MEDIUM 1: session_runtime::start() now returns an explicit
fresh-launch vs replay disposition (session_start_result), and
handle_start_session sets outcome.applied only for a fresh committed
launch. An authenticated idempotent start replay therefore never gains
connection-scoped teardown authority: a broken pipe during a replay can
no longer stop an already-running guest. The control audit event for a
replayed delivery carries the replay disposition
(start_session:replay:<session>).
MEDIUM 2: jsonl_sink truncation now accounts for record delimiters
exactly, so current_bytes_ always tracks the physical file; only
newline-terminated complete records are retained (no blank or partial
lines, bounded read window); the cap is a hard cap (an oversized event
is dropped with a structured operator note; a pre-existing oversized
journal is bounded with a bounded read at construction).
MEDIUM 3: the broken-pipe degrade test now synchronizes through a
mutex-protected condition-variable gate handshake that proves the
dispatch is parked inside the blocked gate before the client resets,
records the start only after the dispatch completes, and the
mark_stopping test destroys every registry lock holder (runtime,
protocol, registry) before the independent registry reopen so the
nonblocking exclusive flock can actually be acquired.
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