refactor: single ACTIVITIES: block with bullet-level trim (T71.2)

Phase 2 T43 added a SECOND ACTIVITIES: block to render guest activity
separately from you+speaker. Two consecutive ACTIVITIES: headers can
read as a duplicate-section bug to the LLM and bloat the prompt.

Consolidate to a single ACTIVITIES: block whose body is composed from
up to three bullets (you, speaker, guest). The block itself is
MUST-tier (always renders); bullet-level trim drops bullets in the
order guest -> group node -> you -> other edges, with the speaker
bullet as the MUST-tier floor (the speaker's own current activity is
the load-bearing slice).

Implementation chose Option B from the polish plan: pre-truncate the
bullets list at trim time before _build_activity_block runs, rather
than introduce a granular tier mode in the trim machinery. Rationale
documented in code; the existing block-level trim ladder gains a
single new toggle (include_you_activity) and the SHOULD-tier
guest_activity_block is gone.

Tests:
- test_single_activities_block_with_three_bullets_when_3_entities:
  exactly one ACTIVITIES: header with all three entity bullets.
- test_tight_budget_drops_guest_activity_bullet_first: speaker bullet
  survives, guest bullet absent under tight budget.
- Existing test_assemble_with_tight_budget_drops_guest_activity_first
  still passes (asserts on bullet absence, not block-header absence).

chat/services/prompt.py

@@ -368,34 +368,57 @@ def assemble_narrative_prompt(
         addressee_name,
     )
 
-    # Activity for present entities. Core (MUST): you + speaker bot.
+    # Activity for present entities — single ACTIVITIES: block with up
-    # Phase 2 (SHOULD-tier): when a third party (guest) is present in
+    # to three bullets (you, speaker, guest). The block itself is
-    # the chat, append their activity in a separate block so it can be
+    # MUST-tier and survives all trims, but bullet-level trim drops
-    # trimmed independently under tight budget.
+    # bullets in the order guest -> you, keeping the speaker bullet
-    activities: list[dict] = []
+    # (the speaker's own current activity is the load-bearing slice).
+    #
+    # T71.2 chose Option B from the polish plan: pre-truncate the
+    # bullets list at trim time before _build_activity_block runs,
+    # rather than introducing a granular tier mode in the trim
+    # machinery. The single-block render avoids the dual-ACTIVITIES:
+    # header that Phase 2 T43 introduced (read by some LLMs as a
+    # duplicate-section bug).
+    you_activity: dict | None = None
     you_act = get_activity(conn, "you")
     if you_act is not None:
-        you_act = dict(you_act)
+        you_activity = dict(you_act)
-        you_act["_display_name"] = (you or {}).get("name") or "you"
+        you_activity["_display_name"] = (you or {}).get("name") or "you"
-        activities.append(you_act)
+
+    speaker_activity: dict | None = None
     bot_act = get_activity(conn, speaker_bot_id)
     if bot_act is not None:
-        bot_act = dict(bot_act)
+        speaker_activity = dict(bot_act)
-        bot_act["_display_name"] = bot["name"]
+        speaker_activity["_display_name"] = bot["name"]
-        activities.append(bot_act)
-    activity_block = _build_activity_block(activities)
 
-    # SHOULD-tier guest activity extension (Phase 2 / Task 43).
+    guest_activity: dict | None = None
-    guest_activity_block: str | None = None
     if guest_id is not None:
         guest_act = get_activity(conn, guest_id)
         if guest_act is not None:
-            guest_act = dict(guest_act)
+            guest_activity = dict(guest_act)
             guest_bot = get_bot(conn, guest_id)
-            guest_act["_display_name"] = (
+            guest_activity["_display_name"] = (
                 guest_bot["name"] if guest_bot else guest_id
             )
-            guest_activity_block = _build_activity_block([guest_act])
+
+    def _activity_block_for(
+        *, include_you: bool, include_guest: bool
+    ) -> str | None:
+        """Render the single ACTIVITIES: block with the requested bullets.
+
+        Speaker bullet is always included (it's the MUST-tier baseline);
+        ``you`` and ``guest`` bullets are toggled by the caller during
+        trim. Returns None when no bullets remain.
+        """
+        bullets: list[dict] = []
+        if include_you and you_activity is not None:
+            bullets.append(you_activity)
+        if speaker_activity is not None:
+            bullets.append(speaker_activity)
+        if include_guest and guest_activity is not None:
+            bullets.append(guest_activity)
+        return _build_activity_block(bullets)
 
