brokerd: recall and memory, decided under built-in grants

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/brokerd/src/grants.rs

@@ -26,6 +26,9 @@ pub struct LoadedGrant {
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct GrantSet {
     grants: Vec<LoadedGrant>,
+    /// The built-in grants of the memory tools, which every set from `from_grants` has. They are
+    /// not the owner's, so `grants` does not list them; matching sees them (`matchable`).
+    builtin: Vec<LoadedGrant>,
 }
 
 impl GrantSet {
@@ -49,17 +52,24 @@ impl GrantSet {
             check_grant(grant, &mut problems);
         }
 
-        if problems.is_empty() {
-            Ok(GrantSet { grants })
-        } else {
-            Err(problems)
+        if !problems.is_empty() {
+            return Err(problems);
         }
+        // The built-ins join only a set that passed: an owner's grant for a memory tool is a
+        // problem above, never a replacement.
+        let builtin = crate::builtin::grants().map_err(|problem| vec![problem])?;
+        Ok(GrantSet { grants, builtin })
     }
 
-    /// The grants in id order.
+    /// The owner's grants in id order.
     pub fn grants(&self) -> &[LoadedGrant] {
         &self.grants
     }
+
+    /// Every grant a call is matched against: the owner's, then the built-ins.
+    pub fn matchable(&self) -> impl Iterator<Item = &LoadedGrant> {
+        self.grants.iter().chain(self.builtin.iter())
+    }
 }
 
 /// A file name is a valid grant id when it is 1 to 64 characters of `a-z`, `0-9` and `-`.
@@ -220,7 +230,18 @@ fn check_grant(grant: &LoadedGrant, problems: &mut Vec<GrantProblem>) {
         );
     }
 
+    // Rule 2b: ids starting `builtin-` are the built-in grants'.
+    if id.starts_with(crate::builtin::RESERVED) {
+        push(
+            problems,
+            file.clone(),
+            None,
+            "grant ids starting builtin- are reserved",
+        );
+    }
+
     // Rule 3: the tool must be one of the four; an unknown tool skips rule 6 but not the others.
+    // The memory tools' grants are built in (M5a spec, section 8).
     match ToolName::parse(&grant.grant.tool) {
         None => push(
             problems,
@@ -228,6 +249,9 @@ fn check_grant(grant: &LoadedGrant, problems: &mut Vec<GrantProblem>) {
             None,
             "unknown tool; only read_file, write_file, shell and http_fetch",
         ),
+        Some(tool) if tool.is_memory() => {
+            push(problems, file.clone(), None, crate::builtin::BUILT_IN)
+        }
         Some(tool) => check_tool_constraints(tool, &file, inner, problems),
     }