feat(wire): AgentEvent::Asked — a pending human-answerable question on the wire

[phall1]

Adds an additive AgentEvent::Asked so a projection consumer (phux-mobile, phux-web) can tell "an agent is waiting on a human" — render the question and raise a notification — without re-deriving it from its local grid. Sibling of ADR-0033's TerminalControl; a structured agent-surface signal, not a new wire tier.

What

• AgentEvent::Asked at event tag 0x09 (after terminal_control's 0x08) on the EVENT (0xB3) stream: { id, question, suggestions: [str], elapsed_seconds: opt<u64> }. Body is field-tagged TLV (id=1, question=2, suggestion=3 repeated, elapsed_seconds=4), so the suggestion list and counter are additive; an older decoder skips it by length to AgentEvent::Unknown.
• v1 trigger — phux-ask title sentinel. The server decides a pane is asking from its terminal title (phux-ask[<id>]:<question>?s=a|b|c), coalesced so a re-asserted marker doesn't re-fire. libghostty-vt surfaces no OSC 9/777, so the title is the closest signal an agent can drive and the server can observe without disturbing the snapshot synthesizer.
• ADR-0035 records the mechanism decision (additive AgentEvent variant vs the spec-only TERMINAL_EVENT/RUN_HOOK).
• Additive: no tag renumbered, no existing bytes change. PROTOCOL_VERSION stays 0.5.0 (CHANGELOG 0.5.0-draft.8).

Why a draft, not 0.6.0

Matches the established convention — every recent additive wire change (ADR-0032/0033, QUIC, per-spawn TERM) landed as a 0.5.0-draft.N with PROTOCOL_VERSION held at 0.5.0 until the release is cut.

Tests / validation (local)

• cargo test -p phux-protocol green (incl. the asked roundtrip, the proptest strategy covering both TerminalControl and Asked, and the forward-compat skip test now using tag 0x0a).
• cargo check -p phux-server --tests green (the title-sentinel emission + agent_asked.rs integration test compile).
• just docs-check green (84 files; CHANGELOG top ↔ PROTOCOL_VERSION sync).

Follow-up

• Full agent-state detection (per-agent manifests and/or opt-in agent hooks; surfacing OSC 9 if libghostty grows the accessor) — phux-2sl6.
• Consumer: phux-mobile already consumes this rev (PHUX_REV) and ships the foreground notification; it will re-pin to this branch's merge commit.

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