feat: surface base + persona system prompts in observer feed (#1103)

Signed-off-by: Will Pfleger <pfleger.will@gmail.com>
Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Co-authored-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@sprout-oss.stage.blox.sqprod.co>

crates/buzz-acp/src/pool.rs

@@ -435,12 +435,7 @@ async fn create_session_and_apply_model(
     // for the session/new request. Only sent when the agent declares protocol
     // version >= 2 (supports systemPrompt); legacy agents ignore it.
     let combined_system_prompt: Option<String> = if agent.protocol_version >= 2 {
-        match (ctx.base_prompt, ctx.system_prompt.as_deref()) {
-            (Some(bp), Some(sp)) => Some(format!("{}\n\n{sp}", bp.trim_end())),
-            (Some(bp), None) => Some(bp.trim_end().to_string()),
-            (None, Some(sp)) => Some(sp.to_string()),
-            (None, None) => None,
-        }
+        framed_system_prompt(ctx.base_prompt, ctx.system_prompt.as_deref())
     } else {
         None
     };
@@ -660,6 +655,26 @@ pub(crate) fn prepend_base_for_legacy(
     }
 }
 
+/// Frame the `session/new` `systemPrompt` so each present prompt carries its own
+/// header, keeping the base/persona boundary recoverable downstream.
+///
+/// The header framing matches the legacy per-turn path (`queue::base_section`
+/// for `[Base]`, `[System]\n{...}` for the persona) so the desktop observer can
+/// split the combined value into labeled sub-sections. Each prompt is wrapped
+/// only when present, so a persona-only agent yields `[System]\n{persona}`
+/// rather than an unlabeled blob that would be mislabeled as `[Base]`.
+fn framed_system_prompt(base_prompt: Option<&str>, system_prompt: Option<&str>) -> Option<String> {
+    match (base_prompt, system_prompt) {
+        (Some(bp), Some(sp)) => Some(format!(
+            "{}\n\n[System]\n{sp}",
+            crate::queue::base_section(bp)
+        )),
+        (Some(bp), None) => Some(crate::queue::base_section(bp)),
+        (None, Some(sp)) => Some(format!("[System]\n{sp}")),
+        (None, None) => None,
+    }
+}
+
 /// Core async function spawned for each prompt.
 ///
 /// Lifecycle:
@@ -2336,6 +2351,36 @@ mod tests {
         assert_eq!(composed, "hello channel");
     }
 
+    // ── framed_system_prompt tests ───────────────────────────────────────────
+    // Pin the session/new systemPrompt framing: each present prompt carries its
+    // own header so the desktop observer can split into labeled sub-sections.
+
+    #[test]
+    fn test_framed_system_prompt_both_present_carries_both_headers() {
+        let framed = framed_system_prompt(Some("base text"), Some("persona text"))
+            .expect("both present yields Some");
+        assert_eq!(framed, "[Base]\nbase text\n\n[System]\npersona text");
+    }
+
+    #[test]
+    fn test_framed_system_prompt_base_only_labels_base() {
+        let framed = framed_system_prompt(Some("base text"), None).expect("base yields Some");
+        assert_eq!(framed, "[Base]\nbase text");
+    }
+
+    #[test]
+    fn test_framed_system_prompt_persona_only_labels_system() {
+        // A bare persona would be mislabeled "Base" downstream — it must carry
+        // its own [System] header even when no base prompt exists.
+        let framed = framed_system_prompt(None, Some("persona text")).expect("persona yields Some");
+        assert_eq!(framed, "[System]\npersona text");
+    }
+
+    #[test]
+    fn test_framed_system_prompt_neither_is_none() {
+        assert!(framed_system_prompt(None, None).is_none());
+    }
+
     // ── parse_thread_response tests ──────────────────────────────────────────
 
     #[test]

desktop/src/features/agents/ui/agentSessionTranscript.ts

@@ -20,6 +20,7 @@ import {
   extractToolIdentity,
   extractToolResult,
   parsePromptText,
+  parseSystemPromptSections,
 } from "./agentSessionTranscriptHelpers";
 
 export { describeRawEvent } from "./agentSessionTranscriptHelpers";
@@ -335,6 +336,27 @@ export function processTranscriptEvent(
           );
         }
       }
+    } else if (event.kind === "acp_write" && method === "session/new") {
+      // The base + persona prompts ride session/new's systemPrompt, framed by
+      // the harness as [Base]/[System]. Surface them as one "System prompt" item
+      // keyed per channel-session — the frame carries no session id (it predates
+      // session creation), and session/new fires once per channel-session, so a
+      // re-created session correctly replaces the prior item.
+      const params = asRecord(payload.params);
+      const systemPrompt = asString(params.systemPrompt);
+      if (systemPrompt) {
+        const sections = parseSystemPromptSections(systemPrompt);
+        if (sections.length > 0) {
+          upsertMetadata(
+            d,
+            `system-prompt:${ch}`,
+            "System prompt",
+            sections,
+            event.timestamp,
+            channelId,
+          );
+        }
+      }
     } else if (event.kind === "acp_read" && method === "session/update") {
       const params = asRecord(payload.params);
       const update = asRecord(params.update);

