refactor(kernel): split ipc/memory/lib/thread by concern; trim comments

crates/platform/src/lib.rs

@@ -26,9 +26,7 @@ pub enum MapError {
 /// The kernel's contract with an architecture. The kernel decides what is
 /// mapped where; the platform only applies those decisions to hardware.
 pub trait Platform {
-    /// User mappings live in `[USER_VA_START, USER_VA_END)`. The platform
-    /// guarantees nothing else is mapped in that window in any address
-    /// space, so page tables covering it are private to each process.
+    /// User mappings live in `[USER_VA_START, USER_VA_END)`; nothing else is mapped there in any space.
     const USER_VA_START: usize;
     const USER_VA_END: usize;
 
@@ -50,9 +48,7 @@ pub trait Platform {
     ) -> Result<(), MapError>;
     /// Removes the mapping at `va` and flushes it from the TLB.
     fn unmap_page(&mut self, process: ProcessId, va: VirtualAddress);
-    /// The frame `va` is mapped to in `process`, if any. Only a lookup:
-    /// the kernel confirms every answer against its own frame table, so a
-    /// wrong answer can make the kernel refuse but never trust a frame.
+    /// The frame `va` maps to in `process`, if any. Advisory: the kernel confirms against its frame table.
     fn translate(&self, process: ProcessId, va: VirtualAddress) -> Option<PhysicalAddress>;
     /// Fills a frame with zeros before it is handed to a process.
     fn zero_frame(&mut self, pa: PhysicalAddress);