Add UDNA Node & Session Lifecycle Documentation

[amir-hameed-mir]

Objective

Create comprehensive, implementer-focused documentation for the complete UDNA node and session lifecycle.

Scope

Define all operational states, transitions, timeouts, and error recovery procedures for:

• Node lifecycle (initialization → operational → shutdown → recovery)
• Session lifecycle (handshake → established → maintenance → teardown)
• Resource management (memory, connections, cryptographic material)

Deliverables

1. State machine specifications with clear pre/post conditions
2. Sequence diagrams for critical flows (cold start, graceful shutdown, crash recovery)
3. Reference tables of timeout values and error codes
4. Implementation guidelines for lifecycle management

Why This Matters

This documentation ensures all UDNA implementations handle startup, operation, and shutdown consistently—critical for interoperability and reliability. Without this, implementers will make different assumptions about timeouts, recovery, and resource cleanup.

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Estimated Effort: 2 weeks
Blocks: Implementation work
Dependencies: Core protocol specification