     # SHOULD-tier group-node block (Phase 2 / Task 43): rendered only
     # when the group_node row is present AND it covers all three of
@@ -469,11 +492,18 @@ def assemble_narrative_prompt(
     last4 = dialogue_full[-4:] if dialogue_full else []
     must_dialogue_block = _build_dialogue_block(last4, earlier_summary=None)
 
+    # MUST-tier ACTIVITIES floor: the speaker bullet alone (you and
+    # guest bullets are dropped first under bullet-level trim before
+    # the block bottoms out at speaker-only).
+    must_activity_block = _activity_block_for(
+        include_you=False, include_guest=False
+    )
+
     must_blocks: list[str | None] = [
         speaker_identity,
         edge_to_addressee,
         scene_block,
-        activity_block,
+        must_activity_block,
         must_dialogue_block,
         closing,
     ]
@@ -498,6 +528,7 @@ def assemble_narrative_prompt(
         include_previous_scene: bool,
         include_memories_top_k: int,
         dialogue_keep: int,
+        include_you_activity: bool = True,
         include_guest_activity: bool = True,
         include_group_node: bool = True,
     ) -> tuple[str, int, list[dict]]:
@@ -520,13 +551,20 @@ def assemble_narrative_prompt(
             if include_previous_scene else None
         )
 
+        # Single ACTIVITIES: block, bullet-level trim (T71.2). Guest
+        # bullet drops first, then the you bullet; speaker bullet is the
+        # MUST-tier floor and always present when an activity row exists.
+        activity_block = _activity_block_for(
+            include_you=include_you_activity,
+            include_guest=include_guest_activity,
+        )
+
         body = _join_blocks([
             speaker_identity,
             edge_to_addressee,
             other_edges_block if include_other_edges else None,
             scene_block,
             activity_block,
-            guest_activity_block if include_guest_activity else None,
             group_node_block if include_group_node else None,
             prev_block,
             memories_block,
@@ -544,16 +582,18 @@ def assemble_narrative_prompt(
     nice_memories_k = min(4, len(memory_summaries))
     include_prev = previous_scene_summary is not None
     include_other = other_edges_block is not None
-    include_guest_activity = guest_activity_block is not None
+    include_you_activity = you_activity is not None
+    include_guest_activity = guest_activity is not None
     include_group_node = group_node_block is not None
 
     def _build(*, prev: bool, mem_k: int, dlg: int, other: bool,
-               guest_act: bool, group: bool) -> tuple[str, int]:
+               you_act: bool, guest_act: bool, group: bool) -> tuple[str, int]:
         body, total, _ = assemble(
             include_other_edges=other,
             include_previous_scene=prev,
             include_memories_top_k=mem_k,
             dialogue_keep=dlg,
+            include_you_activity=you_act,
             include_guest_activity=guest_act,
             include_group_node=group,
         )
@@ -561,8 +601,8 @@ def assemble_narrative_prompt(
 
     body, total = _build(
         prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-        other=include_other, guest_act=include_guest_activity,
+        other=include_other, you_act=include_you_activity,
-        group=include_group_node,
+        guest_act=include_guest_activity, group=include_group_node,
     )
 
     # If under soft, we're done.
@@ -575,8 +615,8 @@ def assemble_narrative_prompt(
         include_prev = False
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
         if total <= budget_soft:
             return _emit(body, user_turn_prose)
@@ -585,8 +625,8 @@ def assemble_narrative_prompt(
         nice_memories_k = 2
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
         if total <= budget_soft:
             return _emit(body, user_turn_prose)
@@ -595,8 +635,8 @@ def assemble_narrative_prompt(
         nice_dialogue_keep = baseline_keep
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
         if total <= budget_soft:
             return _emit(body, user_turn_prose)
@@ -606,35 +646,47 @@ def assemble_narrative_prompt(
         nice_memories_k = max(0, nice_memories_k - 1)
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
 
