LLM Agent Capabilities Should Follow Task Intent and Context Source

LLM agents take real actions, including executing code, modifying files, calling services, and delegating tasks, driven by context sources: user requests, tool results, documents, shell outputs, Skill and MCP instructions, memory. Unlike traditional systems, where capability is predefined, the least-privilege capability an agent needs is dynamic, depending on its task intent: what it wants to do and how. This creates a security and safety challenge: all inputs enter one shared planning channel with equal influence, by adversarial injection or accidental scope widening, yet a user's explicit request and a document's extracted text carry different trust and should not share authority to choose a destination or widen access. Existing defenses constrain operations and information flow; we study task-scoped, multi-source authority composition. We argue that agent capabilities should be scoped to the current task intent, not a sandbox or session lifetime, and that no single context source defines a complete capability. IntentCap composes capabilities from four such sources: user intent, workflow instructions, tool schemas, and runtime environment, with field-level ownership and monotonic narrowing. Each source contributes specific fields, none can fill another's, and the lease only narrows the user's authorized authority, never widens it. IntentCap uses an LLM to generate short-lived leases from these sources, validated by a deterministic checker before any side effect commits and enforced by tool- and OS-level information flow policies. Evaluation shows IntentCap blocks tested violations without rejecting benign actions, each source boundary is independently necessary, and the checker generalizes across tool, execution, placement, and delegation boundaries.