Merge #1284: declare the labs availability metadata in get_labs

The tool module was split into one file per tool on this branch, so the
change lands in tools/get-labs.ts, and the advertised tool list snapshot
gains the two declared fields.

src/lib/mcp/__tests__/__snapshots__/tools-list.write-session.snap

@@ -411,6 +411,74 @@
         "grounding": {
           "type": "string"
         },
+        "searchedWindow": {
+          "type": "string"
+        },
+        "available": {
+          "type": "object",
+          "properties": {
+            "count": {
+              "type": "number"
+            },
+            "firstDate": {
+              "type": "string"
+            },
+            "lastDate": {
+              "type": "string"
+            },
+            "series": {
+              "type": "array",
+              "items": {
+                "type": "object",
+                "properties": {
+                  "series": {
+                    "type": "string"
+                  },
+                  "unit": {
+                    "type": [
+                      "string",
+                      "null"
+                    ]
+                  },
+                  "count": {
+                    "type": "number"
+                  },
+                  "mean": {
+                    "type": "number"
+                  },
+                  "min": {
+                    "type": "number"
+                  },
+                  "max": {
+                    "type": "number"
+                  }
+                },
+                "required": [
+                  "series",
+                  "unit",
+                  "count",
+                  "mean",
+                  "min",
+                  "max"
+                ],
+                "additionalProperties": false
+              }
+            },
+            "reachableWithWindow": {
+              "type": [
+                "string",
+                "null"
+              ]
+            }
+          },
+          "required": [
+            "count",
+            "firstDate",
+            "lastDate",
+            "reachableWithWindow"
+          ],
+          "additionalProperties": false
+        },
         "analyte": {
           "type": "string"
         },

src/lib/mcp/__tests__/tools.test.ts

@@ -510,6 +510,52 @@ describe("get_illness_recovery — condition body site", () => {
 });
 
 describe("get_labs", () => {
+  it.each([{}, { analyte: "LDL" }])(
+    "declares empty-read availability for ordinary and filtered reads: %j",
+    async (args) => {
+      const { z } = await import("zod/v4");
+      const empty = {
+        present: false,
+        reason: "out_of_window",
+        searchedWindow: "lastYear",
+        available: {
+          count: 2,
+          firstDate: "2020-01-01",
+          lastDate: "2020-01-02",
+          reachableWithWindow: null,
+        },
+      };
+      vi.mocked(executeCoachTool).mockResolvedValue(empty);
+      const def = tool("get_labs");
+      const result = await def.run(CTX, args);
+      expect(executeCoachTool).toHaveBeenCalledWith({
+        userId: CTX.userId,
+        name: "get_labs",
+        rawArguments: JSON.stringify(args),
+      });
+      expect(z.object(def.outputShape!).strict().parse(result)).toEqual(empty);
+    },
+  );
+
+  it("keeps output validation closed and availability typed", async () => {
+    const { z } = await import("zod/v4");
+    const schema = z.object(tool("get_labs").outputShape!).strict();
+    expect(z.toJSONSchema(schema).additionalProperties).toBe(false);
+    expect(schema.safeParse({ present: false, unexpected: true }).success).toBe(
+      false,
+    );
+    expect(
+      schema.safeParse({ present: false, searchedWindow: 7 }).success,
+    ).toBe(false);
+    expect(
+      schema.safeParse({ present: false, available: { count: "2" } }).success,
+    ).toBe(false);
+    expect(schema.parse({ present: false, reason: "no_data" })).toEqual({
+      present: false,
+      reason: "no_data",
+    });
+  });
+
   it("forwards the optional analyte filter and returns readings with units + bands", async () => {
     vi.mocked(executeCoachTool).mockResolvedValue({
       present: true,

src/lib/mcp/tools/get-labs.ts

@@ -4,16 +4,14 @@ import { resolveMarkerForRead } from "@/lib/labs/biomarker-resolve";
 import { getLabHistory, LAB_HISTORY_MAX_LIMIT } from "@/lib/mcp/rich-reads";
 import { decodeOffsetCursor } from "@/lib/mcp/pagination";
 import type { McpAuthContext } from "../auth";
+import { coachReadOutput } from "./output-shapes";
 import { runCoachTool, whenModuleOn } from "./shared";
 import { READ_ONLY_ANNOTATIONS, type McpToolDefinition } from "./types";
 
 /** Output schema for `get_labs` — latest-per-biomarker OR a paginated history. */
 const getLabsOutput: z.ZodRawShape = {
-  present: z.boolean(),
-  reason: z.string().optional(),
-  // Latest-mode payload (the Coach labs section, carried opaque).
-  data: z.unknown().optional(),
-  grounding: z.string().optional(),
+  // Latest-mode payload, including typed empty-read availability metadata.
+  ...coachReadOutput,
   // History-mode payload (per-analyte trajectory + pagination).
   analyte: z.string().optional(),
   readings: z