refactor: add prompt_id as hidden type, fix imports, add docstrings

- Add PROMPT_ID as a new hidden type in the Hidden enum, HiddenHolder,
  HiddenInputTypeDict, and execution engine resolution (both V3 and legacy)
- Refactor GetImageSize to use cls.hidden.prompt_id instead of manually
  calling get_executing_context() — addresses reviewer feedback
- Remove lazy import of get_executing_context from nodes_images.py
- Add docstrings to send_progress_text, _display_text, HiddenHolder,
  and HiddenHolder.from_dict

Amp-Thread-ID: https://ampcode.com/threads/T-019ca1cb-0150-7549-8b1b-6713060d3408

comfy_api/latest/_io.py

@@ -1269,9 +1269,16 @@ class V3Data(TypedDict):
     'When True, the value of the dynamic input will be in the format (value, path_key).'
 
 class HiddenHolder:
+    """Holds hidden input values resolved during node execution.
+
+    Hidden inputs are special values automatically provided by the execution
+    engine (e.g., node ID, prompt data, authentication tokens) rather than
+    being connected by the user in the graph.
+    """
     def __init__(self, unique_id: str, prompt: Any,
                  extra_pnginfo: Any, dynprompt: Any,
-                 auth_token_comfy_org: str, api_key_comfy_org: str, **kwargs):
+                 auth_token_comfy_org: str, api_key_comfy_org: str,
+                 prompt_id: str = None, **kwargs):
         self.unique_id = unique_id
         """UNIQUE_ID is the unique identifier of the node, and matches the id property of the node on the client side. It is commonly used in client-server communications (see messages)."""
         self.prompt = prompt
@@ -1284,6 +1291,8 @@ class HiddenHolder:
         """AUTH_TOKEN_COMFY_ORG is a token acquired from signing into a ComfyOrg account on frontend."""
         self.api_key_comfy_org = api_key_comfy_org
         """API_KEY_COMFY_ORG is an API Key generated by ComfyOrg that allows skipping signing into a ComfyOrg account on frontend."""
+        self.prompt_id = prompt_id
+        """PROMPT_ID is the unique identifier of the current prompt/job being executed."""
 
     def __getattr__(self, key: str):
         '''If hidden variable not found, return None.'''
@@ -1291,6 +1300,14 @@ class HiddenHolder:
 
     @classmethod
     def from_dict(cls, d: dict | None):
+        """Create a HiddenHolder from a dictionary of hidden input values.
+
+        Args:
+            d: Dictionary mapping Hidden enum values to their resolved values.
+
+        Returns:
+            A new HiddenHolder instance with values populated from the dict.
+        """
         if d is None:
             d = {}
         return cls(
@@ -1300,6 +1317,7 @@ class HiddenHolder:
             dynprompt=d.get(Hidden.dynprompt, None),
             auth_token_comfy_org=d.get(Hidden.auth_token_comfy_org, None),
             api_key_comfy_org=d.get(Hidden.api_key_comfy_org, None),
+            prompt_id=d.get(Hidden.prompt_id, None),
         )
 
     @classmethod
@@ -1322,6 +1340,8 @@ class Hidden(str, Enum):
     """AUTH_TOKEN_COMFY_ORG is a token acquired from signing into a ComfyOrg account on frontend."""
     api_key_comfy_org = "API_KEY_COMFY_ORG"
     """API_KEY_COMFY_ORG is an API Key generated by ComfyOrg that allows skipping signing into a ComfyOrg account on frontend."""
+    prompt_id = "PROMPT_ID"
+    """PROMPT_ID is the unique identifier of the current prompt/job being executed. Useful for associating progress updates with specific jobs."""
 
 
 @dataclass