[C6] Wire provider spend reporting and shutdown hooks

[ACFHarbinger]

Track completion of the remaining C6 boundary.

Implemented in commit 2342b83:

• per-agent budgets and usage recording;
• automatic wake blocking after exhaustion;
• durable Markdown budget handoff summaries;
• delegation messages and human resume;
• CLI and Tauri command surfaces;
• Shared Hub task browser integration.

Remaining work:

• provider adapters must report spend automatically;
• execution/shutdown hooks must stop uncontrolled provider calls;
• desktop budget controls can be expanded beyond the current backend boundary.

[ACFHarbinger]

Provider-path enforcement is now implemented in 986f284. Tauri AgentSystem checks configured role budgets before LLMClient invocation, records one call unit after successful completions, and triggers the durable handoff when a role reaches its limit. CLI/external adapters remain caller-driven; shutdown hooks remain open. cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace, and npm run build pass.

[ACFHarbinger]

C6 shutdown handling is now implemented in 11fd8f6. Cancelled Tauri provider runs persist a Markdown shutdown handoff and durable delegation message before exiting; the new ca-hub test covers the record. Provider/external-adapter automatic spend reporting remains the remaining C6 gap. Full Clippy, workspace tests, and frontend build pass.

[ACFHarbinger]

The desktop C6 boundary is now complete in 8b096f0: Shared Hub Budget tab supports configuring/resetting agent limits, recording caller-defined usage, viewing paused state, and resuming agents. External-adapter automatic accounting and shutdown hooks remain the open C6 work. npm run build passes.

[ACFHarbinger]

Added atomic pre-call budget enforcement in f18a9a1. ca budget consume and Tauri hub_consume_budget reserve caller-defined units before provider invocation; over-limit requests are rejected, and Tauri AgentSystem uses the same reservation path. External adapters can now adopt this guard directly. Tests, Clippy, and frontend build pass.