config: generalize config_validate into a shared schema engine

require_schema(config, schema) is a generic recursive declarative
checker (nested-dict schema, leaves name required type(s), each
intermediate object node gets its own dict-type check so a wrong-typed
section is named directly instead of surfacing as a confusing "missing
child" error). validate_temp_ctrl() is now just require_schema(config,
TEMPCTRL_SCHEMA) against a declarative schema dict, replacing the
hand-rolled nested loops.

utils/sud_validate.py's static structural check ('steps' must be a
list) now goes through the same require_schema()/SUD_SCHEMA - one
shared mechanism for both server config.json and sud.json documents.
The genuinely dynamic per-step check (ramp.rate required only when a
step sets its own temperature) stays hand-written, since it depends on
the document's content, not just its shape.

Added TestRequireSchema, exercising the generic engine directly
against a schema unrelated to TempCtrl.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F4oEE99rkKVU8L8tkzXWdG

utils/config_validate.py

@@ -6,6 +6,10 @@ class ConfigError(Exception):
 
 
 def require(config, path, type=None):
+    """Generic dotted-path lookup against any nested-dict document - not
+    tied to server config.json's own shape, so this is exactly as usable
+    for a sud.json schedule (see utils/sud_validate.py) as for TempCtrl
+    below."""
     node = config
     parts = path.split('.')
     for i, key in enumerate(parts):
@@ -18,18 +22,52 @@ def require(config, path, type=None):
     return node
 
 
+def require_schema(config, schema, _prefix=''):
+    """Generic declarative counterpart to require(): schema mirrors the
+    document's own shape, with every leaf naming the required type(s) (see
+    TEMPCTRL_SCHEMA below for an example) - one shared mechanism for any
+    config-shaped document with a fixed structure, whether that's server
+    config.json's TempCtrl section or (for the parts of it that are static -
+    see utils/sud_validate.py for the parts that aren't, e.g. per-step
+    conditional requirements) a sud.json schedule.
+
+    A schema value that's itself a dict describes a required sub-object:
+    checked (and reported, on failure, as its own dotted path) before
+    recursing into it, so a wrong-typed intermediate node (e.g. 'TempCtrl'
+    itself not being an object) is named directly rather than surfacing as
+    a confusing "missing" error on one of its children instead."""
+    for key, spec in schema.items():
+        path = '{}.{}'.format(_prefix, key) if _prefix else key
+        if isinstance(spec, dict):
+            require(config, path, type=dict)
+            require_schema(config, spec, path)
+        else:
+            require(config, path, type=spec)
+
+
+_GAIN_SCHEMA = {'kp': (int, float), 'ki': (int, float), 'kd': (int, float), 'kt': (int, float)}
+
+# Only the gains every pid_type actually reads unconditionally are
+# required; anything with its own default elsewhere (Outer.y_hold_min,
+# Inner.Hold.yi_max, the whole Thresholds section - see
+# temp_controller_base.py/temp_controller_fsm.py's DEFAULT_THRESHOLDS)
+# stays optional here too, on purpose.
+TEMPCTRL_SCHEMA = {
+    'TempCtrl': {
+        'pid_type': str,
+        'Outer': _GAIN_SCHEMA,
+        'Inner': {
+            'Heat': _GAIN_SCHEMA,
+            'Hold': _GAIN_SCHEMA,
+            'Cool': _GAIN_SCHEMA,
+        },
+    },
+}
+
+
 def validate_temp_ctrl(config):
     """Checked eagerly at startup so a missing/misnamed PID gain fails with
     a clear message here instead of a bare KeyError mid-__init__ or on the
     first process() tick (this bit us once already: config.json.sim's gain/
-    Model nesting mismatch). Only the gains every pid_type actually reads
-    unconditionally are required; anything with its own default elsewhere
-    (Outer.y_hold_min, Inner.Hold.yi_max, the whole Thresholds section -
-    see temp_controller_base.py/temp_controller_fsm.py's DEFAULT_THRESHOLDS)
-    stays optional here too, on purpose."""
-    require(config, 'TempCtrl', dict)
-    require(config, 'TempCtrl.pid_type', str)
-    for gain in ('kp', 'ki', 'kd', 'kt'):
-        require(config, 'TempCtrl.Outer.{}'.format(gain), (int, float))
-        for branch in ('Heat', 'Hold', 'Cool'):
-            require(config, 'TempCtrl.Inner.{}.{}'.format(branch, gain), (int, float))
+    Model nesting mismatch)."""
+    require_schema(config, TEMPCTRL_SCHEMA)

utils/sud_validate.py

@@ -1,6 +1,18 @@
-from utils.config_validate import ConfigError, require
+from utils.config_validate import ConfigError, require, require_schema
 from components.sud import Sud
 
+# The only part of a sud.json document's shape that's fixed regardless of
+# content - same declarative mechanism validate_temp_ctrl() uses for
+# config.json's TempCtrl section (see config_validate.py's require_schema()).
+# Everything else about a schedule (how many steps, which fields each one
+# overrides vs. inherits from default.step, whether a step needs ramp.rate
+# at all) depends on the document's own content, not just its shape, so it
+# can't be expressed as a static schema - handled by the step loop below
+# instead, still built on the same require()/ConfigError primitives.
+SUD_SCHEMA = {
+    'steps': list,
+}
+
 
 def validate_sud(data):
     """Fail-fast structural check for a sud.json document - same rationale
@@ -15,7 +27,7 @@ def validate_sud(data):
     Reuses Sud._parse_data() itself (rather than re-implementing default-
     merging/step-building) so what's checked here can never drift from what
     actually gets parsed at runtime."""
-    require(data, 'steps', type=list)
+    require_schema(data, SUD_SCHEMA)
     if not data['steps']:
         raise ConfigError("'steps' must be a non-empty list")