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 });
+  });
+});

apps/server/src/log-service.ts

@@ -25,6 +25,14 @@ const MAX_MESSAGE = 4_000;
 const MAX_STACK = 16_000;
 const MAX_CONTEXT_JSON = 16_000;
 
+/** Storm coalescing: a line identical to the LAST persisted one (level+source+message+
+ *  path) within this window of its previous occurrence UPDATES that row (bumping a
+ *  `_repeat` counter in its context) instead of inserting a new one. A continuous storm
+ *  keeps refreshing the window, so it stays ONE row however long it rages — repeated
+ *  errors can't evict unrelated history or grind the appliance disk (field incident
+ *  2026-07-07: one unreachable controller ≈ hundreds of identical rows/minute). */
+const COALESCE_WINDOW_MS = 300_000;
+
 export interface LogRetention {
   /** Delete logs older than this many days. */
   readonly maxAgeDays: number;
@@ -62,6 +70,16 @@ export class LogService {
   readonly #retention: LogRetention;
   /** Reentrancy guard: never let persisting a log itself emit a persisted log. */
   #writing = false;
+  /** The last persisted row, for storm coalescing (in-memory only; a restart just
+   *  starts a fresh row — best-effort, like everything in this sink). */
+  #last: {
+    id: string;
+    key: string;
+    count: number;
+    firstAt: string;
+    lastAtMs: number;
+    baseContext: Record<string, unknown> | null;
+  } | null = null;
 
   constructor(db: Db, retention: LogRetention = DEFAULT_RETENTION) {
     this.#db = db;
@@ -85,22 +103,53 @@ export class LogService {
     if (this.#writing) return;
     this.#writing = true;
     try {
+      const createdAt = row.createdAt ?? new Date().toISOString();
+      const message = clamp(row.message, MAX_MESSAGE) ?? "";
+      const path = clamp(row.path, 512);
+      const key = `${row.level}|${row.source}|${message}|${path ?? ""}`;
+      const nowMs = Date.now();
+
+      // Storm coalescing: identical to the last persisted row, within the window →
+      // bump that row instead of inserting. createdAt moves to the LATEST occurrence
+      // (keeps the storm visible at the top of the newest-first viewer); the first
+      // occurrence's time is preserved in context._firstAt.
+      const last = this.#last;
+      if (last && last.key === key && nowMs - last.lastAtMs <= COALESCE_WINDOW_MS) {
+        const res = this.#db
+          .update(appLogs)
+          .set({
+            context: { ...(last.baseContext ?? {}), _repeat: last.count + 1, _firstAt: last.firstAt },
+            createdAt,
+          })
+          .where(eq(appLogs.id, last.id))
+          .run();
+        if ((res.changes ?? 0) > 0) {
+          last.count += 1;
+          last.lastAtMs = nowMs;
+          return;
+        }
+        // The row was pruned out from under us — fall through to a fresh insert.
+      }
+
+      const id = randomUUID();
+      const baseContext = safeContext(row.context);
       this.#db
         .insert(appLogs)
         .values({
-          id: randomUUID(),
+          id,
           level: row.level,
           source: row.source,
-          message: clamp(row.message, MAX_MESSAGE) ?? "",
-          context: safeContext(row.context),
+          message,
+          context: baseContext,
           httpStatus: row.httpStatus ?? null,
-          path: clamp(row.path, 512),
+          path,
           stack: clamp(row.stack, MAX_STACK),
           userId: row.userId ?? null,
           userAgent: clamp(row.userAgent, 512),
-          createdAt: row.createdAt ?? new Date().toISOString(),
+          createdAt,
         })
         .run();
+      this.#last = { id, key, count: 1, firstAt: createdAt, lastAtMs: nowMs, baseContext };
     } catch {
       // Swallow — diagnostics must never take down the path they observe. (Can't log
       // it; that's the recursion we're guarding against.)