parity(#198/#206): support max_snippet_lines in MCP/CLI output + savings

[amondnet]

Summary

Upstream semble #198 (d561953) added a max_snippet_lines option (cap snippet lines in MCP/CLI output) plus MCP/AGENTS.md instruction tweaks, and #206 (30d36ad) fixed savings accounting when it's used. csp has no equivalent.

Upstream

• max_snippet_lines threaded through cli.py, mcp.py, index/index.py.
• #206: stats.py / index.py compute savings correctly when snippets are truncated.

csp status

• No max_snippet_lines anywhere in crates/ or npm/. Not reflected. #206 is N/A until #198 is adopted.

Decision needed

Adopt the feature (MCP + CLI output snippet cap + savings correctness) or document it as an intentional divergence.

• Decide adopt vs diverge.
• If adopt: thread max_snippet_lines through CLI/MCP output + savings.

Refs

• Upstream: feat: Optimize MCP and AGENTS.md instructions, add snippet_lines MinishLab/semble#198 (d561953), #206 (30d36ad)
• Sync baseline check: eacbe43..949559b, 2026-07-11