fix(analyze): drop transcript timestamp headings from LLM prompt

render_prompt prefixed each recording with a '## <recorded_at>' heading.
No system prompt consumes that timestamp, and the LLM occasionally echoed
it into the final document as a heading. Join recordings with the bare
'\n\n---\n\n' separator instead; chronology is carried by recording order.

Adds a regression test pinning that no RFC3339 timestamp or '##' reaches
the prompt.

closes #8

server/src/analyze/prompt.rs

@@ -4,6 +4,13 @@ use super::AnalysisInput;
 /// JSON input. Recordings with blank text are skipped — they carry no signal
 /// for the LLM and only add noise. Chronological order is taken as given;
 /// callers must sort `recordings` before passing in (the handler does).
+///
+/// Recordings are concatenated with a `\n\n---\n\n` separator and nothing
+/// else: no per-recording heading or timestamp. The `recorded_at` value is
+/// deliberately omitted — no system prompt consumes it, and feeding it as a
+/// Markdown heading caused the LLM to occasionally echo transcript timestamps
+/// into the final document (issue #8). Chronology is carried by the order of
+/// `recordings` alone.
 pub fn render_prompt(input: &AnalysisInput) -> String {
     let mut out = String::new();
     let mut first = true;
@@ -15,9 +22,6 @@ pub fn render_prompt(input: &AnalysisInput) -> String {
             out.push_str("\n\n---\n\n");
         }
         first = false;
-        out.push_str("## ");
-        out.push_str(&r.recorded_at);
-        out.push_str("\n\n");
         out.push_str(r.text.trim());
     }
     out
@@ -48,7 +52,7 @@ mod tests {
             "2026-04-15T10:32:00Z",
             "Patient klagt über Knie.",
         )]));
-        assert_eq!(out, "## 2026-04-15T10:32:00Z\n\nPatient klagt über Knie.");
+        assert_eq!(out, "Patient klagt über Knie.");
     }
 
     #[test]
@@ -57,9 +61,20 @@ mod tests {
             ("2026-04-15T10:32:00Z", "Erste Aufnahme."),
             ("2026-04-15T10:38:15Z", "Zweite Aufnahme."),
         ]));
-        assert!(out.contains("\n\n---\n\n"));
-        assert!(out.starts_with("## 2026-04-15T10:32:00Z"));
-        assert!(out.contains("## 2026-04-15T10:38:15Z"));
+        assert_eq!(out, "Erste Aufnahme.\n\n---\n\nZweite Aufnahme.");
+    }
+
+    /// Regression guard for issue #8: transcript timestamps must never reach
+    /// the LLM prompt — they leaked into the final document as headings.
+    #[test]
+    fn omits_recording_timestamps() {
+        let out = render_prompt(&mk(vec![
+            ("2026-04-15T10:32:00Z", "Erste Aufnahme."),
+            ("2026-04-15T10:38:15Z", "Zweite Aufnahme."),
+        ]));
+        assert!(!out.contains("2026-04-15T10:32:00Z"));
+        assert!(!out.contains("2026-04-15T10:38:15Z"));
+        assert!(!out.contains("##"));
     }
 
     #[test]