diff --git a/evals/evolve.py b/evals/evolve.py
index ea8c650..f773783 100644
--- a/evals/evolve.py
+++ b/evals/evolve.py
@@ -77,7 +77,11 @@ def find_latest_persona() -> tuple[int, PersonaSpec]:
         if match:
             versions.append((int(match.group(1)), path))
     if not versions:
-        raise FileNotFoundError("No persona.vN.md artifacts found.")
+        raise FileNotFoundError(
+            f"No persona.vN.md artifacts found in {ARTIFACTS_DIR}. "
+            f"Seed persona.v1.md in that directory before running evolve, "
+            f"or override the location via ARTIFACTS_DIR before launching."
+        )
     versions.sort(key=lambda x: x[0])
     n, path = versions[-1]
     text = path.read_text(encoding="utf-8")
diff --git a/evals/evolve_persona.py b/evals/evolve_persona.py
index b630aef..4a691b3 100644
--- a/evals/evolve_persona.py
+++ b/evals/evolve_persona.py
@@ -115,7 +115,11 @@ def find_latest_persona() -> tuple[int, PersonaSpec]:
         if match:
             versions.append((int(match.group(1)), path))
     if not versions:
-        raise FileNotFoundError("No persona.vN.md artifacts found.")
+        raise FileNotFoundError(
+            f"No persona.vN.md artifacts found in {ARTIFACTS_DIR}. "
+            f"Seed persona.v1.md in that directory before running evolve_persona, "
+            f"or override the location via ARTIFACTS_DIR before launching."
+        )
     versions.sort(key=lambda x: x[0])
     n, path = versions[-1]
     text = path.read_text(encoding="utf-8")
diff --git a/src/spark_character/codex_provider.py b/src/spark_character/codex_provider.py
index 99dab9b..406bd64 100644
--- a/src/spark_character/codex_provider.py
+++ b/src/spark_character/codex_provider.py
@@ -85,7 +85,10 @@ def call_codex(
             stderr = result.stderr.decode("utf-8", errors="replace") if result.stderr else ""
             raise RuntimeError(f"codex exec failed (rc={result.returncode}): {stderr.strip()[:300]}")
         if not out_path.exists():
-            raise RuntimeError("codex exec did not write the expected output file.")
+            raise RuntimeError(
+                f"codex exec did not write the expected output file at {out_path}. "
+                f"Check codex binary version, sandbox/policy settings, or rerun with --debug to inspect the exec."
+            )
         text = out_path.read_text(encoding="utf-8", errors="replace").strip()
         return text
 
diff --git a/src/spark_character/persona.py b/src/spark_character/persona.py
index dcc674a..1a37167 100644
--- a/src/spark_character/persona.py
+++ b/src/spark_character/persona.py
@@ -78,7 +78,9 @@ def detect_provider_kind(provider) -> str | None:
 def validate_persona_version(version: str) -> str:
     value = str(version or "").strip()
     if not PERSONA_VERSION_PATTERN.fullmatch(value):
-        raise ValueError("Persona version must match vN, for example v8.")
+        raise ValueError(
+            f"Persona version must match vN (for example v8); got {value!r}."
+        )
     return value