SIA v1.8.2 — the agent-note lane moves out

A structural release with no change in behaviour: the agent-note lane moves out of the resident library so the library keeps headroom under the marketplace's per-file scan limit.

The agent-note lane moves out

The multi-writer agent-note lane — note materialization, exactly-once redaction accounting and post-commit acknowledgement — now lives in bin/sianotes.py. It moved verbatim, behind the same bind/invoke facade as siasenses and siagraph: sialib binds its namespace into the child and keeps every original name as a delegate, so each caller, and each test that patches one of those names, still reaches the same code.

Why now

sialib.py had 1,269 bytes left before the release guard's 95% headroom line on the marketplace's 524,288-byte per-file scan cap, so the next fix to the library would trip it. The guard names extraction as the repair, not a raised threshold. The library drops from 496,804 to 488,067 bytes.

Runtime rung

sianotes.py is its own sia-runtime-v17 rung rather than a new member of v16, so an installed v16 tree still hashes under v16 and the update stages the new member. The release contract pins the child's exact export set, as it does for every facade child.

This release carries nothing else, per the extraction rule in docs/ARCHITECTURE.md. The fix it makes room for ships as v1.8.3.