-    # Drop SHOULD-tier blocks in order: guest activity → group node →
+    # Drop SHOULD-tier extras in order:
-    # other edges. (Guest activity goes first per Task 43 spec — it's
+    #   1. guest activity bullet (T71.2: bullet-level trim within the
-    # the most expendable additive context.)
+    #      single ACTIVITIES: block — guest goes first per Task 43 spec)
+    #   2. group node block
+    #   3. you activity bullet (still SHOULD-tier; speaker bullet is the
+    #      MUST-tier floor and never dropped)
+    #   4. other edges
     if include_guest_activity and total > budget_hard:
         include_guest_activity = False
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
 
     if include_group_node and total > budget_hard:
         include_group_node = False
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
+        )
+
+    if include_you_activity and total > budget_hard:
+        include_you_activity = False
+        body, total = _build(
+            prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
+            other=include_other, you_act=include_you_activity,
+            guest_act=include_guest_activity, group=include_group_node,
         )
 
     if include_other and total > budget_hard:
         include_other = False
         body, total = _build(
             prev=include_prev, mem_k=nice_memories_k, dlg=nice_dialogue_keep,
-            other=include_other, guest_act=include_guest_activity,
+            other=include_other, you_act=include_you_activity,
-            group=include_group_node,
+            guest_act=include_guest_activity, group=include_group_node,
         )
 
     if total > budget_hard:

tests/test_prompt.py

@@ -514,6 +514,66 @@ def test_speaker_is_host_uses_host_witness_role(tmp_path, monkeypatch):
     assert captured["witness_role"] == "host"
 
 
+def test_single_activities_block_with_three_bullets_when_3_entities(tmp_path):
+    """T71.2: with you + host + guest present, the assembled prompt
+    contains exactly ONE ``ACTIVITIES:`` header and bullets for all
+    three entities (no duplicate header from the prior dual-block
+    rendering).
+    """
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        _seed_with_guest(conn)
+        msgs = assemble_narrative_prompt(
+            conn,
+            chat_id="chat_bot_a",
+            speaker_bot_id="bot_a",
+            recent_dialogue=[],
+            retrieved_memory_summaries=[],
+        )
+    body = msgs[0].content
+    # Exactly one ACTIVITIES: header.
+    assert body.count("ACTIVITIES:") == 1
+    # Bullets for all three entities (you=Sam, host=Aria, guest=Iris)
+    # — pin on the unique action verbs from the seed data.
+    assert "finishing emails" in body  # you bullet
+    assert "pretending to work" in body  # speaker (host) bullet
+    assert "smirking-distinctively" in body  # guest bullet
+
+
+def test_tight_budget_drops_guest_activity_bullet_first(tmp_path):
+    """T71.2: under tight budget the speaker bullet survives but the
+    guest activity bullet is the first ACTIVITIES: bullet to drop. The
+    block as a whole stays present (it's MUST-tier); only its body
+    contracts.
+    """
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        _seed_with_guest(conn)
+        dialogue = [
+            {"speaker": "you", "text": "line-16 hi there"},
+            {"speaker": "bot_a", "text": "line-17 hey"},
+            {"speaker": "you", "text": "line-18 quiet night"},
+            {"speaker": "bot_a", "text": "line-19 indeed"},
+        ]
+        msgs = assemble_narrative_prompt(
+            conn,
+            chat_id="chat_bot_a",
+            speaker_bot_id="bot_a",
+            recent_dialogue=dialogue,
+            retrieved_memory_summaries=[],
+            budget_soft=250,
+            budget_hard=340,
+        )
+    body = msgs[0].content
+    # Speaker bullet survives (MUST-tier floor).
+    assert "pretending to work" in body
+    assert "ACTIVITIES:" in body
+    # Guest bullet is dropped first under budget pressure.
+    assert "smirking-distinctively" not in body
+
+
 def test_assemble_with_tight_budget_drops_guest_activity_first(tmp_path):
     """Under tight budget MUST blocks survive but SHOULD-tier guest
     activity is dropped first."""