fix(workspace): keep peers visible in coordinator prompt when agent_card is null

Bug: a Design Director coordinator with 6 freshly-created worker peers
rendered an empty `## Your Peers` section in its system prompt — the
hosting registry endpoint correctly returned all 6 peers, but
`summarize_peer_cards()` silently dropped every entry whose
`agent_card` column was null (the default until A2A discovery has
run end-to-end against the worker). The coordinator then refused to
delegate any task because "no peers exist".

Fix: fall back to the registry row's `name` and `role` columns when
`agent_card` is missing, malformed, or wrong-typed, instead of
skipping the peer. The registry endpoint
(`workspace-server/internal/handlers/discovery.go:queryPeerMaps`) has
always returned both fields — they were just being thrown away on
the consumer side. `build_peer_section()` now renders `Role: …` when
the agent_card-derived skill list is empty so the coordinator's
prompt still has something concrete to delegate against.

Also hoists `import json` out of the per-peer loop body to module
level (was previously imported once per iteration).

Tests: new `test_shared_runtime_peer_summary.py` pins all four
fallback cases (null / malformed string / wrong type / null + no
DB name) plus the agent-card-present happy path and the mixed-list
case the coordinator actually consumes. First peer-summary test
coverage `shared_runtime.py` has had — no prior tests existed.

Refs: 2026-04-27 Design Director discovery report from infra team.

workspace/shared_runtime.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 from typing import Any
 
 from a2a.server.agent_execution import RequestContext
@@ -89,33 +90,46 @@ def append_peer_guidance(
 
 
 def summarize_peer_cards(peers: list[dict[str, Any]]) -> list[dict[str, Any]]:
-    """Return compact peer metadata for prompt rendering."""
+    """Return compact peer metadata for prompt rendering.
+
+    Falls back to the registry row's `name` and `role` when `agent_card` is
+    null or unparseable so peers stay visible to delegators even before
+    their A2A discovery roundtrip has populated a card. Without this
+    fallback a coordinator-tier workspace with N freshly-created worker
+    peers would render an empty `## Your Peers` section and refuse to
+    delegate (the regression behind the 2026-04-27 Design Director
+    discovery bug).
+    """
     summaries: list[dict[str, Any]] = []
     for peer in peers:
         agent_card = peer.get("agent_card")
-        if not agent_card:
-            continue
         if isinstance(agent_card, str):
             try:
-                import json
-
                 agent_card = json.loads(agent_card)
             except Exception:
-                continue
+                agent_card = None
         if not isinstance(agent_card, dict):
-            continue
+            agent_card = None
+
+        if agent_card:
+            skills_raw = agent_card.get("skills") or []
+            skills = [
+                s.get("name", s.get("id", ""))
+                for s in skills_raw
+                if isinstance(s, dict)
+            ]
+            name = agent_card.get("name") or peer.get("name") or "Unknown"
+        else:
+            skills = []
+            name = peer.get("name") or "Unknown"
 
-        skills = agent_card.get("skills", [])
         summaries.append(
             {
                 "id": peer.get("id", "unknown"),
-                "name": agent_card.get("name", peer.get("name", "Unknown")),
+                "name": name,
+                "role": peer.get("role") or "",
                 "status": peer.get("status", "unknown"),
-                "skills": [
-                    s.get("name", s.get("id", ""))
-                    for s in skills
-                    if isinstance(s, dict)
-                ],
+                "skills": skills,
             }
         )
     return summaries
@@ -140,6 +154,8 @@ def build_peer_section(
         parts.append(f"- **{peer['name']}** (id: `{peer['id']}`, status: {peer['status']})")
         if peer["skills"]:
             parts.append(f"  Skills: {', '.join(peer['skills'])}")
+        elif peer.get("role"):
+            parts.append(f"  Role: {peer['role']}")
         parts.append("")
     parts.append(instruction)
     return "\n".join(parts)

