feat(audio): Campaign A slice A2 — retail's 2D pan+gain mixer replaces AL 3D

Retail is not a 3D audio engine. Every gameplay buffer is created with
m_3D = 0 and the DirectSound 3D listener the client sets up is dead code;
spatialization is two CPU scalars per voice, frozen at emission. This
slice ports that math and demotes OpenAL to a voice bank.

RetailSoundMixer (new, Core) carries the byte-decoded curve from
SoundManager::GetAttenuation @0x00550020: g = dist < 5 ? vol : 25*vol/d2,
clamped to 1 BEFORE the single master multiply, db = ceil(20*log10 g),
with a hard -50 dB floor at which retail does not start the voice at all
(audible radius ~94.2 m at unity). Pan is PlaySoundInternal @0x00550170's
(int)(-15*sin(delta-bearing)) in whole decibels, truncating toward zero,
forced to dead centre when (int)distance < 5, with no front/back and no
elevation cue. Every AL source is now source-relative with rolloff 0 and
the global distance model is None: AL's InverseDistanceClamped was
first-power (2/d), quieter than retail up close and far louder at range
with no cutoff whatsoever. That was the largest audible divergence in the
subsystem (AP-28, retired here).

RetailVoicePool (new, Core) ports the allocator at 0x0054FEC0: ring scan
for a free or finished slot, then evict the first slot whose DAT priority
is strictly lower, else drop. Eviction compared GAIN before, so a loud
unimportant sound could silence a quiet important one. It lives in Core
because the engine's play path talks to native AL handles and could not
be tested; the pool now has 12 conformance tests.

The listener keeps using the camera position, which the decode shows is
retail-faithful (SmartBox::set_viewer @0x00452D36 hands the same collided
camera Position to SoundManager) — only the heading extraction changes,
since retail reads one compass bearing and never a forward/up basis. An
earlier draft of the plan called this a defect; corrected in the plan so
it is not fixed backwards.

Opus review found and this commit fixes: a linear pan-to-azimuth mapping
that saturated to full separation at 30 degrees (OpenAL Soft's own
speaker angle) where retail gives 15 dB — now inverts the constant-power
pan law, so full deflection reaches 0.776 of the arc and both channels
stay live; the stale FUN_00550ad0 / gain-eviction class header, which
contradicted the register row this commit writes; missing discriminating
tests for clamp order and pan truncation; dead PlayingGain state whose
comment invented a retail symbol; and a third in-tree copy of
Position::heading, now delegating to MoveToMath.PositionHeading.

MasterVolume folds into the mixer's one multiply instead of AL listener
gain, so the cutoff, radius and dB quantisation move with the slider.

Register: AP-28 retired; AP-173 (pan law), AP-174 (volume taxonomy),
TS-64 (two unimplemented sound prefs), TS-65 (volume-squared quirk,
applied on the ambient path only) filed. Research note corrected twice
where its summary contradicted its own decode (30 m dB, floor vs trunc).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/plans/2026-08-08-audio-parity-campaign.md

@@ -128,7 +128,7 @@ Divergent or missing, ranked by audible impact:
 |---|---|---|---|
 | 1 | Probability gate absent: `SoundCookbook.Roll` short-circuits single-entry lists (4,183/4,184 entries!) before any roll; CDF walk instead of `(n−1)` pick + gate | `SoundCookbook.cs` | Idle chatter ~20× too often; nothing ever randomly silent — the "incorrect ambient-ish noise" complaint |
 | 2 | 0xF750 unhandled — zero hits in `src/` | `Core.Net` routing | Every server cue silent (hits, wounds, pickup, locks, lifestone…) |
-| 3 | Falloff: AL `InverseDistanceClamped` ref 2 m ⇒ `2/d` first-power, no −50 dB cutoff; listener = CAMERA; AL 3D pan | engine + `WorldRenderFrameBuilder` | Wrong loudness curve both directions; pan wrong from spring-arm offset (AP-28) |
+| 3 | Falloff: AL `InverseDistanceClamped` ref 2 m ⇒ `2/d` first-power, no −50 dB cutoff; AL's 3D panner instead of retail's ±15 dB angular pan | engine + `WorldRenderFrameBuilder` | Wrong loudness curve in both directions — quieter than retail up close, audible where retail is silent; stereo image wider and 3-D where retail's is a narrow angular pan (AP-28) |
 | 4 | Priority float [0,1] cast to int 0..7 → 4,100 entries collapse to 0; eviction compares gain not priority | `AudioModel`/engine | Eviction ordering gutted under voice pressure |
 | 5 | Volume clamped at field instead of after distance divide | `AudioHookSink` | >1-gain sounds lose up to 3× audible range |
 | 6 | Region ambient system absent (`StartAmbient` stub) | engine | Silent outdoors atmosphere (TS-29 half) |
@@ -172,9 +172,23 @@ Port `GetAttenuation` + pan CPU-side exactly (5 m knee, `25·vol/d²`,
 clamp-after, ceil-dB, −50 dB no-allocate floor, `−15·sin(Δheading)` pan
 ±15 dB with 5 m dead zone, `Sound Features==1` pan disable). OpenAL
 becomes a dumb 2D voice bank: source-relative sources, per-voice gain +
-pan (AL_POSITION ±x from pan only); remove `SelectRetailDistanceModel`
-and listener orientation math. Listener feed moves from camera pose to
-player position/heading. Eviction compares float priority (equal never
+pan (AL_POSITION azimuth from pan only); remove AL's distance model and the
+listener orientation math.
+
+**Listener correction (2026-08-08, from the lane-1 decode):** an earlier draft
+of this plan said the listener must move "from camera pose to player
+position/heading" and listed "listener = CAMERA" as a defect. That was wrong,
+and it was written before lane 1 landed. Retail's listener IS the camera:
+`SmartBox::set_viewer` @ `0x00452D36` hands the same COLLIDED third-person
+camera Position to `SoundManager::SetPlayerPosition`, the sky, and the camera
+setup, refreshed once per rendered frame from `SmartBox::update_viewer` @
+`0x00453CE0` (falling back to the player's own position when the sphere sweep
+fails). acdream's chase camera collides too, so the position source was already
+faithful; only the HEADING extraction changes, since retail reads
+`Frame::get_heading` — one compass bearing — and never a forward/up basis.
+Do not "fix" this back.
+
+Eviction compares float priority (equal never
 evicts); fix the pool citation to `PlaySoundInternal @ 0x0054FEC0`.
 Keep the squared-volume quirk faithful (register row if we later soften
 it). Map settings: Master (ours, AL listener gain) + Effect + Ambient +
@@ -281,8 +295,8 @@ global kill switch.
 
