parity(#247): add per-call `content` parameter to MCP search/find_related and key the session cache on it

[amondnet]

Summary

Upstream semble #247 (9218491) added a per-call content parameter to the MCP search and find_related tools (code | docs | config | all, default = server's configured content). csp's MCP tools have no content argument; the content filter is fixed at server start.

Upstream

• mcp.py: content: ContentSelection | None = None on both tools; _resolve_content_selection maps None → server default, "all" → every ContentType.
• _IndexCache key is now (source_key, tuple[ContentType]); get(source, ref, content); _evict_if_stale / evict take the tuple key.
• cache.py: find_index_from_cache_folder(path, content) stores non-code scopes at index-<scope> (e.g. index-code-docs); clear index/clear orphans glob */index*.
• README MCP tool table updated.

csp status

• crates/csp/src/bin/csp/mcp_server.rs: SearchParams { query, repo, top_k }, FindRelatedParams { file_path, line, repo, top_k } — no content.
• crates/csp/src/mcp.rs::IndexCache holds a single content: Vec<ContentType> and keys entries by source only.
• Disk cache already keys on content (indexing/cache.rs::resolve_cache_dir hashes sourceId + content + ref), so no on-disk layout change is needed.

Tasks

• Add content: Option<ContentSelection> to both tool param structs (schemars enum code|docs|config|all), default = server --content.
• IndexCache key → (source, normalized content); thread content through get / evict / revalidation.
• Update SERVER_INSTRUCTIONS, README.md + README.ko.md MCP tool table, .please/docs/references/semble.md §4.16.
• Tests: same repo with different content yields distinct cache entries.

Refs

• Upstream: feat: add content filter to MCP MinishLab/semble#247 (9218491)
• Sync baseline check: 949559b..6bbbd32, 2026-09-03