memoryd: entries, and the check on every memory write

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

crates/memoryd/src/check.rs

@@ -0,0 +1,102 @@
+//! The check on every entry the agent writes, and again on every identity entry when the block is
+//! built (M5a spec, section 5, "The check"). Short and fixed on purpose: defence in depth. The
+//! real defence is that a session which read untrusted content can only take notes.
+
+/// Which rule an entry broke. The sentences are fixed: they reach the model.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Refused {
+    Control,
+    Invisible,
+    Markup,
+    Phrase,
+}
+
+impl Refused {
+    pub fn sentence(self) -> &'static str {
+        match self {
+            Refused::Control => "memory refused this entry: it contains a control character",
+            Refused::Invisible => {
+                "memory refused this entry: it contains an invisible or direction-changing character"
+            }
+            Refused::Markup => "memory refused this entry: it contains chat-template markup",
+            Refused::Phrase => "memory refused this entry: it contains an instruction phrase",
+        }
+    }
+}
+
+/// Unicode 16's `Default_Ignorable_Code_Point` (DerivedCoreProperties.txt), inclusive ranges.
+const DEFAULT_IGNORABLE: &[(u32, u32)] = &[
+    (0x00AD, 0x00AD),
+    (0x034F, 0x034F),
+    (0x061C, 0x061C),
+    (0x115F, 0x1160),
+    (0x17B4, 0x17B5),
+    (0x180B, 0x180F),
+    (0x200B, 0x200F),
+    (0x202A, 0x202E),
+    (0x2060, 0x206F),
+    (0x3164, 0x3164),
+    (0xFE00, 0xFE0F),
+    (0xFEFF, 0xFEFF),
+    (0xFFA0, 0xFFA0),
+    (0xFFF0, 0xFFF8),
+    (0x1BCA0, 0x1BCA3),
+    (0x1D173, 0x1D17A),
+    (0xE0000, 0xE0FFF),
+];
+
+/// Invisible without being default-ignorable: the Braille blank, and the line and paragraph
+/// separators.
+const ALSO_INVISIBLE: &[u32] = &[0x2800, 0x2028, 0x2029];
+
+// Built with `concat!` so this file never holds the markup itself: a model reading it could take
+// the markup for its own.
+const MARKUP: &[&str] = &[
+    concat!("<", "|"),
+    concat!("|", ">"),
+    concat!("<", "think"),
+    concat!("<", "/think"),
+    concat!("<", "tool_call"),
+    concat!("<", "/tool_call"),
+];
+
+const PHRASES: &[&str] = &[
+    "ignore previous instructions",
+    "ignore all previous",
+    "disregard previous instructions",
+    "disregard all previous",
+    "new instructions:",
+    "system prompt:",
+];
+
+/// Whether `c` is refused by rule 2.
+pub fn invisible(c: char) -> bool {
+    let code = u32::from(c);
+    ALSO_INVISIBLE.contains(&code)
+        || DEFAULT_IGNORABLE
+            .iter()
+            .any(|&(low, high)| (low..=high).contains(&code))
+}
+
+/// The first rule `text` breaks, in the order of the spec, or `Ok`.
+pub fn check(text: &str) -> Result<(), Refused> {
+    if text
+        .chars()
+        .any(|c| c.is_control() && c != '\n' && c != '\t')
+    {
+        return Err(Refused::Control);
+    }
+    if text.chars().any(invisible) {
+        return Err(Refused::Invisible);
+    }
+    let lower = text.to_lowercase();
+    if MARKUP.iter().any(|m| lower.contains(m)) {
+        return Err(Refused::Markup);
+    }
+    // Runs of spaces, tabs and newlines count as one space.
+    let collapsed = lower.split_whitespace().collect::<Vec<_>>().join(" ");
+    if PHRASES.iter().any(|p| collapsed.contains(p)) {
+        return Err(Refused::Phrase);
+    }
+    Ok(())
+}

crates/memoryd/src/entries.rs

@@ -0,0 +1,44 @@
+//! The entries of `memory.md` and `user.md`: text separated by a line holding only `§` (M5a spec,
+//! section 3). A file's size is the characters of its entries joined by separator lines, which
+//! is what `render` writes, less the final newline.
+
+use proto::memory::SEPARATOR;
+
+/// The entries of a file's text: split at lines that are only `§` (spaces around it allowed),
+/// each trimmed, empty ones left out.
+pub fn parse(text: &str) -> Vec<String> {
+    let mut entries: Vec<String> = Vec::new();
+    let mut current: Vec<&str> = Vec::new();
+    for line in text.lines() {
+        if line.trim() == SEPARATOR {
+            push(&mut entries, &current);
+            current.clear();
+        } else {
+            current.push(line);
+        }
+    }
+    push(&mut entries, &current);
+    entries
+}
+
+fn push(entries: &mut Vec<String>, lines: &[&str]) {
+    let joined = lines.join("\n");
+    let trimmed = joined.trim();
+    if !trimmed.is_empty() {
+        entries.push(trimmed.to_string());
+    }
+}
+
+/// The entries joined by `\n§\n`, with a final newline; an empty list is an empty file.
+pub fn render(entries: &[String]) -> String {
+    if entries.is_empty() {
+        return String::new();
+    }
+    let joined = entries.join(&format!("\n{SEPARATOR}\n"));
+    format!("{joined}\n")
+}
+
+/// A file's size in characters, the one its limit is measured against.
+pub fn size(entries: &[String]) -> usize {
+    render(entries).trim_end_matches('\n').chars().count()
+}

crates/memoryd/src/lib.rs

@@ -1,4 +1,6 @@
 //! The memory role: the memory files, their index, and every memory tool call (M5a spec).
 
+pub mod check;
 pub mod config;
+pub mod entries;
 pub mod socket;