Track runtime tasks with structured task packets

Replace the oversized packet model with the requested JSON-friendly packet shape and thread it through the in-memory task registry. Add the RunTaskPacket tool so callers can launch packet-backed tasks directly while preserving existing task creation flows.

Constraint: The existing task system and tool surface had to keep TaskCreate behavior intact while adding packet-backed execution

Rejected: Add a second parallel packet registry | would duplicate task lifecycle state

Confidence: high

Scope-risk: moderate

Reversibility: clean

Directive: Keep TaskPacket aligned with the tool schema and task registry serialization when extending the packet contract

Tested: cargo build --workspace; cargo test --workspace

Not-tested: live end-to-end invocation of RunTaskPacket through an interactive CLI session

rust/crates/runtime/src/lib.rs

@@ -135,8 +135,7 @@ pub use stale_branch::{
     StaleBranchPolicy,
 };
 pub use task_packet::{
-    validate_packet, AcceptanceTest, BranchPolicy, CommitPolicy, RepoConfig, ReportingContract,
-    TaskPacket, TaskPacketValidationError, TaskScope, ValidatedPacket,
+    validate_packet, TaskPacket, TaskPacketValidationError, ValidatedPacket,
 };
 pub use trust_resolver::{TrustConfig, TrustDecision, TrustEvent, TrustPolicy, TrustResolver};
 pub use usage::{