Python a2ui_agent: Refactor a2ui_agent to depend on a2ui_core

[nan-yu]

Description

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. For larger changes, raising an issue first helps reduce redundant work.

Pre-launch Checklist

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have added updates to the CHANGELOG.
• I updated/added relevant documentation.
• My code changes (if any) have tests.
• If my branch is on fork, I have verified that scripts/e2e_test.sh passes.

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[gemini-code-assist]

Code Review

This pull request introduces the a2ui_core Python library, which implements core state management, rendering, message processing, and schema validation for the A2UI v0.9+ specification. Key feedback highlights several critical issues and improvement opportunities: a NameError in model_catalog.py due to an undefined variable, incomplete TR35 date token formatting in function_impls.py, redundant subscriptions for TemplateChildList in generic_binder.py, an inefficient list expansion loop in data_model.py that could trigger OOM errors, silent acceptance of unclosed string literals in expression_parser.py, and a potential AttributeError in data_context.py when handling malformed action events.

[gemini-code-assist]

A NameError will occur here because the variable payload is referenced but has not been defined in this scope. It should be replaced with the dictionary representing the full function call structure.

Suggested change

	target_val = (
	payload
	if (
	hasattr(fn.schema, "model_fields")
	and "call" in fn.schema.model_fields
	)
	else args
	)
	target_val = (
	{"call": name, "args": args}
	if (
	hasattr(fn.schema, "model_fields")
	and "call" in fn.schema.model_fields
	)
	else args
	)

[gemini-code-assist]

The current _format_date implementation only replaces a small subset of the documented TR35 date pattern tokens. Common tokens like yy, MMMM, MMM, EEEE, E, hh, h, and a are completely ignored, which will cause formatting to fail or output raw pattern characters.

Using a single-pass regular expression replacement is the most robust way to map these tokens safely without causing recursive replacement collisions (e.g., replacing d after dd has already introduced %d).

Suggested change

	py_fmt = (
	str(fmt)
	.replace("yyyy", "%Y")
	.replace("MM", "%m")
	.replace("dd", "%d")
	.replace("HH", "%H")
	.replace("mm", "%M")
	.replace("ss", "%S")
	)
	token_map = {
	"EEEE": "%A", "E": "%a",
	"yyyy": "%Y", "yy": "%y",
	"MMMM": "%B", "MMM": "%b", "MM": "%m", "M": "%m",
	"dd": "%d", "d": "%d",
	"HH": "%H", "H": "%H", "hh": "%I", "h": "%I",
	"mm": "%M", "ss": "%S", "a": "%p"
	}
	pattern = re.compile("|".join(sorted(token_map.keys(), key=len, reverse=True)))
	py_fmt = pattern.sub(lambda m: token_map[m.group(0)], str(fmt))

[gemini-code-assist]

The is_dynamic check should exclude TemplateChildList objects (which contain a componentId key) to align with DataContext.resolve_dynamic_value and avoid setting up redundant dummy subscriptions.

Suggested change

	is_dynamic = (
	isinstance(value, dict)
	and "path" in value
	and isinstance(value["path"], str)
	)
	is_dynamic = (
	isinstance(value, dict)
	and "path" in value
	and isinstance(value["path"], str)
	and "componentId" not in value
	)

[gemini-code-assist]

Expanding the list sequentially using a while loop with append is highly inefficient and can lead to Out Of Memory (OOM) errors or performance bottlenecks if an unreasonably large index is passed.

Using extend is much faster, and adding a safety threshold check protects against potential denial of service vectors.

Suggested change

	current = current[token]
	elif isinstance(current, list) and NUMERIC_PATTERN.match(token):
	if idx > 10000:
	raise ValueError(f"Index {idx} exceeds maximum allowed array size.")
	current.extend([None] * (idx - len(current) + 1))

[gemini-code-assist]

An unclosed string literal at the end of an expression is currently accepted silently because the loop terminates at the end of the scanner input without raising an error. It should raise a ValueError to ensure syntax correctness.

Suggested change

	while not scanner.is_at_end():
	c = scanner.advance()
	if c == "\\":
	next_c = scanner.advance()
	if next_c == "n":
	result += "\n"
	elif next_c == "t":
	result += "\t"
	elif next_c == "r":
	result += "\r"
	else:
	result += next_c
	elif c == quote:
	break
	else:
	result += c
	closed = False
	while not scanner.is_at_end():
	c = scanner.advance()
	if c == "\\":
	next_c = scanner.advance()
	if next_c == "n":
	result += "\n"
	elif next_c == "t":
	result += "\t"
	elif next_c == "r":
	result += "\r"
	else:
	result += next_c
	elif c == quote:
	closed = True
	break
	else:
	result += c
	if not closed:
	raise ValueError("Unclosed string literal")

[gemini-code-assist]

If action["event"] is not a dictionary (e.g., if it is malformed or of an unexpected type), calling evt.get("context") will raise an AttributeError. Adding an explicit type check ensures robust defensive programming.

Suggested change

	if isinstance(action, dict) and "event" in action:
	evt = copy.deepcopy(action["event"])
	resolved_context = {}
	if isinstance(evt.get("context"), dict):
	for k, v in evt["context"].items():
	resolved_context[k] = self.resolve_dynamic_value(v)
	evt["context"] = resolved_context
	return {"event": evt}
	if isinstance(action, dict) and "event" in action:
	evt = copy.deepcopy(action["event"])
	if isinstance(evt, dict):
	resolved_context = {}
	if isinstance(evt.get("context"), dict):
	for k, v in evt["context"].items():
	resolved_context[k] = self.resolve_dynamic_value(v)
	evt["context"] = resolved_context
	return {"event": evt}