feat: Replaced 3-tier step function with 5-tier continuous interpolatio…

- "backend/chat_service.py"
- "backend/tests/test_chat.py"

GSD-Task: S04/T01

backend/chat_service.py

@@ -292,42 +292,91 @@ def _build_context_block(items: list[dict[str, Any]]) -> str:
 def _build_personality_block(creator_name: str, profile: dict[str, Any], weight: float) -> str:
     """Build a personality voice injection block from a creator's personality_profile JSONB.
 
-    The ``weight`` (0.0–1.0) determines how strongly the personality should
+    The ``weight`` (0.0–1.0) controls progressive inclusion of personality
-    come through.  At low weights the instruction is softer ("subtly adopt");
+    fields via 5 tiers of continuous interpolation:
-    at high weights it is emphatic ("fully embody").
+
+    - < 0.2:  no personality block (empty string)
+    - 0.2–0.39: basic tone — teaching_style, formality, energy + subtle hint
+    - 0.4–0.59: + descriptors, explanation_approach + adopt-voice instruction
+    - 0.6–0.79: + signature_phrases (count scaled by weight) + creator-voice
+    - 0.8–0.89: + distinctive_terms, sound_descriptions, sound_words,
+                  self_references, pacing + fully-embody instruction
+    - >= 0.9:  + full summary paragraph
     """
+    if weight < 0.2:
+        return ""
+
     vocab = profile.get("vocabulary", {})
     tone = profile.get("tone", {})
     style = profile.get("style_markers", {})
 
-    phrases = vocab.get("signature_phrases", [])
-    descriptors = tone.get("descriptors", [])
     teaching_style = tone.get("teaching_style", "")
     energy = tone.get("energy", "moderate")
     formality = tone.get("formality", "conversational")
+    descriptors = tone.get("descriptors", [])
+    phrases = vocab.get("signature_phrases", [])
 
     parts: list[str] = []
 
-    # Intensity qualifier
+    # --- Tier 1 (0.2–0.39): basic tone ---
-    if weight >= 0.8:
+    if weight < 0.4:
-        parts.append(f"Fully embody {creator_name}'s voice and style.")
+        parts.append(
-    elif weight >= 0.4:
+            f"When relevant, subtly reference {creator_name}'s communication style."
-        parts.append(f"Respond in {creator_name}'s voice.")
+        )
+    elif weight < 0.6:
+        parts.append(f"Adopt {creator_name}'s tone and communication style.")
+    elif weight < 0.8:
+        parts.append(
+            f"Respond as {creator_name} would, using their voice and manner."
+        )
     else:
-        parts.append(f"Subtly adopt {creator_name}'s communication style.")
+        parts.append(
+            f"Fully embody {creator_name} — use their exact phrases, energy, and teaching approach."
+        )
 
     if teaching_style:
         parts.append(f"Teaching style: {teaching_style}.")
-    if descriptors:
-        parts.append(f"Tone: {', '.join(descriptors[:5])}.")
-    if phrases:
-        parts.append(f"Use their signature phrases: {', '.join(phrases[:6])}.")
     parts.append(f"Match their {formality} {energy} tone.")
 
-    # Style markers
+    # --- Tier 2 (0.4+): descriptors, explanation_approach, uses_analogies, audience_engagement ---
+    if weight >= 0.4:
+        if descriptors:
+            parts.append(f"Tone: {', '.join(descriptors[:5])}.")
+        explanation = style.get("explanation_approach", "")
+        if explanation:
+            parts.append(f"Explanation approach: {explanation}.")
         if style.get("uses_analogies"):
             parts.append("Use analogies when helpful.")
         if style.get("audience_engagement"):
             parts.append(f"Audience engagement: {style['audience_engagement']}.")
 
+    # --- Tier 3 (0.6+): signature phrases (count scaled by weight) ---
+    if weight >= 0.6 and phrases:
+        count = max(2, round(weight * len(phrases)))
+        parts.append(f"Use their signature phrases: {', '.join(phrases[:count])}.")
+
+    # --- Tier 4 (0.8+): distinctive_terms, sound_descriptions, sound_words, self_references, pacing ---
+    if weight >= 0.8:
+        distinctive = vocab.get("distinctive_terms", [])
+        if distinctive:
+            parts.append(f"Distinctive terms: {', '.join(distinctive)}.")
+        sound_desc = vocab.get("sound_descriptions", [])
+        if sound_desc:
+            parts.append(f"Sound descriptions: {', '.join(sound_desc)}.")
+        sound_words = style.get("sound_words", [])
+        if sound_words:
+            parts.append(f"Sound words: {', '.join(sound_words)}.")
+        self_refs = style.get("self_references", "")
+        if self_refs:
+            parts.append(f"Self-references: {self_refs}.")
+        pacing = style.get("pacing", "")
+        if pacing:
+            parts.append(f"Pacing: {pacing}.")
+
+    # --- Tier 5 (0.9+): full summary paragraph ---
+    if weight >= 0.9:
+        summary = profile.get("summary", "")
+        if summary:
+            parts.append(summary)
+
     return " ".join(parts)

