docs(developer-guide): fix mermaid syntax error in Flow 19 diagram

Mermaid parses ";" as a statement separator, so the semicolon in the
last message label of Flow 19's sequence diagram truncated the statement
and the diagram rendered as "Syntax error in text" on readthedocs.
Replaced with a comma, and the docs gate now rejects semicolons inside
mermaid blocks; it failed on the offending line before the fix.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: pliablepixels

app/src/tests/agents-contracts.test.ts

@@ -184,6 +184,27 @@ describe('developer docs cite symbols, not line numbers', () => {
     }
     expect(offenders, `line-number citations found:\n${offenders.join('\n')}`).toEqual([]);
   });
+
+  it('no mermaid block contains a semicolon', () => {
+    // Mermaid parses ";" as a statement separator, so a semicolon inside a
+    // message label truncates the statement and the whole diagram renders as
+    // "Syntax error in text" on readthedocs.
+    const offenders: string[] = [];
+    const guideDir = path.join(repoRoot, 'docs/developer-guide');
+    for (const file of fs.readdirSync(guideDir).filter((f) => f.endsWith('.rst'))) {
+      const lines = fs.readFileSync(path.join(guideDir, file), 'utf8').split('\n');
+      let inMermaid = false;
+      lines.forEach((line, i) => {
+        if (/^\s*\.\. mermaid::/.test(line)) {
+          inMermaid = true;
+          return;
+        }
+        if (inMermaid && line.trim() && !/^\s/.test(line)) inMermaid = false;
+        if (inMermaid && line.includes(';')) offenders.push(`${file}:${i + 1} ${line.trim()}`);
+      });
+    }
+    expect(offenders, `semicolons inside mermaid blocks:\n${offenders.join('\n')}`).toEqual([]);
+  });
 });
 
 describe('developer docs reference valid rule IDs', () => {

docs/developer-guide/call-flows.rst

@@ -2096,7 +2096,7 @@ tool and ``ToolDefinition`` cannot express one), never a runtime decision.
        ZM-->>Tool: rows
        Agent->>Agent: grounding and live-data checks
        Agent-->>Panel: this turn's messages
-       Panel->>Panel: render; append context boundary if nearly full
+       Panel->>Panel: render, append context boundary if nearly full
 
 #. **The `?` key opens the assistant window.** ``components/KeyboardShortcuts.tsx``'s
    ``onKeyDown`` treats ``?`` as dual-purpose: when the assistant is enabled