workspace/tests/test_shared_runtime_peer_summary.py

@@ -0,0 +1,111 @@
+"""Pin peer-summary fallback when agent_card is missing.
+
+Regresses the 2026-04-27 Design Director discovery bug:
+`summarize_peer_cards()` previously skipped any peer whose `agent_card`
+was null or unparseable, so a coordinator with freshly-created workers
+saw an empty `## Your Peers` section in its system prompt and refused
+to delegate. The registry endpoint already returns DB `name` + `role`
+on every row regardless of agent_card state — falling back to those
+keeps peers visible while A2A discovery catches up.
+"""
+
+from __future__ import annotations
+
+from shared_runtime import build_peer_section, summarize_peer_cards
+
+
+def _peer(**overrides):
+    base = {
+        "id": "ws-1",
+        "name": "DB Name",
+        "role": "DB Role",
+        "status": "active",
+        "agent_card": None,
+    }
+    base.update(overrides)
+    return base
+
+
+def test_summarize_includes_peer_with_null_agent_card_using_db_fields():
+    summaries = summarize_peer_cards([_peer()])
+    assert len(summaries) == 1
+    assert summaries[0]["id"] == "ws-1"
+    assert summaries[0]["name"] == "DB Name"
+    assert summaries[0]["role"] == "DB Role"
+    assert summaries[0]["status"] == "active"
+    assert summaries[0]["skills"] == []
+
+
+def test_summarize_prefers_agent_card_name_over_db_name():
+    peer = _peer(
+        agent_card={"name": "Card Name", "skills": [{"name": "draft-spec"}]}
+    )
+    summaries = summarize_peer_cards([peer])
+    assert summaries[0]["name"] == "Card Name"
+    assert summaries[0]["skills"] == ["draft-spec"]
+    assert summaries[0]["role"] == "DB Role"
+
+
+def test_summarize_handles_string_agent_card_json():
+    peer = _peer(agent_card='{"name": "JSON Name", "skills": []}')
+    summaries = summarize_peer_cards([peer])
+    assert summaries[0]["name"] == "JSON Name"
+
+
+def test_summarize_falls_back_when_agent_card_string_is_malformed():
+    peer = _peer(agent_card="not-valid-json")
+    summaries = summarize_peer_cards([peer])
+    assert len(summaries) == 1
+    assert summaries[0]["name"] == "DB Name"
+    assert summaries[0]["role"] == "DB Role"
+    assert summaries[0]["skills"] == []
+
+
+def test_summarize_falls_back_when_agent_card_is_wrong_type():
+    peer = _peer(agent_card=42)
+    summaries = summarize_peer_cards([peer])
+    assert len(summaries) == 1
+    assert summaries[0]["name"] == "DB Name"
+
+
+def test_summarize_handles_missing_role_and_name_with_unknown_default():
+    peer = {"id": "ws-2", "status": "active", "agent_card": None}
+    summaries = summarize_peer_cards([peer])
+    assert summaries[0]["name"] == "Unknown"
+    assert summaries[0]["role"] == ""
+
+
+def test_build_peer_section_renders_role_when_skills_empty():
+    section = build_peer_section([_peer()])
+    assert "## Your Peers" in section
+    assert "**DB Name**" in section
+    assert "Role: DB Role" in section
+    assert "Skills:" not in section
+
+
+def test_build_peer_section_prefers_skills_over_role_when_card_present():
+    peer = _peer(
+        agent_card={"name": "Worker", "skills": [{"name": "design"}, {"name": "review"}]}
+    )
+    section = build_peer_section([peer])
+    assert "Skills: design, review" in section
+    assert "Role: DB Role" not in section
+
+
+def test_build_peer_section_mixed_peers():
+    peers = [
+        _peer(id="ws-a"),
+        _peer(
+            id="ws-b",
+            agent_card={"name": "Card B", "skills": [{"name": "build"}]},
+        ),
+    ]
+    section = build_peer_section(peers)
+    assert "id: `ws-a`" in section
+    assert "id: `ws-b`" in section
+    assert "Role: DB Role" in section
+    assert "Skills: build" in section
+
+
+def test_build_peer_section_empty_when_no_peers():
+    assert build_peer_section([]) == ""