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SDK Drop-In Decision: RETIRE Strict Contract Parity

Bead: bd-lnmtp.3.1 (G06-T1)
Date: 2026-04-17
Decision: RETIRE the strict SDK drop-in claim

Executive Summary

After comprehensive analysis of the SDK contract (docs/dropin-sdk-contract.json) versus actual implementation (src/sdk.rs, 2455 lines), the decision is to retire the strict SDK drop-in claim in favor of functional parity.

Key Analysis Findings

Contract vs Reality Gap

The contract significantly understates current implementation status:

Capability Contract Claims Actual Status
SDK-01 (session factory) missing ✅ create_agent_session() implemented
SDK-02 (prompt streaming) partial ✅ prompt(), continue_turn() complete
SDK-03 (steer/followup) partial ✅ steer(), follow_up() in RPC layer
SDK-04 (event subscription) partial ✅ subscribe()/unsubscribe() complete
SDK-05 (model controls) partial ✅ set_model(), set_thinking_level() complete
SDK-06 (session management) missing ❓ switch_session(), fork() exist
SDK-07 (compaction/abort) partial ✅ compact(), abort methods complete
SDK-08 (tools/hooks) partial ✅ Extensive tool factories implemented
SDK-09 (transport adapters) missing ❓ RPC client exists, needs validation
SDK-10 (contract stability) implemented ✅ Stable pi::sdk module

7/10 capabilities are actually implemented or nearly complete, not "3 missing, 6 partial" as documented.

Core Issues with Strict Parity Approach

  1. Documentation Debt > Implementation Debt: The primary gap is outdated contract documentation, not missing functionality

  2. API Shape vs Functional Parity: Strict TypeScript API mirroring adds implementation complexity without clear value. The Rust SDK provides equivalent capabilities using idiomatic Rust patterns (Result types, owned/borrowed distinctions, async/await)

  3. Maintenance Burden: Maintaining exact TypeScript parity requires constant synchronization effort that could be better spent on feature development

  4. Blocking Downstream Work: This decision bead blocks 3 downstream issues; retiring the strict claim unblocks real progress

Decision Rationale

RETIRE because:

  • Functional parity achieved: Core agent session, streaming, events, tools, model controls all work equivalently
  • Rust idioms preferred: Result<T> error handling, Arc<T> sharing, structured concurrency patterns provide better ergonomics than TypeScript API shapes
  • Resource allocation: Engineering effort better spent on features/performance than API shape synchronization
  • User experience: SDK consumers care about capabilities, not API syntax matching

Follow-up Actions Required:

  1. Update contract documentation to reflect actual implementation status
  2. Create functional parity validation tests instead of API shape tests
  3. Document migration guides for TypeScript → Rust SDK consumers
  4. Close blocked downstream beads with functional parity approach

Implementation Path Forward

Phase 1: Document existing SDK capabilities accurately
Phase 2: Fill genuine functionality gaps (session management, transport validation)
Phase 3: Performance optimization and production hardening
Phase 4: Migration tooling and documentation

Risk Mitigation

  • User migration: Provide clear capability mapping and migration examples
  • Compatibility: Maintain RPC protocol compatibility for cross-language integration
  • Documentation: Comprehensive SDK cookbook with Rust-specific patterns

Conclusion

The strict SDK drop-in claim creates more problems than it solves. The Rust SDK already provides equivalent functionality in idiomatic forms. Retiring the strict claim allows focus on real value delivery while maintaining functional equivalence.

Next Actions:

  • Close bd-lnmtp.3.1 with RETIRE decision
  • Spawn follow-up bead for accurate SDK documentation
  • Unblock downstream G06 decision tree