Conversation compaction controls, forward-looking budget scopes, and tool output token truncation

This release introduces first-class conversation compaction controls via CompactionConfig, delta and forward-looking budget scopes for session resumption, tool output token truncation limits, and expanded arithmetic operations on UsageMetadata. It also delivers OS-level terminal sandboxing examples and automated tool wrapper reflection preservation.

• Compaction Configuration: Adds CompactionConfig on AgentConfig to govern sliding-window conversation history compaction through an explicit token ceiling dial (token_threshold), deprecating CapabilitiesConfig.compaction_threshold.
• Forward-Looking Budget Scope: Adds BudgetScope.FORWARD_LOOKING to BudgetConfig to enforce model call and token budgets across newly resumed execution turns without counting previous historical usage.
• Tool Output Token Truncation: Exposes tool_output_truncation_config across agent configurations to cap token output volume initially for run_command executions in localharness.
• UsageMetadata Arithmetic: Supports standard Python arithmetic protocols on UsageMetadata, enabling scalar multiplications, scaling, and accumulating token counts using built-in sum().
• Tool Wrapper Metadata Preservation: Preserves function signature, module name, annotations, and original callable references via wrapped when registering tools with ToolWithSchema.
• Interactive REPL Policy Flattening: Automatically flattens nested policy lists during interactive REPL upgrades so nested command authorization rules correctly upgrade to prompt the user.
• Terminal Command Sandboxing Guide: Added getting-started guide and references demonstrating OS-level command sandboxing using RunCommandConfig(enable_sandbox=True) paired with execution policies.
• Tool Call Deserialization: Fixed dropped tool arguments during tool call handling when incoming payloads provide structured dictionary arguments rather than serialized JSON strings.
• Local Step Trajectory Tracking: Fixed missing provenance metadata by forwarding trajectory_id from incoming tool calls to local connection execution steps.
• Dynamic Content Proto Resolution: Fixed an AttributeError when importing struct_converter in external environments missing internal protobuf definitions by resolving descriptor types dynamically at runtime.