v0.16.1

Highlights

• Subagent collaboration delivery, fixed (TUI): a message from the parent to a running subagent was acknowledged as accepted but frequently never arrived — delivery only happened at child turn boundaries, one shared budget let a short summary spend the only delivery window, and the mailbox was purged when the run ended. A steer sent while the child's turn is live now joins that turn at the child's next step boundary (it never aborts the tool call in flight); the delivery budget is counted separately from the summary-expansion budget; structured-output children keep a guarded delivery turn that preserves their machine-readable contract; a buffered steer that arrives while the turn's Stop hook is awaiting is re-flushed before teardown; a finished run no longer purges its mailbox, and queued mail expires on its own five-minute deadline or is picked up by a later resume. The acknowledgement now says which path a message took.
• Retried sends are deduplicated (agent-core): when the parent re-issues the same directive after a tool hiccup, the subagent sees it once. A dedupe key is registered only after the message actually lands, so a retry after a rejection (mailbox full, deadline elapsed) is attempted honestly.
• Handoff requests say what a good reply looks like (agent-core): a handoff payload now carries expecting (the shape, format, or acceptance criteria wanted back), rendered into the parent notification; free-text fields are flattened onto single lines so the line-oriented body survives the round trip through the transcript parser.
• Foreground/background guidance aligned with reality (agent-core): the main model's prompts now describe a steer as joining a running turn at its next step boundary, keep foreground as the default, and present background as worth considering for long, parallel, or input-hungry work — examples, not requirements, with the model deciding per task.
• Version: all workspace packages bumped to 0.16.1.

Validation

• Typecheck, lint and build green; full repository suite: 513 files, 6,604 tests passed.
• New regression guards were mutation-checked: each guard fails when the behaviour it pins is removed (five mutation probes across this cycle's changes).
• Live end-to-end probe in a fresh process: a subagent blocked inside a long-running tool call received a parent steer mid-run and quoted it back, with the honest mid-run acknowledgement.
• CI and Release pre-checks green on the release commit.