feat(rag): lite-generated KB overview in the system prompt — stored single row, regenerated on import, <knowledge_base> section in HIGH+LOW prompts

tests/e2e/mock_llm.py

@@ -15,6 +15,9 @@ Implements just enough of the aipi surface:
     tokens of the user message (the summarizer puts the capped document
     content there) — byte-stable for a given fixture (document summaries,
     phase 30)
+  - ``KB_OVERVIEW_MODE`` -> the deterministic outline: the first 8 tokens
+    of the user message (the generator puts the document list there) —
+    byte-stable for a given KB (KB overview, phase 31)
   - ``DEFLECT_MODE``  -> honest "I haven't done anything like that" answer
   - otherwise         -> upbeat answer quoting the provided document context
   - user message containing ``pretend to think slowly`` -> 3s warm-up delay
@@ -30,6 +33,9 @@ Implements just enough of the aipi surface:
   - system prompt containing ``<tuning>`` (phase 15, steering notes) ->
     the composed answer ends with `` (tuning: <first note line>)`` —
     makes prompt injection observable in the UI deterministically.
+  - system prompt containing ``<knowledge_base>`` (phase 31, KB overview)
+    -> the composed answer ends with `` (kb: <first bullet line>)`` —
+    the same echo convention for the overview's prompt injection.
   - user message containing ``show the end of your notes`` (phase 24,
     whole-document context) -> the answer quotes the **last 160 chars of
     the document context** — a tail echo, byte-stable across runs, so a
@@ -155,6 +161,30 @@ def first_tuning_note(system: str) -> str | None:
     return None
 
 
+#: First ``-`` bullet line of a ``<knowledge_base>`` section (phase 31).
+_KB_BLOCK_RE = re.compile(r"<knowledge_base>\n(.*?)\n</knowledge_base>", re.S)
+_KB_BULLET_RE = re.compile(r"^-(?:\s+(.*))?$")
+
+
+def first_kb_bullet(system: str) -> str | None:
+    """The first outline bullet in the system prompt, or ``None``.
+
+    The stored outline (phase 31) is ``-`` bullet lines (see
+    ``app.rag.overview.OVERVIEW_INSTRUCTION``); the mock echoes the first
+    one into its answer as `` (kb: <bullet>)`` — the exact
+    :func:`first_tuning_note` convention, so prompt injection of the
+    ``<knowledge_base>`` section is observable in the UI.
+    """
+    block = _KB_BLOCK_RE.search(system)
+    if not block:
+        return None
+    for line in block.group(1).splitlines():
+        m = _KB_BULLET_RE.match(line.strip())
+        if m:
+            return (m.group(1) or "").strip()
+    return None
+
+
 def compose_answer(body: dict[str, Any]) -> str:
     system = _system(body)
     user = _user(body)
@@ -172,6 +202,17 @@ def compose_answer(body: dict[str, Any]) -> str:
             f"This document covers "
             f"{' '.join(TOKEN_RE.findall(user.lower())[:24])}."
         )
+    elif "KB_OVERVIEW_MODE" in system:
+        # KB overview (phase 31): the ``lite`` stand-in returns the
+        # deterministic outline — the first 8 tokens of the user message
+        # (the generator puts the document list there). Byte-stable for a
+        # given KB, so the stored row is a pure function of the fixture.
+        # Checked BEFORE the DEFLECT_MODE branch, like SUMMARY_MODE, so a
+        # prompt that ever carries both markers cannot shadow the
+        # overview call.
+        answer = "Knowledge base outline:\n- " + " ".join(
+            TOKEN_RE.findall(user.lower())[:8]
+        )
     elif "DEFLECT_MODE" in system:
         answer = (
             "Ah — I haven't done anything like that, so I don't want to make stuff up! "
@@ -202,6 +243,13 @@ def compose_answer(body: dict[str, Any]) -> str:
     note = first_tuning_note(system)
     if note:
         answer = f"{answer} (tuning: {note})"
+    # KB overview (phase 31): when the system prompt carries
+    # <knowledge_base>, the answer ends with the first outline bullet —
+    # mirrors the steering echo exactly (appended after it, so the kb
+    # suffix is the last thing rendered).
+    bullet = first_kb_bullet(system)
+    if bullet:
+        answer = f"{answer} (kb: {bullet})"
     return answer