refactor(kinetic): replace production assert in agent_write with explicit guard

[MarcoPorcellato]

Problem

kinetic.agent_write uses assert parent_uuid is not None after alias resolution (line ~650). Assertions are stripped under python -O and are discouraged in production CLI paths per project Clean Code guidelines (docs/BUG_HUNT_REPORT.md §6).

Proposed Solution

Replace with an explicit guard:

if parent_uuid is None:
    print("Internal error: missing target block UUID.", file=sys.stderr)
    raise typer.Exit(code=1)

Files

• src/logseq_matryca_parser/kinetic.py

Definition of Done

• No assert on the agent-write hot path
• make all passes
• Optional one-liner test if a branch becomes reachable