Adds the incremental write path the tap-subscriber cycle streams
record subscriptions through: TraceStore::begin_run opens a run
directory and returns a TraceStreamer; per tap, TapTraceWriter
appends (ts, cell) points into two temp column streams and finish()
assembles the canonical ColumnarTrace JSON by streaming
concatenation (io::copy), removing the temps. index.json is written
last by TraceStreamer::finish, preserving the store's crash
discipline (no index -> NotFound, treat-as-absent).
Compatibility is pinned as an equality property, not a frozen byte
assumption: a new test asserts the streamed output byte-identical to
TraceStore::write's for the same rows (including empty and bool
columns), so the two write paths cannot drift and every reader
(read, read_family, chart) stays untouched. TraceStore::write is
refactored onto shared write_tap_file/write_index helpers used by
both paths. Temp streams open read+write (OpenOptions), since
finish() seeks back and re-reads them.
Verification: cargo test -p aura-registry — 78 passed (3 new:
byte-equality incl. empty+bool, crash shape NotFound, caller-order
index).
refs #283
claude
4ae2297a35