Episode 3: The Agent That Couldn't See What It Was Breaking

def extract_symbols(file_path: str, source: str) -> list[Symbol]:
    """
    Parse source file and extract all symbols with their relationships.
    Returns: functions, types, imports, trait implementations, call sites.
    """
    tree = ts_parser.parse(source.encode())
    symbols = []

    for node in tree.root_node.children:
        if node.type == "function_item":
            symbols.append(Symbol(
                kind="function",
                name=extract_name(node),
                file=file_path,
                line=node.start_point[0],
                calls=extract_call_sites(node),
                signature=extract_signature(node),
            ))
        elif node.type in ("struct_item", "enum_item", "trait_item"):
            symbols.append(Symbol(
                kind=node.type.replace("_item", ""),
                name=extract_name(node),
                file=file_path,
                line=node.start_point[0],
            ))

    return symbols

CREATE NODE TABLE Function(
    name STRING,
    file STRING,
    line INT64,
    signature STRING,
    PRIMARY KEY(name, file)
);

CREATE NODE TABLE Type(
    name STRING,
    kind STRING,
    file STRING,
    PRIMARY KEY(name, file)
);

CREATE REL TABLE CALLS(FROM Function TO Function);
CREATE REL TABLE IMPLEMENTS(FROM Type TO Type);
CREATE REL TABLE USES_TYPE(FROM Function TO Type);

-- Direct and transitive callers of handle_request
MATCH path = (caller:Function)-[:CALLS*1..3]->(target:Function {name: "handle_request"})
RETURN caller.name, caller.file, length(path) as depth
ORDER BY depth;

@mcp_tool
def impact(symbol_name: str) -> ImpactReport:
    """
    Return the blast radius of changing a symbol.
    Includes direct callers, transitive dependents, test coverage, and risk assessment.
    """

@mcp_tool
def context(file_path: str, symbol_name: str) -> SymbolContext:
    """
    Return full context for a symbol: callers, dependencies, tests.
    Use before making a change to understand what you're touching.
    """

@mcp_tool
def query(cypher: str) -> list[dict]:
    """
    Run a raw graph query. For complex dependency questions.
    """

@mcp_tool
def detect_changes(since: str) -> list[ChangedSymbol]:
    """
    Return symbols that changed since a git ref, with their downstream impacts.
    Use at the end of a session to verify change scope matched expectations.
    """