Parked waits: dedicated wire events (TurnParked/TurnWoken) and a TUI heartbeat instead of synthetic Text

[macanderson]

Problem

The parked-wait primitive (#1471) announces the park, the refusal, and the wake as synthetic AgentEvent::Text deltas (crates/stella-core/src/driver/waiting.rs). That was the deliberate slice-1 choice: stella-protocol/src/event.rs is a god file closed to growth and every new variant restales docs/wire (the wire-schema gate), so the event surface was deferred rather than rushed.

Text deltas work but are second-class: consumers cannot distinguish a park from model narration, the deck cannot render a live 'waiting 240s/1800s' heartbeat line, replay cannot skip or summarize the parked span, and stella inspect cannot attribute the wall-clock gap.

What done looks like

• A typed event pair — either AgentEvent::TurnParked { description, poll_interval_secs, deadline_secs } / TurnWoken { reason, polls_used } next to Steered (event.rs:363 area), or a minimal StageKind::Waiting if that proves sufficient. Payload struct can live in a sibling file to keep event.rs growth to the thin variant.
• Wire-name table rows + serde round-trip test (invariant 4); regenerate docs/wire (scripts/export-agentevent-schema.sh / the wire-schema gate).
• Bus lifecycle names agent.turn.parked / agent.turn.woken beside AGENT_STEP_STARTED in crates/stella-core/src/bus.rs (observer-only; do NOT touch names::BLOCKING — its length is pinned by blocking_set_is_exactly_the_documented_nine).
• The deck renders a parked state (heartbeat line or status chip) from the new events; driver/waiting.rs stops emitting the ⏳/▶ Text deltas once a renderer exists.
• The existing witness crates/stella-core/src/driver/tests/parked_wait.rs updated to assert the typed events instead of Text contents.

Constraints

• event.rs and bus.rs are god files at their ceilings — plan line offsets or a justified make file-size-update (AGENTS.md § God files).
• Type doc comments on protocol structs ARE the wire contract — a /// change restales docs/wire; run the schema exporter in the same PR.
• The park loop itself must not change behavior: this is an observability issue, not a semantics one.

Refs #1471.

[macanderson]

Triage 2026-08-06: P2 — observability debt from a deliberate, documented slice-1 deferral; the park loop's semantics are correct, but synthetic Text deltas leave consumers unable to tell a park from model narration and replay/inspect blind to the wall-clock gap. Plan: as specced; next step is the TurnParked/TurnWoken variant pair (payload struct in a sibling file to respect event.rs's ceiling, wire-name rows, serde round-trip, schema regen in the same PR per the doc-comments-are-the-wire-contract rule), then the deck heartbeat and retiring the ⏳/▶ deltas, updating the parked_wait witness to assert the typed events. Do not touch names::BLOCKING — its length is pinned.