feat(a2a-client): surface 410 Gone as 'removed' error so callers can re-onboard (#2429)

Follow-up A to PR #2449 — that PR taught the platform to return 410
Gone for status='removed' workspaces; this PR teaches get_workspace_info
to consume that signal.

Before: every non-200 collapsed into {"error": "not found"}, which
made the 2026-04-30 incident impossible to diagnose — the operator
KNEW the workspace_id existed (they'd just registered it), but the
runtime kept reporting "not found" for a deleted-but-not-purged row.

After: 410 produces a distinct {"error": "removed", "id", "removed_at",
"hint"} dict so callers (heartbeat-loop, channel bridge, dashboard
tools) can surface "your workspace was deleted, re-onboard" instead
of "not found". Falls back to a default hint if the platform body
isn't parseable so the actionable signal doesn't depend on body
shape parity.

Two new tests:
  - TestGetWorkspaceInfo.test_410_returns_removed_with_hint
  - TestGetWorkspaceInfo.test_410_with_unparseable_body_falls_back_to_default_hint

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace/a2a_client.py

@@ -340,7 +340,14 @@ async def get_peers() -> list[dict]:
 
 
 async def get_workspace_info() -> dict:
-    """Get this workspace's info from the platform."""
+    """Get this workspace's info from the platform.
+
+    Distinguishes three failure shapes so callers can handle them
+    distinctly (#2429):
+      - 410 Gone        → workspace was deleted; re-onboard required
+      - 404 / other     → workspace never existed (or transient)
+      - exception       → network / auth failure
+    """
     async with httpx.AsyncClient(timeout=10.0) as client:
         try:
             resp = await client.get(
@@ -349,6 +356,27 @@ async def get_workspace_info() -> dict:
             )
             if resp.status_code == 200:
                 return resp.json()
+            if resp.status_code == 410:
+                # #2429: platform returns 410 when status='removed'.
+                # Surface "removed" + the actionable hint so callers
+                # can prompt re-onboard instead of falling through to
+                # "not found" — which made the 2026-04-30 incident
+                # impossible to diagnose ("workspace not found" with
+                # a workspace_id we KNEW we'd just registered).
+                try:
+                    body = resp.json()
+                except Exception:
+                    body = {}
+                return {
+                    "error": "removed",
+                    "id": body.get("id", WORKSPACE_ID),
+                    "removed_at": body.get("removed_at"),
+                    "hint": body.get(
+                        "hint",
+                        "Workspace was deleted on the platform. "
+                        "Regenerate workspace + token from the canvas → Tokens tab.",
+                    ),
+                }
             return {"error": "not found"}
         except Exception as e:
             return {"error": str(e)}

workspace/tests/test_a2a_client.py

@@ -819,6 +819,48 @@ class TestGetWorkspaceInfo:
 
         assert result == {"error": "not found"}
 
+    async def test_410_returns_removed_with_hint(self):
+        """410 Gone (#2429) → distinct error 'removed' so callers can
+        prompt re-onboard instead of falling through to 'not found'.
+        Body shape passes through removed_at + the platform hint."""
+        import a2a_client
+
+        body = {
+            "error": "workspace removed",
+            "id": "ws-deleted-uuid",
+            "removed_at": "2026-04-30T12:00:00Z",
+            "hint": "Regenerate workspace + token from the canvas → Tokens tab",
+        }
+        resp = _make_response(410, body)
+        mock_client = _make_mock_client(get_resp=resp)
+
+        with patch("a2a_client.httpx.AsyncClient", return_value=mock_client):
+            result = await a2a_client.get_workspace_info()
+
+        assert result["error"] == "removed"
+        assert result["id"] == "ws-deleted-uuid"
+        assert result["removed_at"] == "2026-04-30T12:00:00Z"
+        assert "Regenerate" in result["hint"]
+
+    async def test_410_with_unparseable_body_falls_back_to_default_hint(self):
+        """If the platform's 410 body isn't JSON for some reason, the
+        default hint still surfaces — the actionable signal must not
+        depend on body shape parity with the platform."""
+        import a2a_client
+
+        resp = MagicMock()
+        resp.status_code = 410
+        resp.json = MagicMock(side_effect=ValueError("not json"))
+        mock_client = _make_mock_client(get_resp=resp)
+
+        with patch("a2a_client.httpx.AsyncClient", return_value=mock_client):
+            result = await a2a_client.get_workspace_info()
+
+        assert result["error"] == "removed"
+        assert result["id"] == a2a_client.WORKSPACE_ID
+        assert result["removed_at"] is None
+        assert "Regenerate" in result["hint"]
+
     async def test_exception_returns_error_dict_with_message(self):
         """Network exception → returns {'error': '<exception message>'}."""
         import a2a_client