fix(acp): emit per-section prompt blocks so observer counts every section (#1122)

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

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

@@ -0,0 +1,73 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { buildTranscript } from "./agentSessionTranscript.ts";
+
+const baseEvent = {
+  seq: 1,
+  timestamp: "2026-06-18T00:00:00Z",
+  kind: "acp_write",
+  agentIndex: 0,
+  channelId: "11111111-1111-1111-1111-111111111111",
+  sessionId: "sess-1",
+  turnId: "turn-1",
+};
+
+// --- stub-overflow vanish (pins the pre-existing degraded-frame behavior) ---
+
+test("buildTranscript drops a session/prompt turn whose frame was stubbed by the size trimmer", () => {
+  // When fit_observer_event_to_budget cannot shrink a frame below the cap it
+  // replaces the whole payload with {elided, originalBytes} (no `method`), so
+  // the method-keyed acp_write dispatch matches no arm and there is no terminal
+  // else: the turn produces ZERO transcript items. This is worse than a
+  // "1 section" collapse (the item vanishes entirely) and is pre-existing,
+  // outside the format_prompt seam. Pin it so a later change can't silently
+  // regress the vanish-vs-degrade behavior without updating this test.
+  const stubbed = {
+    ...baseEvent,
+    payload: {
+      elided: "acp_write payload too large",
+      originalBytes: 123456,
+    },
+  };
+
+  assert.deepEqual(buildTranscript([stubbed]), []);
+});
+
+// --- positive control: a well-formed multi-block prompt DOES render ---
+
+test("buildTranscript renders Prompt context + user message for a multi-block session/prompt frame", () => {
+  // Guards the vanish assertion above against a false pass from a broken
+  // import or dispatch: a normal per-section prompt frame must still produce a
+  // user message and a "Prompt context" metadata item.
+  const event = {
+    ...baseEvent,
+    payload: {
+      method: "session/prompt",
+      params: {
+        sessionId: "sess-1",
+        prompt: [
+          { type: "text", text: "[Agent Memory — core]\nremember this" },
+          { type: "text", text: "[Context]\nScope: thread" },
+          {
+            type: "text",
+            text: `[Buzz event: @mention]\nFrom: x (hex: ${"a".repeat(64)})\nContent: hello`,
+          },
+        ],
+      },
+    },
+  };
+
+  const items = buildTranscript([event]);
+  const titles = items.map((i) => i.title);
+  assert.ok(
+    items.some((i) => i.type === "metadata" && i.title === "Prompt context"),
+    `expected a Prompt context metadata item, got titles: ${titles.join(", ")}`,
+  );
+  const promptContext = items.find((i) => i.title === "Prompt context");
+  assert.deepEqual(
+    promptContext.sections.map((s) => s.title),
+    ["Agent Memory — core", "Context", "Buzz event: @mention"],
+    "every section header is counted",
+  );
+});