fix: Rollback instruction util refactoring as its breaking internal customers

Co-authored-by: Shangjie Chen <deanchen@google.com>
PiperOrigin-RevId: 935006608

Author: DeanChensj

.agents/skills/adk-sample-creator/SKILL.md

@@ -30,11 +30,6 @@ The `agent.py` should focus on demonstrating a specific feature or agent pattern
 > [!IMPORTANT]
 > **Model Selection**: Do not set the `model` parameter explicitly (e.g., `model="gemini-2.5-flash"`) on `Agent` instances in sample agents. Instead, let them default to the system-configured model, unless a specific model is explicitly requested by the user.
 
-> [!IMPORTANT]
-> **Context Usage**: Prefer using the unified `Context` class (imported from
-> `google.adk`) instead of the legacy `ToolContext` or `CallbackContext`
-> aliases in callbacks and tool definitions.
-
 Choose one of the following patterns:
 
 #### Pattern A: Workflows (for complex graphs)

contributing/samples/core/nested_state/README.md

@@ -16,7 +16,6 @@
 
 import logging
 import re
-from typing import Any
 
 from ..agents.readonly_context import ReadonlyContext
 from ..sessions.state import State
@@ -47,11 +46,7 @@ async def build_instruction(
   ) -> str:
     return await inject_session_state(
         'You can inject a state variable like {var_name} or an artifact '
-        '{artifact.file_name} into the instruction template.'
-        'You can also inject a nested variable like {var_name.nested_var}.'
-        'If a variable or nested attribute may be missing, append `?` to the '
-        'path or attribute name for optional handling, e.g. '
-        '{var_name.optional_nested_var?}.',
+        '{artifact.file_name} into the instruction template.',
         readonly_context,
     )
 
@@ -83,69 +78,14 @@ async def _async_sub(pattern, repl_async_fn, string) -> str:
     result.append(string[last_end:])
     return ''.join(result)
 
-  def _get_nested_value(obj: Any, path: str) -> Any:
-    """Retrieve nested value from an object based on dot-separated path."""
-    parts = path.split('.')
-    current = obj
-
-    for part in parts:
-      if current is None:
-        return None
-
-      optional = part.endswith('?')
-      key = part.removesuffix('?')
-
-      # Try dictionary access first
-      if hasattr(current, '__getitem__'):
-        try:
-          current = current[key]
-          continue
-        except (KeyError, TypeError) as e:
-          # If dict access fails, fall through to try getattr
-          # UNLESS it's a pure dict which definitely doesn't have attributes
-          if isinstance(current, dict):
-            if optional:
-              return None
-            raise KeyError(f"Key '{key}' not found in path '{path}'") from e
-          pass
-
-      # Try attribute access
-      try:
-        current = getattr(current, key)
-      except AttributeError as e:
-        # Both dict access and attribute access failed.
-        if optional:
-          return None
-        raise KeyError(f"Key '{key}' not found in path '{path}'") from e
-
-    return current
-
-  def _is_valid_path(path: str) -> bool:
-    """Checks if the path is a valid state variable path."""
-    parts = path.split('.')
-    if not parts:
-      return False
-
-    # Check first segment (can have prefix)
-    first_seg = parts[0].removesuffix('?')
-    if not _is_valid_state_name(first_seg):
-      return False
-
-    # Check subsequent segments (must be plain identifiers)
-    for part in parts[1:]:
-      seg = part.removesuffix('?')
-      if not seg.isidentifier():
-        return False
-
-    return True
-
-  async def _evaluate_path(path: str) -> str:
-    if path.startswith('artifact.'):
-      var_name = path.removeprefix('artifact.')
-      optional = var_name.endswith('?')
-      if optional:
-        var_name = var_name.removesuffix('?')
-
+  async def _replace_match(match) -> str:
+    var_name = match.group().lstrip('{').rstrip('}').strip()
+    optional = False
+    if var_name.endswith('?'):
+      optional = True
+      var_name = var_name.removesuffix('?')
+    if var_name.startswith('artifact.'):
+      var_name = var_name.removeprefix('artifact.')
       if invocation_context.artifact_service is None:
         raise ValueError('Artifact service is not initialized.')
       artifact = await invocation_context.artifact_service.load_artifact(
@@ -164,45 +104,22 @@ async def _evaluate_path(path: str) -> str:
           raise KeyError(f'Artifact {var_name} not found.')
       return str(artifact)
     else:
-      try:
-        value = _get_nested_value(invocation_context.session.state, path)
-
+      if not _is_valid_state_name(var_name):
+        return match.group()
+      if var_name in invocation_context.session.state:
+        value = invocation_context.session.state[var_name]
         if value is None:
           return ''
         return str(value)
-      except KeyError as e:
-        raise KeyError(f'Context variable not found: `{path}`.') from e
-
-  async def _replace_match(match) -> str:
-    raw_match = match.group()
-    leading_count = len(raw_match) - len(raw_match.lstrip('{'))
-    trailing_count = len(raw_match) - len(raw_match.rstrip('}'))
-    full_path = raw_match.lstrip('{').rstrip('}').strip()
-
-    if leading_count == trailing_count:
-      n = leading_count
-      is_valid = _is_valid_path(full_path) or full_path.startswith('artifact.')
-      if n % 2 == 0:
-        # Even: Escaped, no evaluation
-        if is_valid:
-          half_n = n // 2
-          return '{' * half_n + full_path + '}' * half_n
-        else:
-          return raw_match
       else:
-        # Odd: Evaluate and wrap
-        if not is_valid:
-          return raw_match
-        evaluated_value = await _evaluate_path(full_path)
-        wrap_braces = (n - 1) // 2
-        return '{' * wrap_braces + evaluated_value + '}' * wrap_braces
-    else:
-      # Asymmetric: fallback to old behavior (treat as N=1 if valid path)
-      if not _is_valid_path(full_path) and not full_path.startswith(
-          'artifact.'
-      ):
-        return raw_match
-      return await _evaluate_path(full_path)
+        if optional:
+          logger.debug(
+              'Context variable %s not found, replacing with empty string',
+              var_name,
+          )
+          return ''
+        else:
+          raise KeyError(f'Context variable not found: `{var_name}`.')
 
   return await _async_sub(r'{+[^{}]*}+', _replace_match, template)