Feat/cfg 005 validate config paths

src/bernstein/core/bootstrap.py

@@ -33,6 +33,7 @@
     from bernstein.core.models import Task
 
 # Import from sub-modules (facade re-exports)
+from bernstein.core.config_path_validation import check_config_paths
 from bernstein.core.log_redact import install_pii_filter
 from bernstein.core.preflight import (
     _claude_has_oauth_session,
@@ -298,6 +299,7 @@ def bootstrap_from_seed(
     if model is not None:
         object.__setattr__(seed, "model", model)
     preflight_checks(seed.cli, port)
+    check_config_paths(seed, workdir)
     effective_cells = cells if cells is not None else seed.cells
 
     # 2. Workspace + catalog + index (silent — errors logged, not printed)

src/bernstein/core/config_path_validation.py

@@ -0,0 +1,153 @@
+"""Validate file paths referenced in bernstein.yaml configuration.
+
+This module provides startup validation for config-referenced paths:
+context_files, agent_catalog, and other filesystem paths. If any path
+does not exist, validation fails with a clear message before run starts.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from bernstein.core.seed import SeedConfig
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass(frozen=True)
+class PathValidationError:
+    """A single path validation failure.
+
+    Attributes:
+        field: Config field name (e.g., "context_files", "agent_catalog").
+        path: The path that failed validation.
+        reason: Human-readable reason for the failure.
+    """
+
+    field: str
+    path: str
+    reason: str
+
+    def __str__(self) -> str:
+        return f"{self.field}: '{self.path}' {self.reason}"
+
+
+@dataclass(frozen=True)
+class PathValidationResult:
+    """Result of validating all config paths.
+
+    Attributes:
+        errors: List of validation errors found.
+    """
+
+    errors: tuple[PathValidationError, ...]
+
+    @property
+    def ok(self) -> bool:
+        """Return True if no validation errors."""
+        return len(self.errors) == 0
+
+    def format_errors(self) -> str:
+        """Format all errors as a newline-separated string."""
+        return "\n".join(f"  - {e}" for e in self.errors)
+
+
+def validate_config_paths(seed: SeedConfig, workdir: Path) -> PathValidationResult:
+    """Validate all file paths referenced in the seed configuration.
+
+    Checks that:
+    - All context_files exist and are readable files
+    - agent_catalog (if set) exists and is a directory
+
+    Args:
+        seed: Validated seed configuration from bernstein.yaml.
+        workdir: Project working directory for resolving relative paths.
+
+    Returns:
+        PathValidationResult with any errors found.
+    """
+    errors: list[PathValidationError] = []
+
+    # Validate context_files
+    for ctx_path in seed.context_files:
+        full_path = Path(ctx_path)
+        # Handle both absolute and relative paths
+        if not full_path.is_absolute():
+            full_path = workdir / ctx_path
+        if not full_path.exists():
+            errors.append(
+                PathValidationError(
+                    field="context_files",
+                    path=ctx_path,
+                    reason="does not exist",
+                )
+            )
+        elif not full_path.is_file():
+            errors.append(
+                PathValidationError(
+                    field="context_files",
+                    path=ctx_path,
+                    reason="is not a file",
+                )
+            )
+
+    # Validate agent_catalog
+    if seed.agent_catalog is not None:
+        catalog_path = Path(seed.agent_catalog)
+        # Handle both absolute and relative paths
+        if not catalog_path.is_absolute():
+            catalog_path = workdir / catalog_path
+        if not catalog_path.exists():
+            errors.append(
+                PathValidationError(
+                    field="agent_catalog",
+                    path=seed.agent_catalog,
+                    reason="does not exist",
+                )
+            )
+        elif not catalog_path.is_dir():
+            errors.append(
+                PathValidationError(
+                    field="agent_catalog",
+                    path=seed.agent_catalog,
+                    reason="is not a directory",
+                )
+            )
+
+    return PathValidationResult(errors=tuple(errors))
+
+
+def check_config_paths(seed: SeedConfig, workdir: Path) -> None:
+    """Validate config paths and exit with clear error if any are missing.
+
+    This is the main entry point for preflight path validation. Call this
+    during startup before the orchestrator begins execution.
+
+    Args:
+        seed: Validated seed configuration from bernstein.yaml.
+        workdir: Project working directory for resolving relative paths.
+
+    Raises:
+        SystemExit: If any config-referenced paths are missing or invalid.
+    """
+    from bernstein.cli.errors import BernsteinError, ExitCode, handle_cli_error
+
+    result = validate_config_paths(seed, workdir)
+    if not result.ok:
+        raise handle_cli_error(
+            BernsteinError(
+                what="Config references invalid paths",
+                why=f"The following paths in bernstein.yaml are missing or incorrect:\n{result.format_errors()}",
+                fix="Create the missing files/directories or update bernstein.yaml to reference valid paths",
+                exit_code=ExitCode.CONFIG,
+            )
+        )
+
+    # Log success for debugging
+    validated_count = len(seed.context_files) + (1 if seed.agent_catalog else 0)
+    if validated_count > 0:
+        logger.debug("Validated %d config path(s)", validated_count)