the reducer with no per-line guard. A single malformed line aborted the entire loadGraph call, and since main() constructs the KnowledgeGraphManager at startup, the server died before it could serve a single request.

This turns a survivable half-write into a total, repeated startup crash.

Fix (src/memory/index.ts)

• saveGraph now writes to a ${path}.${pid}.tmp file and fs.renames it into place — an atomic replace so a crash mid-write can never leave the real file truncated.
• loadGraph reads first (so ENOENT still returns an empty graph), then parses each line inside its own try/catch. Malformed lines are skipped with a stderr warning instead of killing the server.

Verification

cd src/memory && npx vitest run — all 30 tests pass (unchanged, 3 files / 50 tests across the whole memory suite also green). The new code does not alter the JSONL storage schema, so no migration concerns.

Added no new test cases here — a regression test for the truncated-file-resilience path requires truncating a real file on disk and is a good follow-up.

[ZhangJing-gugugaga]

Superseded: the memory fix was folded into PR #4509 ( branch) for a single review. Closing this duplicate.