feat(logs): coalesce repeated identical lines into one row (×N badge)

A line identical to the last persisted row (level+source+message+path)
within a 5-min refreshing window updates that row — context._repeat counts
the fold, _firstAt keeps the first occurrence, createdAt tracks the latest
so the storm stays at the top of the newest-first viewer. A continuous
storm stays ONE row however long it rages, so it can't evict unrelated
history via the 50k row cap or grind the appliance disk. LogsViewer badges
coalesced rows ×N (tooltip: count + first occurrence, sq/en). In-memory
last-row cache only; a pruned-under-us row falls through to a fresh insert.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/log-service-stream.test.ts

@@ -1,4 +1,4 @@
-import { beforeEach, describe, expect, it } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { appLogs, type Db } from "@parking/db";
 import { createTestDb } from "@parking/db/testing";
 import { LogService, pinoDbStream } from "./log-service.js";
@@ -52,3 +52,65 @@ describe("pinoDbStream level encodings", () => {
     expect(teed).toHaveLength(2);
   });
 });
+
+// Storm coalescing: a line identical to the LAST persisted row (level+source+message+
+// path), arriving within 5 min of its previous occurrence, UPDATES that row (bumping
+// context._repeat) instead of inserting — one screaming device can't evict unrelated
+// history. The row's createdAt tracks the LATEST occurrence; the first is preserved in
+// context._firstAt.
+describe("storm coalescing", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("folds a burst of identical error lines into ONE row with a repeat counter", () => {
+    for (let i = 0; i < 200; i++) {
+      stream.write(`{"level":"error","msg":"button-light setAux failed (ctl R3): send ENETUNREACH"}\n`);
+    }
+    const all = rows();
+    expect(all).toHaveLength(1);
+    expect(all[0].context).toMatchObject({ _repeat: 200 });
+    expect(teed).toHaveLength(200); // stdout still gets every line
+  });
+
+  it("keeps first-occurrence time in _firstAt while createdAt tracks the latest", () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-07-08T10:00:00.000Z"));
+    stream.write(`{"level":"warn","msg":"same"}\n`);
+    vi.setSystemTime(new Date("2026-07-08T10:02:00.000Z"));
+    stream.write(`{"level":"warn","msg":"same"}\n`);
+    const [row] = rows();
+    expect(row.createdAt).toBe("2026-07-08T10:02:00.000Z");
+    expect(row.context).toMatchObject({ _repeat: 2, _firstAt: "2026-07-08T10:00:00.000Z" });
+  });
+
+  it("a different message (or level) breaks the run — separate rows", () => {
+    stream.write(`{"level":"error","msg":"boom A"}\n`);
+    stream.write(`{"level":"error","msg":"boom A"}\n`);
+    stream.write(`{"level":"error","msg":"boom B"}\n`);
+    stream.write(`{"level":"warn","msg":"boom B"}\n`);
+    expect(rows()).toHaveLength(3);
+  });
+
+  it("an occurrence past the 5-minute window starts a fresh row", () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-07-08T10:00:00.000Z"));
+    stream.write(`{"level":"error","msg":"slow leak"}\n`);
+    vi.setSystemTime(new Date("2026-07-08T10:06:00.000Z"));
+    stream.write(`{"level":"error","msg":"slow leak"}\n`);
+    expect(rows()).toHaveLength(2);
+  });
+
+  it("a CONTINUOUS storm stays one row past the window (each hit refreshes it)", () => {
+    vi.useFakeTimers();
+    let t = new Date("2026-07-08T10:00:00.000Z").getTime();
+    for (let i = 0; i < 10; i++) {
+      vi.setSystemTime(new Date(t));
+      stream.write(`{"level":"error","msg":"storm"}\n`);
+      t += 240_000; // 4 min apart — each inside the window of the PREVIOUS hit
+    }
+    const all = rows();
+    expect(all).toHaveLength(1);
+    expect(all[0].context).toMatchObject({ _repeat: 10 });
+  });
+});