fix(api): report a dropped summary on the path get_context actually takes

The previous commit added this log to `_select_summary_for_context`, which
only runs when `get_context` is given a `peer_target`. The unified
`config_summary` fixtures set `observer_peer_id`, but the runner does not
forward it, so those requests take `summarizer.get_session_context` instead —
where the same outcome was reported at debug and stayed invisible.

That also retracts the representation-budget explanation for those fixtures.
Nothing is subtracted from the limit on this path: the summary gets 40% of the
requested tokens outright, so at `max_tokens: 4000` a 99-token summary has a
1600-token budget and fits comfortably. The reason it is still absent is not
the budget, and the log now says so on the right path.

Tests cover both paths, and record that the fixtures exercise the one without
a representation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/utils/summarizer.py

@@ -886,12 +886,21 @@ async def get_session_context(
             )
             messages_tokens = token_limit - latest_short_summary["token_count"]
             messages_start_id = latest_short_summary["message_id"]
+        elif latest_short_summary or latest_long_summary:
+            # A summary exists but does not fit the 40% allocation. The caller
+            # receives `summary: null`, which is indistinguishable from a session
+            # that has none, so this is reported rather than left at debug.
+            logger.info(
+                "Summary dropped: budget %s too small (short=%s, long=%s, limit=%s)",
+                summary_tokens_limit,
+                short_len or None,
+                long_len or None,
+                token_limit,
+            )
         else:
             logger.debug(
-                "No summary available for get_context call with token limit %s, returning empty string. Normal if brand-new session. long_summary_len: %s, short_summary_len: %s",
+                "No summary for get_context with token limit %s. Normal for a new session.",
                 token_limit,
-                long_len,
-                short_len,
             )
 
     # Get recent messages after summary

tests/routes/test_session_context_summary.py

@@ -1,10 +1,15 @@
 """How `get_context` decides whether to serve a session summary.
 
-The summary budget is 40% of what remains *after* the peer representation and
-card are subtracted, not 40% of the requested `tokens`. With an observer that
-has accumulated observations, a perfectly valid summary can be dropped and the
-caller just sees `summary: null` — which is what made DEV-2580's
-`config_summary_control` fixtures unsatisfiable.
+Two paths, and which one runs depends on `peer_target`:
+
+- Without it, `summarizer.get_session_context` gives the summary 40% of the
+  requested `tokens`.
+- With it, `sessions._select_summary_for_context` gives it 40% of what remains
+  *after* the peer representation and card are subtracted, so an observer with
+  many observations can starve a perfectly valid summary.
+
+Either way the caller just sees `summary: null`, indistinguishable from a
+session that has none, which is why both paths now log when they drop one.
 """
 
 from __future__ import annotations
@@ -27,8 +32,9 @@ from src.utils.summarizer import (
     _save_summary,  # pyright: ignore[reportPrivateUsage]
 )
 
-# Measured from CI run 33779689337: the 12-message config_summary fixtures
-# produce 12 explicit observations costing ~1176 tokens.
+# Measured from CI run 33779689337: 12 messages from one peer produce 12
+# explicit observations costing ~1176 tokens. Only the `peer_target` path pays
+# this, and the unified `config_summary` fixtures do not take that path.
 _FIXTURE_REPRESENTATION_TOKENS = 1176
 _SHORT_SUMMARY_CAP = 1000  # SUMMARY.MAX_TOKENS_SHORT default
 
@@ -56,11 +62,7 @@ def _stored_summary(token_count: int) -> Summary:
 
 
 def test_representation_can_exhaust_the_budget_entirely() -> None:
-    """`max_tokens: 400` against these fixtures leaves a negative budget.
-
-    No summary of any size could be served, so the original failure was never
-    about the summary being too large.
-    """
+    """A large representation can leave a negative budget on the observer path."""
     adjusted = 400 - _FIXTURE_REPRESENTATION_TOKENS
     assert adjusted < 0
     chosen, _, _ = _select_summary_for_context(
@@ -70,7 +72,7 @@ def test_representation_can_exhaust_the_budget_entirely() -> None:
 
 
 def test_a_conforming_summary_can_still_be_dropped() -> None:
-    """2500 leaves a 529-token budget — under `SUMMARY.MAX_TOKENS_SHORT`."""
+    """With that representation, 2500 leaves 529 — under `SUMMARY.MAX_TOKENS_SHORT`."""
     adjusted = 2500 - _FIXTURE_REPRESENTATION_TOKENS
     chosen, _, _ = _select_summary_for_context(
         _summary_schema(_SHORT_SUMMARY_CAP), None, adjusted, True
@@ -79,7 +81,7 @@ def test_a_conforming_summary_can_still_be_dropped() -> None:
 
 
 def test_fixture_limit_fits_any_conforming_summary() -> None:
-    """4000 is what the unified fixtures now request; it must leave room."""
+    """4000 leaves room even when a representation is subtracted."""
     adjusted = 4000 - _FIXTURE_REPRESENTATION_TOKENS
     assert int(adjusted * 0.4) >= _SHORT_SUMMARY_CAP
     chosen, _, _ = _select_summary_for_context(
@@ -137,3 +139,29 @@ async def test_a_stored_summary_is_served(
     data = client.get(url).json()
     assert data["summary"] is not None
     assert data["summary"]["token_count"] == 99
+
+
+async def test_fixture_path_ignores_representation_budget(
+    client: TestClient,
+    sample_data: tuple[Workspace, Peer],
+    db_session: AsyncSession,
+) -> None:
+    """Without `peer_target`, the summary gets 40% of `tokens` outright.
+
+    The unified `config_summary` fixtures set `observer_peer_id`, but the runner
+    does not forward it to `get_context`, so this is the path they exercise.
+    """
+    workspace, peer = sample_data
+    session_id = str(generate_nanoid())
+    client.post(
+        f"/v3/workspaces/{workspace.name}/sessions",
+        json={"id": session_id, "peers": {peer.name: {}}},
+    )
+    await _save_summary(db_session, _stored_summary(99), workspace.name, session_id)
+    await db_session.commit()
+
+    url = f"/v3/workspaces/{workspace.name}/sessions/{session_id}/context"
+    data = client.get(f"{url}?summary=true&tokens=2500").json()
+
+    assert data["summary"] is not None
+    assert data.get("peer_representation") is None