desktop/src/features/agents/ui/agentSessionTranscriptHelpers.test.mjs

@@ -4,6 +4,7 @@ import test from "node:test";
 import {
   extractPromptText,
   parsePromptText,
+  parseSystemPromptSections,
 } from "./agentSessionTranscriptHelpers.ts";
 
 const HEX = "a".repeat(64);
@@ -122,3 +123,51 @@ test("extractPromptText returns empty string when prompt is missing or not an ar
   assert.equal(extractPromptText({}), "");
   assert.equal(extractPromptText({ params: { prompt: "nope" } }), "");
 });
+
+// --- parseSystemPromptSections: deterministic Base/System split ---
+
+test("parseSystemPromptSections splits both prompts into Base and System", () => {
+  const framed = "[Base]\nbase text\n\n[System]\npersona text";
+  const sections = parseSystemPromptSections(framed);
+  assert.deepEqual(sections, [
+    { title: "Base", body: "base text" },
+    { title: "System", body: "persona text" },
+  ]);
+});
+
+test("parseSystemPromptSections yields one Base section for a base-only frame", () => {
+  const sections = parseSystemPromptSections("[Base]\nbase text");
+  assert.deepEqual(sections, [{ title: "Base", body: "base text" }]);
+});
+
+test("parseSystemPromptSections yields one System section for a persona-only frame", () => {
+  const sections = parseSystemPromptSections("[System]\npersona text");
+  assert.deepEqual(sections, [{ title: "System", body: "persona text" }]);
+});
+
+test("parseSystemPromptSections keeps embedded bracket lines literal in bodies", () => {
+  // A persona that itself contains a [Context]-like line must NOT split into a
+  // spurious sub-section — the body is read literally after the first boundary.
+  const framed = "[Base]\nbase\n\n[System]\nrule one\n[Context]\nrule two";
+  const sections = parseSystemPromptSections(framed);
+  assert.deepEqual(sections, [
+    { title: "Base", body: "base" },
+    { title: "System", body: "rule one\n[Context]\nrule two" },
+  ]);
+});
+
+test("parseSystemPromptSections degrades to a labeled Base when [System] header is elided", () => {
+  // Oversize trim can drop the [System] header mid-string. Without a boundary
+  // the whole value stays under a correctly-labeled Base — no missing label,
+  // no inflated count, just a truncated body.
+  const elided = "[Base]\nbase text …[elided 900000 bytes]… persona tail";
+  const sections = parseSystemPromptSections(elided);
+  assert.deepEqual(sections, [
+    { title: "Base", body: "base text …[elided 900000 bytes]… persona tail" },
+  ]);
+});
+
+test("parseSystemPromptSections returns no sections for empty input", () => {
+  assert.deepEqual(parseSystemPromptSections(""), []);
+  assert.deepEqual(parseSystemPromptSections("   "), []);
+});

desktop/src/features/agents/ui/agentSessionTranscriptHelpers.ts

@@ -49,6 +49,46 @@ export function parsePromptText(text: string): {
   };
 }
 
+/**
+ * Split the framed `session/new` `systemPrompt` into its `Base`/`System`
+ * sub-sections deterministically.
+ *
+ * The harness frames the value as `[Base]\n{base}\n\n[System]\n{persona}`, with
+ * either prompt omitted when absent: base-only is `[Base]\n{base}`, persona-only
+ * is `[System]\n{persona}`. We partition on the FIRST `\n[System]\n` boundary and
+ * read each labeled body literally. Unlike the generic `parsePromptSections`,
+ * embedded `[...]` lines inside a body never start a new section — so a persona
+ * containing a bracketed line, or a mid-string-elided header on an oversize
+ * prompt, can never drop a label or inflate the section count.
+ */
+export function parseSystemPromptSections(
+  systemPrompt: string,
+): PromptSection[] {
+  const sections: PromptSection[] = [];
+
+  // Persona-only frame: no [Base], starts directly with [System].
+  if (systemPrompt.startsWith("[System]\n")) {
+    const body = systemPrompt.slice("[System]\n".length).trim();
+    if (body) sections.push({ title: "System", body });
+    return sections;
+  }
+
+  // Otherwise the head (up to the first [System] boundary, or the whole string)
+  // is the [Base] body.
+  const marker = "\n[System]\n";
+  const at = systemPrompt.indexOf(marker);
+  const head = at === -1 ? systemPrompt : systemPrompt.slice(0, at);
+  const baseBody = head.replace(/^\[Base]\n/, "").trim();
+  if (baseBody) sections.push({ title: "Base", body: baseBody });
+
+  if (at !== -1) {
+    const systemBody = systemPrompt.slice(at + marker.length).trim();
+    sections.push({ title: "System", body: systemBody });
+  }
+
+  return sections;
+}
+
 function parsePromptSections(text: string): PromptSection[] {
   const sections: PromptSection[] = [];
   let current: PromptSection | null = null;