feat: complete fastn-p2p streaming API and remote shell functionality

[amitu]

Summary

Complete implementation of fastn-p2p streaming API and remote shell functionality (rshell/rexec). This is the main tracking PR that implements the complete plan originally outlined in PR #2202, building on the fastn-context foundation from PR #2203.

🎯 Complete Implementation Plan

Phase 1: Basic fastn-context (Minimal) ✅ Completed

• Create fastn-context crate with basic Context struct
• Implement simple context tree (parent/child relationships)
• Add basic cancellation tokens per context
• Move #[fastn_p2p::main] to #[fastn_context::main]
• Basic spawn() with context inheritance
• Completed: PR feat: create fastn-context crate with hierarchical context system for debugging and operations #2203 ✅ (merged to main)

Phase 2: fastn-p2p Streaming API 🔄 In Progress

• Add client module with connect() function
• Implement client::Session with stdin/stdout streams
• Add basic open_uni()/accept_uni() for stderr-like streams
• Add server::Session with protocol negotiation and context integration
• Add Session -> Request conversion (into_request())
• Preserve existing Request methods (get_input, handle)
• Basic context integration (sessions get context)
• Current: PR feat: implement fastn-p2p streaming API foundation for remote shell functionality #2205 ⏳ (API foundation → this feature branch)

Phase 3: Test and Validate ⏳ Next

• Fill in TODO implementations with actual iroh streaming
• Update fastn-p2p-test sender/receiver to use new API
• Test both RPC (Session->Request) and streaming patterns
• Validate iroh connection reuse works correctly
• Scope: End-to-end P2P streaming validation

Phase 4: Remote Shell Integration ⏳ Final

• Update fastn-remote to use fastn-p2p streaming API
• Implement rshell using client::connect() -> Session
• Implement server-side rshell using Session streams
• Add stderr handling via open_uni()/accept_uni()
• Test fastn rshell and fastn rexec commands work
• Scope: Working remote shell over P2P

🔗 Related PRs

• PR feat: create fastn-context crate with hierarchical context system for debugging and operations #2203 ✅ - fastn-context foundation (merged to main)
• PR feat: implement fastn-p2p streaming API foundation for remote shell functionality #2205 ⏳ - fastn-p2p streaming API foundation (→ this feature branch)
• Future PRs - Will be created against this feature branch for Phases 3-4

🎯 Success Criteria

1. ✅ fastn-context integrated - Hierarchical contexts for debugging (PR feat: create fastn-context crate with hierarchical context system for debugging and operations #2203)
2. 🔄 Streaming API complete - Client/server Session types (PR feat: implement fastn-p2p streaming API foundation for remote shell functionality #2205)
3. ⏳ fastn-p2p-test passes - New streaming API validated (Phase 3)
4. ⏳ fastn rshell works - Interactive shell over P2P (Phase 4)
5. ⏳ fastn rexec works - Command execution with separate stderr (Phase 4)
6. ✅ No regressions - Existing fastn-p2p call() functionality preserved

🔧 API Overview

New Streaming API

// Client side streaming
let session = fastn_p2p::client::connect(our_key, target, protocol).await?;
session.stdin   // Send to server
session.stdout  // Receive from server
let stderr = session.accept_uni().await?; // Additional streams

// Server side with context
fn handle_session(session: fastn_p2p::server::Session<Protocol>) {
    let ctx = session.context(); // fastn-context integration
    let request = session.into_request(); // RPC compatibility
}

Minimal Breaking Changes

• Add client::connect() function (new)
• Add client::Session type (new)
• Add server::Session type (new)
• Add Session::into_request() method (new)
• Keep all existing Request

  methods intact ✅

📋 Development Strategy

This feature branch allows us to:

• Build incrementally through focused, reviewable PRs
• Test continuously as each phase completes
• Maintain compatibility throughout development
• Review in chunks rather than one massive change

Goal: Working remote shell over P2P with minimal API surface for immediate use.

The comprehensive monitoring and ecosystem migration will come in follow-up PRs once the core streaming foundation is proven.

🤖 Generated with Claude Code