feat(tts): config-driven voices + two-voice dialogue/narration split (DEC-11)

Voice assignment moves from the hardcoded server map to ~/.config/ratatoskr/
voices.json (per-agent voice + optional narration_voice). An agent with a
narration_voice gets a two-voice split: quoted speech in `voice`, narration in
`narration_voice`, synthesized per-span and stitched under one WAV header.

- new src/ratatoskr/voices.py: load_voice_config (degrade-not-crash),
  segment_dialogue (quote-based, straight + curly), resolve_voice_spans
- tts.py: tts_stream_stitched replaces tts_stream — serial per-span synth,
  span 0 verbatim, spans 1..N header-stripped -> one gapless 48kHz stream;
  a single-span list is a byte-identical passthrough (no single-voice regression)
- server.py: _tts_endpoint resolves spans from app.state.voice_config; the
  hardcoded _TTS_VOICE_MAP is retired; create_app gains a voice_config param
- entrypoint.py: loads voices.json at startup
- contract DEC-11 + INV-TTS-5/6/7; initial config donut->donut,
  sindra->miranda (dialogue) / emmie (narration)

Live-verified on :8765: Sindra mixed turn -> 2 dots calls (emmie+miranda)
stitched into one 48kHz WAV with a single RIFF header; Donut single-voice
unchanged. 545 tests green (incl. new test_voices.py).

tests/test_voices.py

@@ -0,0 +1,116 @@
+"""Tests for ratatoskr.voices — config load + dialogue/narration segmentation (DEC-11)."""
+
+import json
+from typing import ClassVar
+
+from ratatoskr.voices import (
+    DEFAULT_VOICE_CONFIG,
+    load_voice_config,
+    resolve_voice_spans,
+    segment_dialogue,
+)
+
+
+class TestSegmentDialogue:
+    def test_narration_only_no_quotes(self) -> None:
+        assert segment_dialogue("She tilts her head.") == [("narration", "She tilts her head.")]
+
+    def test_straight_quotes_dialogue(self) -> None:
+        assert segment_dialogue('"Hi there."') == [("dialogue", "Hi there.")]
+
+    def test_curly_quotes_dialogue(self) -> None:
+        assert segment_dialogue("“Hi there.”") == [("dialogue", "Hi there.")]
+
+    def test_mixed_narration_and_dialogue_order_preserved(self) -> None:
+        text = "She smiles. “Hello.” She left."
+        assert segment_dialogue(text) == [
+            ("narration", "She smiles. "),
+            ("dialogue", "Hello."),
+            ("narration", " She left."),
+        ]
+
+    def test_empty_and_whitespace_spans_dropped(self) -> None:
+        # The between-quotes gap here is a single space → dropped; leading empty narration too.
+        assert segment_dialogue('"A" "B"') == [("dialogue", "A"), ("dialogue", "B")]
+
+    def test_apostrophe_is_not_a_boundary(self) -> None:
+        # Curly and straight apostrophes stay inside the span (no word split).
+        assert segment_dialogue("Donut’s crown and Carl's cat") == [  # noqa: RUF001
+            ("narration", "Donut’s crown and Carl's cat")  # noqa: RUF001
+        ]
+
+    def test_unbalanced_trailing_open_quote_is_dialogue(self) -> None:
+        assert segment_dialogue('She said "hello') == [
+            ("narration", "She said "),
+            ("dialogue", "hello"),
+        ]
+
+    def test_empty_text(self) -> None:
+        assert segment_dialogue("") == []
+
+
+class TestResolveVoiceSpans:
+    CFG: ClassVar[dict] = {
+        "default": "glados",
+        "agents": {
+            "ratatoskr:donut": {"voice": "donut"},
+            "ratatoskr:sindra": {"voice": "miranda", "narration_voice": "emmie"},
+        },
+    }
+
+    def test_unmapped_agent_single_default_voice(self) -> None:
+        assert resolve_voice_spans(self.CFG, "mimir", "hello") == [("glados", "hello")]
+
+    def test_non_str_agent_id_single_default(self) -> None:
+        assert resolve_voice_spans(self.CFG, ["donut"], "hi") == [("glados", "hi")]
+
+    def test_mapped_no_narration_single_voice(self) -> None:
+        # Donut is dialogue-only (no narration_voice) → whole turn in one voice, no split,
+        # even though the text has no quotes.
+        assert resolve_voice_spans(self.CFG, "ratatoskr:donut", "The crown is mine.") == [
+            ("donut", "The crown is mine.")
+        ]
+
+    def test_mapped_with_narration_splits(self) -> None:
+        spans = resolve_voice_spans(
+            self.CFG, "ratatoskr:sindra", "She smiles. “Hello.”"
+        )
+        assert spans == [("emmie", "She smiles. "), ("miranda", "Hello.")]
+
+    def test_mapped_with_narration_all_dialogue(self) -> None:
+        assert resolve_voice_spans(self.CFG, "ratatoskr:sindra", '"Only speech here."') == [
+            ("miranda", "Only speech here.")
+        ]
+
+    def test_segmentation_empty_falls_back_to_single_span(self) -> None:
+        # Text that segments to nothing (only quote chars) still yields one span, never [].
+        out = resolve_voice_spans(self.CFG, "ratatoskr:sindra", '""')
+        assert len(out) == 1 and out[0][0] == "miranda"
+
+
+class TestLoadVoiceConfig:
+    def test_absent_file_returns_builtin_default(self, tmp_path) -> None:
+        cfg = load_voice_config(str(tmp_path / "nope.json"))
+        assert cfg == DEFAULT_VOICE_CONFIG
+        assert cfg is not DEFAULT_VOICE_CONFIG  # a copy, not the shared constant
+
+    def test_valid_file_loaded(self, tmp_path) -> None:
+        p = tmp_path / "voices.json"
+        p.write_text(json.dumps({"default": "glados", "agents": {"x:y": {"voice": "emmie"}}}))
+        cfg = load_voice_config(str(p))
+        assert cfg["agents"]["x:y"]["voice"] == "emmie"
+
+    def test_malformed_json_falls_back(self, tmp_path) -> None:
+        p = tmp_path / "voices.json"
+        p.write_text("{not json")
+        assert load_voice_config(str(p)) == DEFAULT_VOICE_CONFIG
+
+    def test_missing_agents_mapping_falls_back(self, tmp_path) -> None:
+        p = tmp_path / "voices.json"
+        p.write_text(json.dumps({"default": "glados"}))
+        assert load_voice_config(str(p)) == DEFAULT_VOICE_CONFIG
+
+    def test_default_key_backfilled(self, tmp_path) -> None:
+        p = tmp_path / "voices.json"
+        p.write_text(json.dumps({"agents": {"x:y": {"voice": "emmie"}}}))
+        assert load_voice_config(str(p))["default"] == "glados"