Add grpc-timeout cross-repo discovery scenario

[ben-pepper-sg]

Summary

• Adds a new grpc-timeout-cross-repo scenario under Understanding existing code that demonstrates hard cross-repo discovery across two real OSS repos: github.com/grpc/grpc-go and github.com/connectrpc/connect-go
• Scenario prompt asks the agent to trace how context deadlines are encoded onto the wire in both libraries and identify the key architectural difference
• All code references verified against live repos via Sourcegraph MCP (exact file paths and line numbers)
• Registered as the first entry in the understand-existing-code scenario list to lead with the most dramatic cross-repo contrast

Why this scenario

The existing cross-repo-discovery scenario is effectively single-repo (vscode Settings Sync). This one is genuinely multi-repo: without MCP the agent physically cannot access connect-go source — every fallback (GOPATH cache, filesystem scan, GitHub API) fails, resulting in a partially-inferred answer that misses the core architectural insight. With MCP it discovers both repos in seconds and traces the full path.

Metrics (from live runs):

	Without MCP	With MCP
Time	18 min	5.5 min
Cost	$3.80	$1.32
Quality	0.18	0.88
Tool calls	85	31

Key finding the scenario surfaces

grpc-go embeds deadline handling inside the HTTP/2 transport layer. connect-go elevates it to a first-class Protocol interface (SetTimeout(*http.Request)), making timeout encoding swappable per protocol. This difference is only visible when reading both codebases side by side — which is exactly what MCP enables.

Test plan

• npm run dev — new scenario appears in the picker as "Cross-repo protocol comparison"
• Both agent columns play back with realistic tool call sequences
• Quality breakdown table renders with all 5 rows
• Log download buttons work (stub logs in place; replace with live execution logs before shipping)

🤖 Generated with Claude Code