feat(playrecord): concurrent-capture mode + stopplay (content-gated barge-in)

[tinpotnick]

Summary

Adds a content-gated barge-in primitive to playrecord — a "middle mode" between full-prompt playback and energy interrupt. Instead of inbound energy cutting the prompt on any sound, the caller's answer is captured while the prompt keeps playing, and the controller decides when to interrupt.

Motivated by the multilingual language gate (babble-sip): with N languages a caller must currently sit through the whole greeting before answering, and the existing energy interrupt is too trigger-happy (a cough cuts the prompt, then a failed turn replays everything).

What's new

playrecord({ concurrent: true }) — the recorder opens immediately and runs alongside the player, staying gated by record.startabovepower until the caller actually speaks. Its min/max durations are measured from speech-start (unchanged), so opening early is safe and the ~2s power warm-up conveniently elapses during the prompt. No BargeInState is created — inbound energy never interrupts the prompt. Mutually exclusive with interrupt (concurrent wins).

channel.stopplay() / Command::StopPlay — stop the active player now (play/end reason="stopped"), leaving any running recorder untouched. This is how the controller "fires" the interrupt once it has an acceptable answer.

The recorder's own power thresholds still drive capture in concurrent mode:

• startabovepower → when capture begins (waits for speech)
• finishbelowpower → when the answer is "full" → finished event
• min/maxduration → floor/ceiling on the answer

Only the prompt-interrupt decision is handed to the controller.

Re-arm without replaying the prompt

Key point for the gate's retry path: when an attempt fails and the prompt is still playing, re-listen with a bare record() (which never touches the player) — not a second playrecord (which would rebuild the Player and restart the prompt). Covered by a dedicated interface test.

Scope

Wired through both local and mixed (mixer) command handlers, the napi facade, and the JS control layer (server.js proxy + node.js channelmap/scrub). The existing hard-interrupt path is unchanged.

Testing

• Rust: 118 lib tests (new: concurrent opens the recorder at command-accept time — the inverse of the deferred path). cargo fmt + clippy -D warnings clean.
• Interface (real RTP): 3 new cases — a loud tone during a concurrent prompt does not interrupt; stopplay() ends the prompt (reason "stopped") with the recording preserved; a mid-prompt record() re-arms a fresh capture without restarting the player (exactly one play/start, natural play/end "completed").

Release

• README documents the two barge-in modes.
• Version 3.3.0 → 3.4.0 (additive, backward-compatible).

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