fix: restore Python entry point as Rust trampoline + tool input validation

The Python prism entry point MUST stay — removing it breaks upgrades
because pip/uv removes the executable. The bootstrap.py already
delegates to the Rust binary via execvp when it's available.

Flow: pip installs Python 'prism' → bootstrap.py finds Rust binary →
execvp replaces process with Rust → user sees Rust CLI.

If Rust binary missing: Python CLI runs with fallback commands that
tell user to install the Rust binary.

Also: added tool input validation (2.2) — validates required fields
and types against tool input_schema before execution.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Darth-Hidious

app/agent/core.py

@@ -26,6 +26,32 @@
 MAX_TOOL_RESULT_CHARS = 30_000
 
 
+def _validate_tool_input(tool, args: dict) -> str | None:
+    """Validate tool args against the tool's input_schema. Returns error string or None."""
+    schema = getattr(tool, 'input_schema', None)
+    if not schema or not isinstance(schema, dict):
+        return None
+    props = schema.get('properties', {})
+    required = schema.get('required', [])
+    for field in required:
+        if field not in args:
+            return f"missing required field '{field}'"
+    for key, val in args.items():
+        if key.startswith('_'):
+            continue  # internal fields
+        if key in props:
+            expected_type = props[key].get('type', '')
+            if expected_type == 'string' and not isinstance(val, str):
+                return f"'{key}' must be a string, got {type(val).__name__}"
+            if expected_type == 'integer' and not isinstance(val, int):
+                return f"'{key}' must be an integer, got {type(val).__name__}"
+            if expected_type == 'number' and not isinstance(val, (int, float)):
+                return f"'{key}' must be a number, got {type(val).__name__}"
+            if expected_type == 'array' and not isinstance(val, list):
+                return f"'{key}' must be an array, got {type(val).__name__}"
+    return None
+
+
 def _load_system_prompt(settings_path: str = "") -> str:
     if settings_path:
         p = Path(settings_path).expanduser()
@@ -143,6 +169,11 @@ def _execute_tool_with_hooks(self, tool_name: str, tool_args: dict, call_id: str
                 else:
                     return {"skipped": f"Tool {tool_name} requires approval but no callback set."}
 
+        # Step 3.5: Validate inputs against schema
+        validation_error = _validate_tool_input(tool, effective_args)
+        if validation_error:
+            return {"error": f"Invalid input for {tool_name}: {validation_error}"}
+
         # Step 4: Execute
         try:
             if tool_name == "show_scratchpad":

pyproject.toml

@@ -94,10 +94,8 @@ dev = [
     "flake8>=6.1.0",
 ]
 
-# No Python entry point — the Rust binary IS the CLI.
-# Python is invoked by the Rust binary via prism-python-bridge.
-# [project.scripts]
-# prism = "app.cli.bootstrap:main"  # REMOVED — conflicts with Rust binary
+[project.scripts]
+prism = "app.cli.bootstrap:main"
 
 [project.urls]
 Homepage = "https://github.com/Darth-Hidious/PRISM"