 | Slice | Status | Commit | Gates |
 |---|---|---|---|
-| A1 | **COMPLETE** 2026-08-08 | (this commit) | 42 Core audio tests; full Release suite 11,563 passed / 4 skipped / 0 failed. Closes #355. |
-| A2 | — | — | — |
+| A1 | **COMPLETE** 2026-08-08 | `c69b3bde` | 42 Core audio tests; full Release suite 11,563 passed / 4 skipped / 0 failed. Closes #355. |
+| A2 | **COMPLETE** 2026-08-08 | `6d0156cb` | 118 Core audio tests (mixer + voice pool + cookbook); full Release suite 11,639 passed / 4 skipped / 0 failed. Opus review run and applied — 2 HIGH (pan-law saturation, stale `FUN_00550ad0` header), 5 MEDIUM (untested clamp order / pan truncation / voice pool, dead `PlayingGain`, duplicated heading helper), 5 LOW. Retires AP-28; files AP-173, AP-174, TS-64, TS-65. **Owed: user listening gate.** |
 | A3 | — | — | — |
 | A4 | — | — | — |
 | A5 | — | — | — |

docs/research/2026-08-08-audio-retail-soundmanager-core.md

@@ -633,13 +633,19 @@ finds no caller.
 
 ### D4/D6 numbers side by side (vol = master = 1.0)
 
+> **Corrected 2026-08-08 at the A2 code review:** the 30 m row read −35 dB, which
+> contradicted both its own gain column (0.0278) and the formula —
+> `ceil(20·log10 0.027778) = ceil(-31.13) = -31`. It is now −31. The conformance
+> tests in `RetailSoundMixerTests` recompute every row from the decoded formula
+> rather than reading this table, which is how the slip surfaced.
+
 | distance | retail gain | retail dB (`ceil`) | acdream gain (`2/max(d,2)`) | acdream dB |
 |---|---|---|---|---|
 | 2 m | 1.000 | 0 | 1.000 | 0.0 |
 | 5 m | 1.000 | 0 | 0.400 | −8.0 |
 | 10 m | 0.250 | −12 | 0.200 | −14.0 |
 | 20 m | 0.0625 | −24 | 0.100 | −20.0 |
-| 30 m | 0.0278 | −35 | 0.0667 | −23.5 |
+| 30 m | 0.0278 | −31 | 0.0667 | −23.5 |
 | 50 m | 0.0100 | −40 | 0.0400 | −28.0 |
 | 90 m | 0.00309 | −50 (last audible) | 0.0222 | −33.1 |
 | ≥94.2 m | — | **not played** | 0.0212 | −33.5 |
@@ -670,7 +676,10 @@ Per play (3D):
   if g <= 0: drop
   db = ceil(20*log10(g)); if db < -50: drop
   delta = normalise180( bearing(source -> listener) - listenerHeadingDegrees )
-  pan   = (int)floor(-15 * sin(delta * pi/180))  clamped [-15, 15]
+  pan   = (int)(-15 * sin(delta * pi/180))    # TRUNCATE toward zero (retail _ftol2),
+                                              # NOT floor: they differ by 1 dB for
+                                              # negative pans. Corrected 2026-08-08 at
+                                              # the A2 review; §1 was already right.
   if (int)dist < 5: pan = 0
   allocate voice: ring scan from cursor for free/finished;
                   else first slot with slotPriority < newPriority;