backend/tests/test_chat.py

@@ -681,12 +681,103 @@ async def test_personality_prompt_injected_when_weight_and_profile(chat_client):
     assert len(captured_messages) >= 2
 
     system_prompt = captured_messages[0]["content"]
-    # Personality block should be appended
+    # weight=0.7 → tier 3: signature phrases YES, distinctive_terms NO
     assert "Keota" in system_prompt
-    assert "let's gooo" in system_prompt
+    assert "Respond as Keota would" in system_prompt
     assert "hands-on demo-driven" in system_prompt
     assert "casual" in system_prompt
     assert "high" in system_prompt
+    assert "let's gooo" in system_prompt  # signature phrases included at 0.6+
+    assert "enthusiastic" in system_prompt  # descriptors at 0.4+
+    assert "example-first" in system_prompt  # explanation_approach at 0.4+
+    # Tier 4 fields (0.8+) should NOT be present
+    assert "sauce" not in system_prompt  # distinctive_terms
+    assert "crispy" not in system_prompt  # sound_descriptions
+    assert "brrr" not in system_prompt  # sound_words
+
+
+def test_personality_block_continuous_interpolation_tiers():
+    """Progressive field inclusion across 5 interpolation tiers."""
+    from chat_service import _build_personality_block
+
+    profile = _FAKE_PERSONALITY_PROFILE
+
+    # weight < 0.2: empty
+    for w in (0.0, 0.1, 0.15, 0.19):
+        result = _build_personality_block("Keota", profile, w)
+        assert result == "", f"weight={w} should produce empty block"
+
+    # weight 0.2–0.39: basic tone only
+    for w in (0.2, 0.3, 0.39):
+        result = _build_personality_block("Keota", profile, w)
+        assert "subtly reference Keota" in result
+        assert "hands-on demo-driven" in result
+        assert "casual" in result and "high" in result
+        # Should NOT include descriptors, explanation_approach, phrases
+        assert "enthusiastic" not in result
+        assert "example-first" not in result
+        assert "let's gooo" not in result
+
+    # weight 0.4–0.59: + descriptors, explanation_approach
+    for w in (0.4, 0.5, 0.59):
+        result = _build_personality_block("Keota", profile, w)
+        assert "Adopt Keota" in result
+        assert "enthusiastic" in result  # descriptors
+        assert "example-first" in result  # explanation_approach
+        assert "analogies" in result  # uses_analogies
+        # Should NOT include phrases or tier-4 fields
+        assert "let's gooo" not in result
+        assert "sauce" not in result
+
+    # weight 0.6–0.79: + signature phrases
+    for w in (0.6, 0.7, 0.79):
+        result = _build_personality_block("Keota", profile, w)
+        assert "Respond as Keota would" in result
+        assert "let's gooo" in result  # signature phrases
+        assert "enthusiastic" in result  # still has descriptors
+        # Should NOT include tier-4 fields
+        assert "sauce" not in result
+        assert "crispy" not in result
+
+    # weight 0.8–0.89: + distinctive_terms, sound_descriptions, etc.
+    for w in (0.8, 0.85, 0.89):
+        result = _build_personality_block("Keota", profile, w)
+        assert "Fully embody Keota" in result
+        assert "sauce" in result  # distinctive_terms
+        assert "crispy" in result  # sound_descriptions
+        assert "brrr" in result  # sound_words
+        assert "I always" in result  # self_references
+        assert "fast" in result  # pacing
+        # Should NOT include summary
+        assert "High-energy producer" not in result
+
+    # weight >= 0.9: + summary
+    for w in (0.9, 0.95, 1.0):
+        result = _build_personality_block("Keota", profile, w)
+        assert "Fully embody Keota" in result
+        assert "High-energy producer" in result  # summary
+
+
+def test_personality_block_phrase_count_scales_with_weight():
+    """Signature phrase count = max(2, round(weight * len(phrases)))."""
+    from chat_service import _build_personality_block
+
+    # Profile with 6 phrases to make scaling visible
+    profile = {
+        "vocabulary": {
+            "signature_phrases": ["p1", "p2", "p3", "p4", "p5", "p6"],
+        },
+        "tone": {},
+        "style_markers": {},
+    }
+    # weight=0.6: max(2, round(0.6*6)) = max(2,4) = 4 → first 4 phrases
+    result = _build_personality_block("Test", profile, 0.6)
+    assert "p4" in result
+    assert "p5" not in result
+
+    # weight=1.0: max(2, round(1.0*6)) = 6 → all phrases
+    result = _build_personality_block("Test", profile, 1.0)
+    assert "p6" in result
 
 
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