test(lab): add Asterisk lab — a fake PSTN for media validation

An Asterisk instance that answers calls, plays an IVR, holds with music and
connects a "human", so the gateway has something real to dial that is not the
PSTN: no charges, no strangers, no E911 exposure.

Asterisk rather than Kamailio because the unproven risks are media risks.
Kamailio is a proxy — it routes signalling and answers nothing, so it would
forward the INVITE and find nobody home. Asterisk is a B2BUA: it answers,
plays prompts and collects DTMF, which is the hold-slayer scenario itself.
Kamailio remains the better model for trunk registration/digest auth later.

No application changes are needed to use it. SIP_TRUNK_HOST is just an
address, so the production code path runs unmodified — there is no test-only
branch anywhere in the gateway. It also means safety is structural: while the
trunk points at the lab there is no route to the PSTN at all, an absence of
route rather than a policy that could be misconfigured.

Nine scenarios (1001-1008 plus an echo test) cover the baseline call, the
IVR/DTMF path, hold-then-human, long hold, busy, no-answer, remote hangup and
silence.

The image ships no sound files, so sounds/generate.py synthesises three
fixtures from fixed seeds — byte-identical on every run, which is what makes
a classifier regression distinguishable from noise. Verified against
AudioClassifier: music→MUSIC 0.85, speech→LIVE_HUMAN 0.75,
silence→SILENCE 1.00. The speech formants deliberately avoid the DTMF bands;
the first version landed on a valid pair and classified as a keypress.

Anonymous inbound calls are refused, and endpoint matching is by source
address — Asterisk's default matches the From-header domain, which Hold
Slayer populates from its SIP bind address (0.0.0.0 on a wildcard bind).

Generated audio and the rendered per-host configs are gitignored: the former
is reproducible from a fixed seed, the latter carry a host-specific IP and
the lab password.

Known limit, documented in the README: MediaPipeline.create_tap is a stub, so
the classifier receives no audio on a live call. RTP flows and Asterisk plays
audio, but the tap is never fed — the fixture results above were measured by
feeding the classifier directly. This blocks scenarios 1002/1003/1004.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/lab/dialplan/extensions.conf

