Add native audio/image efferent surfaces + projector proof-of-shape

audio-surface.el / image-surface.el: own-core additive-synthesis WAV and
raster-PNG renderers (integer-only DSP, since EL has no floats), rendered
from learned engram signatures via a pluggable surface-profile
abstraction (surface-profile.el). audio-demo.el / image-demo.el are
drivers. NOTE: demo files hardcode absolute paths to this worktree's own
directory — will need a path fixup before landing.

elp/projector/ is a Python package the author's own README marks as
"STAGING/PROOF-OF-SHAPE — not the deliverable", superseded by the native
.el surface-profile work above; kept as a validated architecture proof.
Generated output (elp/faculty/{out,sig}, elp/projector/out,
__pycache__) intentionally excluded.

elp/projector/projectors/midi.py

@@ -0,0 +1,133 @@
+"""midi.py — the MUSIC surface projector: geometry -> symbolic music (MIDI).
+
+The first NON-TEXT surface, and the proof of the general shape. "Music is
+language and it is math" (Will): symbolic music is tractable and geometry-native,
+so it is the natural efferent twin to try first after text.
+
+CRUCIALLY this projector does NOT read the realized sentences. It reads the IR's
+GEOMETRY facet — ``block.provenance`` — and DECODES each edge onto a musical
+surface. That is the whole thesis of the multimodal projector: the same
+geometry-carrying IR drives text AND music; a text projector reads the words, a
+music projector reads the meaning-geometry. The mapping is deterministic and
+faithful to the geometry's structure:
+
+    relation lemma  -> scale degree      (same relation -> same pitch class;
+                                          meaning has a consistent sonic form)
+    polarity        -> mode              (aff = major third above; neg = minor
+                                          third / lowered — SACRED polarity is
+                                          audible, a negated edge sounds negated)
+    confidence      -> note duration     (stronger grounding rings longer)
+    importance      -> velocity          (more important source = louder)
+    section         -> phrase + register shift (structure becomes musical form)
+
+Own-the-core: a Standard MIDI File is a header chunk + a track chunk of
+delta-timed events. We emit the raw bytes with ``struct`` — no external MIDI
+library. Format 0, one track.
+"""
+from __future__ import annotations
+
+import io
+import os
+import struct
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+from document_ir import DocumentIR, Provenance  # noqa: E402
+from projectors.base import TwoStageProjector, register  # noqa: E402
+
+_TICKS = 480                      # ticks per quarter note
+_C_MAJOR = [0, 2, 4, 5, 7, 9, 11]  # semitone offsets of a diatonic scale
+
+
+def _vlq(n: int) -> bytes:
+    """MIDI variable-length quantity encoding of a delta time."""
+    if n == 0:
+        return b"\x00"
+    out = bytearray()
+    out.append(n & 0x7F)
+    n >>= 7
+    while n:
+        out.insert(0, (n & 0x7F) | 0x80)
+        n >>= 7
+    return bytes(out)
+
+
+def _degree_for(relation: str) -> int:
+    """Stable scale degree for a relation lemma (same relation -> same pitch)."""
+    if not relation:
+        return 0
+    return sum(ord(c) for c in relation.lower()) % len(_C_MAJOR)
+
+
+def _note_for(p: Provenance, base: int) -> tuple[int, int, int]:
+    """(pitch, velocity, duration_ticks) for one geometry edge."""
+    root = base + _C_MAJOR[_degree_for(p.relation)]
+    # polarity -> mode: affirmed edges take the bright major third, negated edges
+    # take the darker minor third. The negation is AUDIBLE and never dropped.
+    third = 4 if p.polarity == "aff" else 3
+    pitch = max(24, min(96, root + (third if p.confidence >= 0.5 else 0)))
+    velocity = int(56 + 60 * min(1.0, max(0.0, p.importance)))
+    velocity = max(40, min(120, velocity))
+    # confidence -> duration: quarter .. dotted-half
+    dur = int(_TICKS * (0.5 + 1.5 * min(1.0, max(0.0, p.confidence))))
+    return pitch, velocity, dur
+
+
+# a mode-profile: the pluggable musical knob (the peer's mode_profile). Scale +
+# tempo. Swapping this profile re-voices the SAME geometry — surface as parameter.
+_DEFAULT_PROFILE = {"scale": _C_MAJOR, "tempo_us": 500000,
+                    "registers": [60, 55, 64, 50, 67, 48], "program": 0}
+
+
+class MidiProjector(TwoStageProjector):
+    """geometry -> symbolic music, in the shared two-stage shape.
+
+    ``plan(frame)``  -> a music_spec: an ordered list of note dicts derived
+                        deterministically from the frame's provenance geometry
+                        (the peer's ``plan(frame, profile) -> spec``).
+    ``realize(spec)`` -> Standard MIDI File bytes (the peer's
+                        ``realize(spec, profile) -> surface``; here the surface
+                        is symbolic MIDI, the minimal audio proof — a richer
+                        additive-synth audio projector conforms identically).
+    """
+
+    surface = "midi"
+    media_type = "audio/midi"
+    ext = "mid"
+    modality = "audio"
+
+    def __init__(self, profile: dict | None = None):
+        self.profile = profile or _DEFAULT_PROFILE
+
+    # -- stage 1: meaning-geometry -> music_spec (reads the GEOMETRY facet) -- #
+    def plan(self, doc: DocumentIR) -> list[dict]:
+        registers = self.profile["registers"]
+        spec: list[dict] = []
+        for si, sec in enumerate(doc.sections):
+            base = registers[si % len(registers)]
+            provs = [p for p in sec.all_provenance()
+                     if p.kind in ("fact", "interpretation")]
+            for i, p in enumerate(provs):
+                pitch, vel, dur = _note_for(p, base)
+                spec.append({"pitch": pitch, "velocity": vel, "dur": dur,
+                             "rest_before": (_TICKS // 2) if (si > 0 and i == 0) else 0,
+                             "relation": p.relation, "polarity": p.polarity})
+        return spec
+
+    # -- stage 2: music_spec -> MIDI bytes (own-core, no library) ------------ #
+    def realize(self, spec: list[dict]) -> bytes:
+        ev = bytearray()
+        ev += _vlq(0) + b"\xFF\x51\x03" + struct.pack(">I", self.profile["tempo_us"])[1:]
+        ev += _vlq(0) + bytes([0xC0, self.profile["program"] & 0x7F])
+        for note in spec:
+            ev += _vlq(note["rest_before"]) + bytes([0x90, note["pitch"], note["velocity"]])
+            ev += _vlq(note["dur"]) + bytes([0x80, note["pitch"], 0])
+        ev += _vlq(0) + b"\xFF\x2F\x00"
+        track = bytes(ev)
+        buf = io.BytesIO()
+        buf.write(b"MThd" + struct.pack(">IHHH", 6, 0, 1, _TICKS))
+        buf.write(b"MTrk" + struct.pack(">I", len(track)) + track)
+        return buf.getvalue()
+
+
+register(MidiProjector())