feat(prompt_optimizer): dspy/gepa as default — noop only when explicit

Auto-detect replaces hard-coded noop default:
  - dspy if dspy-ai is importable
  - gepa otherwise (built-in evolutionary loop, zero extra deps)
  - noop only when provider = "noop" is set explicitly

PromptOptimizerConfig.provider defaults to "" (auto).
Updated test: factory default asserts dspy|gepa, not noop.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: rithulkamesh

devsper/config/schema.py

@@ -315,7 +315,7 @@ class PromptOptimizerConfig(BaseModel):
     provider: "noop" | "dspy" | "gepa"  (override with DEVSPER_PROMPT_OPTIMIZER env var)
     """
 
-    provider: str = "noop"
+    provider: str = ""   # "" = auto (dspy if installed, else gepa). "noop" disables.
     # DSPy-specific
     dspy_optimizer: str = "bootstrap"  # "bootstrap" | "mipro" | "bootstrap_random"
     max_demos: int = 4

devsper/prompt_optimizer/factory.py

@@ -4,7 +4,10 @@
 Resolution order:
   1. DEVSPER_PROMPT_OPTIMIZER env var
   2. config.prompt_optimizer.provider (devsper.toml)
-  3. Default: "noop"
+  3. Auto-detect: "dspy" if dspy-ai is importable, else "gepa"
+     (GEPABackend ships a built-in evolutionary loop — no extra install needed)
+
+Set provider = "noop" explicitly to disable optimization.
 """
 
 from __future__ import annotations
@@ -75,7 +78,17 @@ def _resolve_provider_name(config=None) -> str:
         if provider:
             return provider
 
-    return "noop"
+    # 3. Auto-detect: prefer dspy if importable, otherwise gepa
+    return _autodetect()
+
+
+def _autodetect() -> str:
+    """Return 'dspy' if dspy-ai is installed, else 'gepa' (always available)."""
+    try:
+        import dspy  # noqa: F401
+        return "dspy"
+    except ImportError:
+        return "gepa"
 
 
 def _opt_cfg(config=None):

tests/test_evals.py

@@ -232,12 +232,13 @@ def test_noop_backend_health():
     assert asyncio.run(backend.health()) is True
 
 
-def test_factory_default_is_noop():
+def test_factory_default_is_dspy_or_gepa():
+    """Default is dspy if installed, gepa otherwise — never noop."""
     reset_prompt_optimizer()
     import os
     os.environ.pop("DEVSPER_PROMPT_OPTIMIZER", None)
     opt = get_prompt_optimizer()
-    assert opt.name == "noop"
+    assert opt.name in ("dspy", "gepa"), f"Expected dspy or gepa, got {opt.name}"
     reset_prompt_optimizer()