review classifier: plain table cells, no backslash escapes

docs/swarm/review-classifier.md

@@ -398,11 +398,14 @@ followed by the table when there is one. A comment neither approves nor
 blocks the merge: nine timeouts and one pass post a comment, not an
 approval.
 
-The controller flattens every cell to one line, with `|`, backticks, brackets, `<`, `>`,
+The controller flattens every cell to one line and backslash-escapes the
-`&`, `#` and other markup characters escaped, and a zero-width space after
+characters that could end the cell or start markup, math or raw HTML: `|`, `\`,
-each `@`, `#`, `!`, `://` and `www.`, so a model's `reason` can't break the
+backticks, `[`, `]`, `<`, `>`, `&`, `*`, `~`, `$`, and `_` except between two
-table, embed markup, mention anyone, reference an issue or PR, or carry a
+letters or digits (`ci_metrics.rs` stays as is). Ordinary punctuation such as
-link.
+`(`, `)` and `.` passes through unescaped. Each `@`, `#`, `!`, `://` and `www.`
+gets a zero-width space after it, with no backslash, so a model's `reason`
+can't break the table, embed markup, mention anyone, reference an issue or PR,
+or carry a link. The prompt asks the model for plain text in `reason`.
 
 ## Runtimes
 

swarm-controller/src/review_classifier/review.rs

@@ -842,26 +842,37 @@ fn overall_line(overall: Overall) -> &'static str {
     }
 }
 
-/// `text` as one table cell's inline text: on one line, with every character
+/// `text` as one table cell's inline text: on one line, with a backslash before
-/// that could end the cell, start markup, math (`$`) or raw HTML escaped, and a zero-width
+/// every character that could end the cell, start markup, math (`$`) or raw
-/// space after every `@`, `#`, `!`, `://` and `www.`, so it carries no live
+/// HTML, and a zero-width space after every `@`, `#`, `!`, `://` and `www.`, so
-/// mention, issue or PR reference, or link. The forge links issue and PR
+/// it carries no live mention, issue or PR reference, or link. The forge links
-/// numbers and bare URLs itself, so the escapes alone don't stop those.
+/// issue and PR numbers and bare URLs itself, so the escapes alone don't stop
+/// those; `#` and `!` get only the zero-width space.
+///
+/// `_` is escaped except between two alphanumerics, where it can't open
+/// emphasis (`ci_metrics.rs`). Other punctuation, such as `(`, `)`, `.` and
+/// `:`, passes through: it starts no markup inside a table cell, and the `[`
+/// that would make `(` a link target is escaped.
 fn cell(text: &str) -> String {
     let mut out = String::with_capacity(text.len());
     for (i, word) in text.split_whitespace().enumerate() {
         if i > 0 {
             out.push(' ');
         }
-        for c in word.chars() {
+        let chars: Vec<char> = word.chars().collect();
+        for (j, &c) in chars.iter().enumerate() {
             match c {
-                '\\' | '|' | '`' | '*' | '_' | '~' | '[' | ']' | '(' | ')' | '<' | '>' | '&'
+                '_' if j > 0
-                | '$' => {
+                    && chars[j - 1].is_alphanumeric()
+                    && chars.get(j + 1).is_some_and(|n| n.is_alphanumeric()) =>
+                {
+                    out.push(c);
+                }
+                '\\' | '|' | '`' | '*' | '_' | '~' | '[' | ']' | '<' | '>' | '&' | '$' => {
                     out.push('\\');
                     out.push(c);
                 }
                 '#' | '!' => {
-                    out.push('\\');
                     out.push(c);
                     out.push('\u{200b}');
                 }
@@ -1932,7 +1943,7 @@ mod tests {
             .count();
         assert_eq!(unescaped, 5, "{line}");
         assert!(
-            line.contains("\\!\u{200b}\\[\\]") && line.contains("\\<b\\>"),
+            line.contains("!\u{200b}\\[\\]") && line.contains("\\<b\\>"),
             "{line}"
         );
     }
@@ -1965,8 +1976,33 @@ mod tests {
         let text = cell("see https://evil.example/x, WWW.evil.example, #1, o/r#3 and !4");
         assert_eq!(
             text,
-            "see https://\u{200b}evil.example/x, WWW.\u{200b}evil.example, \\#\u{200b}1, \
+            "see https://\u{200b}evil.example/x, WWW.\u{200b}evil.example, #\u{200b}1, \
-             o/r\\#\u{200b}3 and \\!\u{200b}4"
+             o/r#\u{200b}3 and !\u{200b}4"
+        );
+    }
+
+    #[test]
+    fn a_plain_reason_reads_without_backslashes() {
+        assert_eq!(
+            cell("an added #[allow(clippy::foo)] in ci_metrics.rs (see main_loop_v2.rs)"),
+            "an added #\u{200b}\\[allow(clippy::foo)\\] in ci_metrics.rs (see main_loop_v2.rs)"
+        );
+    }
+
+    #[test]
+    fn an_underscore_escapes_unless_it_sits_between_alphanumerics() {
+        // Presence control: the edge underscores are escaped.
+        assert_eq!(
+            cell("_em_ __b__ a_ _b a__b snake_case"),
+            "\\_em\\_ \\_\\_b\\_\\_ a\\_ \\_b a\\_\\_b snake_case"
+        );
+    }
+
+    #[test]
+    fn a_reason_with_markup_characters_keeps_them_inert() {
+        assert_eq!(
+            cell(r"a\b `c` *d* ~e~ [f] <g> &h; i|j $k"),
+            r"a\\b \`c\` \*d\* \~e\~ \[f\] \<g\> \&h; i\|j \$k"
         );
     }
 

swarm-review-classifier/src/prompt.rs

@@ -26,7 +26,7 @@ Answer with exactly one JSON object and nothing else, no code fence:
 - \"no-match\": the answer is no.
 - \"not-applicable\": the question does not concern anything this pull request changes.
 - \"certainty\": how sure you are of that verdict, 0 to 100.
-- \"reason\": one or two sentences saying why.";
+- \"reason\": one or two sentences saying why, in plain text only: no markdown, no backticks, no backslash escapes.";
 
 /// The shared context: the PR's commits with their full messages, then its
 /// diff with lockfiles collapsed. Built once per run.