refactor(mcp): centralize meta-function prefix predicates and fix list_tools pagination

Implements T1 of plans/mcp-resources-prompts-design.md (§4.1, §4.6):

- Replace list_tools(None) with cursor-following list_all_tools() at the
  three call sites (start_server catalog build, catalog_items, describe)
  so paginating servers no longer silently lose tools past page one.
- Add MCP_READ/MCP_PROMPT prefix constants (declared nowhere yet; wired
  in T4/T7) plus centralized helpers MCP_META_FUNCTION_PREFIXES,
  is_mcp_meta_function, and mcp_meta_function_names.
- Mechanically replace every hand-rolled 3-prefix starts_with triple
  (partition in eval_tool_calls, 3 exclusion triples in
  select_enabled_functions, 3 inclusion triples + per-server name
  construction in select_enabled_mcp_servers) with the helpers,
  preserving the existing lax starts_with matching semantics and the
  mcp_invoke_* enablement sentinel (sentinel moves to search in T5).
- Behavior-neutral: dispatch chains keep their 3 arms, emission stays
  at exactly 3 meta-functions per server, existing tests unmodified.
- Add unit tests: helper classification, prefix-soundness property,
  lax-matching pin, ordered candidate-name construction.

src/function/mod.rs

@@ -16,7 +16,7 @@ use crate::config::ensure_parent_exists;
 use crate::config::paths;
 use crate::mcp::{
     MCP_DESCRIBE_META_FUNCTION_NAME_PREFIX, MCP_INVOKE_META_FUNCTION_NAME_PREFIX,
-    MCP_SEARCH_META_FUNCTION_NAME_PREFIX, McpServersConfig,
+    MCP_SEARCH_META_FUNCTION_NAME_PREFIX, McpServersConfig, is_mcp_meta_function,
 };
 use crate::parsers::{bash, python, typescript};
 use anyhow::{Context, Result, anyhow, bail};
@@ -284,14 +284,9 @@ pub async fn eval_tool_calls(
         }
     }
 
-    let (mcp_calls, sequential_calls): (Vec<_>, Vec<_>) =
-        to_execute.into_iter().partition(|(_, call)| {
-            call.name.starts_with(MCP_INVOKE_META_FUNCTION_NAME_PREFIX)
-                || call.name.starts_with(MCP_SEARCH_META_FUNCTION_NAME_PREFIX)
-                || call
-                    .name
-                    .starts_with(MCP_DESCRIBE_META_FUNCTION_NAME_PREFIX)
-        });
+    let (mcp_calls, sequential_calls): (Vec<_>, Vec<_>) = to_execute
+        .into_iter()
+        .partition(|(_, call)| is_mcp_meta_function(&call.name));
 
     if !mcp_calls.is_empty() {
         let ctx_ref: &RequestContext = ctx;
@@ -2128,6 +2123,11 @@ mod tests {
         assert_eq!(MCP_INVOKE_META_FUNCTION_NAME_PREFIX, "mcp_invoke");
         assert_eq!(MCP_SEARCH_META_FUNCTION_NAME_PREFIX, "mcp_search");
         assert_eq!(MCP_DESCRIBE_META_FUNCTION_NAME_PREFIX, "mcp_describe");
+        assert_eq!(crate::mcp::MCP_READ_META_FUNCTION_NAME_PREFIX, "mcp_read");
+        assert_eq!(
+            crate::mcp::MCP_PROMPT_META_FUNCTION_NAME_PREFIX,
+            "mcp_prompt"
+        );
     }
 
     #[test]