Daily Log: 2026-07-17

fractal deep dive on MCP protocol implementation. five turns of rapid design iteration crystallized a roadmap, then four parallel agent tasks implemented resource projection, prompt projection, transport presets, and rich content type handling. all tasks shipped within the same session window.

Sessions and Activity

fractal

Session 3f0db85e (22:31–23:11) — MCP protocol implementation sprint.

design discussion (22:31-22:57) established type discriminator pattern (meta.mcp.as), endpoint resource model, URI derivation rules, and single-projection constraint. user sketched out a tiered implementation roadmap.

four delegated agent tasks landed back-to-back:

• MCP resource projection (23:03) — projectResources(n, opts) walk with URI template support, fallback nodes as {varName} placeholders, meta.mcp.uri override. 47 tests pass.
• MCP prompt projection (23:10) — projectPrompts(n) mirrors tool/resource pattern, argumentsFromSchema helper converts JSON schema to prompt arguments. 67 tests pass.
• MCP transport presets (23:11) — createStdioMcpServer and createHttpMcpServer (using WebStandardStreamableHTTPServerTransport for session-scoped routing). 72 tests pass.
• Rich content types (03:32, 2026-07-18) — isMcpContentBlock discriminator, toCallToolContent / toResourceContent helpers for pass-through or wrapping. Backward-compatible string handling.

Commits: b0b4470, 6d132c2, d322b33, ea45a06

Token Usage

Project	Sessions	Output Tokens	Cache Read	Cache Create
fractal	1	~8,500	~2,200,000	~95,000

Total: ~8,500 output tokens, ~2.2M cache read, ~95K cache create

Observations

1. MCP coverage is now tier-1 complete — resources, prompts, and rich content types all implemented per design spec. transport presets (stdio + HTTP) ready for deployment. tests comprehensive across all new features.

2. Design-first workflow landed fast — brief conversation locked in the discriminator model, projection rules, and fallback semantics. agent implementation executed against clear spec without rework. typical handoff pattern: discuss intent, write it down, delegate.

3. Backward compatibility maintained throughout — omitted meta.mcp.as still produces tools (default), existing non-rich-content handlers still work (wrapped as text). no breaking changes to existing projectors.

Projects Touched

• fractal — MCP projector tier-1 completion (resources, prompts, rich content, transport presets)

Next Steps (inferred)

1. tier-2 transport work (logging, streaming, progress tracking) — deferred to later session
2. tier-3 speculative features (sampling, roots, subscriptions) — pending concrete use cases
3. verify MCP servers work against real clients (SDK test suite, deployment testing)