@@ -0,0 +1,144 @@
+; ---------------------------------------------------------------------------
+; Hold Slayer lab dialplan — a fake bank phone tree
+; ---------------------------------------------------------------------------
+; Each extension is one scenario Hold Slayer must handle. Everything here is
+; deterministic on purpose: real hold music varies per call, so a classifier
+; regression on the PSTN is indistinguishable from noise. Against a fixed
+; prompt the answer is binary.
+;
+; Hold Slayer dials these as `number` with SIP_TRUNK_HOST pointing here.
+; ---------------------------------------------------------------------------
+
+[globals]
+; Lab-generated audio (tests/lab/sounds/, built by generate.py). The Asterisk
+; image ships with no sounds at all, and these are synthesised from a fixed
+; seed so the classifier sees byte-identical input on every run.
+;   lab-speech  -> must classify LIVE_HUMAN
+;   lab-music   -> must classify MUSIC
+;   lab-silence -> must classify SILENCE
+GREETING=lab-speech
+INVALID=lab-speech
+
+[hold-slayer-lab]
+
+; --- 1001: immediate answer, speech, hangup -------------------------------
+; Baseline. Proves INVITE→200→ACK→RTP→BYE and that audio flows both ways.
+; The classifier should report LIVE_HUMAN throughout.
+exten => 1001,1,NoOp(LAB 1001: immediate answer)
+ same => n,Answer()
+ same => n,Wait(1)
+ same => n,Playback(${GREETING})
+ same => n,Playback(lab-speech)
+ same => n,Wait(20)
+ same => n,Playback(lab-speech)
+ same => n,Hangup()
+
+; --- 1002: IVR menu, branches on DTMF -------------------------------------
+; THE important one. Proves send_dtmf genuinely emits RFC 2833 and that
+; Asterisk receives the digits — currently a no-op in MockSIPEngine.
+; Press 1 → accounts (answers as human). Press 2 → cards (hold, then human).
+exten => 1002,1,NoOp(LAB 1002: IVR menu)
+ same => n,Answer()
+ same => n,Wait(1)
+ same => n,Set(TRIES=0)
+ same => n(menu),Background(lab-speech)
+ same => n,WaitExten(8)
+ same => n,Set(TRIES=$[${TRIES} + 1])
+ same => n,GotoIf($[${TRIES} < 3]?menu)
+ same => n,Playback(lab-speech)
+ same => n,Hangup()
+
+; Option 1 — straight to a "human"
+exten => 1,1,NoOp(LAB 1002: caller pressed 1 -> accounts)
+ same => n,Playback(lab-speech)
+ same => n,Playback(lab-speech)
+ same => n,Wait(15)
+ same => n,Hangup()
+
+; Option 2 — hold queue, then a "human"
+exten => 2,1,NoOp(LAB 1002: caller pressed 2 -> cards, hold)
+ same => n,Playback(lab-speech)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-speech)
+ same => n,Wait(15)
+ same => n,Hangup()
+
+exten => i,1,NoOp(LAB 1002: invalid entry)
+ same => n,Playback(${INVALID})
+ same => n,Goto(1002,menu)
+
+exten => t,1,NoOp(LAB 1002: entry timeout)
+ same => n,Goto(1002,menu)
+
+; --- 1003: hold music, then a human ---------------------------------------
+; The whole hold-slayer loop in one call: classify music → stay on hold →
+; detect the human → ring the owner. 60s of MoH is long enough for several
+; classifier windows (CLASSIFIER_WINDOW_SECONDS defaults to 3.0).
+exten => 1003,1,NoOp(LAB 1003: hold then human)
+ same => n,Answer()
+ same => n,Wait(1)
+ same => n,Playback(lab-speech)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-speech)
+ same => n,Playback(lab-speech)
+ same => n,Wait(30)
+ same => n,Hangup()
+
+; --- 1004: long hold ------------------------------------------------------
+; Exercises MAX_HOLD_TIME and HOLD_CHECK_INTERVAL. 10 minutes.
+exten => 1004,1,NoOp(LAB 1004: long hold)
+ same => n,Answer()
+ same => n,Wait(1)
+ same => n,Playback(lab-speech)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-music)
+ same => n,Playback(lab-speech)
+ same => n,Wait(15)
+ same => n,Hangup()
+
+; --- 1005: busy -----------------------------------------------------------
+; Failure path: the call must be marked FAILED with no stuck leg.
+exten => 1005,1,NoOp(LAB 1005: busy)
+ same => n,Busy(20)
+ same => n,Hangup()
+
+; --- 1006: ring, never answer ---------------------------------------------
+; Timeout path. Rings for 120s without answering.
+exten => 1006,1,NoOp(LAB 1006: ring no answer)
+ same => n,Progress()
+ same => n,Wait(120)
+ same => n,Hangup()
+
+; --- 1007: answer, then remote hangup after 5s ----------------------------
+; Proves remote-BYE handling and that the call persists to the DB on hangup.
+exten => 1007,1,NoOp(LAB 1007: quick remote hangup)
+ same => n,Answer()
+ same => n,Playback(${GREETING})
+ same => n,Wait(5)
+ same => n,Hangup()
+
+; --- 1008: answer, then silence -------------------------------------------
+; Classifier SILENCE vs the no-audio case. 45s of nothing.
+exten => 1008,1,NoOp(LAB 1008: silence)
+ same => n,Answer()
+ same => n,Playback(lab-silence)
+ same => n,Wait(40)
+ same => n,Hangup()
+
+; --- echo test ------------------------------------------------------------
+; Not a scenario — a debugging aid. Echoes audio back so you can confirm
+; bidirectional RTP by ear when something looks wrong.
+exten => 1099,1,NoOp(LAB 1099: echo test)
+ same => n,Answer()
+ same => n,Playback(lab-speech)
+ same => n,Echo()
+ same => n,Hangup()
+
+; Anything else: reject explicitly rather than failing obscurely.
+exten => _X.,1,NoOp(LAB: unknown extension ${EXTEN})
+ same => n,Answer()
+ same => n,Playback(${INVALID})
+ same => n,Hangup()